8.0 Cumulative Risk Characterization/ Assessment Section 408( b)( 2)( D)( v) of the Federal Food, Drug, and Cosmetic Act ( FFDCA), as amended by the Food Quality Protection Act ( 1996) stipulates that when determining the safety of a pesticide chemical, EPA shall base its assessment of the risk posed by the chemical on, among other things, available information concerning the cumulative effects to human health that may result from dietary, residential, or other non occupational exposure to other substances that have a common mechanism of toxicity. The reason for consideration of other substances is due to the possibility that low level exposures to multiple chemical substances that cause a common toxic effect by a common mechanism could lead to the same adverse health effect as would a higher level of exposure to any of the other substances individually. A person exposed to a pesticide at a level that is considered safe may in fact experience harm if that person is also exposed to other substances that cause a common toxic effect by a mechanism common with that of the subject pesticide, even if the individual exposure levels to the other substances are also considered safe.

Dichlorvos is a member of the organophosphate ( OP) class of pesticides. Other members of this class of pesticides are numerous and include azinphos methyl, chlorpyrifos, chlorpyrifos methyl, diazinon, dichlorvos, dicrotophos, dimethoate, disulfoton, methamidophos, methidathion, monocrotophos, naled, oxydemeton methyl, phorate, phosmet, pirimiphos methyl, and trichlorfon to name a few. EPA considers organophosphates to express toxicity through a common biochemical interaction with cholinesterase which may lead to a myriad of cholinergic effects and, consequently the organophosphate pesticides should be considered as a group when performing cumulative risk assessments. HED published the final guidance that it now uses for identifying substances that have a common mechanism of toxicity ( FR 64( 24) 5796 5799, February 5, 1999) " Proposed Guidance of Cumulative Risk Assessment for Chemicals that have a Common Mechanism of Toxicity" was made available for public comment in the Federal Register ( 65 FR 40644, June 30, 2000 . The Agency presented this approach to the FIFRA/ FQPA Science Advisory Panel in late September, 2000. The SAP reviewed revised methods used to conduct a preliminary cumulative risk assessment for organophosphate pesticides in 2002 ( US EPA, 2002), found at http:// www. epa. gov/ scipoly/ sap/ 2002/ index. htm.

The Agency has completed a cumulative risk assessment for OPs, ( US EPA, 2001) and a revised cumulative risk assessment for OPs, ( US EPA, 2002a) which can be found on the Agency's web site http:// www. epa. gov/ pesticides/ cumulative/ rra op/. It assesses the cumulative effects of exposure to multiple OPs, including dichlorvos.

Dichlorvos is closely related to naled and trichlorfon, which are members of the organophosphate class of pesticides. Naled and trichlorfon both metabolize or degrade to dichlorvos in food, water, or the environment. Therefore, FQPA requires OPP to estimate aggregate risk from consumption of food and water, containing dichlorvos derived from naled and trichlorfon and from residential exposure to dichlorvos from the use of those pesticides. The current assessment Page 175 of 338 addressed only the risks posed by dichlorvos, resulting from the uses of dichlorvos, naled, and trichlorfon.

9.0 Occupational Exposure/ Risk Pathway Risk is expressed as a Margin of Exposure ( MOE)

MOE = NOAEL Exposure where both the NOAEL and the Exposure are expressed in the same units ( mg/ kg/ day for dermal or inhalation exposure during application or mg/ m3 for exposure to dichlorvos vapors). Dermal exposures include a dermal absorption factor of 11%, because the exposure is compared to an oral NOAEL. The target MOE for occupational scenarios varies from 30 to 100. ( See Table 4.4).

The risk assessment has been changed from previous versions to use the North American Free Trade Agreement ( NAFTA) recommended breathing rate of 1.0 m3 / hr rather than the rate recommended in the guidelines or the default breathing rate used in PHED. This change increases the inhalation MOEs, and therefore decreases the estimated risk to occupational and residential handlers. The risk assessment uses the recommended body weight of 70 kg for the acute, short term, and intermediate term risk assessments.

AMVAC has requested voluntary cancellation of the following uses. Mushroom house, greenhouse, and warehouse hand held fogger Lawn, Turf, and Ornamental uses Total release fogger Crack and Crevice uses The following label changes will be made: A Restricted Entry Interval ( REI) of 18 hours for mushroom houses, and 12 hours for greenhouse uses.

Toxicological Doses and Endpoints for Occupational Exposure Assessment are presented in Table 9.0. Occupational exposure and risk estimates for applicators are presented in Table 9.1 below. Occupational post application exposure and risk estimates are presented in Table 9.2 below. Page 176 of 338 Table 9.0. Summary of Toxicological Doses and Endpoints for Dichlorvos for Use in Occupational Human Health Risk Assessments Exposure Scenario Point of Departure Uncertainty Factors Level of Concern for Risk Assessment Study and Toxicological Effects Acute Dermal BMDL10 = 0.8 mg/ kg/ day dermal absorption= 11% UFA = 10x UFH = 10x Occupational LOC MOE = 100 Rat acute oral cholinesterase studies  RBC and Brain ChE depression. NOAEL = 1 mg/ kg/ day, LOAEL = 5 mg/ kg/ day, BMD = 1.6 mg/ kg/ day for brain ChE depression ( F)

Short, Intermediateand Long Term Dermal Oral study LOAEL= 0.1 mg/ kg/ day dermal bsorption= 11% UFH = 10x UFL = 3x Occupational LOC MOE = 30 Human 21 day oral study LOAEL = 0.1 mg/ kg/ day based on RBC ChE depression Acute Inhalation ( 1 day) Oral study BMDL10 = 0.8 mg/ kg/ day ( inhalation absorption rate = 100%) Air concentration Equivalent = 0.8 mg/ m 3 * UFA = 10x UFH = 10x or 3x** Occupational LOC MOE = 100/ 30** Rat acute oral cholinesterase studies  RBC and Brain ChE depression. NOAEL = 1 mg/ kg/ day, LOAEL = 5 mg/ kg/ day, BMD = 1.6 mg/ kg/ day for brain ChE depression ( F)

Short and Intermediate term Inhalation of vapors Oral study LOAEL= 0.1 mg/ kg/ day UF= 30 Concentration equivalent= 0.35 mg/ m 3 * UFH = 10x UFL = 3x Occupational LOC MOE = 30 Human 21 day oral study LOAEL = 0.1 mg/ kg/ day based on RBC ChE depression Short and Intermediate Term Inhalation during application LOAEL= 0.1 mg/ kg/ day UFH = 10x UFL = 3x Occupational LOC MOE = 30 Human 21 day oral study LOAEL = 0.1 mg/ kg/ day based on RBC ChE depression Long Term Inhalation of vapors BMDL10 = 0.07 mg/ m 3 UFA = 10x UFH = 3x** Occupational LOC = 30 2 year Rat Inhalation BMD = 0.15 mg/ m 3 based on RBC ChE depression ( F)

Cancer ( oral, dermal, inhalation) " suggestive" evidence of carcinogenicity not quantifiable under the 1999 Draft Agency Cancer Guidelines Point of Departure ( POD) = A data point or an estimated point that is derived from observed dose response data and used to mark the beginning of extrapolation to determine risk associated with lower environmentally relevant human exposures. NOAEL = no observed adverse effect level. LOAEL = lowest observed adverse effect level. UF = uncertainty factor. UFA = extrapolation from animal to human ( intraspecies). UFH = potential variation in sensitivity among members of the human population ( interspecies). UFL = use of a LOAEL to extrapolate a NOAEL. UFS = use of a short term study for long term risk assessment. UFDB = to account for the absence of key date ( i. e., lack of a critical study). MOE = margin of exposure. LOC = level of concern. N/ A = Not Applicable * Calculation of concentration equivalent BMDL10 and LOAEL Acute Inhalation BMDL10 0.8 mg/ kg/ day x 0.35 kg / 0.34 m3/ day = 0.8 mg/ m3 Short and Intermediate term inhalation of vapors LOAEL 0.1 mg/ kg/ day x 70 kg / 20 m3/ day = 0.35 mg/ m3 ** Since the NOAEL is expressed in concentration units ( RfC methodology), the interspecies extrapolation factor is 3x ( for the acute and long term inhalation scenarios), for a total UF of 30 for acute inhalation and long term inhalation. Page 177 of 338 9.0.1. Mushroom House ( a). Application Application of dichlorvos to mushroom houses may be made by coarse spray and paint on applications. Foggers would be permitted if the applicator is outside the mushroom house. The exposures for coarse spray applications were derived from ORETF data. The Outdoor Residential Exposure Task Force ( ORETF) has recently completed several surrogate mixer/ loader/ applicator studies addressing lawn care operators ( LCOs). ( Bangs, 2001; Jaquith, 2001). The hose end sprayer scenario from the ORETF studies will be used to estimate exposures to applicators in mushroom houses. Estimates of the surface areas that would be painted or sprayed during dichlorvos application were derived from mushroom culture textbooks and are considered to be conservative ( Jaquith 1998d and n). This application scenario is considered to be intermediate term ( several months) because a single individual may treat different mushroom houses on different days due to the cyclic nature of mushroom culture.

Coarse Spray and Paint on Applications. For the coarse spray, data from the ORETF lawn care study were used; protective clothing varied with the application method, and included long pants, long sleeved shirt and gloves, or coveralls plus long pants, long sleeved shirt and gloves. The label does not specify protective clothing needed. Dermal and inhalation exposure and total exposure resulting in an MOE of 46 is not considered to be of concern, compared to the target MOE of 30. If an additional layer of protective clothing were added, the absorbed dermal dose would be cut approximately in half, and the MOE of 88 would be adequate.

( b). Post application For reentry exposure, it was assumed that a worker reenters a ventilated mushroom house 12 or 24 hours after treatment and is exposed for 8 hours. This is a short term exposure because workers may be exposed multiple times on subsequent days. The MOE at a 12 hour REI of 23 is less than the target MOE of 30, and is of concern. The MOE at a 24 hour REI of 58 is greater than the target MOE of 30, and is not of concern. AMVAC has submitted an amendment, changing the label REI to 18 hours.

9.0.2. Greenhouse ( a). Application There are currently no end use product labels with directions for use for greenhouses. However, the technical label for Dichlorvos allows use of up to 2.0 g/ 1000 cu. ft. Previously, smoke generators were registered, and were considered to result in negligible applicator exposure since the applicator vacates the premises immediately upon activation of the smoke generator. This application scenario is considered to be short term because treatment would not be expected to occur in a given greenhouse more than once a week. The baseline MOE is 46, which is not of concern. Page 178 of 338 ( b). Post application The dermal exposure for reentry into greenhouses following the use of dichlorvos was obtained using data from a greenhouse culture textbook, data on turf transferable residues from a chlorpyrifos/ dichlorvos study ( Goh, K. S., et. al. 1986), and a standard transfer coefficient of 2500 cm2/ hr, from ExpoSAC Policy 003. Inhalation exposure estimates were modeled assuming the initial concentration at the maximum rate, assuming first order kinetics and an air exchange rate from a textbook ( Mastalerz, 1977). This is considered to be a short term exposure scenario ( Jaquith, 1998d).

