       U. S. ENVIRONMENTAL PROTECTION AGENCY

Washington, D.C. 20460

OFFICE OF

PREVENTION, PESTICIDES

AND TOXIC SUBSTANCES

PC Code: 053501

DP BARCODE: D308030

MEMORANDUM							DATE:  December 13, 2006

SUBJECT: 	Response to Registrant’s Comments on Methyl Parathion

FROM:	Amer Al-Mudallal, Chemist

		Edward Odenkirchen, Ph.D., Senior Biologist

		Environmental Risk Branch 1

		Environmental Fate and Effects Division (7507P)

THRU:	Nancy Andrews, Branch Chief

Environmental Risk Branch 1

		Environmental Fate and Effects Division (7507P)

TO:		Laura Parsons, Risk Manager

John Pates, RM Reviewer

		  SEQ CHAPTER \h \r 1 Special Review and Reregistration Division (7508P)

Attached are EFED’s responses to the Registrant’s comments on Methyl Parathion.  If you have any questions, Please contact Amer Al-Mudallal at<PHONE_NUMBER> or Edward Odenkirchen at<PHONE_NUMBER>.  Thank you.

III. Comments on EPA’s Ecological Risk Assessment

Formulations (page 14 of 40)

EFED Response:  The registrant claims that EFED’s risk assessment approach for conducting a combined ecological risk assessment for the EC and encapsulated (MCAP) formulations of methyl parathion “distorts” the risk evaluation for both formulations.  No further details were provided to substantiate this claim.  EFED cannot fully address this issue without a more complete discussion on toxicity and environmental fate differences for the different formulations of methyl parathion.

The ecological risk assessment considered all submitted data regardless of formulation. This strategy is consistent with the screening-level ecological risk assessment process to address toxicity and environmental fate processes of the active ingredient. Formulation effects on environmental fate properties are considered in volatility and field dissipation studies.  Additionally, formulation effects on toxicity are considered when there are sufficient data to ensure differential toxicity among formulations.  However, the most sensitive species endpoints are used for calculation of risk quotients. For methyl parathion, the registrant did not provide a comparison of environmental fate and toxicity data for the EC and MCAP formulations to warrant characterization of formulation effects.

Aquatic Organism Risk Assessment

EPA’s Model Inputs

●  Soil absorption constant. (page 15 of 40)

EFED Response: The Koc of 5100 used is described in Hornsby, et al.(1996) as “an ‘estimate,’ meaning either (a) an unusually wide range of values have been reported and we had no reason to select any one value as a ‘best’ value, or (b) no experimental value is available but a reasonable estimation was possible” or a value was “calculated from some more fundamental property”. The Koc of 487 ml/g used by EFED was chosen based on experimental data submitted by the registrant.  A repeat the adsorption-desorption laboratory study, because the soils of the original study were autoclaved, has not been submitted for consideration.

The Koc of 487 ml/g used by EFED is conservative, but not unreasonable given the data reported in outside literature.  Simple partition coefficients for methyl parathion can range from 3 to 147 (median=50) (Howard, 1991). Sanchez-Martin and Sanchez-Camazanoe, (1991) found that the methyl parathion sorption on soil was correlated to the soil organic carbon content.  They found the mean Koc for methyl parathion is 697 ml/g across 8 mineral soils.  Hornsby, et al. (1996) reports organic carbon partitioning coefficients of 424 and 14000 ml/g in addition to the 5100 discussed by the registrant.

EFED discussed the adsorption coefficient of ethyl parathion further in the revised EFED ethyl parathion RED chapter. EFED stands by the use of the use of a Koc of 487 ml/g.

●  Aerobic soil half-life. (page 15 of 40)

EFED Response: The half-life for parent methyl parathion (3.75 days) was derived from upgradable supplemental data; the study provided useful information for methyl parathion, but the study was deemed as supplemental because of  inadequate identification of degradation products. Quantitatively, the aerobic soil metabolism half-life of methyl parathion, assuming a normal distribution, can range anywhere from an approximate mean half-life or central tendency of 3.75 days to an upper bound 90th percentile upper confidence limit (UCL) of the mean (11.25 days).  As per interim guidance on model input parameters, the 90th percentile UCL of the mean is used in PRZM-EXAMS modeling in situations where the only one half-life is available. This correction factor assumes that half-lives in different soils are normally distributed. The correction factor is used to incorporate uncertainty in the variability of the half-lives.

