Holden ( 1986) wrote that the WDNR sampling program was criticized for a number of reasons including that the quality assurance and quality control procedures ( QA/ QC) were not always followed during some stages of sampling and analysis ( Holden, 1986) . Holden ( 1986) further indicates that " Harkin et al. ( 1984) noted in their WIS WRC report Pesticides in Groundwater beneath the Central Sand Plain of Wisconsin that some detections of pesticides in initial screening were false positives and were not supported by resampling and reanalysis by more sensitive analytical methods. "

Aldicarb and aldicarb sulfone were also found in this study and in follow up studies, while disulfoton was apparently not found in follow up sampling. Aldicarb is no longer registered for use in Wisconsin.

The criticisms of the WDNR study must, however, be put in some sort of perspective. First, a study that did not follow QA/ QC criteria does not and should not automatically mean that the data is bad or wrong, the detections may be correct ( presence and magnitude) . Frequently " older" monitoring studies often had problems associated with them, such as QA/ QC problems, limited pesticide usage information, and no knowledge about the study area' s hydrology. Frequently, studies with QA/ QC programs are poorly designed, so that the results may be meaningless.

Pesticide residues not being found in follow up sampling may be the result of dissipation processes and should not be used to discount detections in earlier samples. The environmental fate properties and site hydrology must also be considered. Because ground water is a dynamic system, pesticides may be present at one sampling event and not at another. So when the sample is collected, in relationship to pesticide use and rainfall, is important. All that can be said is that residues were not found in follow up samples. It is unknown which samples were re analyzed with more sensitive methods.

The disulfoton detections in the Central Sand Plain may have been the result of preferential flow and transport processes. Literature documents preferential flow in the Central Sand Plain. Thus,

25 disulfoton residues may have by passed the soil matrix and gone directly to ground water which is possibly reflected in the " high" level of the detections. Although preferential flow is currently an ongoing area of research and much remains unknown, it is known that preferential flow is influenced by a number of factors, including rainfall amounts, intensity, and frequency. Disulfoton generally appears to be not very persistent under aerobic soil conditions and therefore may also not be very persistent in aquifers that are aerobic. Therefore it may have also been missed by utilizing a predetermined sampling schedule ( e. g. , monthly) . Whereas a persistent chemical, such as aldicarb and aldicarb sulfone, will be found at greater frequencies and be less dependent upon timing of sampling. Disulfoton usage history before the detections and prior to the follow up sampling is not specified.

Surface Water: A monitoring study was conducted to evaluate the effectiveness of Best Management Practices ( BMP) in a 3616 acre watershed in the Nomini Creek Watershed, Westmoreland County, Virginia. Approximately half of the watershed is in agriculture and the other half is forested. The major focus of this study was surface water quality rather than ground water quality. The detections of parent disulfoton in surface water samples ( 0.037 to 6.11 µ g/ L) collected ( Table 10) in the Nomini Creek Watershed study fell within an order of magnitude with the estimated environmental concentrations ( EECs) obtained from the PRZM/ EXAMS models for parent disulfoton which range from 0.21 to 1.14 µ g/ L for annual mean daily concentrations and 7.14 to 26.75 µ g/ L for peak daily values.

Table 10. Disulfoton detections in Surface Water samples collected in the Nomini Creek Watershed ( Virginia) , during 1986.

Sample date Site Number: Sample # Concentration ( g/ L)

8/ 18/ 86 QN1: 1 ( 9: 13 am) 6.11 8/ 18/ 86 QN1: 2 ( 12: 25 pm) 0.37 9/ 28/ 86 QN2: ( only 1 sample) 1.62 NAWQA : Disulfoton residues have been detected in surface water at a low frequency in the USGS NAWQA study. The percentage of detections with disulfoton concentrations > 0.01 µ g/ L for all samples, agricultural streams, urban streams were 0.27% , 0.20, and 0.61% , respectively. The corresponding maximum concentrations were 0.060, 0.035, and 0.037 µ g/ L. Disulfoton has not been detected in ground water in the NAWQA study. Although pesticide usage data is collected for the different NAWQA study units, the studies are not targeted, specifically for disulfoton.

26 STORET : About 50 percent of the well samples reported in STORET had low levels ( < 1 µ g/ L) of disulfoton residues. However, there were indications of some high concentrations ( the other 50% were reported as < 250 µ g/ L) , which may be a reflection of how the data were reported as the disulfoton concentrations in the monitoring were not always known. This is because the detection limit was extremely high or not specified, and/ or the limit of quantification was not stated or extremely high. Disulfoton concentrations were simply given as less than a value. Therefore, considerable uncertainty exists with respect to the STORET monitoring data.

Limitations of Monitoring Data The interpretation of the monitoring data is limited by the lack of correlation between sampling dates and the use patterns of the pesticide within the study   s drainage basin. Additionally, the sample locations were not associated with actual drinking water intakes for surface water nor were the monitored wells associated with known ground water drinking water sources. Also, due to many different analytical detection limits, no specified detection limits, or extremely high detection limits, a detailed interpretation of the monitoring data is not always possible. Limitations for the monitoring studies include the use of different limits of detection between studies, lack of information concerning disulfoton use around sampling sites, and lack of data concerning the hydro geology of the study sites. The spatial and temporal relationship between disulfoton use, rainfall/ runoff events and the location and time of sampling cannot often be adequately determined. Thus, it is not always possible to judge the significance of the level or the lack of detections.

Although no assessment can be made for degradates due to lack of data, limited data suggests that the degradates are more persistent ( > 200 days) than disulfoton, suggesting their presence in water for a longer period of time than the parent. The degradates also appear to be more mobile than the parent compound.

vii. Limitations of this Modeling Analysis There are number of factors which limit the accuracy and precision of this modeling analysis including the selection of the high end exposure scenarios and maximum number of applications and rates, the quality of the data, the ability of the model to represent the real world, and the number of years that were modeled. There are additional limitations on the use of these numbers as an estimate of drinking water exposure. Individual degradation/ metabolism products were also not considered due to lack of data. Another major uncertainty in the current EXAMS simulations is that the aquatic degradation rate used an estimated rate due to lack of data. Direct aquatic photolysis was also included. The total disulfoton residue decline rate was estimated from data, but Kocs and hydrolysis rates for D. sulfoxide and sulfone were not known and assumed to be equal to those of parent disulfoton. These limitations influence the estimates of pesticides transported off the field ( loading files) to the pond, plus the degradation once in the pond.

Spray is determined by method of pesticide application, and is assumed to be 0% percent when applied as broadcast ( granular) or in furrow, 5% for ground spray, and 15% for aerial spray for 27 the farm pond, and 6.4% ground and 16.4% aerial spray for the Index Reservoir scenario ( Jones et al. , 2000) .

Tier II scenarios are also ones that are likely to produce high concentrations in aquatic environments. The scenarios were intended to represent sites that actually exist and are likely to be treated with a pesticide. These sites should be extreme enough to provide a conservative estimates of the EEC, but not so extreme that the model cannot properly simulate the fate and transport processes at the site. The EECs in this analysis are accurate only to the extent that the sites represent the hypothetical high exposure sites. The most limiting aspect of the site selection is the use of the   standard pond   which has no outlet. . It also should be noted that the standard pond scenario used here would be expected to generate higher EECs than most water bodies, although, some water bodies would likely have higher concentrations ( e. g. , a shallow water bodies near agriculture fields that receive direct run off from the treated field) .

The quality of the analysis is also directly related to the quality of the chemical and fate parameters available for disulfoton. Acceptable data are available, but rather limited. Data were not available for degradates and the aquatic aerobic metabolism rate was not known, but estimated. Degradates with greater persistence and greater mobility would be expected to have a higher likelihood of leaching to ground water, with greater concentrations in surface water. The measured aerobic soil metabolism data is limited, but has sufficient sample size to establish an upper 90% confidence bound on the mean of half lives for the three aerobic soils tested in the laboratory ( and submitted to EFED) and reported in the EFED One liner Database ( MRIDs 40042201, 41585101, 43800101) . The use of the 90%  upper bound value may be sufficient to capture the probable estimated environmental concentration when limited data are available. PRZM assumes pesticide decline follows first order kinetics. As discussed in the aerobic soil metabolism section, disulfoton doesn' t entirely follow first order kinetics.

The models themselves represent a limitation on the analysis quality. These models were not specifically developed to estimate environmental exposure in drinking water so they may have limitations in their ability to estimate drinking water concentrations. Aerial spray drift reaching the pond is estimated from Spray Drift Task Force ( SDTF) preliminary data to be 15 percent of the application rate and for ground spray it is 1 percent of the application rate. No drift was assumed for broadcast or in furrow applications. Another limitation is the lack of field data to validate the predicted pesticide run off. Although, several of the algorithms ( volume of run off water, eroded sediment mass) are somewhat validated and understood, the estimates of pesticide transport by PRZM3 has not yet been fully validated Other limitations of PRZM are the inability to handle within site variation ( spatial variability) , crop growth, and the overly simple water balance. Another limitation is that 20 to 40 years of weather data were available for the analysis. Consequently there is a 1 in 20, 27, 36, or 40 chance that the true 10% exceedence EECs are larger than the maximum EEC in the analysis. If the number of years of weather data were increased, it would increase the level of confidence that the estimated value for the 10% exceedence EEC was close to the true value.

EXAMS is primarily limited because it is a steady state model and cannot accurately characterize the dynamic nature of water flow. A model with dynamic hydrology would more 28 accurately reflect concentration changes due pond overflow and evaporation. Thus, the estimates derived from the current model simulates a pond having no outlets, flowing water, or turnover. Another major limitation in the current EXAMS simulations is that the aquatic ( microbial) and abiotic degradation pathways were adequately considered. The binding potential of the degradates is not known and was not considered.

Another important limitation of the Tier II EECs for drinking water exposure estimates is the use of a single 10 hectare drainage basin with a 1 hectare pond. It is unlikely that this small system accurately represents the dynamics in a watershed large enough to support a drinking water utility. It is unlikely that an entire basin, with an adequate size to support a drinking water utility would be planted completely in a single crop or be represented by scenario being modeled. The pesticides would more likely be applied over several days to weeks rather than on a single day. This would reduce the magnitude of the conservative concentration peaks, but also make them broader, reducing the acute exposure, but perhaps increasing the chronic exposure.

3. Ecological Effects Hazard Assessment A. Toxicity to Terrestrial Animals i. Birds, Acute and Subacute An acute oral toxicity study using the technical grade of the active ingredient is required to establish the toxicity of a pesticide to birds. The preferred test species is either mallard duck or bobwhite quail. Results of this test are tabulated below. Acute oral testing was also performed with the 15G formulation of disulfoton. Additionally, acute oral testing was required for the two major degradation products of disulfoton, disulfoton sulfone and disulfoton sulfoxide, due to their relative persistence. These test results are as follows:

29 Table 11. Avian Acute Oral Toxicity Species % ai LD50 ( mg/ kg) Toxicity Category MRID No. Author/ Year Study Classification Mallard ( Anas platyrhynchos) 97 6.54 very highly toxic 00160000 1984/ Hudson supplemental Northern bobwhite quail ( Colinus virginianus) technical 12.0 highly toxic EDODIS00 Hill core Northern bobwhite quail ( Colinus virginianus technical 28 highly toxic 0095655 1977 core Northern bobwhite quail ( Colinus virginianus) technical 31 highly toxic 0095655 1977 core Northern bobwhite quail ( Colinus virginianus) 98.7 39 highly toxic 42585803 / 1992 core Ring necked pheasant ( Phasianus colchicus) technical 11.9 highly toxic 00160000 1987/ Hudson core Red winged blackbird ( Agelaius phoeniceus ) technical 3.2 very highly toxic 1987 supplemental Northern bobwhite quail ( Colinus virginianus) 15G 220 moderately toxic 25525 1969 core Northern bobwhite quail ( Colinus virginianus) 15G 97 moderately toxic 25525 1969 core Northern bobwhite quail ( Colinus virginianus) 15G 14.5 highly toxic 0095655 1984 supplemental Northern bobwhite quail ( Colinus virginianus) 15G 29 highly toxic EDODIS00 1984 supplemental Northern bobwhite quail ( Colinus virginianus) sulfone metabolite 87.4 18 highly toxic 42585103 1992 core Northern bobwhite quail ( Colinus virginianus) sulfoxide metabolite 85.3 9.2 very highly toxic 42585102 1992 core 30 These results indicate that disulfoton is highly toxic to very highly toxic to avian species on an acute oral basis. The guideline requirement ( 71 1) is fulfilled ( MRID # 42585803) . Additionally, the two major metabolites of disulfoton, disulfoton sulfone and disulfoton sulfoxide, are highly toxic and very highly toxic, respectively. Guideline 71 1 is fulfilled for the two major degradates of disulfoton ( 42585103 and 42585102) .

Two subacute dietary studies using the technical grade of the active ingredient are required to establish the toxicity of a pesticide to birds. The preferred test species are mallard duck ( a waterfowl) and bobwhite quail ( an upland gamebird) . Subacute dietary testing on the two major metabolites of disulfoton, disulfoton sulfone and disulfoton sulfoxide, were also required, due to the relative persistence of these degradates. Results of all avian subacute dietary tests are as follows:

Table 12. Avian Subacute Dietary Toxicity Species % ai LC50 ( ppm) Toxicity Category MRID No. Author/ Year Study Classification Northern bobwhite quail ( Colinus virginianus) technical 544 moderately toxic 0094233 Lamb/ 1973 core Mallard duck ( Anas platyrhynchos) technical 510 moderately toxic 0034769 Hill/ 1975 core Japanese quail ( Coturnix japonica) technical 333 highly toxic 0034769 Hill/ 1975 supplemental Mallard duck ( Anas platyrhynchos) sulfone metabolite 87.4 622 moderately toxic 42585101 1992 core Northern bobwhite quail ( Colinus virginianus) sulfone metabolite 87.4 558 moderately toxic 42585106 1992 core Mallard duck ( Anas platyrhynchos) sulfoxide metabolite 85.3 823 moderately toxic 42585104 1992 core Northern bobwhite quail ( Colinus virginianus) sulfoxide metabolite 85.3 456 highly toxic 42585105 1992 core These results indicate that disulfoton is highly toxic to avian species on a subacute dietary basis. The guideline requirement ( 71 2) is fulfilled ( ACC # 0094233 and 0034769) . Additionally, the major metabolites of disulfoton, disulfoton sulfone and disulfoton sulfoxide, are moderately to highly toxic to avian species on a dietary basis. Guideline 71 2 is fulfilled for both metabolites ( MRID # 42585101, 42585106, 42585104, and 42585105) .

31 ii. Birds, Chronic Avian reproduction studies using the technical grade of the active ingredient are required for disulfoton because the following conditions are met: ( 1) birds may be subject to repeated or continuous exposure to the pesticide, especially preceding or during the breeding season, ( 2) the pesticide is stored or accumulated in plant or animal tissues, and/ or, ( 4) information derived from mammalian reproduction studies indicates reproduction in terrestrial vertebrates may be adversely affected by the anticipated use of the product. Disulfoton meets all of these conditions. The preferred test species are mallard duck and bobwhite quail. Results of these tests are tabulated below.