The total daily dermal exposure that would occur after a 2 hour REI is estimated to be 1.2 µ g/ kg/ day. The dichlorvos concentrations available for inhalation exposure were modeled ( Jaquith, 1998d), and concentrations depended on the ventilation used. The estimated respiratory component of exposure would be 0.00035 mg/ m3. The resulting MOE with a 2 hour REI of 78 is not of concern, compared to the target MOE of 30. At a 12 hr REI, the total MOE is > 650 and is not of concern, compared to the target MOE of 30.

9.0.3. Domestic Animal Premises ( food and nonfood) and Direct Animal Sprays, Feedlots, Manure Treatment, Garbage Dumps, and Baits ( a). Application Dairy barn application and direct application to dairy cattle were used as the reference facility for these exposure assessments ( Jaquith 1998l). There are no data addressing the use of dichlorvos in other types of animal facilities. Worker exposure from direct application to animals is based on dairy cattle treatment. Although permitted on product labels, the Agency does not believe that direct application to livestock animals with a handheld sprayer is used. Rather, some type of automated equipment is used to apply dichlorvos directly to animals. Space and premise treatments also help control insects on animals. Since several registered products provide guidance on use with a handheld sprayer, the exposure and risk are estimated here for that application method, which is expected to result in a much higher exposure than automated methods. While some labels indicate that daily application ( probably for direct application to cattle) is allowable, the use assessment indicates that the material is applied at 2 week intervals ( Dow, M., 1985). This assessment assumes daily applications over several months, and is therefore considered to be an intermediate term scenario.

Cattle. Exposure assessments for direct application to dairy cattle using hand held sprayers as a surface spray or space spray were conducted using PHED V1.1. Applicators were assumed to be wearing long sleeved shirt, long pants, and gloves. Gloves are not currently required on the label. Absorbed dermal doses were estimated to range from 0.009 to 0.22 µ g/ kg/ day and respiratory doses from 0.008 to 0.039 µ g/ kg/ day, depending on application equipment. These total MOEs would range from 440 to 59000, and are not considered to be of concern.

Poultry. Applicator exposure data for cattle cannot be extrapolated to poultry, because of the different application method and less frequent applications. Individual animals are less likely to be treated directly and the equipment is more likely to be automated. As a result, exposure from Page 179 of 338 applying dichlorvos to poultry is expected to be much lower than for cattle. Therefore, no separate assessment has been done.

Domestic Animal Premises. Barn sizes were obtained from the dichlorvos Qualitative Use Assessment ( QUA) ( Dow, M., 1985). Assuming that a worker wears long sleeve shirt, long trousers, shoes and impervious gloves at a minimum, risks from dichlorvos application to domestic animal premises are lower than the risks from direct application to cattle, with total MOEs from 440 to 5900, and do not exceed the Agency's level of concern. Gloves are not currently required on all dichlorvos labels.

Feedlots include stockyards, corrals, holding pens and other areas where large groups of animals are contained. EPA assumes that some type of power sprayer capable of treating a large number of animals in a short time is probably used. A short application time period in an outdoor or partially enclosed area would minimize exposure to less than that of dairy applications.

Manure Treatment. The application equipment used for manure applications may be similar to those used in a dairy barn; however, the application time would probably be less and the treated area would be well ventilated  either outdoors or in a partially enclosed area. The MOE for applicators is expected to be greater than the target MOE for manure use.

( b). Reentry There are no data addressing potential reentry into animal facilities. Re entry exposure to animal premises would not be expected to exceed reentry exposure for greenhouses, and would be expected to be considerably less, since animal premises are usually outdoors or well ventilated, where minimal dermal contact is expected.

9.0.4. Food Manufacturing Plant, Warehouse Treatment ( a). Application Dichlorvos can be applied to warehouses with wall mounted automatic foggers. Exposure to mixer/ loaders through automatic application is expected to be negligible; however, there would still be reentry exposure.

( b). Post application In estimating reentry exposure, EPA assumed 24 hours elapsed before reentry is allowed, the label REI; and that workers in food manufacturing plants spend 8 hours per day in the treated area, and 2 hours per day in warehouses. Absorbed dermal exposure was measured for the hands only, which is likely to be the greatest route of dermal exposure, and represents an average of the total exposure measured for three work stations, and was negligible compared to the inhalation exposure. This exposure scenario was considered to be acute due to rapid dissipation of dichlorvos ( 1 day) and sporadic use. ( Jaquith, D., 2000a; Jaquith, D, 1993c). Page 180 of 338 The dermal exposure estimate is 0.00022 mg/ kg/ day for food manufacturing plants. The mean air concentration of dichlorvos in a food manufacturing plant is estimated to be 0.053 mg/ m3 , 24 hours after application, which results in an exposure of 0.006 mg/ kg/ day. The estimated air concentration in a warehouse after a 24 hour REI is 0.074 mg/ m3 . This is an acute exposure scenario with an MOE of 130 ( target MOE is 100) for food manufacturing plants, and 650 for warehouses, neither of which is of concern.

9.0.5. Railcars and Trucks ( a). Application Dichlorvos can be applied to railcars and trucks as a fog or as a surface spray. This is a short term exposure scenario. One to ten railcars or trucks could be treated in a single day. Application with a surface spray would have MOEs of 320, compared to a target MOE of 30, which would not be of concern.

( b). Post application In estimating reentry exposure, EPA assumed 6 hours elapsed before reentry is allowed, and that workers could spend 1 hour per truck or railcar and could load 4 railcars or trucks per day. Workers loading rail cars or trucks would not be expected to have dermal exposure to dichlorvos. The air concentration was estimated using initial air concentrations calculated from the application rate, and assuming ventilation similar to a food processing establishment. This exposure scenario was considered to be short term due to rapid dissipation of dichlorvos. ( Jaquith, D., 2005). The air concentration 6 hours after treatment is estimated to be 0.018 mg/ m3. The MOE would be 94, which is not of concern, compared to the target MOE of 30. There is considerable uncertainty about the air exchange rate. Under the conditions described, the air exchange rate could be as low as 1/ 3 per hour.

9.0.6. Insect Traps Exposure is believed to be negligible since the pesticide is in the form of an impregnated strip in a sealed package, which is opened and the applicator leaves, and the traps are placed in outdoor areas ( such as forests) where there is no human exposure.

9.0.7. Occupational Uses of Resin Strips The dichlorvos label contains the following use patterns and restrictions.

Garbage Cans, Trash Dumpsters, Catch Basins, Utility Enclosures. Keep lid on can and dumpster closed.

Animal Buildings, Milk Rooms. Do not contaminate food, water or foodstuffs. Do not contaminate milk or milking equipment. Page 181 of 338 Agricultural Commodities: Bulk Storage of raw grains, corn, soybeans, cocoa beans, and peanuts. No restrictions.

Reptile Houses and Terrariums. Make sure that the reptiles can not touch or contact the strip.

Exposure to dichlorvos from these use patterns is expected to be small compared to the use of resin strips in homes, provided that workers are in the facilities treated for short periods of time. Refer to table 6.3 for exposure and risk information. Page 182 of 338 Table 9.1 Occupational Applicator Exposure and Risk Estimates1 Scenario Endnote Duration # ai/ day Dermal unit exposure Inhalation unit exposure Dermal Exposure Inhalation Exposure Total Exposure Dermal MOE Inhalation MOE Total MOE Mushroom house & Greenhouse 2  ORETF Hose End Sprayer Intermediate term 2.6 0.52 0.001 0.00212 0.00004 0.0022 47 2700 46  ORETF Hose End Sprayer +

coveralls Intermediate term 2.6 0.27 0.001 0.00110 0.00004 0.00061 91 2700 88 Direct animal treatment 3  Hand Held Sprayer Intermediate term 0.092 0.17 0.017 0.000025 0.000023 0.000047 4100 4400 2100  Backpack Sprayer ( 471) Intermediate term 0.092 2.6 0.017 0.000376 0.000023 0.000399 270 4400 250  Backpack Sprayer ( 416) Intermediate term 0.092 0.27 0.017 0.000039 0.000023 0.000062 2600 4400 1600  Portable Sprayer on Cart Intermediate term 0.092 0.69 0.052 0.000100 0.000068 0.000168 1000 1500 600 Dairy barns  space spray 4  Hand Held Sprayer Short term 0.033 0.17 0.017 0.000009 0.000008 0.000017 11000 12000 5900  Backpack Sprayer ( 471) Short term 0.033 2.6 0.017 0.000135 0.000008 0.000143 740 12000 700  Backpack Sprayer ( 416) Short term 0.033 0.27 0.017 0.000014 0.000008 0.000022 7100 12000 4500  Portable Sprayer on Cart Short term 0.033 0.69 0.052 0.000036 0.000025 0.000060 2800 4100 1700 Dairy barns  surface spray  Hand Held Sprayer Short term 0.053 0.17 0.017 0.000014 0.000013 0.000027 7100 7600 3700  Backpack Sprayer ( 471) Short term 0.053 2.6 0.017 0.000217 0.000013 0.000230 460 7600 440  Backpack Sprayer ( 416) Short term 0.053 0.27 0.017 0.000022 0.000013 0.000036 4400 7600 2800  Portable Sprayer on Cart Short term 0.053 0.69 0.052 0.000057 0.000039 0.000097 1700 2500 1000 Rail cars and trucks 5  Surface Spray Short term 0.28 0.67 0.0032 0.00030 0.000013 0.00031 330 7700 320 Feedlots 6 Short term Manure 7 Short term Garbage Dumps 8 Short term No data; not expected to exceed dairy barn exposure NOTES: The parameters and assumptions used in calculating the margins of exposure are found in the endnotes below , Risk is expressed as a Margin of Exposure ( MOE)

MOE = NOAEL , where both the NOAEL and the Exposure are expressed in mg/ kg/ day or mg/ m3 Exposure Page 183 of 338 The target MOE for occupational exposure scenarios is 30.

1. Occupational Exposure assumptions. An average worker weighs 70 kg and has a respiratory volume of 1.0 m3 / hour ( NAFTA Value). At a minimum, the following protective clothing was used in the exposure scenarios: gloves, long sleeve shirt, long pants 2. Mushroom Houses and Greenhouses Mushroom Houses  coarse spray. A typical mushroom operation is believed to consist of 10 houses, each with a volume of 30000 ft3 ( 850 m3). The label does not specify protective clothing needed. If an individual treats all 10 houses at a rate of 2 grams per 1000 ft3 the amount handled in a day would be:

Amount handled ( lb ai/ day) = 30000 ft3/ house x 10 houses/ day x 2 g/ 1000 ft3 = 1.3 lb ai/ day 454 g/ lb ai Workers are assumed to be wearing a single layer of clothing and gloves. A second assessment was done for applicators wearing coveralls. Data from the ORETF lawn care study were used ( liquid formulation, hose end sprayer).