Until such time that EFED adopts a probabilistic exposure assessment, EFED will use the 90th percentile UCL of the mean in an attempt to be reasonable and protective of non-target populations.

ions less than 100 μg/g.

Finally, for foliar-applied insecticides such as methyl parathion, the relationship between application interval and the aerobic soil metabolism half-life may not be strong.

●  Foliar dissipation. (page 16 of 40)

EFED Response: EFED did include foliar dissipation in the original EECs to the extent possible in the PRZM-EXAMS modeling. The model includes two input cards for foliar dissipation. The first, the “foliar extraction” card, regulates what mass fraction of the pesticide will wash off the leaves with a centimeter of rainfall. EFED sets this to 0.5 as a default.

The second input card is decay rate on foliage. Foliar decay data was not available for methyl parathion. Foliar dissipation includes not only decay, but other processes such as washoff and volatilization. Therefore, the use of foliar dissipation in this input slot would account for decay, but double-count for foliar washoff. Therefore, it would have been inappropriate to use the foliar dissipation value in the model.

Bacterial degradation in water. (page 16 of 40)

EFED Response: The registrant is correct  in noting that  a standard fitting procedure of first-order degradation kinetics (ln transformed concentration vs time) does not   describe the initial rapid degradation phase of methyl parathion in MRID  42069601.   EFED recalculated the half-life estimate with both linear regression fitting procedures using ln transformed concentration data v time  and non-linear regression fitting of the 2 parameter, exponential decay model using non-transformed concentration data v time.   Fitting procedures were conducted using Sigmaplot 2000 Regression Wizard.    This analysis yields the following results:

Co (y-intercept)	 			K(days-1)	    Half-life         	 R2

Linear Regression        2.9548 (19.19% of initial dose)(P=0.0049)   0.1705 (P=0.0202)	   4.06		0.62

Non-Linear Regression	89.24 % of initial dose (P<0.0001)	         0.5432 (P<0.0001) 	   1.3		0.99

This analysis indicates that methyl parathion degradation appears to follow a hockey-stick type degradation pattern with rapid degradation rate   followed by slower degradation rate.   The incorporation of  a non-linear half-life in the PRZM/EXAMS modeling is not expected to alter the risk assessment because current EFED Input Parameter Guidance recommends using an estimate of the 90th percentile of the mean half-life, which is  3 * 1.3 days or 3.9 days.  This value is not different than the 4.1 days used in the original exposure assessment.

Appropriation of EPA’s model for estimating concentrations of pesticides in water (page 17 of 40)

EFED Response:  The registrant claims the Pesticide Root Zone Model (PRZM) and EXposure Analysis Modeling System (EXAMS) have not been validated according to the Guidelines for Exposure Assessment (FRC-4129-5).  Therefore, they believe the Agency is in violation of the Data Quality Control Act.

The PRZM and EXAMS  models were developed by the Office of Research and Development in the US Environmental Protection Agency.  Since the initial versions of PRZM and EXAMS were developed, these models have undergone continuous upgrading and evaluation to improve alogrithims and capabilities for predicting pesticide concentrations in surface water  and ground water.  Validation and evaluation of  the models has been conducted by academics, regulated industry, and government agencies.

Examples of open literature validation and calibration exercises for PRZM :

Muller, T., R. E. Jones, P. B. Bush and P. A. Banks. 1991.  Comparison of  PRZM and GLEAMS Computer Model Predictions with Field Data for Alachlor, Metribuzin, and Norflurazon Leaching. Environmental Toxicity and Chemistry 11:427-436.

Durburow, T. E., N. L. Barnes, S. Z. Cohen, G. L.  Horst, and A. E. Smith. 2000.  Calibration and Validation of Runoff and Leaching Models for Turf Pesticides, and Comparison with Monitoring Results in Fate and Management of Turfgrass Chemicals editors J. Marshall Clark and Michael P. Kenna.  ACS Symposium Series 743.  ACS, Washington D.C.

Parrish, R. S., C. N. Smith and F. K. Fong.  1992.  Tests of Pesticide Root Zone Model and the Aggregate Model for Transport and Transformation of Aldicarb, Metolachlor, and Bromide. J Environ. Qual. 21: 685-697

Pennel, K. D.,  A. G. Hornsby, R.E. Jessup, and P. S. C. Rao. 1990 Evaluation of Five Simulation Models for Predicting Aldicarb and Bromide Behavior Under Field Conditions. Water Resources Research.  26(11): 2679-2693.