Table 13. Avian Reproductive Toxicity Species % ai NOAEC/ LOAEC ( ppm) Endpoints Affected MRID No. Author/ Year Study Classification Northern bobwhite quail ( Colinus virginianus) 98.7 37/ 74 hatchling body weight 43032501 / 1993 core Mallard duck ( Anas platyrhynchos) 98.3 37/ 80 adult and hatchling body weight 43032502 / 1993 core There was a statistically significant reduction in hatchling body weight at 74 ppm in the bobwhite quail study; however, there were no significant differences in hatchling body weights by day 14 post hatch. No other effects were observed in this study.

Adult and hatchling body weights were significantly reduced at 80 and 164 ppm in the mallard study, and body weight gain in adults was significantly reduced throughout the study at these two treatment levels as well. Other effects observed at the 164 ppm level were: significantly fewer eggs laid per hen, reduced eggshell strength and thickness, reduced number of hatchlings as a percent of viable embryos, reduced number of 14 day survivors as a percent of normal hatchlings, reduced viable embryos as a percent of eggs set, and reduced 14 day survivors as a percentage of eggs set. The guideline requirement for avian reproduction testing ( 71 4) is fulfilled ( MRID # 43032501, and 43032502) .

iii. Mammals, Acute and Chronic Wild mammal testing is required on a case by case basis, depending on the results of lower tier laboratory mammalian studies, intended use pattern and pertinent environmental fate characteristics. In most cases, rat or mouse toxicity values obtained from the Agency' s Health Effects Division ( HED) substitute for wild mammal testing. These toxicity values are reported in the Table below.

32 Table 14. Mammalian Acute Toxicity Species % ai Test Type Toxicity Values/ category MRID No.

Mule deer ( Odocoileus hemionus )

Domestic goat ( Capra hircus )

Laboratory rat ( Rattus norvegicus) 97 97 94.4 acute oral acute oral acute oral 2.5 mg/ kg very highly toxic < 15 mg/ kg very highly toxic 1.9 mg/ kg females I 6.2 mg/ kg males I 00160000 00160000 072293 Laboratory mouse ( Mus musculus) 94.4 acute oral 8.2 mg/ kg ( female) I 7.0 mg/ kg ( male) I 072293 Laboratory rat ( Rattus norvegicus) sulfone metabolite acute oral 11.24 mg/ kg ( female) I 0071873 Test results indicate that disulfoton is very highly toxic ( Category I) to small mammals on an acute oral basis. Testing on the sulfone metabolite also indicates very high acute oral toxicity.

Table 15. Mammalian Chronic Toxicity Species % ai Test Type Toxicity Values/ category MRID No.

Laboratory rat ( Rattus norvegicus) 97.8 2 generation reproduction maternal NOAEC= 2.4 ppm/ LOAEC= 7.2 ppm repro NOAEC= 0.8 ppm/ LOAEC= 2.4 ppm 261990 The two generation rat reproduction study provided a reproductive NOEC level of 0.8 ppm. Parameters affected in the study included decreased litter size, lowered pup survival, and decreased pup weight.

iv. Insects A honey bee acute contact study using the technical grade of the active ingredient is required for disulfoton because its use may result in honey bee exposure. Results of this test are as follows:

33 Table 16. Nontarget Insect Acute Contact Toxicity Species % ai LD50 ( F g/ bee) Toxicity Category MRID No. Author/ Year Study Classification Honey bee ( Apis mellifera ) technical 4.1 moderately toxic 05004151 1968 core Honey bee ( Apis mellifera) sulfone metabolite 91.6 0.96 highly toxic 42582902 1992 core Honey bee ( Apis mellifera) sulfoxide metabolite 85.3 1.11 moderately toxic 42582901 1992 core The results indicate that disulfoton is moderately toxic to bees and disulfoton sulfone, and disulfoton sulfoxide are very highly toxic to bees on an acute contact basis. The guideline requirement ( 141 1) is fulfilled for parent disulfoton ( MRID # 05004151) , as well as for the two major metabolites ( MRID # 42582902, 42582901) .

A honey bee toxicity of residues on foliage study using the typical end use product was submitted for disulfoton. The results of this study are tabulated below.

Table 17. Nontarget Insect Toxicity of Residues on Foliage Species Formulatio n LD50 ( lb. / A) Toxicity Category MRID or ACC # Author/ year Guideline Classification Honey bee ( Apis mellifera 8 E. C. > 1.0 0163423 core The results indicate that disulfoton residues on foliage are not toxic to honey bees at application rates up to 1.0 lb / A. Guideline 141 2 is fulfilled for disulfoton ( ACC # 0163423) .

v. Terrestrial Field Testing Terrestrial field testing was conducted for disulfoton because of the high toxicity of the chemical in relation to expected environmental concentrations. Three field studies were originally required in the 1985 Registration Standard, but only one screening level field study and one residue monitoring study were submitted. The Level I ( screening) field study was conducted on potatoes in Benton county, Washington, using the 15G formulation ( MRID # 410560 01) . The study did show mortality to wildlife from the use of the 15G formulation on potatoes; since it was a screening study, there were no further conclusions. If no mortality had been observed, the study would not have been classified as core as the study design and carcass searching techniques were insufficient to negate the presumption of risk. The study fulfilled Guideline 71

34 5 only because adverse effects were seen. The fact that bird and mammal carcasses were found even with such an insensitive study design emphasizes the high acute risk this chemical poses to terrestrial vertebrates.

The residue monitoring study ( MRID # 412018 01) was conducted with Di Syston 8 ( foliar) on potatoes in Michigan. Disulfoton was aerially applied to potatoes 3 times at 1 lb ai/ acre in Michigan. The results of this study indicated that there was hazard to terrestrial wildlife from the foliar application of disulfoton, and also suggested that a full Level 1 field study was needed with the foliar application. An second residue monitoring study ( MRID # 411189 01) was performed, in which disulfoton was soil incorporated by ground equipment, ( initially in furrow at planting at 3 lb ai/ acre and 6  7 weeks later as a side dressing at 3 lbs ai/ acre) . Although the residues on vegetation were much lower in this second study as compared to the first, nevertheless they posed potential acute and chronic risk especially to small mammals.

B. Toxicity to Freshwater Aquatic Animals i. Freshwater Fish, Acute Two freshwater fish toxicity studies using the technical grade of the active ingredient are required to establish the toxicity of a pesticide to fish. The preferred test species are rainbow trout ( a Coldwater fish) and bluegill sunfish ( a warmwater fish) . Results of these tests are as follows:

35 Table 18. Freshwater Fish Acute Toxicity Species % ai LC50 ( ppb ai) Toxicity Category MRID No. Author/ Year Study Classification Rainbow trout ( Oncorhynchus mykiss) 98 tech 15G 65EC sulfone metabolite sulfoxide metabolite 1,850 3,000 13,900 3,500 > 9,200 60,300 moderately toxic moderately toxic slightly toxic moderately toxic moderately toxic slightly toxic 40098001 F. L. Mayer/ 1986 0068268 Lamb/ 1972 0068268 Lamb/ 1972 0068268 Lamb/ 1972 42585111 Gagliano/ 1992 42585110 Gagliano/ 1992 core core core core core core Bluegill sunfish ( Lepomis macrochirus 98.0 Tech 15G 65EC 20E sulfone metabolite sulfoxide metabolite 300 39 250 59 8.2 112 188 highly toxic very highly toxic highly toxic very highly toxic very highly toxic highly toxic highly toxic 40098001 F. L. Mayer/ 1986 0068268 Lamb/ 1972 0068268 Lamb/ 1972 0068268 Lamb/ 1972 229299 1962 42585108 Gagliano/ 1992 42585107 Gagliano/ 1992 core core core core supplemental core core Channel catfish ( Ictalurus punctatus ) 98.0 4, 700 moderately toxic 40098001 Mayer/ 1986 core Goldfish ( Carassius auratus ) 90 7,200 moderately toxic 229299 1962 supplemental Largemouth bass ( Micropterus salmoides ) 98.0 60 very highly toxic 40098001 Mayer/ 1986 core Fathead minnow ( Pimphales promelas ) 98.0 4, 300 moderately toxic 40098001 Mayer/ 1986 core Guppy 90 280 highly toxic 229299 supplemental 36 These results indicate that parent disulfoton is very highly toxic to slightly toxic to freshwater fish on an acute basis. The two major metabolites, disulfoton sulfone and disulfoton sulfoxide, are highly toxic to slightly toxic to freshwater fish on an acute basis. The rainbow trout, a Coldwater species, appears to be somewhat less sensitive than the warmwater species to disulfoton and its metabolites. The guideline requirement ( 72 1) is fulfilled for parent disulfoton, disulfoton sulfone, and disulfoton sulfoxide.

ii. Freshwater Fish, Chronic A freshwater fish early life stage test using the technical grade of the active ingredient is required for a pesticide when it may be applied directly to water or if the end use product is expected to be transported to water from the intended use site, and the following conditions are met: ( 1) the pesticide is intended for use such that its presence in water is likely to be continuous or recurrent regardless of toxicity, ( 2) any aquatic acute LC50 or EC50 is less than 1 mg/ l, ( 3) the EEC in water is equal to or greater than 0.01 of any acute LC50 or EC50 value, or, ( 4) the actual or estimated environmental concentration in water resulting from use is less than 0.01 of any acute LC50 or EC50 value and any one of the following conditions exist: studies of other organisms indicate the reproductive physiology of fish may be affected, physicochemical properties indicate cumulative effects, or the pesticide is persistent in water ( e. g. , half life greater than 4 days) . The preferred test species is rainbow trout, but other species may be used. . Freshwater fish early life stage testing was required for disulfoton due to the likelihood of drift and runoff from the application sites, the likelihood of repeated or continuous exposure from multiple applications, and the high acute toxicity to several species of freshwater fish. Results of this test are tabulated below.

Table 19. Freshwater Fish Early Life Stage Toxicity Species % ai NOAEC/ LOAEC ( ppb ai) MATC ( ppb) Endpoints Affected MRID No. Author/ Year Study Classification Rainbow trout ( Oncorhynchus mykiss) 98 220/ 420 300 growth 41935801 1991 core The guideline requirement ( 72 4a) is fulfilled ( MRID 41935801) .

A freshwater fish life cycle test using the technical grade of the active ingredient is not required for disulfoton. A marine/ estuarine fish life cycle test was conducted with disulfoton, since the marine/ estuarine species is more sensitive than the freshwater species. This is discussed in section c ii , below.

iii. Freshwater Invertebrates, Acute A freshwater aquatic invertebrate toxicity test using the technical grade of the active ingredient 37 is required to establish the toxicity of a pesticide to invertebrates. The preferred test species is Daphnia magna . Results of this test are tabulated below.

Table 20. Freshwater Invertebrate Toxicity Species % ai LC50/ EC50 ( ppb ai) Toxicity Category MRID No. Author/ Year Study Classification Waterflea ( Daphnia magna) Waterflea ( Daphnia magna)

Waterflea ( Daphnia magna 98.6 Sulfone metabolite 87.4 sulfoxide metabolite 85.3 13.0 35.2 64 very highly toxic very highly toxic very highly toxic 00143401 Heimbach/ 1985 42585112 Gaglaino/ 1992 42585109 Gagliano/ 1992 core core core Scud ( Gammarus fasciatus ) 98 technical 52 27 very highly toxic very highly toxic 40098001 Mayer/ 1986 05017538 1972 supplemental supplemental Glass shrimp ( Palaemonetes kadiakensis ) 98 3.9 very highly toxic 40094602 1980 supplemental Stonefly ( Acroneuria pacifica ) 89 < 8.2 very highly toxic 229299 1962 supplemental Stonefly ( Pteronarcys californica ) 98 5.0 very highly toxic 40098001 Mayer/ 1986 core The results indicate that disulfoton and its metabolites, disulfoton sulfone and disulfoton sulfoxide, are very highly toxic to aquatic invertebrates on an acute basis. The guideline requirement ( 72 2) is fulfilled.

iv. Freshwater Invertebrate, Chronic A freshwater aquatic invertebrate life cycle test using the technical grade of the active ingredient is required for a pesticide if the end use product may be applied directly to water or expected to be transported to water from the intended use site, and the following conditions are met: ( 1) the pesticide is intended for use such that its presence in water is likely to be continuous or recurrent regardless of toxicity, ( 2) any aquatic acute LC50 or EC50 is less than 1 mg/ l, or, ( 3) the EEC in water is equal to or greater than 0.01 of any acute EC50 or LC50 value, or, ( 4) the actual or estimated environmental concentration in water resulting from use is less than 0.01 of any aquatic acute EC50 or LC50 value and any of the following conditions exist: studies of other 38 organisms indicate the reproductive physiology of invertebrates may be affected, physicochemical properties indicate cumulative effects, or the pesticide is persistent in water ( e. g. , half life greater than 4 days) . The preferred test species is Daphnia magna . Freshwater aquatic invertebrate life cycle testing was required for disulfoton. Results of this test are tabulated below.

Table 21. Freshwater Aquatic Invertebrate Life Cycle Toxicity Species % ai NOAEC/ LOAE C ( ppb) MATC ( ppb) Endpoints Affected MRID No. Author/ Year Study Classifica tion Waterflea ( Daphnia magna) 98 0.037/ 0.070 0.051 survival, length, and # young/ adult 41935802 Blakemore/ 1991 core Waterflea ( Daphnia magna) 99.3 Sulfone 0.14/ 0.27 0.19 length 43738001 Bowers/ 1995 core Waterflea ( Daphnia magna) 98.9 Sulfoxide 1.53/ 2.97 2.13 Weight & length 43738002 Bowers/ 1995 core The guideline requirement ( 72 4) is fulfilled ( MRID # 41935802) .

v. Freshwater Field Studies A microcosm study was conducted to evaluate the effects of runoff of disulfoton on a simulated aquatic field system ( MRID # 435685 01/ Cook and Kennedy, 1994) . Three dose levels   3, 10, 30 ppb   were established in two replicate tanks per dose. Each tank was dosed 4 times at 7 day intervals. The study demonstrated that 3 ppb is the maximum acceptable toxicant concentration ( MATC) for this chemical in aquatic systems. At treatment levels of 3 ppb and higher, adverse effects were seen on zooplankton numbers, zooplankton community similarity, adult macro invertebrate population numbers, and adult macroinvertebrate community composition; however, some recovery trend was observed on all of these parameters at 10 ppb and many at 30 ppb by the end of the 77 day study. A bluegill LC50 of 25 ppb and LC10 of 4.7 ppb was established for the first 27 days during which the four applications occurred.