AMVAC does not have a coarse spray registered. There was a canceled product, EPA Reg. No. 72 375 that had use directions for the coarse spray or paint on application to mushroom houses. The use specified 0.25 lb of a 0.5% solution to treat 100 sq ft. If we assume that a typical mushroom house is 6000 sq ft, the amount handled per day would be about1.5 lb ai/ day. Thus, the mushroom/ greenhouse assessment presented in this table estimates a somewhat higher exposure than what would be expected.

Greenhouse  The average greenhouse has an estimated volume was 85,000 ft3. A typical operation was assumed to consist of 10 greenhouses which could be treated in a single day. Treatment was estimated to be 3.75 minutes per house or 26 minutes ( 0.44 hrs) per day. Dichlorvos is applied at the rate of 1.4 grams of active ingredient per 1,000 ft3. Workers were assumed to be a single layer of clothing and gloves. Treatment would not be expected to occur in a given greenhouse more than once a week, resulting in a short term exposure scenario. Workers are assumed to weigh 70 kg. The unit exposures were 14 mg/ lb ai handled for dermal exposure, and 0.19 mg/ lb ai handled for inhalation exposure.

The typical application rate for dichlorvos in a greenhouse is 1.4 g per 1000 ft3. The amount handled per greenhouse would be:

Amount handled ( lb ai/ greenhouse) = 1.4 g ai/ 1000 ft3 x 85000 ft3/ greenhouse = 120 g ai/ greenhouse = 0.26 lb ai/ greenhouse The amount handled per day would be:

Amount handled ( lb ai/ day) = 0.26 lb ai/ greenhouse x 10 greenhouses/ day = 2.6 lb ai/ day 3. Domestic Food/ Non food Animals ( non poultry). Worker exposure from direct application to animals is based on dairy cattle treatment. A one percent solution of dichlorvos is applied with a handheld sprayer. An average herd of dairy cattle consists of 65 head, each requiring 24 seconds to spray, two times per day during treatment. Fly control is required from May to October with application expected to be occurring weekly rather than 2 x per day during this time ( 26 times per year). Although permitted on product labels, EPA does not believe that direct application with a handheld sprayer is used. Rather, some type of automated equipment is used to apply dichlorvos directly to animals. Space and premise treatments also help control insects on animals. Since several registered products provide guidance on use with a handheld sprayer, the exposure and risk are estimated here for that application method, which is expected to result in a much higher exposure than automated methods. The exposure assessment for direct application to dairy cattle using a handheld sprayer was conducted using PHED V1.1. Applicators were assumed to wear long sleeve shirts, long pants, and gloves. Page 184 of 338 Domestic Food/ Non food Animals ( poultry). Data for cattle cannot be extrapolated to poultry, because of the different application method and less frequent applications. However, individual animals are less likely to be treated directly and the equipment is more likely to be automated. As a result, exposure from applying dichlorvos to poultry is expected to be much lower than for cattle, and no separate assessment is done.

4. Domestic Animal Premises  Dairy Barns. An average dairy barn has the dimensions 30 ft x 100 ft x 9 ft ( total area covered is 5,340 ft2 ). ( Dow, M., 1985).

Dichlorvos is applied at two week intervals for 22 weeks, one barn per day. A 1.0 percent solution of dichlorvos is applied using a low pressure hand sprayer at a rate of 0.0115 lb a. i. per 1000 ft2. A worker wears long sleeve shirt, long trousers, shoes and impervious gloves at a minimum. The unit exposure varies depending on the equipment used.

5. Rail cars and trucks. Calculation is shown for treating 10 rail cars or trucks per day. Dermal absorption is assumed to be 11 percent. Applicators are assumed to wear long sleeve shirts, long pants, gloves, and a respirator ( 90% protection). Coveralls, although required on some labels, are not included for surface application. An applicator treating 10 rail cars per day handles 0.28 lb ai/ day. The dermal unit exposure is 0.67 mg/ lb ai, and the inhalation unit exposure is 0.0032 mg/ lb ai.

0.28 lb dichlorvos x 0.67 mg/ lb ai x 0.11 ( dermal absorpting factor) = 0.00030 mg/ kg/ day 70 kg applicator 0.28 lb dichlorvos x 0.0032 mg/ lb ai = 0.000013 mg/ kg/ day 70 kg applicator 6. Feedlots include stockyards, corrals, holding pens and other areas where large groups of animals are contained. EPA assumes that some type of power sprayer capable of treating a large number of animals in a short time is probably used. A short application time period in an outdoor or partially enclosed area would minimize exposure to less than that of dairy applications.

7. Manure. The MOE is expected to be greater than 100 for manure use. Application equipment may be similar to those used in a dairy barn; however, the application time would probably be less and the treated area would be well ventilated  either outdoors or in a partially enclosed area.

8. Garbage Dumps. Exposure at a garbage dump is believed to be less than dairy exposure. Page 185 of 338 Table 9.2. Summary of Occupational Post Application Exposure and Risk Estimates for Dichlorvos Current Exposure ( mg/ kg/ day) Current MOE MOE USES NOTES EXPOSURE PATTERN1 Dermal Inhalation Dermal Inhalation Total OCCUPATIONAL EXPOSURE 1 Target MOEs for all short term post application Occupational Scenarios are 30, and for acute post application scenarios, are 100.

i. Mushroom house 2 Reentry ( 12 hour REI) Short term 0.0002 0.044 mg/ m 3 450 24 23 Reentry ( 24 hour REI) Short term 0.0002 0.016 mg/ m 3 450 66 58 ii. Greenhouse 3 Reentry ( 2 hour REI) Short term 0.0012 0.00035 mg/ m 3 80 3000 78 Reentry ( 12 hour REI) Short term 0.00012 < 0.00035 mg/ m 3 800 > 3000 > 650 Reentry ( 24  hour REI) Short term < 0.00012 < 0.00035 mg/ m 3 > 800 > 3000 > 650 i ii. Food Manufacturing Plant

Reentry ( 24 hour REI) 4 acute 0.00022 0.053 mg/ m 3 ( 0.006 mg/ kg/ day) 3600 130 130 iv. Warehouse treatment

Reentry ( 24 hour REI, 1 hr exposure) 5 acute 0.00022 0.074 mg/ m 3 ( 0.001 mg/ kg/ day) 3600 800 650 v. Railcars and trucks ( 8 hr REI) 6 Short term 0.0187 mg/ m 3 ( 0.0010 mg/ kg/ day) 94 94 NOTES: The following notes define the assumptions used in calculating the margins of exposure. Page 186 of 338 1. Risk is expressed as a Margin of Exposure ( MOE)

MOE = NOAEL , where both the NOAEL and the Exposure are expressed in mg/ kg/ day or mg/ m3 Exposure The target MOE for all short term post application occupational exposure is 30, and for all acute post application scenarios is 100.

Occupational Exposure assumptions. An average worker weighs 70 kg and has a respiratory volume of 1.0 m3 / hour ( NAFTA Value). At a minimum, the following protective clothing was used in the exposure scenarios: gloves, long sleeve shirt, and long pants. Addition of a respirator to the PPE requirements would reduce estimated inhalation exposure by 90%, which would not change the MOEs by more than a factor of 2.

2. Mushroom Houses  reentry. For reentry exposure, it was assumed that a worker reenters a ventilated mushroom house 12 or 24 hours after treatment and is exposed for 8 hours. The post application exposures for mushroom houses were derived from a study conducted by the California Department of Food and Agriculture ( CDFA) ( now the California EPA) in which air and surface residues were measured in mushroom houses where dichlorvos had been applied ( Maddy 1981, Jaquith 1998d). This was a limited study measuring surface residues and air concentrations in 2 4 mushroom houses over 24 hours.

Wipe sampling was only conducted in 2 mushroom houses, preventing any analysis of the distribution of surface residues in these facilities. The highest surface concentration, 0.026 µ g/ cm2, was reported 3 hours after application. The last sampling point was at 12 hours after application, when the surface residues averaged 0.007 µ g/ cm2. There was no clear trend in the air concentrations. Air samples were collected at 30 minutes, and 1, 3, 6, 12, and 24 hours. Only two samples were taken at the 24 hour sampling period. The air concentrations of dichlorvos averaged 0.022, 0.044, and 0.016 mg/ m3, at 6, 12, and 24 hours after treatment, respectively. The transfer coefficient was obtained from the ExpoSAC policy 003, to be 2500 cm2/ hr. Because of the aeration pattern of mushroom houses, the volatility of dichlorvos, and dissipation of dichlorvos in mushroom houses, this is considered to be a short term exposure scenario. Respirators are not worn during reentry.

Dermal Exposure ( µ g/ kg/ day) = 0.007 µ g/ cm2 x 2500 cm2 / hr x 8 hr/ day x 1/ 70 kg x 0.11 ( Absorb)

= 0.22 µ g/ kg/ day = 0.00022 mg/ kg/ day Estimated dermal post application risk = NOAEL = 0.1 mg/ kg/ day = 450 ( Target MOE = 30, ARI = 450/ 30 = 15)

Exposure 0.00022 mg/ kg/ day The inhalation risk estimate includes a factor to adjust for the hours of exposure. The endpoint converted to concentration units assumed 24 hours exposure per day. Workers in mushroom houses are exposed for 8 hours.

Estimated inhalation post application risk = NOAEL = 0.35 mg/ m3 x 24hr = 24 ( Target MOE = 30)

( 12 hour REI) Exposure 0.044 mg/ m3 8 hr The label REI is now 18 hours.

3. Greenhouse  reentry. The dermal exposure for reentry into greenhouses following the use of dichlorvos was obtained using data from a greenhouse culture textbook, data on turf transferable residues from a chlorpyrifos/ dichlorvos turf study ( Goh, K. S., et. al. 1986), and a transfer coefficient of 2500 cm2/ hr, from the ExpoSAC Policy 003. Inhalation exposure estimates were modeled assuming the initial concentration at the maximum rate, assuming first order kinetics and an air exchange rate from a textbook ( Mastalerz, 1977). This is considered to be a short term exposure scenario ( Jaquith, 1998d). Page 187 of 338 The dislodgeable foliar residues reported in the Goh study were 0.04 µ g/ cm2, 2  6 hours after application, and 0.004 µ g/ cm2, 10 hours after application of 2 g dichlorvos/ 1000 ft3.