Ma, Q.L., Wauchope, R.D., Hook, J.E.; Johnson, A.W., Truman, C.C., Dowler, C.C., Gascho, G.J.; Davis, J.G., Sumner, H.R., Chandler, L.D. 1998. GLEAMS, Opus, and PRZM-2  model predicted versus measured runoff from a coastal plain loamy sand. Transactions of the ASAE.1998, 41: 1, 77-88.

Mueller, T.C. (1994): Comparison of PRZM computer model predictions with field lysimeter data for dichlorprop and bentazon leaching. Journal of

Environmental Science and  Health. Part A, Environmental Science and Engineering. 1994, 29: 6, 1183-1195.

Sadeghi, A.M.; Isensee, A.R.; Shirmohammadi, A. (1995): Atrazine movement in soil: comparison of field observations and PRZM simulations. Journal of Soil   Contamination.1995, 4: 2, 151-161.

Industry efforts to validate the PRZM model:

FIFRA Environmental Modeling Validation Task Force.

PRZM/EXAMS evaluations to support risk assessments:

FIFRA Science Advisory Panel Meeting, December 10-11, 1997. Use of Water Models in FQPA Drinking Water Assessments. Crystal City, VA

FIFRA Science Advisory Panel Meeting,  July 29-30, 1998.  Proposed Methods for Basin-scale Estimation of Pesticide Concentrations in Flowing Water and Reservoirs for Tolerance Reassessment. Crystal City, VA.

The registrant indicates PRZM/EXAMS modeling is not accurate because methyl parathion detection frequencies from USGS studies are lower than detection frequencies predicted from modeling.  Additionally, they believe the dissipation rate from PRZM simulations are different than observed in the field.  Therefore, they believe the model is not accurately predicting all dissipation pathways for methyl parathion.

The Agency believes the PRZM/EXAMS and their use in FIFRA and FQPA risk assessments have been extensively peer-reviewed.  The PRZM/EXAMS model approach has been generally accepted as an appropriate refined screening level model for FIFRA and FQPA risk assessments.  The comparison of model predicted concentrations with ambient water monitoring data such as USGS/NAWQA requires a complete understanding of the targeted nature of the monitoring relative to pesticide use site and pesticide use timing.  The Agency expects the PRZM/EXAMS models to over predict  peak pesticide concentrations and detection frequencies when compared to USGS/NAWQA  monitoring studies.  The Agency is willing to consider any targeted field scale monitoring data for methyl parathion in  the risk characterization for methyl parathion.   Differences in model predicted and field dissipation rates may suggest the model is not accounting for all dissipation pathways.  However, it may also indicate the variable nature of field dissipation processes among fields.

Incident data cited by EFED for aquatic organisms (page 18 of 40)

EFED Response:  Should a redraft of the ecological risk assessment be warranted, the information presented would be considered in any reevaluation of incident data.

Terrestrial Organisms  Risk Assessment

            1.  Limitations of the assessment (page 19 of 40)

EFED Response:  EFED acknowledges that the tools for risk assessment are similar to the screening level assessment methods.  However, risk management decisions involve multiple lines of evidence which are incorporated in the document.  EFED can apply other tools (e.g. probabilistic approaches) should risk managers decide this is necessary.

2. 	Use of data that do not adhere to the principals of Data Quality Control Act. (page 20 of 40)

EFED Response: Re-evaluation of the Penwalt study could be performed under the Agency’s current literature evaluation procedure.  Switching to next highest dietary acute LC50 could be performed for RQ calculations.  It would only make a difference to seeds RQ all other RQs would still be above non-listed acute LOC.

Use of certain field studies (page 21 of 40)

EFED Response: Discussion of the relevance of these studies to current labels should be included if a redrafting of the ecological risk assessment is warranted.