The North Carolina Cooperative Extension Service submitted two stream surveys conducted in five of the major Christmas tree farming in North Carolina. Although neither survey was targeted for disulfoton, nor analyzed for chemical residues they attempted to reflect the impact to aquatic macro invertebrates from the overall cultural practices associated with Christmas tree farming in Western North Carolina. The first survey, conducted by Department of Environmental Health and Natural Resources ( DEHNR) , examined one station on each of 11 streams ( Lenant, D. 1999 unpublished) . Eight of the11 streams were sampled once ( in May 39 presumably after the April/ May application of disulfoton) . The 3 other streams were sampled a second time in August as a means to correct for likely seasonal changes in the species composition of Ephemeroptera, Plecoptera and Trichoptera ( EPT) . The second survey was conducted from 12/ 98 thru early to late summer 1999 ( Sidebottom, J. 2000 unpublished) The survey examined 5 sites   each consisting of an area adjacent to or downstream from a Christmas tree farm paired with its own reference site ( either a station on the same stream, but above the tree farm or a second stream) . The data collected included the total number of insects and the break out ( expressed as a % of insects) for mayflies, stoneflies, caddisflies, riffle beetles and   other   insects. . A species list for mayflies, stoneflies and caddisflies along with an index of their sensitivity and the dates collected was provided for 3 of the 5 sites. See the risk to aquatic organisms section on page 64 for further discussion of results and the significance to the disulfoton risk assessment.

C. Toxicity to Estuarine and Marine Animals i. Estuarine and Marine Fish, Acute Acute toxicity testing with estuarine/ marine fish using the technical grade of the active ingredient is required for a chemical when the end use product is intended for direct application to the marine/ estuarine environment or the active ingredient is expected to reach this environment because of its use in coastal counties. The preferred test species is sheepshead minnow. Marine/ estuarine acute testing was conducted with disulfoton. Results of these tests are tabulated below.

Table 22. Acute Toxicity of Disulfoton to Estuarine/ Marine Fish Species % ai LC50 ( ppb) Toxicity Category MRID No. Author/ Year Study Classification Sheepshead minnow ( Cyprinodon variegatus)

Sheepshead minnow ( Cyprinodon variegatus ) 95.5 97.8 520 1000 highly toxic highly toxic 4022840 Mayer/ 1986 40071602 Surprenant/ 1986 supplemental core Sheepshead minnow ( Cyprinodon variegatus ) Sulfone metabolite 100% 1060 moderately toxic 44369901 Lam/ 1997 core Sheepshead minnow ( Cyprinodon variegatus ) Sulfoxide metabolite 98.2% 11300 slightly toxic 44369902 Lam/ 1997 core The results indicate that disulfoton is highly toxic to estuarine/ marine fish on an acute basis. The guideline requirement ( 72 3a) is fulfilled for parent disulfoton ( MRID # 40071602) and the sulfone and sulfoxide metabolites ( MRID # 44369901 and 44369902, respectively) .

40 ii. Estuarine and Marine Fish, Chronic Estuarine/ marine fish early life stage and life cycle tests using the technical grade of the active ingredient were required for disulfoton due to the high acute toxicity to estuarine/ marine fish. The results of these studies are as follows:

Table 23. Chronic Toxicity of Disulfoton to Marine/ Estuarine Fish Species % a. i. Test Type NOEC/ LOEC ( ppb) MAT C ( ppb) Parameters Affected MRID # Author/ year Classification Sheepshead minnow ( Cyprinodon variegatus ) 97.4 early life stage 16.2/ 32.9 23.1 survival, length, wet weight 42629001 Lintott/ 1993 core Sheepshead minnow ( Cyprinodon variegatus ) 98 life cycle 0.96 1 / 2. 9 1.7 fecundity, morphological abnormalities, growth, hatching success 43960501 Dionne/ 1996 supplemental 1 An actual NOEC was not achieved in this study. The value reported here is an EC05, extrapolated using linear regression.

The results indicate that disulfoton impacts the reproductive ability, as well as the growth and larval survival, of sheepshead minnows at levels as low as 2.9 ppb. The guideline requirements ( 72 4 and 72 5) are fulfilled ( MRID # 42629001 and 43960501, respectively) .

iii. Estuarine and Marine Invertebrates, Acute Acute toxicity testing with estuarine/ marine invertebrates using the technical grade of the active ingredient is required for a pesticide when the end use product is intended for direct application to the marine/ estuarine environment or the active ingredient is expected to reach this environment because of its use in coastal counties. The preferred test species are mysid shrimp and eastern oyster. Estuarine/ marine invertebrate testing was required for disulfoton. Results of these tests are as follows:

41 Table 24. Acute Toxicity of Disulfoton to Estuarine/ Marine Invertebrates Species % ai. LC50/ EC50 ( ppb) Toxicity Category MRID No. Author/ Year Study Classification Eastern oyster ( Crassostrea virginica)

Eastern oyster ( Crassostrea virginica)

Eastern oyster ( Crassostrea virginica) 97.8 tech 95.5 720 900 720 highly toxic highly toxic highly toxic 40071603 Surprenant/ 1986 120480 / 1965 40228401 Mayer/ 1986 core supplemental core Mysid ( Mysidopsis bahia ) 97.8 100 very highly toxic 40071601 Surprenant/ 1986 core Brown shrimp ( Penaeus aztecus ) 95.5 15 very highly toxic 40228401 Mayer/ 1986 supplemental The results indicate that disulfoton is very highly to highly toxic to estuarine/ marine invertebrates on an acute basis. The guideline requirements ( 72 3b and 72 3c) are fulfilled ( MRID # 40071603 and 40071601, respectively) .

iv. Estuarine and Marine Invertebrate, Chronic An estuarine/ marine invertebrate life cycle toxicity test is required for a pesticide if the end use product may be applied directly to water or expected to be transported to water from the intended use site, and the following conditions are met: ( 1) the pesticide is intended for use such that its presence in water is likely to be continuous or recurrent regardless of toxicity, ( 2) any aquatic acute LC50 or EC50 is less than 1 mg/ l, or, ( 3) the EEC in water is equal to or greater than 0.01 of any acute EC50 or LC50 value, or, ( 4) the actual or estimated environmental concentration in water resulting from use is less than 0.01 of any aquatic acute EC50 or LC50 value and any of the following conditions exist: studies of other organisms indicate the reproductive physiology of invertebrates may be affected, physicochemical properties indicate cumulative effects, or the pesticide is persistent in water ( e. g. , half life greater than 4 days) . Estuarine/ marine invertebrate testing was required for disulfoton due to its high acute toxicity to estuarine/ marine organisms, and the greater acute sensitivity of marine/ estuarine organisms compared to freshwater organisms. The results of this test are as follows:

42 Table 25. Life Cycle Toxicity of Disulfoton to Estuarine/ Marine Invertebrates Species % ai NOEC/ LOE C ( ppb) MATC ( ppb) Parameters Affected MRID # Author/ Year Classificatio n Mysid ( Mysidopsis bahia ) 98.5 2. 35 1 / 8. 26 5. 30 growth 43610901 Davis/ 1995 core 1 A NOEC was not achieved in the study, so an extrapolated EC05 for growth was calculated using linear regression. The MATC reported is the mean between the EC05 and LOEC values.

The growth of mysids was adversely affected at levels of 8.26 ppb and higher. Production and survival of young was adversely affected at levels of 120 ppb and higher.

v. Estuarine and Marine Field Studies No estuarine or marine field study data is available for disulfoton.

D. Toxicity to Plants i. Terrestrial Currently, terrestrial plant testing is not required for pesticides other than herbicides except on a case by case basis ( e. g. , labeling bears phytotoxicity warnings, incidents of plant damage have been reported, or literature indicating phytotoxicity is available) . The insecticide disulfoton does have phytotoxicity warnings on product labels; therefore, Tier I terrestrial plant testing ( Guideline 122 1) is required for disulfoton. No such data have been submitted to date.

ii. Aquatic Plants Aquatic plant testing is not required for pesticides other than herbicides except on a case by case basis ( e. g. , labeling bears phytotoxicity warnings, incidents have been reported involving plants, or literature is available that indicates phytotoxicity) . The insecticide disulfoton does have phytotoxicity warnings on product labels; therefore, Tier I aquatic plant testing ( Guideline 122 2) is required for disulfoton. No such data have been submitted to date.

4. Ecological Risk Assessment Risk assessment integrates the results of the exposure and ecotoxicity data to evaluate the likelihood of adverse ecological effects. One method of integrating the results of exposure and ecotoxicity data is called the quotient method. For this method, risk quotients ( RQs) are calculated by dividing exposure estimates by ecotoxicity values, both acute and chronic.

RQ = EXPOSURE/ TOXICITY 43 RQs are then compared to OPP' s levels of concern ( LOCs) . These LOCs are criteria used by OPP to indicate potential risk to nontarget organisms and the need to consider regulatory action. The criteria indicate that a pesticide used as directed has the potential to cause adverse effects on nontarget organisms. LOCs currently address the following risk presumption categories: ( 1) acute  potential for acute risk is high regulatory action may be warranted in addition to restricted use classification ( 2) acute restricted use  the potential for acute risk is high, but this may be mitigated through restricted use classification ( 3) acute endangered species  the potential for acute risk to endangered species is high regulatory action may be warranted, and ( 4) chronic risk  the potential for chronic risk is high regulatory action may be warranted. Currently, EFED does not perform assessments for chronic risk to plants, acute or chronic risks to nontarget insects, or chronic risk from granular/ bait formulations to mammalian or avian species.

The ecotoxicity test values ( i. e. , measurement endpoints) used in the acute and chronic risk quotients are derived from the results of required studies. Examples of ecotoxicity values derived from the results of short term laboratory studies that assess acute effects are: ( 1) LC50 ( fish and birds) ( 2) LD50 ( birds and mammals ( 3) EC50 ( aquatic plants and aquatic invertebrates) and ( 4) EC25 ( terrestrial plants) . Examples of toxicity test effect levels derived from the results of long term laboratory studies that assess chronic effects are: ( 1) LOEC ( birds, fish, and aquatic invertebrates) ( 2) NOEC ( birds, fish and aquatic invertebrates) and ( 3) MATC ( fish and aquatic invertebrates) . For birds and mammals, the NOEC value is used as the ecotoxicity test value in assessing chronic effects. Other values may be used when justified. Generally, the MATC ( defined as the geometric mean of the NOEC and LOEC) is used as the ecotoxicity test value in assessing chronic effects to fish and aquatic invertebrates. However, the NOEC is used if the measurement end point is production of offspring or survival.

44 Risk presumptions, along with the corresponding RQs and LOCs are tabulated below.

Table 26. Risk Presumptions for Terrestrial Animals Risk Presumption RQ LOC Birds and Wild Mammals Acute Risk* EEC 1 / LC50 or LD50/ sqft 2 or LD50/ day 3 0.5 Acute Restricted Use EEC/ LC50 or LD50/ sqft or LD50/ day ( or LD50 0.2 < 50 mg/ kg)

Acute Endangered Species EEC/ LC50 or LD50/ sqft or LD50/ day 0.1 Chronic Risk EEC/ NOAEC 1 1 abbreviation for Estimated Environmental Concentration ( ppm) on avian/ mammalian food items 2 mg/ ft 2 3 mg of toxicant consumed/ day LD50 * wt. of bird LD50 * wt. of bird * In the past, this category read   Acute High Risk.   The EFED is changing the wording of the conclusions to   Acute Risk   when the acute LOC exceedences are based solely on a screening level assessment. .

45 Table 27. Risk Presumptions for Aquatic Animals Risk Presumption RQ LOC Acute Risk* EEC 1 / LC50 or EC50 0.5 Acute Restricted Use EEC/ LC50 or EC50 0.1 Acute Endangered Species EEC/ LC50 or EC50 0.05 Chronic Risk EEC/ MATC or NOAEC 1 1 EEC = ( ppm or ppb) in water * In the past, this category read   Acute High Risk.   The EFED is changing the wording of the conclusions to   Acute Risk   when the acute LOC exceedences are based solely on a screening level assessment. .

Table 28. Risk Presumptions for Plants Risk Presumption RQ LOC Terrestrial and Semi Aquatic Plants Acute Risk* EEC 1 / EC25 1 Acute Endangered Species EEC/ EC05 or NOEC 1 Aquatic Plants Acute Risk* EEC 2 / EC50 1 Acute Endangered Species EEC/ EC05 or NOAEC 1 1 EEC = lbs ai/ A 2 EEC = ( ppb/ ppm) in water * In the past, this category read   Acute High Risk.   The EFED is changing the wording of the conclusions to   Acute Risk   when the acute LOC exceedences are based solely on a screening level assessment. .

A. Risk to Nontarget Terrestrial Animals i. Acute and Chronic Risk to Birds and Mammals from Nongranular products.

Nongranular formulations of disulfoton are applied either as a foliar spray ( often by air) , or as a spray directly to soil either preplant, or to soil beside the crop ( potato side dressing) . Foliar sprays are assumed to settle directly onto vegetation and other avian and mammalian food items. The residues on these food items are estimated by using a nomograph reported Hoerger and Kenega, 1972, and as modified by Fletcher, et al, 1994.

The acute risk quotients for broadcast applications of nongranular products are presented below.