The total daily dermal exposure that would occur after a 2 hour REI is estimated to be:

Dermal Exposure ( µ g/ kg/ day) = 0.04 µ g/ cm2 x 2500 cm2 / hr x 8 hrs/ day x 0.11 ( dermal absorption factor) x 1/ 70 kg = 1.25 µ g/ kg/ day ( 0.00125 mg/ kg/ day)

Dermal MOE = NOAEL = 0.1 mg/ kg/ day = 80 Exposure 0.00125 mg/ kg/ day Estimated inhalation post application risk = NOAEL = 0.35 mg/ m3 x 24 hr = 3000 ( 2 hour REI) Exposure 0.00035 mg/ m3 8 hr 4. Reentry  Food manufacturing plant. Dichlorvos can be applied to food processing facilities with wall mounted automatic foggers. In estimating reentry exposure to food processing facilities, EPA assumed 24 hours elapsed before reentry is allowed, as required on labels; and that workers spend 8 hours per day on the day following treatment. Dichlorvos is applied at the rate of 2.0 grams active ingredient per 1,000 ft3 over a period of 125 minutes per application. Hand rinses were done and air concentrations were measured at 0, 3, 6, 10, 22, and 42 hours after application. Dermal exposure was measured for the hands only and represents an average of the total exposure measured for three work stations. Because significant exposure occurs for only one day and occurs sporadically, this is considered an acute reentry scenario and MOEs are calculated using the BMDL10 of 0.8 mg/ kg for inhibition of rat cholinesterase.

The dermal exposure calculated in the original review ( Jaquith 1993c), 0.00027 mg/ kg/ day, has been corrected for the application rate ( 2.0/ 2.4), resulting in a dermal exposure estimate of 0.00022 mg/ kg/ day.

The dermal MOE = 0.8/. 00022 = 3600 Mean air concentrations of dichlorvos in a food handling establishment following treatment using a fogger at 2.4 g ai/ 1000 ft3. Means include samples from all sites and two different heights. ( Jaquith, D., 2000a; Jaquith, D, 1993c).

Hours After Application Mean Conc. ( mg/ m3) Conc. Corrected for application rate ( mg/ m3)

0 10.0 8.3 3 2.7 2.2 6 0.62 0.52 10 0.37 0.31 22 0.13 0.11 42 0.052 0.043 An exponential decay curve C = C0 x e kt was fit to the data where C0 = 0.93 mg/ m3 and k = 0.10 / hour. The corresponding equation for average concentration over the interval from t1 to t2 is Cavg = C0 x ( e kt1  e kt2) / k( t2 t1). For the interval from 24 to 32 hours, the average concentration is 0.053 mg/ m3. The dose on a mg/ kg basis is: Page 188 of 338 Dose ( mg/ kg) = 0.053 mg/ m3 x 1.0 m3/ hr x 8 hr ÷ 70 kg = 0.006 mg/ kg.

The acute inhalation MOE is: MOE = 0.8 ÷ 0.006 = 130 5. Reentry  warehouse. Dichlorvos can be applied to food warehouses with wall mounted automatic foggers. In estimating reentry exposure to warehouse facilities,

EPA assumed 24 hours elapsed before reentry is allowed, as required on labels; and that workers spend 60 minutes per day in the treated area. Dichlorvos is applied at the rate of 2.0 grams active ingredient per 1,000 ft3 over a period of 125 minutes per application. Dermal exposure was measured for the hands only and represents an average of the total exposure measured for three work stations. Because significant exposure occurs for only one day and occurs sporadically,

this is considered an acute reentry scenario and MOEs are calculated using the BMDL10 of 0.8 mg/ kg for inhibition of rat cholinesterase.

The dermal exposure is described in footnote ( 4).

The methodology for inhalation exposure and risk are described in footnote ( 4). Assuming a worker reenters a treated warehouse 24 hours after application and works for one hour, the average dichlorvos concentration in the interval from 24 to 25 hours is 0.074 mg/ m3. The dose on a mg/ kg basis is:

0.074 mg/ m3 x 1.0 m3/ hr x 1 hr / 70 kg = 0.0010 mg/ kg/ day MOE = 0.8 mg/ kg/ day = 800 0.0010 mg/ kg/ day 6. Reentry  railcars and trucks. Dichlorvos can be applied to railcars and trucks as a space spray, or as a surface spray. Some labels allow up to 2 g ai/ 1000 ft3,

others allow up to 2.5 g ai/ 1000 ft3. The initial concentration of dichlorvos from 2.5 g ai/ 1000 ft3 would be 88 mg/ m3. The concentration at later time intervals can be calculated from the equation, Ct = C0 x e kt, where k = 1, based on an assumed air exchange rate of 1 air change per hour. In estimating reentry exposure, EPA assumed 8 hours elapsed before reentry is allowed, and that workers could spend 1 hour per truck or railcar and could load 4 railcars or trucks per day. Workers loading rail cars or trucks would not be expected to have dermal exposure to dichlorvos. The air concentration was estimated using initial air concentrations calculated from the application rate, and assuming ventilation similar to a food processing establishment ( k= 1). This exposure scenario was considered to be short term due to rapid dissipation of dichlorvos. ( Jaquith, D., 2005).

Integrating the equation for a period of 8 to 9 hours,

Ct =  88 mg/ m3 x ( e 9  e 8) = 0.0187 mg/ m3 0.0187 mg/ m3 x 1.0 m3/ hr x 1 hr/ truck x 4 trucks / 70 kg = 0.0011 mg/ kg/ day MOE = 0.1 mg/ kg/ day = 94 0.0011 mg/ kg/ day There is considerable uncertainty about the air exchange rate. Under the conditions described, the air exchange rate could be as low as 1/ 3 per hour Page 189 of 338 10.0 Data Needs and Label Requirements 10.1 Toxicology There are no outstanding toxicology data requirements.

10.2 Product Chemistry The discrepancy in the percent of active ingredient in several of the technicals must be resolved.

10.3 Residue Chemistry The residue chemistry database for dichlorvos is reasonably complete. All labels must conform to the use pattern reflected in the residue data submitted. The following data requirements remain outstanding.

GLN 860.1380: Storage Stability Data The Reregistration requirements for storage stability data are not fulfilled. Information pertaining to the storage intervals and conditions of samples of the following commodities, from studies that were reviewed in the Residue Chemistry Chapter of the Guidance Document, must be submitted: packaged and bagged raw agricultural commodities and processed food; bulk stored raw agricultural commodities; milk; eggs; and meat, fat, and meat byproducts of dairy cows and poultry. Alternatively, the registrant may demonstrate that there are sufficient residue data which are supported by storage stability data to support all registered uses of dichlorvos.

The available storage stability data indicate that residues of dichlorvos are stable under frozen storage conditions for up to 90 days in/ on plant commodities, up to 4.5 months in/ on peanuts, and up to 8 weeks in animal commodities.

GLN 860.1480: Meat, Milk, Poultry, Eggs The Reregistration requirements for data pertaining to this guideline topic are not completely fulfilled. A dermal magnitude of the residue study must be submitted for swine. No additional data are required for milk and edible tissues of ruminants, and for eggs and edible tissues of poultry. Swine use is on the labels for EPA Reg. Nos. 572 246 and 47000 130.

10.4 Occupational and Residential Exposure All labels must conform to the parameters used in this risk assessment. Protective clothing requirements at least as stringent as that used in this risk assessment must be added to the label. Labels permitting fogging must be clarified to state that hand held foggers are not permitted, and that the applicator must be outside the treated area during application. Page 190 of 338 The greenhouse exposure study requirement has been satisfied by a generic study on malathion, which allowed the Agency to determine a transfer coefficient for harvesting greenhouse grown cut flowers. MRID 46513901, ( Dole, T and M. Lloyd, 2005)

Dichlorvos from trichlorfon. Outstanding exposure data requirements exist for trichlorfon. A TTR study with analyses for trichlorfon and dichlorvos in the turf and in the toddler breathing zone above the turf ( 18") is requested to confirm the exposure estimates in this document. The study must be conducted at an appropriate pH ( approx. 7). A field dissipation study may be substituted, provided it meets these requirements.

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US EPA. 1998a. PHED Surrogate Exposure Guide. Estimate of Worker Exposure from the Pesticide Handlers Exposure Database, Version 1.1. August, 1998.

US EPA, 2000. " Benchmark Dose Technical Guidance Document" Draft report. Risk Assessment Forum, Office of Research and Development, U. S. Environmental Protection Agency. Washington, DC. EPA/ 630/ R 00/ 001 US EPA 2001. Preliminary OP Cumulative Risk Assessment. December 3, 2001. http:// www. epa. gov/ pesticides/ cumulative/ pra op/

US EPA, 2002. Methods Used to Conduct a Preliminary Cumulative Risk Assessment for Organophosphate Pesticides. Report from the FIFRA Scientific Advisory Panel Meeting of February 5 7, 2002 ( Report dated March 19, 2002). SAP Report 2002 01. http:// www. epa. gov/ scipoly/ sap/ index. htm# june.

US EPA 2002a. Revised Organophosphorus Pesticide Cumulative Risk Assessment. Office of Pesticide Programs, U. S. Environmental Protection Agency. Washington, DC. June 10, 2002. http:// www. epa. gov/ pesticides/ cumulative/ rra op/ Page 200 of 338 Appendices 1.0 TOXICOLOGY DATA REQUIREMENTS The toxicology data requirements ( 40 CFR 158.340) for food uses for dichlorvos are in Table 1. Use of the new guideline numbers does not imply that the new ( 1998) guideline protocols were used.