Use of literature data concerning the sub-lethal effects of methyl parathion on birds (page 21 of 40)

EFED Response: EFED discussed effects on avian maternal behavior and provided both effects levels and indications of exposure (in bold) in the following examples:

“Brewer et al. (1988; MRID 44371604) reported brood abandonment and mortality among wood duck and teal hens in a field treated with 1.25 lb ai/acre methyl parathion, but not in a control field. Two-thirds of the nesting hens from the treated field had significantly depressed brain cholinesterase levels.  Mortality among ducklings in the treated field (84%) was greater than that in the control field (42%) by 22 days post-spray.”

“Kendall, et al. (1984; MRID 44413601) reported a 39% increase in mortality among nesting starlings in a treated field.  Since this effect did not correlate with ChE depression, the authors surmised that changes in maternal behavior or depressed food abundance might have been to blame. This same study reported nest abandonment by mallards and teals adjacent to a field treated at 0.6 lbs ai/A.”

“Mineau (1991) reports that two-week old northern bobwhite quail did not discriminate between untreated food and diets containing 45 or 90 ppm methyl parathion, and initially (0-24 hour post-dose) chose treated over untreated food. This indicates that there will be little avoidance of treated food sources.”

“Edwards (1968; MRID 00090488) noted that birds sprayed with 0.5 lb ai/A of methyl parathion suffered a 20% weight loss shortly after the spraying, but recovery was rapid.”

These data are presented to provide further context with regard to risks that are based on the RQ calculations.

Conclusions about reproductive effects on birds (Page 21 of 40)

EFED Response:  While shell breaking strength was a sensitive endpoint in the Bennett and Bennett (1990) study, egg production (eggs/hen/day) was also a sensitive endpoint and was an observed effect in the northern bobwhite quail reproduction study used in the risk assessment.  Egg production data in Bennett and Bennett (1990) show a NOEC of 14 ppm and a LOEC of 20 ppm.  These concentrations compare closely with the NOEC and LOEC values used in the risk assessment for RQ calculation (see the following table).

Avian Reproduction Endpoints from the Registration Eligibility Document Ecological Risk Assessment

Species/

Study Duration

% ai

NOEC

 (ppm)

LOEC

(ppm)

LOEC

Endpoints

MRID No.

Author/Year

Study Classification

Northern bobwhite quail

(Colinus virginianus)

Tech

6.27

15.5

Number of eggs laid; eggs set/hen; adult female bodyweight

41179302

Beavers/1988

Core

Mallard duck

(Anas platyrhynchos)

Tech

14.7

>14.7

No effects at highest conc.

41179301

Beavers/1988

Supplemental

Cheminova  is correct that Bennett and Bennett (1990) did indicate that the dose-related reproduction effects observed were apparently due to dose-related reductions in food consumption.  However, Cheminova has failed to mention that the authors also indicated that pesticide-induced anorexia is “frequently observed in laboratory studies with organophosphates and confounds the ability to determine whether are due to chemical toxicity, reduced food consumption, a change in metabolic efficiency due to chemical exposure, or a combination of reasons.”

Cheminova is correct that egg production effects in Bennett and Bennett (1990) were observed by 3 days of methyl-parathion exposure.  Cheminova appears to be arguing that a more protracted exposure period than the single day modeled for the RQ calculations is warranted.  This argument was considered in the context of the expected residue decline following the maximum EEC estimate.  A 2.4-day foliar dissipation half-life and a first order decline function were used to estimate the number of days following maximum EEC for which residues of methyl-parathion would exceed the reproduction NOEC of 6.27 ppm.  The following table presents these estimates.

It is important to note that for all single application and multiple application scenarios modeled, methyl-parathion residues exceed the NOEC for well over 3 days.  This is the time for the onset of egg production effects in Bennet and Bennett (1990)) for at least 3 of the avian  food groups modeled.  Even if a egg production NOEC of 14 ppm from the Bennett and Bennett (1990) study was substituted for the NOEC used to calculate RQs, the number of days residues would exceed this toxicity threshold would still be greater than 3 days for almost all food groups in almost all exposure scenarios modeled.  One should also recall that the foliar dissipation decline does not account for the potential for the highly toxic oxon moiety of methyl parathion to be formed and so exposures estimated in this fashion are not likely to be conservative representation of total toxic exposure.