46 Table 29. Avian and Mammal Acute Risk Quotients for peak exposure levels based on maximum residue values. Assuming an avian dietary LC50 of 333 ppm ( Japanese quail) , and mammal LD50 of 1.9 mg/ kg and a 3.3 day half life The mammalian LD50 of 1.9 mg/ kg was used to estimate 1 day LC50s for three different sized mammals: 15 gram mammal that eats 0.95 of its body weight per day: LC50 = 2 ppm 35 gram mammal that eats 0.66 of its body weight per day: LC50 = 2.9 ppm 1000 gram mammal that eats 0.15 of its body weight per day: LC50 = 12.7 ppm Formula: 1 day LC50 = LD50 ( mg/ kg) / proportion of body weight consumed Use Scenarios Maximum Exposure ( EEC in ppm) 1 and RQ EEC/ LC50 BIRDS MAMMALS short grass broad leaf long grass seeds fruit short grass broad leaf long grass seeds fruit Tobacco ; soil ( ground) ; 4 lbs ai/ acre; 1 appl per season EEC RQ 960 540 440 60 2.8 1. 6 1.3 0.2 960 540 440 60 15 g 35 g 1000 g 480 331 75 270 186 42 220 151 34 30 20 4 Beans; soil ; 2 lbs ai/ acre; 1 appl per season EEC RQ 480 270 220 30 1.4 0. 8 0.7 0.1 480 270 220 30 15 g 35 g 1000 g 240 186 42 135 93 21 110 75 17 15 10 2 Broccoli and wheat; soil; 1 lbs ai/ acre; 1 appl per season. EEC RQ 240 135 110 15 0.7 0.4 0. 3 < 0.1 240 135 110 15 15 g 35 g 1000 g 120 82 18 67 46 10 55 37 8 7 5 1 Potato; soil ( ground) ; 4 lbs ai/ acre; 2 appl per season; 14 day interval EEC RQ 1010 568 463 63 3.0 1. 7 1.4 0.2 1010 568 463 63 15 g 35 g 1000 g 505 348 79 284 195 44 231 159 36 31 21 4 Pecans & potatoes; ( aerial/ ground) ; 1 lb ai/ acre; 3 appl per season; 14 day interval ( Cotton; soil ( ground) ; 1 lb ai/ acre; 3 appl per season; 21 day interval: : should have slightly less risk due to less distribution of spray and peak & average residues are lower ) EEC RQ 253 142 116 15 0.7 0. 4 0.3 < 0.1 253 142 116 15 15 g 35 g 1000 g 126 87 19 71 48 11 58 40 9 7 5 1 Sorghum; soil ( aerial/ ground) ; 1 lb ai/ acre; 2 appl per season; 14 day interval ( Barley; foliar ( aerial/ ground) ; 1.0 lb ai/ acre; 2 appl per season; 21 day interval: should have slightly lower risk off site, since peak and average residues are lower; however, on site the risk may be higher due to crop foliage being sprayed directly)

( Spring wheat; foliar ( aerial/ ground) ; 0.75 lb ai/ acre; 2 appl per season; 30 day interval: should have slightly lower risk off site, since peak and average residues are lower. EEC RQ 252 142 115 15 0.7 0. 4 03 < 0.1 252 142 115 15 15 g 35 g 1000 g 126 87 19 71 48 11 57 40 9 7 5 1 Sorghum; foliar ( aerial/ ground) ; 0.5 lb ai/ acre; 3 appl per season; 14 day interval ( Cotton; foliar ( aerial/ ground) ; 0.5 lb ai/ acre; 3 appl per season; 21 day interval: should have slightly lower risk since peak and average residues are lower ) EEC RQ 126 71 58 7 0.4 0. 2 0.2 < 0.1 126 71 58 7 15 g 35 g 1000 g 63 43 9 35 24 5 29 20 4 3 2 0.5 47 1 The maximum exposure level is the highest level estimated based on the Hoerger and Kenega nomograph as modified by Fletcher, 1994. For scenarios with single applications, the maximum level is the concentration immediately after the treatment. For scenarios with multiple applications, the maximum concentration is that which occurs immediately after the final application. Bolded RQs meet or exceed the acute risk LOC ( 0.5) as well as the restricted use and endangered species LOCs. ; < 0.1 indicates no LOCs are exceeded; 0.1 or higher suggest effects to endangered or threatened species; 0.2 or higher indicates use pattern should be considered for restricted use The results of the risk screen indicate acute LOCs for risk, restricted use and endangered species are exceeded for birds at application rates above 1 lb ai / acre, and for mammals at all application rates.

Although soil applications are intended to be applied to bare soil, the risk quotients do include residues on grass and broad leaf plant material. Not only does this represent risk that might occur from contaminated vegetation inadvertently left in the fields at the time of treatment, but also compensates for not being able to address such additional routes of exposure as dermal, inhalation or drinking contaminated water. Within fields at the time of planting, vegetation is expected to be sparse, thereby reducing exposure and risk; however, the vegetation on the field margins will receive drift from both ground and aerial applications. Furthermore, many of disulfoton   s soil applied, soil incorporated ground applications are side dressings to emergent crops such as potatoes and cotton. In those instances, residues do appear on the under story of the crop and any weeds that are not incorporated ( especially those at the field edge) . The primary food items remaining in tilled fields are seeds and invertebrates. Insect residue were not estimated using the nomograph, however, for screening purposes, residues on insects may be similar to seeds and broad leafs, depending on the size of the insects.

Another source of uncertainty in the acute risk assessment for mammals is the credibility of the 1 day LC50 values derived from the rat LD50 of 1.9 mg/ kg when comparing the range of the 1 day LC50s ( 2 12.7 ppm) to the rat LC50 ( 320 ppm 95% CI [ 0  infinity ] ) for demeton. Demeton is an active ingredient that consists of a mixture of two isomers   demeton  S and demeton O in a ratio of 65: 35. Demeton O is structurally identical to the oxygen analog of disulfoton. The following tables illustrate the toxicological similarity between demeton and disulfoton.

48 Table 30. Toxicity of Demeton to Birds and mammals Species LC50 95% CI Source ( ppm)

Mallard 598 488 733 Hill 1975 Bobwhite quail 596 472 768 Hill 1975 Japanese quail 275 218 345 Hill 1986 Ring necked 665 572 773 Hill 1975 Pheasant Rat 319 0 infinity McCaan 1981 LD50 ( mg/ kg)

Rat  male 6.2 Gaines 1969 Rat female 2.5 Gaines 1969 Red wing Blackbird 2.37 22.0 a Schafer 1983 Table 31. Toxicity of Disulfoton to Birds and mammals Species LC50 95% CI Source ( ppm)

Mallard 510 415 625 Hill 1975 Bobwhite quail 715 617 827 Hill 1975 Japanese quail 334 275 405 Hill 1986 Ring necked 634 547 737 Hill 1975 Pheasant LD50 95% CI ( mg/ kg)

Rat  male 6.82 5.9 7.8 Gaines 1969 Rat female 2.3 1.7 3.1 Gaines 1969 Red wing Blackbird 3.2 1.8 5.6 Schafer 1983 a Range of LD50 values obtained in multiple studies 49 The above data suggests a very similar toxicity profile for demeton and disulfoton. Therefore, one might consider disulfoton   s rat dietary LC50 to be approximately 320 ppm. Unfortunately, there is uncertainty for this assumption due to the extremely wide 95% CI for demeton   s rat dietary LC50 study  zero to infinity. Even when allowing for the possibility the LC50 is 320 ppm would mean foliar applications of 1.0 lb ai/ A applied more than once would exceed the acute risk LOC  especially for herbivores. However, higher rates of soil directed sprays applied by ground equipment would not exceed the acute risk for herbivores.

The following table presents a screening level chronic risk assessment for both birds and mammals. The toxicity values used in the table are the NOAEL from the avian reproduction study ( 37 ppm) and the mammal 2 generation rat reproduction study ( 0.8 ppm) . Both peak EECs and time weighted averages of EECs based on Fletcher maximum residues are used to calculate risk quotients. The peak EEC is shown only for short grass, since that would represent the highest level. The time weighted averages of maximum EECs are calculated by dissipating maximum residues over 30 days and averaging the daily residues.

50 Table 32. Avian and Mammal Chronic Risk Quotients based on peak ( for short grass) and maximum 30 day average levels. Assuming an avian NOAEL of 37 ppm ( Bobwhite) , a mammal NOAEL of 0.8 ppm and a 3.3 day halflife Nongranular Use Scenarios 30 day Maximum Average EEC in ppm 1 and RQs AVIAN and MAMMALS CHRONIC RQs ( EEC / NOAEL)

short grass ( peak residue) broad leaf long grass seeds/ fruit Tobacco ; soil ( ground) ; 4 lbs ai/ acre; 1 appl per season EEC AVIAN RQ MAMMAL RQ 168 ( 960) 94 77 10 4.5 ( 25) 210 ( 1200) 2.5 117 2 96 0.2 12 Beans; soil ; 2 lbs ai/ acre; 1 appl per season EEC AVIAN RQ MAMMAL RQ 84 ( 480) 47 38 5 2.2 ( 13) 105 ( 600) 1.2 58 1 47 0.1 6 Broccoli and wheat; soil; 1 lbs ai/ acre; 1 appl EEC AVIAN RQ MAMMAL RQ 42 ( 240) 23 19 2.6 1 ( 6) 52 ( 300) 0.6 28 0.1 23 < 0.1 3 Potato; soil ( ground) ; 4 lbs ai/ acre; 2 appl per season; 14 day interval EEC AVIAN RQ MAMMAL RQ 331( 1010) 186 152 20 8.9 ( 27) 413 ( 1262) 5 232 4 190 0.5 25 Pecans & potatoes; ( aerial/ ground) ; 1 lb ai/ acre; 3 appl per season; 14 day interval ( Cotton; soil ( ground) ; 1 lb ai/ acre; 3 appl per season; 21 day interval: : should have slightly lower risk due to less off site distribution of spray and peak & average residues are lower) EEC AVIAN RQ MAMMAL RQ 88 ( 253) 49 40 5 2.4 ( 6.8) 110 ( 316) 1.3 61 1 50 0.1 6 Sorghum; soil ( aerial/ ground) ; 1 lb ai/ acre; 2 appl per season; 14 day interval ( Barley; foliar ( aerial/ ground) ; 1.0 lb ai/ acre; 2 appl per season; 21 day interval: should have slightly lower risk off site, since peak and average residues are lower; however, on site the risk may be higher due to crop foliage being sprayed directly)

( Spring wheat; foliar ( aerial/ ground) ; 0.75 lb ai/ acre; 2 appl per season; 30 day interval: should have slightly lower risk off site, since peak and average residues are lower; however, on site the risk may be slightly higher due to crop ed directly) EEC AVIAN RQ MAMMAL RQ 82 ( 252) 46 38 5 2 ( 6.8) 102 ( 315) 1.2 57 1 47 0.1 6 per season.

foliage being spray 51 Table 32. Avian and Mammal Chronic Risk Quotients based on peak ( for short grass) and maximum 30 day average levels. Assuming an avian NOAEL of 37 ppm ( Bobwhite) , a mammal NOAEL of 0.8 ppm and a 3.3 day halflife Nongranular Use Scenarios 30 day Maximum Average EEC in ppm 1 and RQs AVIAN and MAMMALS CHRONIC RQs ( EEC / NOAEL)

Sorghum; foliar ( aerial/ ground) ; 0.5 lb ai/ acre; 3 appl per season; 14 day interval EEC 44 ( 126) 24.9 20 2. 7 1.2 ( 3.4) 55 ( 157) 0.6 31 0.5 25 < 0.1 3 ( Cotton; foliar ( aerial/ ground) ; 0.5 lb ai/ acre; 3 appl per season; 21 day interval: should have slightly lower risk since peak and average residues are lower ) AVIAN RQ MAMMAL RQ 1 The exposure level is based on the maximum level for each vegetation category in the Hoerger and Kenega nomograph as modified by Fletcher, 1994. The 30 day average is the average of each daily residue value on the food item dissipated using a 3.3 day halflife. For uses with multiple applications, each subsequent application deposits ( adds) another maximum residue to the residue remaining from the previous application( s) and that maximum residue is dissipated over time, a total of 30 days. Bolded RQs meet or exceed the chronic risk LOC ( 1)

The above two risk assessment tables were derived from exposure estimates based on maximum Fletcher residue values. The risk screen did not differentiate between foliar treatments and soil applications. It is recognized that applications to bare soil, while not precluding residues on vegetation in and around the field, probably reduce the opportunity and extent of exposure. This would be significant to both the acute risk and chronic risk. The following discussion reports the results of two field residue monitoring studies ( MRID 411169 01 and 41201801) reflecting the difference in exposure for liquid formulations of disulfoton associated with foliar and soil applications.

Exposure from aerial applications to foliage Disulfoton as liquid Di syston 8E was aerially applied to potatoes 3 times at 1 lb ai/ acre in Michigan ( MRID 41201801) . Potato foliage was collected from five treated fields; 6 sample stations in each field. Samples were collected the day before and the day after each of the three treatments, and then on day 7 and 14 after the third ( final) treatment. Residues on noncrop vegetation adjacent to, and invertebrates in, treated fields were also measured. Samples were collected the day after each of three aerial applications of 1 lb ai/ acre and 7 days after the third ( last) application. The following table shows the peak, mean and upper bound of the 95 % confidence interval residue values of all fields after each treatment.

52 Table 33. The highest mean, 95 % confidence interval ( CI) and peak residues reported during the residue monitoring of terrestrial compartments following 3 aerial applications of Di syston 8E at 1.0 lbs ai/ A to potato fields.

Use Rate Applic. potato foliage off site non target invertebrates in or Number ( mean residues ppm) vegetation ( mean near treatment site residues ppm) ( mean residues ppm)

1 9 59 ( 95% CI) 7.1 1.6 2 18 78 ( 95% CI) 25 2.7 3 20 60 ( 95% CI) 9.3 4.5 for all upper 95% CI= 71 upper 95% CI= 11 1 lb ai/ acre ( at 6 10 day intervals) upper 95% CI= 78 mean= 41 peak= 105 treatments mean = 14 peak = 152 mean = 3 peak = 16 As will be discussed these results appear to clearly support Fletcher mean values for broad leaves. The potato foliage was sprayed directly and the mean of 41 ppm for all treatments was only slightly less than Fletcher   s mean for broad leaves ( 45 ppm for a single application and 47 for 3 applications) . Though the lower bound 95% CI for application # 1 was 9 ppm ( well below a single application mean of 45 ppm) , the upper bound 95% CI of 78 ppm for application # 2 was 1.7 times higher than Fletcher   s mean of 47 ppm for 3 applications. . The peak on the targeted potato leaves ( 105 ppm) was less than Fletcher   s maximum for broadleaves ( 135 ppm for a single application and 142 ppm for 3 applications) . Nevertheless the peak residue ( 152 ppm in application # 2) for vegetation in the adjacent areas was greater than Fletcher   s maximum for both a single and for 3 applications. Wind direction at the time of application may account for the seeming contradicting location of the peak values. Approximately 50% of the time the wind was moving away from the direction of the within field sampling station and approximately 40% of the time the wind direction was away from the sample station just outside the field perimeter. These monitoring results, coupled with those for azinphos methyl applied to apple orchards ( MRID 411397 01 & 411959 01) , support EFED   s assumption that foliar residues resulting from both single and multiple applications to foliage are estimated reasonably well using Fletcher values in a dissipation model.

Concerning the residues on invertebrates ( peak of 16 ppm and an upper bound mean 95% CI of 11 ppm) , it is acknowledged that an assumed direct application did not produce residues equal to those on broadleaves ( theoretically reflective of small insects) , but did compare favorably with Fletcher   s estimates for large insects ( maximum of 16 ppm and a mean of 7 ppm for 3 applications) . The question arises as to whether the sample pool consisted of   small   or   large   53 invertebrates. Furthermore, some of the individuals comprising the sample may have been on the underside of a leaf at the time of application and only acquired residues from contacting contaminated soil or leaves. Whereas those individuals ( especially the potato beetle) sprayed directly had died. These individuals contained higher residues, but were not part of the pool. Exposure from ground applications sprayed to soil A residue monitoring study was conducted in potato fields in Michigan ( MRID 411189 01) . Disulfoton was applied at 3 lb ai/ A as an in furrow spray application and again as a side dressing after 6 7 weeks. Invertebrates, crop and other vegetation, and soil were sampled within 24 hours after both applications. Invertebrates were collected in grids of pitfall traps in five fields, and potato beetles were collected on foliage by sampling stations. Soil samples were collected from the soil surface to a depth of 2 3 cm. Vegetation was available for sampling only after the second application. Mean and maximum residue values are found in the following table. The limit of detection was 0.09 ppm.