Technical Test Required Satisfied 870.1100 Oral Toxicity.............................................................. 870.1200 Dermal Toxicity ......................................................... 870.1300 Inhalation Toxicity...................................................... 870.2400 Primary Eye Irritation.................................................. 870.2500 Primary Dermal Irritation............................................. 870.2600 Dermal Sensitization................................................... yes yes yes yes yes yes yes yes yes yes yes yes 870.3100 Oral Subchronic ( rodent) ............................................ 870.3150 Oral Subchronic ( nonrodent)....................................... 870.3200 21 Day Dermal........................................................... 870.3250 90 Day Dermal........................................................... 870.3465 90 Day Inhalation....................................................... yes yes no no yes yes yesa yes 870.3700a Developmental Toxicity ( rodent).................................. 870.3700b Developmental Toxicity ( nonrodent) ............................ 870.3800 Reproduction.............................................................. yes yes yes yes yes yes 870.4100a Chronic Toxicity ( rodent)............................................. 870.4100b Chronic Toxicity ( nonrodent) ....................................... 870.4200a Oncogenicity ( rat)....................................................... 870.4200b Oncogenicity ( mouse)................................................. 870.4300 Chronic/ Oncogenicity ................................................. yes yes yes yes yes yesb yes yesb yes yes 870.5100 Mutagenicity  Gene Mutation  bacterial ..................... 870.5300 Mutagenicity  Gene Mutation  mammalian ................ 870.5xxx Mutagenicity  Structural Chromosomal Aberrations .... 870.5xxx Mutagenicity  Other Genotoxic Effects ....................... yes yes yes yes yes yes yes yes 870.6100a Delayed Neurotox. ( hen)............................................ 870.6100b 90 Day Neurotoxicity ( hen) ......................................... 870.6200a Neurotox. Screening Battery ( rat)............................... 870.6200b 90 Day Neuro. Screening Battery ( rat)......................... 870.6300 Developmental Neurotoxicity ...................................... yes no yes yes yes yes yes yes yes 870.7485 General Metabolism ................................................... 870.7600 Dermal Penetration .................................................... yes yes yes yes Special Studies for Ocular Effects Oral ( rat) .................................................................... Subchronic Oral ( rat) .................................................. Six month Oral ( dog) .................................................. no no no a = subchronic ( oral) dog study is satisfied by chronic dog study b = chronic toxicity in rats and oncogenicity in rats are satisfied by chronic toxicity/ carcinogenicity rat study Page 201 of 338 2.0 REFERENCES FOR TOXICOLOGY STUDIES Alternative Selection for Acute RfD:

Study Selected: Acute Cholinesterase Study  Humans Non guideline MRID: 44248802 Title: Dichlorvos: A Study to Investigate the Effect of a Single Oral Dose on Erythrocyte Cholinesterase Inhibition in Healthy Male Volunteers; Gledhill, AJ; March 25, 1997 Executive Summary: Dichlorvos was administered in a single oral dose of 70 mg ( equivalent to 1 mg/ kg bw) in corn oil by capsule to fasted young healthy male volunteers. Prior to dosing, baseline RBC cholinesterase activity was measured on study days  22,  20,  18,  15,  13,  11,  8,  6,  4 and immediately prior to dosing. The study subjects were medically supervised for clinical signs and body temperature changes for 24 hours and for RBC cholinesterase inhibition for up to fourteen days after administration of the DDVP capsules. Plasma cholinesterase was not measured in this study.

Under study conditions, no adverse clinical signs or changes in body temperature were reported. When the group mean RBC cholinesterase activities were analyzed, there were statistically significant reductions ( p  0.01) from the predose mean on days 5/ 6, day 7, and day 14. These statistically significant reductions represent percent decreases of 10, 12, and 11%, respectively. No reduction in RBC cholinesterase activity was apparent at other reporting periods. The individual predose values used to calculate the mean RBC cholinesterase activity varied by 17% for volunteer 1, 16% for volunteer 2, 6% for volunteer 3, 10% for volunteer 4, 7% for volunteer 5, and 9% for volunteer 6.

The NOAEL for RBC cholinesterase depression is 1.0 mg/ kg bw and a LOAEL was not established in the study.

Although the study results indicate that a significant decrease in mean RBC cholinesterase was first observed at 5/ 6 days after treatment, with significance also seen at 7 and 14 days posttreatment, measurements at posttreatment days 1 and 3 were not significantly different from baseline. These results are inconsistent with known information on the chemical. Namely, given the rapid bioavailability and metabolism of dichlorvos, it is unlikely that a significant decrease in RBC cholinesterase would first be observed at day 5/ 6 posttreatment and not also at days 1 and 3 posttreatment. The statistical significance observed could be attributed to variation among individual participants.

Lack of information on time of peak effect.

In the acute human study, the first cholinesterase measurement was recorded 24 hours after dosing. In the study ( MRID 46153303) on the measurement of RBC and brain ChE activity in pre weaning and adult female rats treated with a single dose of 15 mg/ kg dichlorvos, time course data Page 202 of 338 demonstrate that the time of peak effect for both RBC and brain ChE measurements is 1 3 hours post dosing. Therefore, the absence of biologically significant RBC ChE depression in the human study may be due to the absence of blood sampling at the time of peak effect ( 1 3 hours), since in the human study, the first measurement did not occur until 24 hours after dosing.

Based on the information on time to peak effect, we conclude that the lack of cholinesterase measurements prior to 24 hours post treatment in the acute human study may have influenced the apparent NOAEL. We have therefore opted not to use the acute human study for regulatory purposes.

CITATION: G. Milburn ( 2003) Dichlorvos: developmental neurotoxicity study in rats. Central Toxicology Laboratory, Alderley Park, Macclesfield, Cheshire, UK. Laboratory report number CTL/ RR0886/ Regulatory/ Report, November 10, 2003. MRID 46153302. Unpublished.

G. Milburn ( 2003) Dichlorvos: preliminary developmental neurotoxicity study in rats. Central Toxicology Laboratory, Alderley Park, Macclesfield, Cheshire, UK. Laboratory report number CTL/ RR00885/ Regulatory/ Report, October 13, 2003. MRID 46153301. Unpublished.

SPONSOR: Amvac Chemical Corporation. EXECUTIVE SUMMARY:

In a developmental neurotoxicity study ( 2003, MRID 46153302, study RR0886) Dichlorvos ( 99.0% a. i., batch # ST120700) was administered to 30 time mated female Alpk: APfSD ( Wistar derived) rats per group by gavage in de ionized water at dose levels of 0, 0.1, 1.0, or 7.5 mg/ kg bw/ day from gestation day ( GD) 7 through postnatal day ( PND) 7 and direct treatment of the F1 offspring was carried out during PND 8 22, inclusive. On PND 5, litters were culled to 8 pups ( 4/ sex as closely as possible), and litters containing fewer than 7 pups and/ or fewer than 3 pups of each sex were removed from the study. The dams were subjected to a functional observational battery ( FOB) on GDs 10 and 17 and on PNDs 2 and 9. The F1 offspring were observed for attainment of preputial separation or vaginal patency. Animals were allocated from within litters for use in the following investigations: functional observational battery assessments ( PNDs 5, 12, 22, 36, 46, and 61); locomotor activity assessment ( PNDs 14, 18, 22, and 60); auditory startle habituation ( PNDs 23 and 61), water maze testing ( PND 24 27 or PND 59 62); and post mortem investigations including brain weight, neuropathology, and morphometry ( PNDs 12 and 63). Dosing was based on a preliminary developmental neurotoxicity study in rats ( MRID 46153301).

One high dose female was sacrificed on LD 3 due to clinical signs ( pallor, piloerection, and slightly hunched posture and thin appearance) and had a pale liver at necropsy. One mid dose female died on GD 24 due to parturition difficulties. There were no treatment related effects on maternal body weight, FOB parameters, or gestation length. The maternal NOAEL is 7.5 mg/ kg/ day, the highest dose tested. A maternal LOAEL was not established. Page 203 of 338 During LD 1 5, the control, low, mid, and high dose groups, respectively, had pup mortality of 22.6, 17.4, 17.5, and 28.1%, and there were total litter losses of 20.0, 10.0, 17.9, and 18.5% of the litters in these same respective groups. There were 2 total litter resorptions in the high dose group. The number of litters available which were used for F1 offspring was 23, 21, 21, and 14 and the viability indices were 77.4, 82.6, 82.5, and 69.0% for the control, low, mid, and high dose groups, respectively.

Due to the low number of pups available in the high dose group, it was necessary to combine this study ( RR0886) with a repeat study ( 2004, MRID 46239801; study No. RR0988) consisting of controls and a dose level of 7.5 mg/ kg in order to have sufficient pups for all assessments.

The DNT Committee determined that the two DNT studies combined ( RR0886 and RR0988) had acceptable numbers of total pups examined in the controls and high dose groups (> 35 pups/ sex examined in combined studies) and, therefore, the developmental results of the combined studies could be evaluated for the NOAEL/ LOAEL. The classification of the studies taken together was changed from unacceptable/ non guideline to Acceptable/ non guideline. A comparison of the developmental findings showed that the auditory startle reflex habituation Vmax in PND 23 high dose males in study RR0886 had statistically significant increases ( 37 49%) in 4 out of 5 blocks and study RR0988 had increases ( 7 15%), although not statistically significant, in this same Vmax parameter in PND 23 high dose males in 5 out of 5 blocks in comparison to controls for each study.

Therefore, the developmental/ offspring NOAEL was determined to be 1.0 mg/ kg/ day ( based on study RR0886) and the developmental/ offspring LOAEL was 7.5 mg/ kg/ day ( based on both studies RR0886 and RR0988) with the effect being increases in auditory startle reflex habituation Vmax in PND 23 high dose males in both studies.

This study when combined with the accompanying study is classified Acceptable/ non guideline and may be used for regulatory purposes. It does satisfy the guideline requirement for a developmental neurotoxicity study in rats [ OPPTS 870.6300, § 83 6; OECD 426 ( draft)], pending review of the positive control data.

CITATION: G. M. Milburn ( 2004) Dichlorvos: supplemental developmental neurotoxicity study in rats. Central Toxicology Laboratory, Alderley Park, Macclesfield, Cheshire, UK SK10 4TJ. Laboratory report number CTL/ RR0988/ Regulatory/ Report, January 28, 2004. MRID 46239801. Unpublished.

SPONSOR: Amvac Chemical Corporation.

EXECUTIVE SUMMARY: In a preliminary developmental neurotoxicity study ( MRID 46153301) Dichlorvos ( 99.0% a. i., batch # ST120700) was administered by gavage in de ionized water to 15 time mated female Alpk: APfSD ( Wistar derived) rats per dose at dose levels of 0, 0.1, 1.0, or 7.5 mg/ kg bw/ day from gestation day ( GD) 7 through postnatal day ( PND) 22. In life observations included maternal clinical signs, body weight, and food consumption ( during gestation) and the number, survival, clinical signs, and body weight of the pups. Erythrocyte ( RBC) and whole brain acetylcholinesterase ( AChE) activities were measured as follows: in 5 dams/ group Page 204 of 338 on GD 22; in 5 dams/ group on PND 22; in selected fetuses from the dams killed on GD 22 ( blood from sufficient fetuses to attain adequate pooled sample volume and whole brain from 4 fetuses/ sex/ litter); and in 5 pups/ sex/ group ( 1 per litter where possible) on each of PNDs 2, 8, 15, and 22. Plasma AChE activity was not measured.

There were no maternal deaths during the study. Three dams had abnormal clinical signs: one control dam with piloerection on day 26; one mid dose dam with observations of paleness ( days 24 26), hunched, subdued behavior ( day 26), and a total litter loss by day 26 ( LD 3); and one high dose dam with irregular breathing on days 25 27. There were no treatment related effects on maternal food consumption, maternal body weight, or gestation length. The study author mentioned body weight decreases in high dose dams beginning on LD 11, but these were of insufficient magnitude to be considered biologically significant ( just 3 4% less than controls). Under the conditions of this study, the LOAEL for maternal systemic toxicity ( other than acetylcholinesterase inhibition) is not identified, and the NOAEL is greater than or equal to 7.5 mg/ kg bw/ day.