Avian Reproduction Risk Quotients for Single and Multiple Applications for Major Use Crops and the Number of Days Following Maximum EEC Where Exposure Would Equal or Exceed Reproduction NOEC (6.27 ppm) Based on a 2.4 Day Foliar Half-Life

Single Application

Multiple Application

Site1 (# Apps,

App. Interval in days)

App.Rate

(lbs ai/A)

Food Items

Maximum EEC (ppm)

Reproduction

RQ

(EEC/

NOEC)

Exposure days above NOEC

Reproduction

RQ

(EEC/

NOEC)

Exposure days above NOEC

Rice, Grasses

(6,3)

0.79

Short

grass

190

30.3

11.8

181.8

18.0

Tall

grass

87

13.9

9.1

83.4

15.3

Broadleaf

plants/Insects

107

17.1

9.8

102.6

16.0

Seeds

12

1.9

2.2

11.4

8.4

Sunflower

(3,5)

1

Short

grass

240

38.3

12.6

114.9

16.4

Tall

grass

110

17.5

9.9

52.5

13.7

Broadleaf

plants/Insects

135

21.5

10.6

64.5

14.4

Seeds

15

2.4

3.0

7.2

6.8

Soybean,

 (6,3)

Corn (all)

 (6,2)

1

Short

grass

240

38.3

12.6

229.8

18.8

Tall

grass

110

17.5

9.9

105.0

16.1

Broadleaf

plants/Insects

135

21.5

10.6

129.0

16.8

Seeds

15

2.4

3.0

14.4

9.2

Alfalfa

(4,42)

1

Short

grass

240

38.3

12.6

153.2

17.4

Tall

grass

110

17.5

9.9

70.0

14.7

Broadleaf

plants/Insects

135

21.5

10.6

86.0

15.4

Seeds

15

2.4

3.0

9.6

7.8

Cotton

(10,3)

3

Short

grass

720

114.8

16.4

1,148.0

24.4

Tall

grass

330

52.6

13.7

526.0

21.7

Broadleaf

plants/Insects

405

64.6

14.4

645.9

22.4

Seeds

45

7.2

6.8

71.8

14.8

Cheminova indicates that the  Meyers et al. (1990) study involving a single oral dose exposure to methyl parathion would be the most appropriate study to compare with the single day exposure assumption.  However, it appears that the Meyers et al.  (1990) approach with a single oral dose would not capture the more prolonged exposure profile suggested by the above analysis.

Appropriate data for estimating dietary residues (page 22-30 of 40)

EFED Response:

●  The field data indicating a rapid decline of methyl parathion in food items has been incorporated in into the terrestrial wildlife risk assessment, where default foliar dissipation half-life assumption of 35 days has been replaced by a half-life of 2.4 days.

●  The nomogram is only dependent upon application rate.  The residue modeling that incorporates the nomogram (e.g. FATE and ELFATE) also considers application number, application interval, and foliar dissipation.  The comment is correct that, should higher tier assessments be conducted, additional information could be considered with respect to other factors related to application, and the use of such information would be dictated by its quality.

●  While the Agency agrees that understory plants and the insects residing on them may be important food sources for some species, they do not constitute the only food sources within an agroecosystem.  Seeds and fruit present on plant stalks and insects in the upper canopy could also be important food sources for avian wildlife that is adapted to a surface gleaning feeding guild.  Indeed, the environment immediately adjacent to a treated crop, receiving much the same application rate as the crop itself, is likely to be important feeding habitat for edge-residing wildlife.  In such cases the effects of crop canopy interception would not be as extensive as directly on the field.  The Agency agrees that, should a higher Tier assessment be performed with methyl-parathion, feeding habits, canopy effects and timing漠灡汰捩瑡潩潣汵敢洠牯畦汬⁹癥污慵整 Ɽ椠慤慴漠敲楳畤獥楷摬楬敦戠桥癡潩Ⱳ愠摮愠 牧湯浯捩瀠慲瑣捩獥愠敲愠慶汩扡敬മ

●  The Agency agrees that reducing daily consumption of methyl-parathion contaminated dietary items would reduce daily exposure.  However, given the high reproduction RQs from the existing assessment, pesticide-contaminated dietary items would have to be assumed to comprise less than 1% of the diet for there not to be a dietary risk.  The commenter suggests that data are available showing avian and mammalian avoidance of methly-parathion.  Without a reference the Agency cannot follow up this assertion and indeed, assuming such behavior would have to involve near total avoidance for it to reduce exposure levels below reproduction risk levels of concern.