Table 34. Highest mean and ( maximum) residues reported during the residue monitoring of terrestrial compartments following 2 soil applications by ground equipment of Di syston 8E at 3.0 lbs ai/ A Application Invertebrates Soil Edge of field Potato Foliage ( ppm) ( ppm) vegetation ( ppm) ( ppm)

1 ( in furrow) 0.3 ( 0.9) 0.19 ( 1.8) 0.2 ( 0.9) 4.0 ( 26) *

2 ( side dressing) 0.4 ( upper 95% 2.9 ( upper 95% 3.5 ( upper 95% 8.0 upper 95% CI= 0.6) 1.8 14) 22 CI= 11) 54 CI= 16) 44 * Just prior to 2 nd application In contrast to foliar applications, ground applications to soil result in residues far below those predicted in EFED' S initial screen using Fletcher values. However it is noted ( especially for systemic pesticides) , residues are found in food items of non target organisms. In addition, as was previously stated, compensation must be made for the condition of a field ( the vegetation and invertebrates in the field at the time of application) and other routes of exposure besides ingestion of food. Mammals appear to be at risk both acutely and chronically from soil applications ( particularly side dressing) . The peak and mean residues in all media, except for invertebrates, exceed the the extrapolated 1 day LC50' s ( ranging for 2 to 12.7 ppm) and the chronic NOAEC ( 0.8 ppm) . The Agency acknowledges that the extrapolated mammalian 1 day LC50s for disulfoton may exaggerate the actual acute risk.

Risks from foliar treatments Tests were conducted by the Denver Wildlife Research Center ( Evans et al. 1970; MRID 54 413591 01) to examine the feasibility of using foliar applications of disulfoton to control jackrabbits. Although few details of the tests were provided, some information was gathered on risks to wildlife from foliar applications of disulfoton.

Unspecified numbers of jackrabbits and cottontail rabbits were introduced into enclosed plots six hours after foliar application to barley plants ( 12 days post emergence) at rates of 1, 2, 5, or 25 lb ai/ A. None of the cottontails died. No jackrabbit mortality was reported for the 1 lb ai/ A application, but mortality was 100% at rates of 2, 5, and 25 lb ai/ A. Additional tests were then conducted in enclosures planted with barley, alfalfa, wheat, or range grasses treated with a foliar application of 2 lb ai/ A. Unspecified numbers of jackrabbits, cottontails, pigmy rabbits, domestic rabbits, wild and game farm pheasants, and mallards were introduced post spray and exposed for anywhere from 0.5 to 13 days. Most or all jackrabbits died; but no mortality of other species was reported. Cholinesterase levels were reported as normal for cottontails, partridge, sage grouse, and pheasants.

Jackrabbits killed on spray plots in the pen tests also were fed to unspecified numbers of coyotes, dogs, golden eagles, a great horned owl, and a red tailed hawk. The number of jackrabbits consumed and their residue levels were not reported. Commercial mink also were fed digestive tracts, eviscerated carcasses, and uneviscerated carcasses of jackrabbits killed on 2 lb ai/ A spray plots. All secondary consumers fed continuously for anywhere from 3 to 30 days with no mortality, although some ChE depression was noted. In conclusion, it appears that foliar applications up to 1.0 lb ai/ A ( unless applied 3 or more times at intervals of less than 10 days) will not result in mortality to non rodents.

Because dietary LC50 values for birds are in the range of 333 to 827 ppm, EFED initially concluded that residues at these levels are not likely to be a significant acute risk to birds. More will be said abut the uncertainty of this conclusion in the risk characterization section. However there is a potential for chronic effects to birds since the NOAEC of 37 is exceeded by the peak residues found in crop foliage ( 44 ppm) and non crop vegetation ( 54 ppm) along the field borders. Given the fact that the LOAEC ( 78 ppm for bobwhite quail) is only slightly above the field residues there is uncertainty as to what duration of exposure will produce an adverse reproductive effect in birds. Furthermore some endpoints not examined under laboratory conditions could be negatively impacted under field conditions. These end points could include successful mating, nesting behavior or care of young. Adverse impact may occur either after a brief exposure to concentrations at the NOAEC level or a longer period at even lower levels.

ii. Risk from Granular Formulations of Disulfoton Birds and mammals may be exposed to granular pesticides ingesting granules when foraging for food or grit. They also may be exposed by other routes, such as by walking on exposed granules or drinking water contaminated by granules. The number of lethal doses ( LD50s) that are available within one square foot immediately after application ( LD50s/ ft 2) is used as the risk quotient for granular/ bait products. Risk quotients are calculated for three separate weight class of animals: 1000 g ( e. g. , waterfowl or medium sized mammal) , 180 g ( e. g. , upland gamebird or 55 small mammal) , and 20 g ( e. g. , songbird or very small mammal) .

The acute risk quotients for broadcast applications of granular products are tabulated below.

Table 35. Avian and Mammal Acute Risk Quotients for Granular Products ( Broadcast) Based on a Mallard LD50 of 6.54 mg/ kg and a rat LD50 of 1.9 mg/ kg.

LD50s per animal are calculated by multiplying the weight of the animal ( kg) by the LD50 in mg/ kg.

0. 020 Kg ( 20 g) bird LD50= 0. 13mg per bird Mammal LD50= 0. 038mg per mammal 0. 180 Kg ( 180 g) bird LD50= 1. 17 mg per bird Mammal LD50= 0. 34mg per mammal 1. 00 Kg ( 1000 g) bird LD50= 6. 54 mg per bird Mammal LD50= 1. 9mg per mammal Site/ Application Method/ Rate in lbs ai/ A Mammal or Bird Body Weight ( g) Mammal Acute RQ 1 ( LD50/ ft 2 ) Avian Acute RQ 1 ( LD50/ ft 2 )

Sorghum or Barley unincorporated 1 ( 10.41 mg/ sq ft) 20 273 a 79 a 1 ( 10.41 mg/ sq ft) 180 30 a 8 a 1 ( 10.41 mg/ sq ft) 1000 5 a 1. 5 a 1 RQ= mg per sq ft / LD50 per animal mg/ sq ft = ( app rate [ lb ai per acre ] * 453,590 [ mg per lb ] ) / 43,560 [ sq ft per acre ] LD50 per animal = LD50 ( mg/ kg) * wt ( kg) a= acute risk, restricted use and endangered species LOCs have been exceeded The results of this risk screen indicate that for broadcast applications of granular products, avian acute risk, restricted use, and endangered species levels of concern are exceeded at application rates equal to or above 1.0 lb ai/ A.

56 57 The acute risk quotients for banded or in furrow applications of granular products are as follows:

Table 36. Avian and Mammal Acute Risk Quotients for Granular Products ( Banded or In furrow) Based on a Mallard LD50 of 6.54 mg/ kg and a rat LD50 of 1.9 mg/ kg.

LD50s per animal are calculated by multiplying the weight of the animal ( kg) by the LD50 in mg/ kg.

0. 020 Kg ( 20 g) bird LD50= 0. 13mg per bird Mammal LD50= 0. 038mg per mammal 0. 180 Kg ( 180 g) bird LD50= 1. 17mg per bird Mammal LD50= 0. 34mg per mammal 1. 00 Kg ( 1000 g) bird LD50= 6. 54mg per bird Mammal LD50= 1. 9mg per mammal Site/ method oz ai per 1000 ft of row Band Width % granules left on surface after soil incorp. Exposure Concentration mg ai/ sq ft RQ ( LD50 / sq ft) AVIAN MAMMAL 20 gram animal 180 gram animal 1000 gram animal Tobacco/ Banded / Incorporated 6 0.5 15 51 avian 392a 43a 7a ( 4.0 lb ai/ A) mammal 1342a 150a 26a Potatoes/ In furrow / Incorporated 3.45 ( 3.0 lb ai/ A) 0.5 1 1.9 avian 15a 1.6a 0.3b mammal 51a 5.7a 1.0a Potatoes/ banded / Incorporated 3.45 ( 3.0 lb ai/ A) 0.5 15 29 avian 225a 25a 4.5a mammal 763a 85a 15.2a Vegetable ( cole crops, etc. ) / banded, incorporated 1.1 0. 5 15 9.36 avian 72a 8a 1.4a ( 0.97 lb ai/ A) mammal 246a 27a 4a 1 RQ= mg per sq ft / LD50 per animal mg/ sq ft = [ ( oz ai per 1000 ft * 28349 mg/ oz) ] [ % % unincorporated ( decimal) / bandwidth ( ft) * 1000 ft ] LD50 per animal = LD50 ( mg/ kg) * wt ( kg) a= acute risk, restricted use and endangered species LOCs have been exceeded b= restricted use and endangered species LOCs have been exceeded 58 Table 37. Avian and Mammal Acute Risk Quotients for Granular Products Based on a Mallard LD50 of 6.54 mg/ kg and a rat LD50 of 1.9 mg/ kg.

LD50s per animal are calculated by multiplying the weight of the animal ( kg) by the LD50 in mg/ kg.

0. 020 Kg ( 20 g) bird LD50= 0. 13mg per bird Mammal LD50= 0. 038mg per mammal 0. 180 Kg ( 180 g) bird LD50= 1. 17mg per bird Mammal LD50= 0. 34mg per mammal 1. 00 Kg ( 1000 g) bird LD50= 6. 54mg per bird Mammal LD50= 1. 9mg per mammal Site/ method lbs ai/ acre Band Width % granules left on surface after soil incorp. Exposure Concentration mg ai/ sq ft RQ ( LD50 / sq ft) AVIAN MAMMAL 20 gram animal 180 gram animal 1000 gram animal Rasberries/ Banded / Incorporated 11.75 oz ai/ 1000 ft ( 8 lb ai/ A) 2 15 25 avian 192a 21a 3.8 mammal 657a 73a 13a Christmas trees / spot treatment broadcast ( Sec 3) 3.75 oz prod/ tree with 1.5 inch diam at 4 ft.

0.562 oz ai / tree( ~ 2 sq ft) 1700 trees/ A ( 59.7 lbs ai/ A) 100 7966b avian 61276a 6808a 1218a mammal 209631a 23429a 4193a Christmas trees / spot treatment broadcast ( North Carolina 24 C) 5 gr product per tree 0.026 oz ai / tree( ~ 2 sq ft) 1700 trees/ A ( 2. 76 lbs ai/ A) 100 368b avian 2830a 314a 56a mammal 9684a 1082a 193a 1 RQ= mg per sq ft / LD50 per animal mg/ sq ft = [ ( oz ai per 1000 ft * 28349 mg/ oz) ] [ % % unincorporated ( decimal) / bandwidth ( ft) * 1000 ft ] LD50 per animal = LD50 ( mg/ kg) * wt ( kg) a= acute risk, restricted use and endangered species LOCs have been exceeded b= estimated by : ( oz ai/ tree) ( 28349 mg/ oz) / 2 sq ft/ tree The disulfoton 15G ( 15% ai) granule is applied in cotton, grains, sorghum, peanuts, soybeans, tobacco, coffee, nonbearing fruit trees, pecans, vegetables, flowers, shrubs, trees, and ground cover. The results of this screening level risk assessment indicate that for both birds and mammals acute risk, restricted use, and endangered species levels of concern are exceeded for banded and in furrow applications of granular products at registered maximum application rates equal to or above the lowest rate of 1.1 oz ai/ 1000 ft. Granules may be intentionally consumed as grit, mistaken for seeds, or may be ingested if attached to food items ( e. g. , earthworms) . Even when granules are incorporated that does not preclude exposure to birds and mammals. Fisher and Best ( 1995) examined granule availability in Iowa cornfields and found that 6% of granules applied in banded treatment were available on the soil surface, and granules were found in gizzards of 39% of 256 birds collected.

The LD50 per square foot screening approach for granulars can be refined by estimating how many disulfoton granules might be eaten by a bird in a day. Based on field counts and granule voiding experiments, 95% of the birds collected in Iowa cornfields were estimated to consume < 18 granules per day. For the savannah sparrow ( Passerculus sandwichensis ) , median consumption was 11 granules per day, with 5% of the individuals estimated to consume > 23 granules/ day ( Fisher and Best 1995) . A Di Syston 15G granule weighs 0.083 mg ( Balcomb et al. 1984, cited in MRID 413591 01) and thus contains 0.01245 mg ai. Eleven granules would contain 0.13695 mg ai. If an adult savannah sparrow weighs 20 g ( Dunning 1984) ; then an individual consuming 11 granules in a day ingests 0.13695 mg ai which equates to 6.8475 mg ai/ kg of its body weight. Assuming the LD50 for the sparrow is comparable to that for the red winged blackbird ( 3.2 mg/ kg) , a sparrow ingesting 11 granules would be exposed to 2.14 times the theoretical dose lethal to 50% of the population. In a laboratory study, 10 20 granules of Di Syston 15G were required to kill one out of five house sparrows ( weighs 28 gr) and red winged blackbirds ( weighs 60 gr) respectively ( Balcomb et al. 1984) . Since the test level in the study were 1,5,10 and 20 granules; it is possible the actual number of granules required to kill a house sparrow was from 6 to 9 and 11 to 19 for the red wing blackbird. Disulfoton granules may pose an even greater risk to mammals than to birds. Mammals may not intentionally eat granules, but granules can be consumed if attached to food items ( e. g. , soil invertebrates, seeds on the ground) or mistaken as food items ( e. g. , seeds) . Assuming an LD50 of 1.9 mg/ kg as for the female rat, a 20 g rodent would need to ingest only 0.038 mg ai ( 1.9 mg ai x 0.02 kg bw) to receive a dose lethal to 50% of the population. That dose could theoretically be obtained by eating 3 granules ( 0.038 mg ai/ 0.01245 mg ai/ granule) . The point to emphasize is that for any application described in the above table, at the time of application and until the granules disintegrate, there are sufficient numbers of unincorporated granules within a square foot to cause mortality   especially to small birds and mammals. .

Besides the intentional or inadvertent consumption of granules by birds and mammals, additional oral exposure to disulfoton is possible from consumption of soil during the disintegration of the granules. Estimates of soil ingestion by wildlife indicate that soil can comprise as much as 17 30% of the diet of species of some sandpipers and woodcock, presumably from consumption of soil organisms such as earthworms, which typically contain 20 30% soil ( Beyer et al. 1994) . Other species reported with soil in their diet include Canada geese ( 8% soil) , raccoon ( 9% soil) , armadillo ( 17% soil) , wood ducks ( 11% soil) , wild turkeys ( 9% soil) , and white footed mice ( Peromyscus leucopus ) fed foods containing either 0, 2% , 5% , and 15% soil ate equivalent amounts of food regardless of soil content ( Beyer et al. 1994) . Dermal contact of granules and contaminated soil also could increase an individual' s exposure. Disulfoton is a Toxicity Category I pesticide for dermal toxicity ( LD50 of 3.6 mg/ kg for mammals) , although the importance of dermal exposure of birds and mammals is uncertain in the field. Lastly, since disulfoton is systemic, non target organisms are exposed when ingesting invertebrates and plant foliage where granules have been applied.