There were no treatment related effects on the overall proportion of pups born alive, the mean percentage of live pups per litter, or live litter size on LD 1. Pup survival, body weight, and clinical signs were unaffected by treatment. Two dams had total litter losses: one mid dose dam had a total litter loss by LD 3, and one low dose dam had a total litter loss ( of 1 pup) by LD 2. An increased proportion of male pups in the mid dose group ( 64.8% vs. 46.2% for controls; p< 0.01) was considered incidental to treatment because there was no similar finding at the highest dose level. Under the conditions of this study, the LOAEL for offspring toxicity ( other than acetylcholinesterase inhibition) is not identified, and the NOAEL is greater than or equal to 7.5 mg/ kg bw/ day.

In maternal animals, RBC AChE activity was biologically significantly inhibited at the mid and high dose treatment levels on GD 22 by 25% and 48%, respectively ( p< 0.01) and on LD 22 by 24% and 50%, respectively ( p< 0.05 and p< 0.01). RBC AChE activity was also inhibited in high dose male and female ( GD 22) fetuses by 28% ( p< 0.5) [ p< 0.05] and 21% ( n. s.), respectively. There were no treatment related effects on RBC AChE activity in male or female pups. The LOAEL for dichlorvos erythrocyte acetylcholinesterase inhibition in maternal rats is 1.0 mg/ kg bw/ day, with a NOAEL of 0.1 mg/ kg bw/ day. The LOAEL for erythrocyte acetylcholinesterase inhibition in offspring or fetuses is 7.5 mg/ kg bw/ day ( based on male and female fetuses on GD 22), and the NOAEL is 1.0 mg/ kg bw/ day.

In maternal animals, whole brain AChE activity was biologically significantly inhibited in highdose animals on GD 22 and LD 22 by 59% and 67%, respectively ( p< 0.01). Brain AChE activity was also inhibited in high dose male and female ( GD 22) fetuses by 16% ( p< 0.5) [ p< 0.05] and 21%, respectively ( p< 0.01). There were no treatment related effects on brain AChE activity in male or female pups. The LOAEL for brain acetylcholinesterase inhibition in maternal animals is 7.5 mg/ kg bw/ day, with a NOAEL of 1.0 mg/ kg bw/ day. The LOAEL for brain acetylcholinesterase inhibition in offspring or fetuses is 7.5 mg/ kg bw/ day ( based on male and female fetuses on GD 22), and the NOAEL is 1.0 mg/ kg bw/ day.

Based on the results of this study, dose levels of 0, 0.1, 1.0, and 7.5 mg/ kg bw/ day were chosen for the main study. Page 205 of 338 CITATION: Milburn, G. M.. ( 2003) Dichlorvos: time course of cholinesterase inhibition in pre weaning and adult rats. Central Toxicology Laboratory, Cheshire, UK SK10 4TJ. Doc. No. CTL/ AR7310/ Regulatory/ Report. 26 SEPT 2003. MRID 46153303. Unpublished.

Twomey, K. ( 2002) Dichlorvos ( DDVP): Acute cholinesterase inhibition study in rats. Central Toxicology Laboratory, Cheshire, UK SK104T3. Laboratory report number CTL/ AR7079/ SUM/ Regulatory/ Report; Study No. AR7079, 30 MAY 2002. MRID 45805701. Unpublished.

Twomey, K. ( 2002) Dichlorvos ( DDVP): Second acute cholinesterase inhibition study in rats. Central Toxicology Laboratory, Cheshire, UK SK104TJ. Laboratory report number CTL/ AR7126/ SUM/ Regulatory/ Report; Study No. AR7126, 19 JUNE 2002. MRID 45805702. Unpublished.

Twomey, K. ( 2002) Dichlorvos ( DDVP): Third acute cholinesterase inhibition study in rats. Central Toxicology Laboratory, Alderley Park, Macclesfield, Cheshire, UK SK104TJ. Laboratory report number CTL/ AR7138/ Regulatory/ Report; Study No. AR7138, 26 JUNE 2002. MRID 45805703. Unpublished.

Moxon, M. E. ( 2002) Dichlorvos: Acute cholinesterase inhibition study in preweaning rats. Central Toxicology Laboratory, Cheshire, UK SK104T3. Laboratory report number CTL/ AR7147/ Regulatory/ Report; Study No. AR7147, 22 NOV 2002. MRID 45842301. Unpublished.

Moxon, M. E. ( 2003) Dichlorvos: Repeat dose cholinesterase inhibition study in pre weaning and young adult rats. Central Toxicology Laboratory, Cheshire, UK SK104TJ. Laboratory report number CTL/ KR1490/ Regulatory/ Report; Study No. KR1490, 24 OCT 2002. MRID 46153304. Unpublished.

SPONSOR: AMVAC, Los Angeles, CA EXECUTIVE SUMMARY: In a series of special comparative cholinesterase inhibition ( ChEI) studies, Dichlorvos ( DDVP; 99% a. i., lot # ST 120700) was administered by gavage to groups of either Sprague Dawley or Wistar rats. For time course evaluation ( MRID 46153303) 5 females/ group were given a single oral dose of 0 or 15 mg/ kg on PND 15 or 42 and sacrificed 1, 3, 8, 24, or 72 hours later. In three acute studies ( MRIDs 45805701, 45805702, 45805703) groups of 5 adult rats/ sex were given a single oral dose of 0, 1, 5, 15, or 35 mg/ kg and sacrificed one hour post dosing or on post dosing days 8 and 15. In a fourth acute study, groups of 5 pre weaning rats/ sex were given a single oral dose of 0, 1, 5, or 15 mg/ kg on PND 8, 15, or 22 and terminated one hour post dosing. Finally repeated administration was studied by giving seven daily doses of 0, 0.1, 7.5, or 15 mg/ kg/ day to groups of 5 rats/ sex beginning on either PND 12 or 42; animals were Page 206 of 338 sacrificed one hour after the last dose. RBC and brain ChE activities were measured in all animals in each study. Plasma enzyme activity was not measured in any study.

Based on the analytical data for MRID 45805701, the low dose animals were actually dosed with 2.1 mg/ kg, rather than the desired dose of 1.0 mg/ kg/ day. For the remaining studies, the analytical data indicated that the mixing procedure was adequate and that the difference between nominal and actual dosage to the study animals was acceptable for all studies.

At a single dose of 35 mg/ kg, one female died with cholinergic signs and four males were killed for humane reasons due to severe toxicity. The remaining animals of both sexes given 35 mg/ kg displayed some or all of the following signs: decreased activity, lachrymation, miosis, irregular breathing, clonic convulsions, tremors/ fasciculations, prostration, decreased righting and splay reflexes, and salivation. A single dose of 15 mg/ kg resulted in miosis and fasciculations in one adult female, and tremors in one male and one female on PND 8 and one female on PND 22. No treatment related clinical signs were observed in animals of the 1 or 5 mg/ kg dose groups following acute exposure.

Following repeated exposure of pre weaning rats, tremors were observed in 5/ 5 males and 5/ 5 females at 15 mg/ kg/ day on 3 5 days of the dosing interval. In young adult rats at 15 mg/ kg/ day, tremors were observed in 3/ 5 males and 5/ 5 females on one to four days of the dosing interval. In addition, tremors were seen in one adult male after the last dose of 7.5 mg/ kg/ day. No clinical signs of toxicity were observed in the remaining groups.

Acute exposure to doses   5 mg/ kg resulted in clear dose related inhibition of enzyme activity in both compartments in all groups. At 1 mg/ kg, RBC enzyme activity was significantly inhibited in PND 8 females, and PND 15 males and females, but not adults. Brain enzyme activity from animals treated with 1 mg/ kg was not significantly inhibited in adult or pre weaning males and females. Although there was inhibition of brain enzyme activity at the low dose in MRID 45805701, the actual analytical dose at this level was 2.1 mg/ kg and not 1 mg/ kg. Repeat of the 1 mg/ kg dose level was identified as a NOAEL for brain enzyme inhibition as demonstrated in other acute studies.

Two studies included recovery groups held for up to 15 days post exposure. RBC enzyme activity of males and females treated with 35 mg/ kg remained slightly inhibited by 9 15% at 8 days after exposure. This is not considered biologically significant. No inhibition of RBC enzyme activity was seen at any other dose at 8 or 15 days post dosing. Brain enzyme activity was not affected at any dose during the recovery interval. Brain and RBC enzyme activities were maximally inhibited one hour after dosing in both adult and pre weaning female rats. Thereafter, ChE inhibition in both compartments decreased to approximately control levels by 8 hours post dosing.

Dose related inhibition of RBC and brain ChE activities was also apparent after repeated dosing in both adult and pre weaning rats. Biologically significant inhibition of RBC enzyme activity (> 50%) occurred at doses of 7.5 and 15 mg/ kg/ day in both sexes of adults and pre weaning and at the low dose for adult animals ( 11 17%). Brain enzyme activity was statistically and biologically inhibited in both sexes at doses of 7.5 and 15 mg/ kg/ day for adults (> 50%) and at all doses for pups (> 20%). Page 207 of 338 For acute exposure:

the adult LOAEL for brain ChEI is 5 mg/ kg for males and females the adult NOAEL for brain ChEI is 1 mg/ kg for males and females;

the offspring LOAEL for brain ChEI is 5 mg/ kg ( both sexes) the offspring NOAEL for brain ChEI is 1 mg/ kg ( both sexes)

the adult LOAEL for red blood cell ChEI is 5 mg/ kg ( both sexes) the adult NOAEL for red blood cell ChEI is 1 mg/ kg ( both sexes);

the offspring LOAEL for red blood cell ChEI is 1 mg/ kg ( both sexes) the offspring NOAEL for red blood cell ChEI is not identified.

For acute exposure, the overall adult LOAEL for cholinesterase inhibition in rats is 5 mg/ kg based on enzyme inhibition in brain and red blood cells; the adult NOAEL is 1 mg/ kg.

For acute exposure, the overall offspring LOAEL for cholinesterase inhibition in rats is 1 mg/ kg based on enzyme inhibition in red blood cells; the offspring NOAEL was not identified.

For repeated exposure:

the adult LOAEL for brain ChEI is 7.5 mg/ kg/ day ( both sexes) the adult NOAEL for brain ChEI is 0.1 mg/ kg/ day;

the offspring LOAEL for brain ChEI is 0.1 mg/ kg/ day ( both sexes) the offspring NOAEL for brain ChEI is not identified;

the adult LOAEL for red blood cell ChEI is 0.1 mg/ kg/ day ( both sexes) the adult NOAEL for red blood cell ChEI is not identified;

the offspring LOAEL for red blood cell ChEI is 7.5 mg/ kg/ day ( both sexes) the offspring NOAEL for red blood cell ChEI is 0.1 mg/ kg/ day;

For repeated exposure, the overall adult LOAEL for cholinesterase inhibition in rats is 0.1 mg/ kg/ day based on enzyme inhibition in red blood cells; the adult NOAEL is not identified.