●  The Agency agrees that the likelihood that a bird will consistently feed in areas with the highest residues decreases with the number of days of exposure modeled.  However, the risk assessment has demonstrated that exposure times for both lethal and reproduction effects with methyl parathion are very short.  Of course the full distribution of potential combinations of daily exposures over a variety of exposure windows could be explored by probabilistic methods, should a refinement to the existing risk assessment be warranted.

●  EFED has incorporated the referenced data into its refined risk assessment approaches.  Should a reevaluation of the ecological risk assessment be warranted, these data could be used in the context of these refined exposure assessment tools.

Estimates of dietary exposure of methyl parathion to mammals (Page 30 of 40)

EFED Response: EFED used the standard dietary ingestion rate assumptions in this risk assessment.  To determine the impact of the alternative values presented in the comments, EFED looked at the existing mammal  RQs for 15 and 35 g mammals and reduced them by a factor reflecting the difference between standard intake assumptions and alternatives in the comments.  Data for the prairie vole from the comment was excluded in this analysis, as the study involved laboratory feeding of the animals with dried oats and dry grass not fresh material as is modeled for the risk assessment.  Cited data for the deer mouse were also excluded as the intake numbers reflect laboratory consumption of dry rat chow not natural food items  In no comparison of standard assumption to alternative ingestion rates from acceptable data cited in the comments is the difference more than a factor of 2 (e.g, 15 g insectivore 95% vs 49%, 15 g seed eater 21% versus 18%, 35 g 66% vs 30% ).  Such a factor would not reduce the RQs below acute risk levels of concern for any 15 or 35g mammals except for 35g granivores on for three use scenarios modeled: Grasses rice 0.79 lb/acre, field/sweet corn 1 lb/acre, alfalfa/barley/oats/rye/wheat 1.25 g/acre.  It should be noted that no multiple application scenarios were modeled, so it is possible that multiple applications for the above use scenarios (to the extent that the label allows) could still exceed the acute risk LOC.

●  NRDC Comment 1

. . . we find that the half-life for methyl parathion in aquatic media is 175 days and the half-life for methylparathion in soil is anywhere from 10 days to two months (PAN-UK 1998). These half-lives for both aquatic and terrestrial media are not all that short and still result in what we believe to be significant opportunities for exposure in humans, fish and wildlife and the environment. After all, you have to keep in mind that the acute toxicity of methyl parathion is so high, and uptake is so

efficient (oral, dermal, and inhalation or any combination thereof) that in many instances it only takes one exposure to kill an organism.

EFED Response:  For aquatic exposure modeling EFED used environmental fate property values in accordance with established procedures.  The acute effects risk assessment for aquatic organisms is based on an estimated single day exposure.  Similarly, both acute lethality and reproduction risk assessments for terrestrial vertebrates are based on a peak single day exposure.

●  NRDC Comment 2

. . . the initial degradation (and metabolic) product is methyl paraoxon, a compound that is considered at least three orders of magnitude MORE TOXIC than the parent compound methyl parathion due to its incredible cholinesterase-inhibiting abilities.

EFED Response:  Available dietary residue studies do not show significant detections of the paraxon in crops treated in the field with methyl parathion.  Similarly, while finished drinking water may show formation of the oxon, raw surface waters do not.

●  NRDC Comment 3

In amphibians, Johnson and Prine (1976) found that exposure to only 25 μg/l methylparathion over 24 hrs caused juvenile western toads (Bufo boreas) to lose their tolerance to temperature, a sublethal effect that likely becomes lethal rather rapidly. Methyl parathion (Folidol M50 formulation) contained in simulated rice paddy overflow water was found to cause mortality in giant toads (Bufo marinus) at levels as low as 280μg/l (Calumpanget al. 1997). In another study, frogs exposed to 1.0 mg/l methyl parathion suffered changes in the composition of their connective tissue matrices, which  resulted in malformations of the spinal column (scoliosis) and/or limbs (short and think long bones  with the epiphyses grossly twisted; Alvarez et al. 1995). Further, a study by Fleming et al. (1982) showed that parathion actually bioaccumulated in cricket frogs (Acris crepitans), thereby posing a serious secondary poisoning hazard to American kestrels (Falco sparverius). Studies by Hall and Kolbe (1980) and Hall (1990) further document bioaccumulation of parathion and other organophosphorus insecticides in amphibians, which is cause for great concern, particularly for amphibian predators that are likely to die from secondary poisoning.