A field study conducted in potato fields in Washington indicated that application of 15G granules can cause mortality of birds and mammals ( MRID 410560 00) . The fields were treated with two applications, each at a rate of 3 lbs ai/ A   one in furrow at planting and one side dressing 4 to 6 weeks later. Forty one bird species and 8 mammal species were observed in the potato fields during the study. During transect searches, 32 casualties were reported. However,

59 based on the Agency' s guidance for terrestrial field studies ( EPA 1986) , EFED concluded that the amount of area searched ( 5.5 acres) was not sufficient and that transects were too far apart for adequately locating carcasses. Moreover, only 2 of the 32 casualties were analyzed for disulfoton residues. Despite methodological problems with the study, EFED accepted it as a core study because it demonstrated mortality to wildlife inhabiting potato fields treated with 15G granules. Both in furrow and banded applications indicate mortality may be expected to occur. The table below summarizes the residue levels resulting from the two soil incorporated applications of Di Syston 15G.

Table 38. Mean and ( maximum) total disulfoton residues resulting from two applications of Di Syston 15 G Application Invertebrates Potato Foliage ( ppm) ( ppm)

1 ( in furrow) 0.14 ( 0.41) n/ a 2 ( side dressing) 0.9 ( 5.2) 7.5 ( 25)

Although these residues are considerably below concentrations anticipated to cause mortality, when coupled with 1) other routes of exposure  ingestion of granules and drinking from contaminated puddles   and 2) hypersentivity of some non targets organisms ( i. e. , jackrabbits and Swainson   s hawks) some mortality is possible.

The application of granular formulations of disulfoton to raspberry and Christmas tree may include hand operation   either dispensing or incorporation of granules; consequently there is a greater potential for granules to remain above ground. Although the labels for Christmas trees refers to incorporation or watering ( within 48 hours) usually incorporation can not be conducted and April rainfall rather than irrigation is generally relied upon to activate the granules. Therefore the granules may remain intact and above ground for at least several days. There are several additional factors that confound the amount and type of exposure wild life may encounter from disulfoton on the granules. Number one, the distribution of the granules under the drip line will range from a teaspoon being fanned out in several square feet or else a side dressing along two sides of each row of trees. Number two, present cultural practices include leaving vegetation between the rows and under the drip line. This vegetation may obscure an animal   s view of granules that have sifted through the cover or if moist, allow the granule to adhere to the leaf surface and be consumed by herbivores. Number three, after a rainfall the granules will dissolve and residues of disulfoton will appear in puddles and be taken up in vegetation. In light of these factors there is a high degree of uncertainty as to the degree of risk to wild life.

Christmas tree farms and the adjacent areas   forests and or pasture   provide excellent habitat for a great variety of wild life. The North Carolina Christmas Tree community has submitted numerous testimonials emphasizing the ever increasing numbers and diversity of wild life . This includes game animals such as turkey rearing young amidst the trees, song birds, rodents and foxes. Although this information is intended to suggest there is little or no negative impact from not only disulfoton, but other pesticides or cultural practices as well, the Agency would prefer to receive documented surveys or research before making a final determination.

60 Chronic Risk from Granular Formulations Estimating long term exposure from granular applications is difficult, since the granules are not expected to remain in tact over extended periods. The chemical is expected to become distributed in the soil, as the granules dissipate. . However, given that disulfoton is chronically toxic to birds and mammals at low dietary concentrations, granular applications may contribute to chronic risk.

iii. Insects Currently, EFED does not assess risk to nontarget insects. Results of acceptable studies are used for recommending appropriate label precautions. Disulfoton and its sulfoxide and sulfone metabolites are classified as highly toxic to the honeybee on an acute contact and oral basis, therefore, toxicity label language is required. Current labeling includes the appropriate bee toxicity warning statement.

B. Risk to Nontarget Freshwater and Estuarine Animals The following table shows the specific toxicity values that were used in assessing acute and chronic risk to aquatic and marine organisms. Species that demonstrated ranges of sensitivity were used, not just the most sensitive species.

61 Table 39. Toxicity endpoints used in assessing risk of aquatic organisms for disulfoton Species * Test Type Results ( ppb) Source of Data Freshwater Species Rainbow trout Acute LC50= 1850 40098001 Bluegill Acute LC50= 39 00068268 Channel catfish Acute LC50= 4700 40098001 Rainbow trout Early Life Stage NOAEC= 220 41935801 Bluegill Early Life Stage* * estimated NOAEC= 4.6 No study conducted Water flea Acute EC50= 13 00143401 Glass shrimp Acute EC50= 3.9 40094602 Stonefly Acute EC50= 5 40098001 Water flea Reproduction NOAEC= 0.037 41935802 Marine Species Sheepshead minnow Acute LC50= 520 40228401 Sheepshead minnow Early Life Stage NOAEC= 16.2 42629001 Sheepshead minnow Full Life Cycle EC05= 0.96* * * 43960501 Eastern Oyster Acute EC50= 720 40228401 Mysid Acute EC50= 100 40071601 Brown shrimp Acute EC50= 15 40228401 Mysid Life Cycle EC05= 2.35* * * 43610901 * The species listed and used in risk assessment were selected from the toxicity data because they seemed to represent a distribution of sensitivity. * * An early life stage study was not conducted with bluegill. The only freshwater fish chronic study was with rainbow trout. In the case of disulfoton, rainbow trout are significantly less sensitive than bluegill. So in an effort to translate this difference in sensitivity to the chronic risk assessment, a NOAEC for bluegill was calculated based on the ratio of acute toxicity. The lowest rainbow trout LC50= 1850 ppb. The bluegill LC50= 39. The ratio of trout to bluegill is 39/ 1850= 0.021. 0.021 X the trout NOAEC of 220 ppb = 4.6 ppb. There is uncertainty in this value, since it is estimated, and not derived from an actual toxicity test. * * * The study did not produce a NOAEC, however, the responses at the different concentrations were plotted used to estimate the concentration at which 5% effects would be expected, or an EC05.

Tier II estimated environmental concentrations ( EECs) for a variety of disulfoton applications were calculated to generate aquatic exposure estimates for use in the ecological risk assessment. In the risk quotient tables below, both freshwater and marine species are included in the same table. The first table presents the acute risk quotients based on modeling, the second table presents the chronic risk quotients. The modeling represents exposure in a 1 hectare 2 meter deep enclosed pond receiving runoff and drift from a 10 hectare treated field. This scenario is considered relatively conservative, but may not represent the highest exposure in all cases, since water bodies can be shallower, and thus may have higher exposure potential. On the other hand, many water bodies are larger, and have flow that may dilute concentrations. Long term exposures are especially uncertain when applied to flowing streams and rivers and estuaries and 62 may over estimate the risk. However, not all estuaries involve rapid exchange of water, so these estimates are not automatically considered overly conservative for all estuaries. .

Table 40. Acute risk quotients for freshwater and marine fish and invertebrates .

Acute risk quotients; peak EEC/ LC50 Use Pattern EEC ppb Freshwater surrogate species Marine surrogate species fish invertebrates fish invertebrates LC50 ( ppb) > bluegill 39 rainbow trout 1850 channel catfish 4700 glass shrimp 3.9 stonefly 5 water flea 13 sheepshead m. 520 brown shrimp 15 mysid 100 oyster 720 Tobacco soil 4.0 lb ai/ a 1 app per yr incorp 2.5 inches peak 26.7 0.6 < 0.01 < 0.01 6.8 5. 3 2.0 0.05 1.7 0.2 0. 03 Tobacco soil ( granular) 4.0 lb ai/ a 1 app per yr incorp 2.5 inches peak 18.4 0. 4 < 0.01 < 0.01 4.7 3. 6 1.4 0.03 1.2 0.18 0.02 Potato foliar 1.0 lb ai/ a 3 app at 14 day int. not incorporated peak 15.0 0. 3 < 0.01 < 0.01 3.8 3. 0 1.1 0.02 1.0 0.1 0. 02 Cotton soil 1.0 lb ai/ a 3 app at 21 day int. not incorporated peak 14.8 0. 3 < 0.01 < 0.01 3.7 2. 9 1.1 0.02 0.9 0.14 0.02 Barley foliar 1.0 lb ai/ a 2 app at 21 day int. not incorporated peak 9.2 0. 2 < 0.01 < 0.01 2.3 1. 8 0.7 0.01 0.6 0.09 0.01 Spring Wheat foliar 0.75 lb ai/ a 2 app at 30 day int. not incorporated peak 8.9 0.2 < 0.01 < 0.01 2.2 1. 7 0.6 0.07 0.59 0.08 0.01 Potato soil 4.0 lb ai/ a 2 app at14 day int. incorp to 2.5 inches peak 7.1 0. 18 < 0.01 < 0.01 1.8 1. 4 0.5 0.01 0.47 0.07 < 0.01 Barley soil ( granular) 0.83 lb ai/ a 2 app at 21day int. not incorporated peak 7.1 0. 18 < 0.01 < 0.01 1.8 1. 4 0.5 0.01 0.47 0.07 < 0.01 Risk quotients exceeding the acute risk LOC of 0.5 are bolded The LOC for restricted use is 0.1 The LOC for endangered species is 0.05 The screening assessment results indicate that except for the highest application to tobacco, the acute risk LOC has not been exceeded for fish. Estuarine fish appear to be a far less risk than freshwater fish. On the other hand, the RQs for all modeled uses exceed the acute risk LOC for 63 64 fresh water invertebrates. Although two of the three test species of estuarine invertebrates did not suggest risk, based on the brown shrimp, estuarine invertebrates are at acute risk from all modeled crops. Especially for estuarine invertebrates there is uncertainty as to the degree of the acute risk.

Table 41. Chronic risk quotients for freshwater and marine fish and invertebrates .

Chronic risk quotients; ave. EEC/ NOAEC or EC05 Use Pattern EEC ppb Freshwater surrogate species Marine surrogate species fish inverteb rates fish inverte brates NOAEC ( ppb)   > bluegill 4. 6 rainbow trout 220 water flea 0. 037 sheepshea d life cycle 0. 96 Sheepshead early life st. 16. 2 Mysid life cycle EC05= 2. 35 Tobacco soil 4.0 lb ai/ a 1 app per yr incorp 2.5 inches 21 d 17.9 60 d 9.9 2 < 0. 1 483 10.3 0.6 7.6 Tobacco soil ( granular) 4.0 lb ai/ a 1 app per yr incorp 2.5 inches 21 d 12.5 60 d 6.7 1.4 < 0. 1 337 6.9 0.4 5 Potato foliar 1.0 lb ai/ a 3 app at 14 day int. not incorporated 21 d 10.4 60 d 6.9 1.5 < 0. 1 281 7.1 0.4 4.4 Cotton soil 1.0 lb ai/ a 3 app at 21 day int. not incorporated 21 d 8.0 60 d 4.9 1 < 0. 1 216 5.1 0.4 3.4 Barley foliar 1.0 lb ai/ a 2 app at 21 day int. not incorporated 21 d 5.9 60 d 3.7 0. 8 < 0.1 159 3.8 0.2 2.5 Spring Wheat foliar 0.75 lb ai/ a 2 app at 30 day int. not incorporated 21 d 4.5 60 d 2.6 0. 5 < 0.1 121 2.7 0.1 1.9 Potato soil 4.0 lb ai/ a 2 app at14 day int. incorp to 2.5 inches 21 d 4.3 60 d 2.3 0. 5 < 0.1 116 2.4 0.1 1.8 Barley soil ( granular) 0.83 lb ai/ a 2 app at 21day int. not incorporated 21 d 5.4 60 d 3.8 0. 8 < 0.1 145 3.9 0.2 2.2 Risk quotients exceeding the chronic risk LOC are bolded Risk quotients for invertebrates and fish are based on 21 and 60 day EECs respectively Both fish and invertebrates are likely to experience chronic effects based on modeled EECs. Freshwater invertebrates are at much greater risk than fish or estuarine invertebrates.

Risk to Freshwater Organisms from the use of Disulfoton 15 on Christmas Trees in North Carolina The use of Disulfoton 15 G in Christmas tree farms at this time can not be modeled for potential surface water contamination. EFED assumes the estimated concentration for the North Carolina 24 ( c) use pattern   2.75 lbs ai/ A unincorporated   may be similar to the values for the single 4.0 lb ai/ A incorporated application of granular disulfoton to tobacco. Based on this assumption there is acute risk to aquatic invertebrates and chronic risk to freshwater fish and aquatic invertebrates. Since this preliminary screen of the 24( c) exceeds levels of concern, the Sec 3 use at 59.7 lbs ai/ A would exceed ( perhaps by 20 fold) the same levels of concern for aquatic life and the acute risk for fish as well. However, even if the receiving body of water was a pond ( as was modeled for tobacco) this assumption has uncertainty because although the Christmas tree use pattern has a lower rate and current cultural practices recommend maintaining vegetation under the trees and between the rows; nevertheless the material is not incorporated. Therefore while the first two conditions may reduce the estimated concentrations below those for tobacco, the third condition may increase the concentrations.

The North Carolina Christmas tree industry has provided information that has contributed to a refinement of EFED   s risk assessment for aquatic organisms from Christmas tree farming. Firstly, the primary and nearly exclusive use site for Disulfoton 15 G on Christmas trees throughout the United States is on Fraser fir grown in 6 counties in Western North Carolina, thereby localizing the exposure and precluding any estuarine exposure. Secondly, the primary aquatic sites adjacent to tree farms are streams, not ponds. Residues in these streams will be lower and of shorter duration than would be expected for a pond. Thirdly, two rapid assessment macro invertebrate surveys of streams in the Western region of North Carolina have been submitted. The following is a brief discussion of those results.

In the 1998 study conducted by the North Carolina Department of Environmental Health and Natural Resources ( DEHNR) , 8 of 11 streams were sampled once in May ( presumably after the April/ May application of disulfoton) at one location. The 3 other streams were sampled a second time in August as a means to correct for likely seasonal changes in the species composition of Ephemeroptera, Plecoptera and Trichoptera ( EPT) . These three Orders of invertebrates are considered to be sentinel species indicative of overall water quality.

In spite of some concerns such as the mixed influence of cattle or development along with Christmas tree farms and the preference for a more rigorous study design ( i. e. residue analysis and more frequent sampling) the Agency considered the survey   s utility in light of several factors: an on site visit in June 2000; the support for the protocol as described in the EPA publication: EPA 841 B 99 002; the nation wide use of disulfoton on Christmas trees is primarily in this region where it has been used for 20 years and the submission of a second survey conducted from December 1998 through mid to late summer 1999.