For repeated exposure, the overall offspring LOAEL for cholinesterase inhibition in rats is 0.1 mg/ kg/ day based on enzyme inhibition in brain; the offspring NOAEL is not identified.

The cholinesterase activity measurements following an acute oral dose of dichlorvos demonstrate approximately equal susceptibility between juvenile and adult rats. In contrast, results from repeated exposures show that juvenile rats are more susceptible than adults for brain ChEI. In pups the brain ChE activity appeared to be more sensitive than RBC enzyme activity. This susceptibility for brain cholinesterase was observed in terms of the dose level at which an effect was observed Page 208 of 338 ( i. e., the LOAEL for brain cholinesterase inhibition was lower for juveniles than for adults). However, the LOAEL for RBC enzyme inhibition was lower for adults than for juvenile rats. The fact that brain enzyme activity in young animals was the most sensitive to inhibition by the test article is of concern for potential developmental neurotoxicity.

Taken together these studies are classified Acceptable/ Non guideline for the determination of RBC and brain cholinesterase activities following treatment with dichlorvos in adult and juvenile rats. Main deficiencies include omission of plasma measurements and lack of assessment in dams and fetuses on GD 20.

870.6100 ( 81 7) Acute Delayed Neurotoxicity  Hen. MRID 41004702 CITATION: Beavers, J.; Driscoll, C.; Dukes, V.; et al. ( 1988) DDVP: An Acute Delayed Neurotoxicity Study in Chickens: Final Report: Project No. 246 103. Unpublished study prepared by Wildlife International Ltd. 86 p. ( MRID 41004702 EXECUTIVE SUMMARY: In an acceptable acute delayed neurotoxicity study ( MRID 41004702), groups of ten chickens were exposed either to vehicle ( distilled water), DDVP at 16.5 mg/ kg, or the positive control, Tri o tolyl Phosphate ( TOCP), at 600 mg/ kg in corn oil. All birds treated with DDVP were administered an intramuscular injection of atropine sulfate at 5 mg/ kg concurrent with DDVP dosing ( the oral LD50 value of DDVP in chickens not administered atropine is reported at 16.15 mg/ kg); atropine also was administered at 2 mg/ kg on an individual basis as needed to DDVP treated birds.

After 21 days, DDVP treatment and vehicle control birds were redosed ( with atropine treatment as previously) and observed for an additional 21 days before sacrifice. TOCP treated birds were sacrificed 21 days after the initial dose.

During the first forced locomotor activity evaluation on day 3, two hens ( G30 and G37) of the DDVP treated group displayed slight to moderate ataxia, and refused to walk or perform the second walk. By day 7 ( the second evaluation) hen G37 was noted as being slightly ataxic when dropped, appeared normal during the hop, but refused to walk alone. This bird appeared normal when standing or walking in a group, but refused to move when alone; this hen continued to refuse to walk alone at each evaluation except for day 25. On days 36 and 39, the same hen also refused to hop. However, when observed in a group, this bird did not appear ataxic, and appeared to move in a normal manner.

On histopathological examination, bird G37 showed swelling of the axis cylinder and nerve fiber degeneration in the sciatic nerve. Nerves from 5/ 10 positive control ( TOCP treated) hens showed evidence of peripheral neuropathy, while those from 5/ 10 hens showed no significant neural degenerative lesions; however, 3/ 5 of these hens had exhibited slight to moderate ataxia during locomotor assessments. In summary, there were no brain or spinal cord degenerative changes in any of the control, TOC, or DDVP treated groups. However, there were sciatic nerve degenerative changes in 0/ 10, 5/ 10, and 1/ 10 in the negative control, TOCP, and DDVP groups, respectively. Page 209 of 338 Although the authors considered the results equivocal, the findings have been interpreted by HED as indicating a positive result for DDVP for acute delayed neurotoxicity.

870.3100 ( 82 1) 13 Week Gavage Study in Sprague Dawley Rats  MRID 41004701 CITATION: Kleeman, J. ( 1988) 13 Week Gavage Toxicity Study with DDVP in Rats: Final Report: Project ID: HLA 6274 102. Unpublished study pre pared by Hazleton Laboratories America, Inc. 294 p. MRID 41004701.

EXECUTIVE SUMMARY: In an acceptable 13 week subchronic study ( MRID 41004701), Crl: CDR( SD) BR rats, 10/ sex/ group, were gavaged with 0, 0.1, 1.5 or 15 mg DDVP/ kg/ day, 5 days/ week, " for at least 13 weeks." The following ( Table 5) summarizes possible effects:

Table 5.

Controls 0.1 mg DDVP/ kg/ day 1.5 mg DDVP/ kg/ day 15 mg DDVP/ kg/ day Effect M F M F M F M F Reduced RBC count, hemoglobin & hematocrit Week 14     +  + +

Higher Mean Corpuscular Volume        +

Higher Cholesterol       +

Reduced Plasma ChE Week 7 Week 14         + + + + + + + +

Reduced RBC ChE Week 7 Week 14        + + + + + + + + +

Reduced Brain ChE ( termination)       + +

In addition, salivation and/ or urine stains were noted in some high dose males and females at approximately 30 to 60 minutes post dosing. According to Table 12 ( p. 52) of MRID 41004701, at terminal sacrifice 2/ 10 high dose and 1/ 10 low dose females ( but no control females) had generalized retinal atrophy. On page 79 " unilateral retinal degeneration" occurred in 1/ 9 control females, 1/ 10 in the low dose group, 0/ 10 in the mid dose, and 2/ 10 in the high dose. Males in the high dose group had a noticeably ( but not significantly) elevated mean liver weight at termination ( 14.14 g vs. a control value of 12.46 g). However, the mean liver to body weight ratio was significantly ( p   0.05) elevated ( to a value of 0.0293 vs. a control value of 0.0267). Page 210 of 338 The following mean plasma and RBC cholinesterase measurements were obtained for weeks 7 and 14:

Table 6.

Males ( Week 7) Females ( Week 7)

Dosage Level ( mg/ kg/ day) Plasma ChE mu/ mL Mean ( S. D.) RBC ChE mu/ mL Mean ( S. D.) Plasma ChE mu/ mL Mean ( S. D.) RBC ChE mu/ mL Mean ( S. D.)

0 318 ( 67.3) 1195 ( 163.1) 813 ( 326.2) 1269 ( 246.9)

0.1 285 ( 32.0) 1166 ( 244.3) 933 ( 382.1) 1148 ( 125.9)

1.5 226*( 48.5) 903*( 138.0) 692 ( 89.7) 956*( 145.8)

15 112*( 24.2) 629*( 109.3) 338*( 79.0) 740*( 95.4)

* Reported as statistically significant, with p   0.05. Data are from Tables 13 and 14, p. 53 and 54 of MRID 41004701.

Table 7.

Males ( Week 14) Females ( Week 14)

Dosage Level ( mg/ kg/ day) Plasma ChE mu/ mL Mean ( S. D.) RBC ChE mu/ mL Mean ( S. D.) Plasma ChE mu/ mL Mean ( S. D.) RBC ChE mu/ mL Mean ( S. D.)

0 314 ( 56.7) 1358 ( 145.5) 1091 ( 462.0) 1321 ( 82.3)

0.1 282 ( 59.9) 1247 ( 113.9) 1150 ( 485.2) 1212*( 81.4)

1.5 259 ( 69.9) 1014* ( 62.6) 1020 ( 257.0) 1002*( 81.5)

15 204*( 45.1) 787*( 103.6) 575*( 142.2) 874*( 86.8)

* Reported as statistically significant, with p   0.05. Data are from Tables 13 and 14, p. 53 and 54 of MRID 41004701.

According to MRID 41004701 ( p. 29): " The apparent decrease of inhibitory effect at week 14 [ as compared to week 7] may have been due to a longer post treatment interval before blood collection and partial recovery of cholinesterase activity."

The following mean brain cholinesterase measurements were obtained at termination:

Table 8. Page 211 of 338 Dosage Level ( mg/ kg/ day) Males Brain ChE mu/ mL Mean ( S. D.) Females Brain ChE mu/ mL Mean ( S. D.)

0 1105 ( 376.6) 1338 ( 490.0)

0.1 1213 ( 656.4) 1290 ( 376.2)

1.5 1060 ( 183.2) 1290 ( 336.5)

15 791*( 290.0) 680*( 216.6)

* Reported as statistically significant, with p   0.05.

In the review [ HED Doc. No. 007448] it is stated that: " The data presented demonstrate that administration of DDVP at doses of 0, 0.1, 1.5 and 15 mg/ kg[/ day] resulted in no adverse effect on body weight or food consumption. Although hematology parameters were reduced, it is doubtful whether the reductions were biologically significant, because the reductions were within ten percent of control values. Plasma and RBC cholinesterase activity [ sic] were reduced in mid and high dose animals, and RBC cholinesterase activity was reduced in 0.1 mg/ kg[/ day] females at 14 weeks. However, the investigators did not consider the RBC cholinesterase reduction in low dose females to be biologically significant since it was less than ten percent below control. The reduction of brain cholinesterase activity in high dose male and female rats at study termination was biologically significant."

" No other changes were seen in the test animals which could be attributed to administration of the test compound. The increased liver/ body [ weight] ratio seen in high dose males was not accompanied by any body weight or enzyme changes."

The data presented support a LOAEL of 1.5 mg/ kg[/ day] based on cholinesterase inhibition ( plasma and RBC in females and RBC in males). The NOAEL is 0.1 mg/ kg[/ day]. A NOAEL of 1.5 mg/ kg/ day may be defined based on decreased brain cholinesterase activity in both sexes.

870.6100 ( 82 5) Subchronic Neurotoxicity Study in Hens  MRID 43433501 CITATION: Redgrave, V. ( 1994) DDVP: 28 Day Neurotoxicity in the Domestic Hen: Lab Project Number: AVC 1/ 921405: RAD 2/ 942053. Unpublished study prepared by Huntingdon Research Centre, Ltd. 465 p. MRID 43433501.

EXECUTIVE SUMMARY: Groups of 21 adult domestic hens were given oral daily doses by gavage of 0, 0.3, 1.0, or 3.0 mg DDVP/ kg in distilled water. Fourteen birds from each group were treated for 28 days; an interim sacrifice of 6 birds/ group was performed on day 49 and the final sacrifice of 6 birds/ group was performed on day 77. Satellite groups of three birds from each Page 212 of 338 original group of 21 were sacrificed on day 4 and day 30 for brain cholinesterase and brain and spinal cord neurotoxic esterase activity. An additional group of four birds was administered 0.1 mg DDVP/ kg for 28 days for cholinesterase determination only. A positive control group of 21 hens was administered 7.5 mg TOCP/ kg, and sacrificed as described above.