EFED Response:  Discussion of the relevance of these studies to assessing risks to amphibians and their predators should be included if a redrafting of the ecological risk assessment is warranted.  The extent to whcic such data are quantitatively incorporated in any revised risk assessment would be based on a review of the quality of each study.

●  NRDC Comment 4

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 is commonly used in other countries (e.g.,Venezuela) as an avicide to intentionally kill songbirds. The work of Basili and Temple (1999) has documented huge mass mortality events involving dickcissels (Spiza americana) that flock in agricultural areas. These international mortality incidents cannot be ignored and must be included in any ecological risk assessment of methyl parathion.

EFED Response:   EFED has documented the avian incident data available at the time of the drafting of the risk assessment.  If other data are pertinent to the application rates and methods for methyl parathion in the United States, this information should be considered in any warranted redrafting of the risk assessment.

●  NRDC Comment 5

In addition to lethal effects, there are a wide range of debilitating sublethal effects seen following exposure to methyl parathion. Both methyl parathion and its closely related chemical analog ethyl parathion have been found to cause reproductive, physiological, biochemical, and behavioral effects that ultimately lead to premature mortality in exposed organisms.  Reproductive effects such as decreased productivity (% eggs hatching/% nests successful) have been documented in songbirds exposed to parathion. Physiological effects such as reduced daily food consumption (anorexia) and decreased body temperature (hypothermia) have been documented in songbirds and upland game birds exposed to parathion. Behavioral effects may be the most insidious and damaging of the sublethal effects. Decreased ability to avoid predators, decreased nest attentiveness during incubation and maternal care following hatching, and increased brood abandonment by females have been documented in upland gamebirds, gulls, and waterfowl (King et al. 1984, White et al. 1979, 1983).

EFED Response:   The avian risk assessment has included discussions of the potential of methyl parathion to adversely affect birds through effects on egg production, maternal behavior, anorexia, and increases in sensitivity as a result of exposure to漠桴牥攠癮物湯敭瑮污猠牴獥潳獲䤠⁴獩椠灭牯慴 瑮琠潮整琠慨⁴桴楲歳愠獳獥浳湥⁴污潳焠慵瑮瑩 瑡癩汥⁹楤捳獵敳⁳潣据牥獮映牯氠瑥慨楬祴愠摮映慲 歮爠灥潲畤瑣潩晥敦瑣⁳獡椠摮捩瑡摥戠⁹桴兒挠 污畣慬楴湯⁳湡潣灭牡獩湯⁳楷桴攠瑳扡楬桳摥䰠癥 汥⁳景䌠湯散湲മ

●  NRDC Comment 6

In mammals, exposure to the OP insecticide methyl parathion has been found to result in loss of motor coordination in bats (Clark 1986), reduced predator escape response (Galindo et al. 1985), altered hearing ability in squirrel monkeys (Reischl et al. 1975), a decreased ability to learn (Reiter et al. 1973), and suppression of the immune system (Street and Sharma 1975). In rats, Zhu et al. (2001) found that repeated dermal exposures of as little as 1 mg/kg/day methyl parathion resulted in sustained inhibition of cholinesterase activity and impairment of both motor function and memory. These subtle yet insidious sublethal effects are never monitored in wildlife species, so they almost always go undetected unless morbid animals are found by accident. It seems that we often miss these types of sublethal effects in humans even when we are looking hard for them, so it is clear that we are barely seeing the tip of the iceberg when it comes to negative impacts of methyl parathion on ourselves and our environment.

EFED Response:   The mammalian wildlife risk assessment identifies concerns for acute lethal and reproduction risks for methyl parathion for all uses assessed.  While other sublethal effects may be evident it is unclear how this information would alter the existing conclusions of the mammalian wildlife risk assessment.

●  NRDC Comment 7

f both EC and microencapsulated (ME) formulations. The LD50s for each formulation (0.111 μg/bee and 0.214μg/bee, respectively) indicate very high toxicity to bees. The ecosystem service that bees and other  pollinators provide to humans is invaluable and many of our most important food crops require  pollination by bees and other organisms that continue to decline in the face of our continued heavy reliance on pesticides.

EFED Response:  The ecological risk assessment includes a discussion of the impacts of various formulations of methyl parathion on pollinators.