65 The second survey examined 5 sites   each consisting of an area adjacent or downstream from a Christmas tree farm paired with its own reference site ( either a station on the same stream, but above the tree farm or a second stream. Quantification  included the total number of insects and the break out ( expressed as a % of insects) for mayflies, stoneflies, caddisflies, riffle beetles and   other   insects. A species list for mayflies, stoneflies and caddisflies along with and index of their sensitivity and the dates collected was provided for 3 of the 5 sites. Data for each of the reported 3 pairs of sites were analyzed using ANOVA.

Unlike the DEHNR survey where various communities ( leaf packs, riffles, banks and large rocks and logs) were sampled, only the riffle community was sampled. Like the DEHNR survey, no residue analysis was performed for any pesticide including disulfoton. Again the researcher made the point that the protocol seeks to detect whether an impact is occurring due to the combination of numerous influences without quantifying the degree of exposure to a specific chemical( s) .

The Agency concurs with the investigators that when implementing ( but not limited to) conservation measures such as establishing ground cover throughout the farm, constructing and maintaining the fewest number of roads and bridges, creating a riparian zone to include vegetation and trees and employing Integrated Pest Management practices, there appears to be   . . . . little negative effect on the fauna of adjacent streams. . . .   The slight negative effect that was observed seemed to impact stoneflies ( Plecoptera) more than the two other orders   caddisflies ( ( Trichoptera) and mayflies ( Ephemeroptera)  that were the focus of the survey.

In summary, the two surveys suggests that when conservation measures associated with Christmas tree farming in the Western counties of North Carolina are implemented, there may be only slight, short term impact to aquatic macro invertebrates from disulfoton use. Aquatic macro invertebrates appear to have the capacity to recover from any impact that could be caused by disulfoton use on Christmas trees in Western North Carolina.

66 C. Exposure and Risk to Nontarget Plants Although Tier I terrestrial and aquatic plant testing is required for disulfoton due to label phytotoxicity warnings, no data on plant toxicity has been submitted at this time. Therefore, the risk to nontarget plants cannot be assessed.

5. Endangered Species The following endangered species LOCs have been exceeded for disulfoton: avian acute, avian chronic, mammalian acute, mammalian chronic, freshwater fish acute, freshwater invertebrate acute, freshwater invertebrate chronic, marine/ estuarine fish acute, marine/ estuarine fish chronic, marine/ estuarine invertebrate acute, and marine/ estuarine invertebrate chronic. Endangered terrestrial, semi aquatic and aquatic plants also may be affected, based on label statements indicating phytotoxicity.

The OPP Endangered Species Protection Program ( ESOP) is developing ways to protect endangered species from hazardous pesticides. Limitations on the use of disulfoton will be required to protect endangered and threatened species, but these limitations have not been defined and may be formulation specific. EPA anticipates that a consultation with the Fish and Wildlife Service may be conducted in accordance with the species based priority approach described in the ESOP. After completion of consultation, registrants will be informed if any required label modifications are necessary. Such modifications would most likely consist of the generic label statement referring pesticide users to use limitations contained in county Bulletins.

6. Disulfoton Incident Reports There are both bird and fish kills reported for disulfoton. The following are summaries of incidents reports available to the Agency.

BIRD INCIDENTS: 1. Young County, TX, 6/ 18/ 93. Eighteen Swainson   s hawks were found dead and one found severely disabled in a cotton field. The cotton seed had been treated with disulfoton seed treatment prior to planting, about 10 days before the birds were discovered. According to field personnel, no additional applications of organophosphorus or carbamate pesticides had been made in the vicinity of the field. Autopsies revealed no signs of trauma or disease. Laboratory analysis of the birds revealed insect material in the gastrointestinal tracts. Residue chemistry analysis of this material indicated the presence of disulfoton ( approximately 7 ppm) ; no other organophosphorus or carbamate insecticides were present. Apparently, the hawks had fed on insects, which had been feeding on the young cotton plants. The systemic nature of the pesticide appears to have resulted in plant residues, which were then taken up by the insects, at levels high enough to cause mortality in the hawks. This may be the first documented incident of this type of exposure in a captor species. ( L. Lyon, Div. of Environmental Contaminants, U. S. Fish and Wildlife Service, Arlington, VA. Presented at the SETAC 18th annual meeting, San Francisco, CA, 1997) . The Agency has been able to confirm the incident through personal communication with Stephen Hamilton, the Special Agent of the U. S. Fish and Wildlife in charge of the investigation, who stated there was no evidence of misuse.

2. Sussex County, DE, 4/ 26/ 91. Nine American robins found dead following application of granular disulfoton at a tree nursery. Corn and soybeans were also in the vicinity. No 67 laboratory results were obtained. Certainty index is probable for disulfoton. ( Incident Report No. I000116 003) .

3. Puerto Rico, 1/ 24/ 96. Six grackles fell dead from a tree in the yard of a private residence. A dead heron and a dead owl were also found in the vicinity. The use site and method were not reported. Birds had depressed acetyl cholinesterase. Residue analysis on gut contents of one of the grackles found disulfoton residues of 12.37 ppm wet weight. Certainty index of this incident is highly probable for disulfoton. ( Incident Report No. I003966 004) .

FISH INCIDENTS 1. Onslow County, NC, 6/ 22/ 91. A fish kill occurred in a pond at a private residence. The pond received runoff from a neighboring tobacco field. Analysis of the water in the pond revealed the presence of disulfoton and several other pesticides, including endosulfan. Disulfoton sulfoxide was found in the water at a concentration of 0.32 ppb. Endosulfan had the highest concentration ( 1.2 F g/ L) , and is toxic to fish, but disulfoton cannot be ruled out as a possible cause of death. No tissue analysis was conducted. The certainty index of this incident for disulfoton is   possible.   ( ( Incident Report No. B0000216 025) .

2. Onslow County, NC, 4/ 29/ 91. A fish kill occurred in a pond, which was adjacent to a tobacco field and a corn field. Rain followed the application of pesticide, and more than 200 dead fish were found floating in the pond. Water and soil samples were collected within a week after the incident. Several organophosphorus pesticides, as well as atrazine and napromide, were found in all soil samples taken from around the pipe that ran from the field to the pond, but none of the samples contained detectable disulfoton. The pesticide applicator failed to follow packaging guidance on safe handling of the pesticides. Additionally, the corn and tobacco fields were 62 82 feet uphill from the pond, which violates the requirement that these pesticides not be applied within 140 feet of a waterway. The certainty index for this incident is   unlikely   for disulfoton ( ( Incident Report No. I000799 004) .

3. Johnston County, NC, 6/ 12/ 95. A fish kill occurred in a commercial fish pond. Crop fields nearby had been treated with pesticides. Water, soil and vegetation samples were taken and analyzed for a variety of pesticides. Disulfoton, as well as several other pesticides was found in the samples. The level of disulfoton in the vegetation samples was 0.2 2.5 ppm. The certainty index for this incident is   possible   for disulfoton. . ( Incident Report No. I003826 002) .

4. Arapahoe County, CO, 6/ 14/ 94. A fish kill occurred following application of Di Syston EC. to wheat, which was followed by a heavy rain. Water samples collected contained disulfoton sulfoxide at levels of 29.5 48.7 ppb, and disulfoton sulfone at 0.0199 0.214 ppb. The wheat field was located several miles from the pond. The volume of run off water raised the level of the pond fifteen feet. In addition to the rapid rise of the water level there was a large mass of sediment and vegetation that may have resulted in a severe drop in the Biological Oxygen Demand levels. The certainty index for this incident is   possible   for disulfoton. . ( Incident Report No. I001167 001) .

Some of these incident reports tend to support the conclusions of the risk screens indicating LOCs for acute risk are exceeded.

68 Risk Characterization A. Characterization of the Fate and Transport of Disulfoton i. Water Exposure ( a) Surface Water Disulfoton is likely to be found in runoff water and sediment from treated and cultivated fields. However, the fate of disulfoton and its degradates once in surface water and sediments, and the likely concentrations therein, cannot be modeled with a high degree of certainty since data are not available for the aerobic and anaerobic aquatic degradation rates. Surface water concentrations of disulfoton and total disulfoton residues were estimated by using PRZM3 and EXAMS models using several different scenarios ( barley, cotton, potato, tobacco, and spring wheat) . The large degree of latitude available in the disulfoton labels also allows for a wide range of possible application rates, total amounts, application methods, and intervals between applications. Considering the relatively rapid rate of microbial degradation in the soil ( < 20 day aerobic soil metabolism half life) and direct aquatic photolysis, disulfoton parent may degrade fairly rapidly in surface water. However, peak concentrations of disulfoton in the farm pond appear capable of being quite high, with 1 year in 10 peak surface water concentrations of 7.14 to 26.75 F g/ L and 90 day concentrations of 1.73 to 6.87 µ g/ L for the parent compound. The mean EECs of the annual means of disulfoton ranged from 0.21 to 1.14 µ g/ L. Although there is a lack of some environmental fate data for the degradates, the assessment suggests that the degradates will reach higher concentrations than the parent because they are more persistent and probably more mobile. The estimated peak concentrations for the total disulfoton residues in the farm pond ranged from 15.43 to 58.48 µ g/ L, 90 day average ranged from 12.20 to 35.30 µ g/ L, and the mean of the annual means ranged from 3.89 to 9.32 µ g/ L. Water samples collected at the site of a fish kill in Colorado contained D. sulfoxide at levels of 29.5 48.7 µ g/ L, and D. sulfone at 0.0199 0.214 µ g/ L. The aerobic soil metabolism studies show that the maximum sulfoxide residues are about 58 percent of total radioactive material, thus, the sulfoxide concentrations suggest that parent disulfoton concentrations could range from 50.8 to 83.9 µ g/ L. The ratio of the disulfoton sulfoxide concentration to the average maximum disulfoton concentration was higher ( 74% ) in the microcosm study ( MRID # 4356501) than in the soil residues ( 58% ) .

The estimated drinking water concentrations ( EDWC) for parent disulfoton and total disulfoton residues were also determined using the IR and PCA concepts. The peak concentrations of disulfoton in IR appear capable of being quite high, with 1 year in 10 peak surface water concentrations of 7.13 to 44.20 F g/ L and annual mean concentrations of 0.43 to 2.77 µ g/ L for the parent compound. The mean EECs of the annual means of disulfoton ranged from 0.23 to 1.31 µ g/ L. Although there is a lack of some environmental fate data for the degradates, the assessment suggests that the degradates will reach higher concentrations than the parent because they are more persistent and probably more mobile. The estimated 1 in 10 year peak concentrations for the total disulfoton residues in the IR ranged from 20.83 to 104.92 µ g/ L and annual mean ranged from 5.10 to 16.25 µ g/ L, and the mean of the annual means ranged from 2.55 to 10.42 µ g/ L. These values will also be highly affected by the value selected for PCA.

Surface water samples were collected in a study to evaluate the effectiveness of Best Management Practices ( BMP) in a Virginia watershed. Approximately half of the watershed is 69 in agriculture and the other half is forested. The detections of parent disulfoton in surface water samples ranged from 0.037 to 6.11 µ g/ L and fell within an order of magnitude with the estimated environmental concentrations ( EECs) obtained from the PRZM/ EXAMS models.

Surface water monitoring by the USGS in the NAWQA ( USGS, 1998) project found relatively few detections of disulfoton in surface water with a maximum concentration of 0.060 µ g/ L. As noted above disulfoton degradates were reported in surface water, when a rainfall event occurred following application to wheat, where fish kills occurred; pesticide residue concentrations ranged from 29.5 to 48.7 µ g/ L for D. sulfoxide and 0.02 to 0.214 µ g/ L ( Incident Report No. I001167 001) .

A search of the EPA   s STORET ( 10/ 16/ 97) data base resulted in the identification of disulfoton residues at a number of locations. Often the values ranged from 0.01 to 100.0 F g/ L with most of the values reported as   actual value is less than this value.   Thus, , when a value of 100.00 µ g/ L is reported, it is not known how much less than 100.0 F g/ A the actual value is known to be less. Thus there is considerable uncertainty surrounding some of the data in STORET.

( b) Ground Water The SCI GROW ( Screening Concentration in Ground Water) screening model developed in EFED was used to estimate disulfoton concentrations in ground water ( Barrett, 1999) . SCI  GROW represents a " vulnerable site" , but not necessarily the most vulnerable conditions, treated ( here) with the maximum rate and number of disulfoton applications, while assuming conservative environmental properties ( 90 percent upper confidence bound on the mean aerobic soil half life of 6.12 days and an average Koc value of 551 mL/ g) . The maximum disulfoton concentration predicted in ground water by the SCI GROW model ( using the maximum rate 4 lb. a. i. / ac and 2 applications  potatoes) was 0.05 µ g/ L. The maximum total disulfoton residue concentration predicted in ground water by the SCI GROW model for the same scenario is 3.19 µ g/ L ( except 90 percent upper bound on mean half life of total residues is 259.6 days) .

Ground water monitoring data generally confirms fairly rapid degradation and low mobility in soil, because of the relatively low levels and frequency of detections of parent disulfoton in ground water. There were no ground water detections of parent disulfoton in the USGS NAWQA ( USGS, 1998) with a limit of detections of 0.01 or 0.05 µ g/ L, depending upon method.

Most of the studies recorded in the PGWDB ( USEPA, 1992) also reported no disulfoton detections. Disulfoton residues ranging from 0.04 to 100.00 µ g/ L were reported for studies conducted in Virginia ( 0.04 to 2.87 µ g/ L) and Wisconsin ( 4.00 to 100.00 µ g/ L) . Of specific interest are areas where the concentrations of parent disulfoton reported in the studies ( VA and WI) exceeded the estimate of 0.05 µ g/ L obtained from EFED' s SCI GROW ( ground water screening model) model. It should be noted that the Wisconsin data received some criticism which influences the certainty of these detections, no such criticisms or limitations exist for the Virginia study.

The major issues, concerning the Wisconsin study ( Central Sands) were that the study may not have followed QA/ QC on sampling and the failure of follow up sampling to detect disulfoton residues in ground water as suggested by Holden ( 1986) , have been considered by EFED in the 70 ground water quality assessment. The Central Sands of Wisconsin are known to be highly vulnerable to ground water contamination. There are regions within the United States that have conditions that are highly vulnerable to ground water contamination and regularly have pesticides detected in ground water which far exceeds values seen elsewhere. Several of these areas are well documented, e. g. , Long Island, Suffolk County, NY and Central Sands in WI. Although, some questions have been levied against the disulfoton detections in Wisconsin, the occurrence of disulfoton at the levels reported cannot be ruled out.

There were no detections of disulfoton, disulfoton sulfoxide, and disulfoton in the ground water monitoring study conducted in North Carolina. Efforts were made to place the wells in vulnerable areas where the pesticide use was known, so that the pesticide analyzed for would reflect the use history around the well. Seven Christmas tree, one wheat, and two tobacco growing areas were sampled for disulfoton. Limitations of the study include that sites were sampled only twice and the limits of detections were high ( e. g. , > 1.0 µ g/ L) for some of disulfoton analytes. Uncertainties associated with the study include whether two samples from eight wells are adequate to represent the ground water concentrations of disulfoton residues, did DRASTIC correctly identify a site' s vulnerability, and were the wells placed down gradient of the use areas.

The SCI GROW model represents a " vulnerable site" , but not necessarily the most vulnerable. Several things should be considered. First, the Virginia and Wisconsin monitoring studies were probably conducted in areas vulnerable to ground water contamination. The level of certainty with respect to vulnerability is probably greater for Wisconsin ( relatively less uncertainty) than for Virginia ( relatively more uncertainty ) . The occurrence of preferential flow and transport processes has been also noted in Wisconsin ( and is also possible in Virginia) and may ( speculation) have contributed to the " high" concentrations ( especially in WI) when the initial sampling occurred, but not necessarily in the follow up sampling) . The knowledge concerning the disulfoton use in areas in association with the wells is not well known ( high uncertainty) . Some notable limitations of modeling and monitoring are presented elsewhere in this document ( c) Drinking Water The estimates of disulfoton residues in drinking water in an index reservoir adjusted by percent crop area in the watershed is using the coupled PRZM/ EXAMS models. The Agency recommends that the 1 out of 10 year peak values be used the acute surface drinking water level for parent disulfoton, and for chronic levels use either the 90 day and annual average. The maximum values are: 44.20, 2.77, and 1.31 µ g/ L or the peak, 90 day mean, and long term mean, respectively. For the total disulfoton residues the peak, 90 day mean, and long term mean are 104.92, 53.47, and 10.42 µ g/ L. The EDWCs for both parent disulfoton and TDR exceed the DWLOC values estimated by the Agency. The EDWCs values for the parent disulfoton have less uncertainty than the total residue, because there is more certainty surrounding the " estimated" aerobic aquatic metabolism half life for the estimated aerobic aquatic half life for the total disulfoton residues. It is recommended that the Virginia data be considered in the " quantitative" drinking water assessment for ground water exposure. The Wisconsin data should be noted and addressed more qualitatively. Highly vulnerable areas, such as the Central Sand Plain, do not represent the entire use area and can probably be better mitigated or managed a local or state level. Specifically, it is recommended that the 2.87 µ g/ L be used for acute and chronic exposure from ground water. Based upon the fate properties of 71 disulfoton, the sulfoxide and sulfone degradates ( more persistent and probably more mobile) have a greater probability of being found in ground water. It is likely that ground water and surface water monitoring study ( ies) may be required to better assess the potential exposure from the degradates ( and also parent) in addition to the additional fate data requirements.

The registrant disagreed with aquatic dissipation half life of 259 days for total disulfoton residues and cites a microcosm study ( MRID 43568501) and an open literature study ( La Corte et al. , 1994; 1995) which they believe provide data relevant to aquatic dissipation. However, aerobic and anaerobic aquatic metabolism studies which could provide valid model inputs for the degradates disulfoton sulfone and disulfoton sulfoxide have not been submitted. Although the registrant provided the Agency with additional information concerning the fate of disulfoton residues in water under controlled artificial conditions ( MRID 43568501 and LaCorte et al. , 1995) , this information is limited and cannot be used for model inputs. Specifically, these studies provide information concerning the combined effects of hydrolysis, photolysis, and metabolism, with photodegradation contributing significantly to the dissipation. ( An input value for photodegradation was included in the modeling, so this process was incorporated into the dissipation of disulfoton as simulated in the modeling. ) Model input values should be derived from studies which isolate a given process, i. e. , aquatic metabolism, from other routes of dissipation which are considered separately by the model. EFED believes it is not appropriate to use dissipation values, such as those provided in the studies cited by the registrant, as inputs for models which are intended to simulate dissipation from a variety of individual processes.

The 259 day half life was the upper 90% confidence bound on the mean of total residue half lives in aerobic soil metabolism studies ( MRIDs 40042201, 41585101, 43800101) . Because there are no studies for individual degradates from which model inputs can be derived, and because these degradates are of toxicological concern, it is appropriate to use total residue data from the existing studies. The assessment could be refined if studies for the individual degradates were conducted and model inputs could be derived from these studies. The aerobic soil metabolism half life is used to estimate the aerobic aquatic half life when aerobic aquatic data are not available. OPP has noted that this contributed to the uncertainty of the water assessment.

EFED thinks that it is appropriate to use total residues to estimate exposure when there are toxic degradates and when data are not available for the individual degradates. This will contributed to the uncertainty of the water assessment.

B. Characterization of risk to nontarget species from Disulfoton Birds: Birds: Acute risk to birds is predicted especially for use patterns involving the 15 G formulation. All modeled application rates and methods for the 15 G formulation exceed the acute risk level of concern for birds, regardless of size. Robins were reported to have been killed following the application of a disulfoton granular product to a tree nursery. Carcasses were found during terrestrial field testing of disulfoton on potatoes, confirming the presumption of acute risk to birds. Since disulfoton is a systemic pesticide, the granular formulations can result in exposure through food items due to uptake by the plant tissues in addition to direct exposure to any unincorporated granules.

72 Foliar applications of liquid formulations present the greatest risk to herbivorous birds. Based on the results of field studies, the residue levels on sampled invertebrates are well below those predicted by EFED' s models, consequently insectivores did not appear to be at risk. However, there is field evidence suggesting that some species are extremely sensitive to disulfoton such that even low concentrations caused mortality. The Swainson   s hawk kill appears to be the result of consuming grasshoppers. The hawks crop contents were analyzed and contained residues around 8 ppm. Finally, live blue jays collected 6 to 7 hrs after a pecan orchard was sprayed at 0.72 lbs ai/ A had brain cholinesterase inhibition from 32 to 72% ( White et al. 1990) . Although it is unknown whether these birds would eventually die, Ludke et al. 1975 suggest that inhibition > 50% in carcasses is evidence that death was caused by some chemical agent. Furthermore, it should be recognized that these birds were not only feeding on contaminated food, but also were impacted by dermal and inhalation exposure.

Ground applications of liquid formulations to soil, even at 4.0 lb ai/ A would not be expected to cause mortality to birds. Field studies have demonstrated that residue concentration within food items   vegetation, invertebrates and seeds   in or on the edge of fields are well below those used in screening level assessments and empirically derived from aerial applications. However, in light of the points made in the previous paragraph, some mortality is possible given the possible multiple routes of exposure and hypersensitivity of some species.

Chronic risk to herbivorous birds are predicted from exposure to disulfoton when assuming birds are exposed to peak residues for a short period of time or average Fletcher maximum residues for longer periods. Based on reduced hatchling weight, the NOAEC is 37; both for bobwhite quail and mallard duck. Foliar applications and aerially applied soil sprays are estimated to result in 30 day average residues ( based on maximum Fletcher values) on vegetation exceeding the avian chronic level of concern for application rates equal or greater than a single application of 1 lb ai/ A. A residue monitoring study for Di Syston 8E in potatoes showed the peak residues on vegetation was 105 ppm after the initial application and 152 ppm following a second application 6 to 10 days later. In the same study, the means of the 3 applications for vegetation in and adjacent to fields were 41 and 14 ppm respectively. The upper bound 95% mean for the vegetation adjacent to the fields was 71 ppm. Therefore even empirically derived residues suggest that the chronic LOC is exceeded on foliage, but not invertebrates for a short time following aerial applications. It is anticipated that since the sulfone and sulfoxide degradates of disulfoton were similar in acute toxicity to parent disulfoton they would have similar chronic NOAECs. These degradates extend the time that total disulfoton residues are available for consumption. Since many of the applications of disulfoton occur in the spring, overlapping the breeding season for most bird species, there is the potential for significant reproductive impacts.

Mammals: Acute risk to mammals is expected for use patterns involving the 15 G formulation. All modeled application rates and methods exceed the acute risk level of concern for mammals, regardless of the mammals   size. . Small mammal carcasses were found during terrestrial field testing of disulfoton on potatoes, confirming the presumption of acute risk to mammals. Since disulfoton is a systemic pesticide, the granular formulations can result in exposure through food items due to uptake by the plant tissues in addition to direct exposure to any unincorporated granules.

Applications of the liquid formulations especially by air can result in mammals being exposed to multiple routes of exposure   dermal, inhalation, drinking contaminated water as well as 73 ingestion of contaminated food items. The persistent sulfone and sulfoxide degradates are also toxic to mammals, thereby increasing the potential risk from the application of disulfoton. The registrant has suggested that mammals as well as birds can consume an equivalent of 2 to 3 LD50' s as part of their diet and not be adversely effected. Although this may be true for a population of laboratory test animals, individuals will vary in their sensitivity and can die as a result of inability to avoid predation, secure prey or thermoregulate. Numerous pen studies were conducted with cottontail and jack rabbits exposed to single applications ranging from 1 to 25 lbs ai/ A. While no mortality occurred to cottontails, at the 2 lb ai/ A rate and above jackrabbits suffered 100% mortality. Secondary poisoning did not occur when the jackrabbit carcasses were fed to a number of avian and mammalian carnivores. The apparent difference between the pen study results and the acute mortality predicted in the risk assessment screen is largely due to the possibility that the calculated 1 day LC50s ( ranging from 2 to 12.7 ppm) discounts the rapid metabolism of disulfoton. However, using the demeton LC50 of 320 ppm with its wide ranging confidence interval ( 0 to infinity) also adds uncertainty to the question of disulfoton   s acute risk to mammals.

Chronic risk to mammals is predicted. As was previously discussed in the above acute and chronic sections for birds, there are several reasons why small mammals are likely to be at even greater risk, not the least of which is the extremely low NOAEC of 0.8 ppm. All modeled and empirically derived residues for all sites exceed the chronic risk level of concern for mammals. Finally, the persistence of the sulfone and sulfoxide degradates, which are also toxic to mammals, increases the likelihood of chronic risk to mammals.

Non target Insects: Disulfoton and its sulfoxide and sulfone degradates are moderately to highly toxic to bees, however a residual study with honey bees indicated no toxicity for applications up to 1 lb ai/ A.

Freshwater Fish: Most of the modeled use patterns did not exceed acute risk levels of concern for freshwater fish. Only the two soil applications at 4.0 lb ai \ A of the liquid formulation exceeded acute risk. All other scenarios exceeded the restricted use and endangered species levels of concern. There is, however, a large amount of variation in freshwater fish species   sensitivity to disulfoton, as evidenced in the toxicity data table. The microcosm study included bluegill sunfish. Following the last application of 30 ppb, 10% of the fish died. Several kills of freshwater fish have occurred from applications of disulfoton to different crops  both as registered uses as well as from misuse.

Chronic risk to freshwater fish may occur from uses where single application rates are equal to 4 lb ai/ a and from 3 applications of 1 lb ai/ A. . The single freshwater fish species ( rainbow trout) , for which chronic toxicity data was available, demonstrates significantly less sensitivity to disulfoton than several other species ( bluegill sunfish, bass, guppy) . Therefore, an estimated chronic NOEC value was calculated using the chronic to acute ratio for the rainbow trout, as described earlier. Based on the estimated chronic NOAEC for bluegill, chronic effects would occur from the present uses on tobacco, foliar treatments of potatoes and repeated soil treatments of cotton. Christmas tree plantations were not modeled, however the high application rate ( possibly 47 lbs ai/ A) and sloped land may be a potentially risky site.

Freshwater Invertebrates: All modeled crop scenarios exceeded the acute risk level of concern, but the highest risk quotients were less than 10. Again, the risk is further increased due to the toxicity and persistence of the degradates of disulfoton. Microcosm study results 74 indicated that there was recovery of most phyla examined at 3 ppb and long term impacts for most phyla at 30 ppb. Therefore 10 ppb is probably a concentration where short term effects will occur, but recovery can be anticipated.

Chronic risk to freshwater invertebrates is predicted to from the use of disulfoton. All of the modeled crop scenarios greatly exceeded the level of concern, sometimes by a factor of several hundred. Invertebrate life cycle testing with disulfoton shows that it impacts reproductive parameters ( number of young produced by adults) in addition to survival and growth. The 21 day average EECs for the modeled sites ranged from 4.3 to 17.9 ppb. For the most part these EECs are within the range where recovery was occurring in the microcosm. However there is uncertainty as to how much more reliable the microcosm may be as a predictor of safety.

Estuarine and Marine Fish: Although acute and restricted risk levels of concern were not exceeded for estuarine and marine fish, the endangered species level of concern was exceeded for several of the modeled crop scenarios ( cotton, potatoes and wheat) . As was note among the freshwater fish, there can be substantial species differences in sensitivity to disulfoton. Therefore, it is possible that the single marine/ estuarine fish species tested ( Sheepshead minnow) does not fully represent the true range of sensitivity found in a marine or estuarine ecosystem, and this assessment may therefore underestimate the true risk to marine/ estuarine fish. There is also some uncertainty in using the PRZM/ EXAMS EECs derived for ponds to predict exposure to marine/ estuarine organisms. The scenarios modeled are based on hydrologic data for freshwater habitats. The exposure in a marine or estuarine habitat may be higher or lower than that predicted for a freshwater habitat, resulting in higher or lower risk to marine/ estuarine organisms.

Chronic risk to estuarine and marine fish is predicted from the use of disulfoton. Both early life stage and full life cycle testing demonstrated a variety of effects at low levels of disulfoton. Risk quotients based on the early life stage toxicity endpoint exceeded the level of concern for cotton, potatoes and tobacco. The highest risk quotients were based on numerous life cycle toxicity endpoints   fecundity, hatching success and growth; consequently the chronic level of concern was exceeded for all modeled scenarios. Estuarine fish spawning in the upper reaches of tributaries of bays would be a greatest risk. However the likelihood of this risk is uncertain for several reasons: 1) the required time the adults must be exposed to disulfoton in order for their reproductive systems to be effected and 2) the residency time of disulfoton residues in tidal or flowing water. Even if adults are effected after an exposure of only a week, disulfoton may be moved out of an area within several days.

Estuarine and Marine Invertebrates: Three of the five modeled scenarios ( cotton, potatoes, and tobacco) resulted in exceedences of the estuarine/ marine invertebrate acute risk level of concern. All the remaining uses exceeded the restricted use level of concern. Similar uncertainty exists as to the validity of the exposure scenario for invertebrates as was just described for estuarine fish.

Chronic risk to marine/ estuarine invertebrates is predicted. All of the modeled crop scenarios exceeded the chronic level of concern. The much shorter life cycle of invertebrates as compared to fish, increases the likelihood that only a brief exposure ( a few day or even hours) of adults to disulfoton concentrations around the NOAEC is sufficient to negatively impact reproduction. The degree to which the freshwater microcosm is a predictor of safety for the estuarine invertebrates in highly uncertain. Only the mysid shrimp has been tested and it was acutely and 75 chronically less sensitive than freshwater Daphnia. Therefore, on the basis of this limited data, the chronic impact to estuarine invertebrates not only appears to be lower than for freshwater invertebrates, but is likely to be low.