Mortality occurred in 1 bird in the 1.0 mg/ kg dose group and in 4 birds in the 3.0 mg/ kg dose group. Subdued behavior, unsteadiness, and vomiting were observed in the 3.0 mg/ kg group shortly after dosing from day 4 to day 29. Clinical signs were also observed in 2 birds after dosing with 1.0 mg/ kg on days 2 and 14. No delayed motor ataxia was observes, and there was no clear evidence of organophosphate induced delayed neuropathy. Decreased body weight was observed during the first 14 days of dosing at 1.0 and 3.0 mg/ kg, but compensatory increases occurred from day 14 onward. Brain cholinesterase activity was decreased at day 4 in the 1.0 mg/ kg and 3.0 mg/ kg dose groups ( 44% and 63% decrease, respectively, compared to controls); and, at day 30, brain cholinesterase was dose dependently decreased by 26%, 34%, and 54% in the 0.3, 1.0, and 3.0 mg/ kg dose groups, respectively. A slight increase in minimal axonal degeneration was observed at 1.0 and 3.0 mg/ kg. The positive control responded appropriately.

A LOAEL of 0.3 mg/ kg can be defined based on decreased brain cholinesterase activity. The NOAEL is 0.1 mg/ kg/ day. A NOAEL of 0.3 mg/ kg is defined based on axonal degeneration of more than one level of the spinal cord at 1.0 mg/ kg and above of DDVP. This study meets the guideline requirements of 82 5 and is classified as Acceptable.

870.3200 ( 83 2a) Two Year Gavage Study in F344 Rats. NTP TR 342, MRID 40299401 CITATION: Chan, P. ( 1987) NTP Technical Report on the Toxicology and Carcinogenesis Studies of Dichlorvos ( CAS No. 62 73 7) in F344/ N Rats and B63F1 Mice: ( Gavage Studies): NTP TR 342. Draft Technical Report of July, 1987 prepared for public review and comment. US Dept. of Health and Human Services, Public Health Service, Publication No. NIH 88 2598. 239 p. MRID 40299401.

EXECUTIVE SUMMARY: In an oncogenicity gavage study ( MRID 40299401), 4 or 8 mg/ kg/ day dichlorvos ( DDVP) ( 97.8 98.2% a. i., lot SDC 092179, batch 01) in corn oil ( Mazola ® " 100% pure") was administered as 5 mL/ kg to 60 F344 rats/ sex/ dose 5 days/ week for 103 weeks followed by a one week observation period. The controls received corn oil only. Five rats/ sex/ dose were used only for plasma and RBC cholinesterase ( ChE) determination after 6, 12, 24, 36, 52, 78, and 104 weeks and 5 rats/ sex/ dose were used for brain and sciatic nerve histology at study termination. The doses employed were based on results of a 13 week subchronic study where 10 rats/ sex/ dose were given 0, 2, 4, 8, 16, 32, or 64 mg/ kg/ day DDVP. All rats given 32 or 64 mg/ kg/ day and some rats given 16 mg/ kg/ day had tremors, diarrhea, and convulsions and died during the study, whereas the surviving rats had no clinical signs or weight loss.

Mortality and weekly body weight gains were similar in treated and control animals. Clinical signs among treated males included brown fur around the nose, mouth, and anal areas, leaning head, and diarrhea, and among treated females included vaginal discharge, wet fur in peri anal or pelvic area, and diarrhea. From 6 78 weeks, plasma ChE levels in the 4 and 8 mg/ kg/ day treated groups were lower than the respective control levels by 52 72% and 53 72% in males and by 75 85% and 82 Page 213 of 338 88% in females, respectively. At 104 weeks, plasma ChE among treated groups of both sexes were only 4 18% below controls, perhaps due to the intervening week without treatment. RBC ChE levels were more variable: values were decreased ( 13 65%) in both dose group females for weeks 6 78 and in the high dose males ( 17 90%) for weeks 24 104, but in the low dose males were decreased ( 34 49%) only for weeks 36 78. Treatment time did not appear to be directly related to ChE inhibition. No gross lesions were found in the control or treated animals. The incidences of hepatic cytoplasmic vacuolation, renal tubule mineralization, and adrenal cortical vacuolation were increased in high dose males and of pancreatic ( acinar) atrophy were increased in high dose females ( p   0.05); it was unclear whether these effects were treatment related. Results of the brain and sciatic nerve histology examinations were not given.

Under the conditions of this study, 4 mg/ kg/ day was identified as the LOAEL for both sexes of rats based on decreased RBC and plasma ChE levels. A NOAEL was not identified.

Treatment related neoplastic lesions were seen in both sexes of rats. Males had an increased incidence ( p   0.05) of lung adenoma ( 8 mg/ kg/ day), mononuclear cell leukemia ( both doses), and pancreatic acinar adenoma ( both doses). Females had an increased incidence of mammary gland fibroadenoma ( p   0.05 for both doses); an additional high dose female had mammary gland fibroma.

This study was classified as " supplementary for chronic study; minimum for oncogenicity" when the Data Evaluation Report was originally prepared ( 1987). Although this study did not follow the " Subdivision F" guidelines for chronic toxicity, the most sensitive end point for toxicity, namely ChE inhibition, was measured and used as a basis for NOAEL. Therefore, this study should be valid for performing risk assessment.

870.3200 ( 83 2b) Two Year Gavage Study in B6C3F1 Mice. NTP TR 342. MRID 40299401 CITATION: Chan, P. ( 1987) NTP Technical Report on the Toxicology and Carcinogenesis Studies of Dichlorvos ( CAS No. 62 73 7) in F344/ N Rats and B63F1 Mice: ( Gavage Studies): NTP TR 342. Draft Technical Report of July, 1987 prepared for public review and comment. US Dept. of Health and Human Services, Public Health Service, Publication No. NIH 88 2598. 239 p. MRID 40299401 EXECUTIVE SUMMARY: In an oncogenicity gavage study ( MRID 40299401), dichlorvos ( DDVP) ( 97.8 98.2% a. i., Lot SDC 092179, batch 01) in corn oil ( Mazola ® " 100% pure") was administered to 60 B6C3F1 mice/ sex/ dose 5 days/ week for 103 weeks followed by a one week observation period. Males were given 10 or 20 mg/ kg/ day DDVP, females 20 or 40 mg/ kg/ day DDVP, and controls corn oil only; the dosing volume was 10 mL/ kg. Five mice/ sex dose were used only for plasma and RBC cholinesterase ( ChE) determination after 6, 12, 24, 36, 52, 78, and 104 weeks and 5 mice/ sex/ dose were used for brain and sciatic nerve histology at study termination. The doses employed were based on results of a 13 week study where 10 mice/ sex/ dose were given 0, 5, 10, 20, 40, 80, or 160 mg/ kg/ day DDVP; all males and 9 females given 160 mg/ kg/ day died during the study. The survivors had no dose related body weight changes, toxic signs, or significant pathology. Page 214 of 338 No treatment related mortality or body weight changes were observed, however, all male mice used for ChE determination died when blood was withdrawn at 24 weeks. Reported clinical signs consisted of a slight increase of left pelvic masses in high dose males and of distended abdomens in treated females. Plasma ChE levels in males were 54 62% and 69 76% lower than controls at 10 and 20 mg/ kg/ day, respectively, from 6 24 weeks ( death of mice precluded further analysis). Plasma ChE levels in females were 64 73% and 79 90% lower than controls at 20 and 40 mg/ kg/ day, respectively from weeks 6 78, but were similar to or higher than controls at week 104, perhaps due to the intervening week without treatment. RBC ChE levels were more variable: levels were decreased ( 26 46%) at week 24 in both sexes and by 11 33% at weeks 36, 52, and 104 in females, but were similar to or greater than controls at weeks 6 and 12 ( both sexes, both doses) and 78 ( females, both doses). Treatment time did not appear to be directly related to ChE inhibition. No treatment related gross or microscopic lesions were found and no lesions were seen in the animals used to investigate brain and sciatic nerve histology. Under the conditions of this study, a LOAEL of 10 mg/ kg/ day was identified based on the decreased RBC and plasma ChE levels in males. A NOAEL was not identified.

The incidence of forestomach squamous cell papilloma was increased in high dose males ( 5/ 50 vs. 1/ 50 for controls, p = 0.06) and females ( 18/ 50 vs. 5/ 50 for controls, p   0.05); forestomach carcinoma also occurred in 2/ 50 high dose females. Three high dose males each had one unusual neoplasm: glandular stomach carcinoid/ carcinoma, duodenal adenocarcinoma, or a duodenal adenomatous polyp.

This oncogenicity study was classified as " core minimum" when the Data Evaluation Report was originally prepared ( 1987).

870.4200 ( 83 2) 80 Week Feeding/ Carcinogenicity study in Rats  TXR007765, NCI, 1977 EXECUTIVE SUMMARY: In an 80 week feeding/ carcinogenicity study ( NCI, 1977), groups of fifty 36 43 day old Osborne Mendel rats/ sex were administered DDVP ( 94%) at dose levels ( timeweighted average) of 150 or 326 ppm ( 7.5 and 16.3 mg/ kg/ day by standard convention methods). The dosage for the high dose group was 1000 ppm ( 50 mg/ kg/ day) for the first 3 weeks and was then changed to 300 ppm ( 15 mg/ kg/ day) for the remaining 77 weeks due to toxicity. A matched control group of 10 rats/ sex was included. The pooled control group consisted of 60 male and 60 female rats. All animals were observed twice daily for signs of toxicity, weighed at regular intervals, and palpated for masses at each weighing. Gross and microscopic examination of all major tissues, organs and gross lesions were made from sacrificed animals, and where feasible, from animals found dead. Rats were sacrificed at 110 111 weeks.

Severe signs of toxicity including tremors, rough hair coat, diarrhea and poor appearance were observed in the 1000 ppm DDVP group during the first 3 weeks. All groups showed slight or moderate degrees of toxicity during the first year. Treated animals showed an increased frequency of toxic signs during the second year consisting of rough hair coats, epistaxis, hematuria, alopecia, dark urine, bloating and abdominal distension. No compound related mortality was reported. Survival was 64% and 76% in males in the low and high dose groups, respectively, for over 105 weeks. Survival was 80% and 84% in females in the low and high dose groups, respectively, for Page 215 of 338 over 105 weeks. During the first year and a half, body weights of male and female rats in the highdose group were consistently lower than the low dose and matched control groups. Thyroid follicular hyperplasia was increased in males in the low dose group ( 7%) and high dose group ( 10%) when compared to controls ( 0%). The incidence of alveolar macrophages was increased in treated males ( 14 28%) and treated females ( 42 44%) when compared to controls ( 0 10%). The incidence of interstitial fibrosis of the myocardium was increased in treated males ( 24 32%) and treated females ( 30 38%) when compared to controls ( 10%). Malignant fibrous histiocytoma was increased in male rats in the low dose group ( 8%) and high dose group ( 16%) when compared to pooled controls ( 3%, linear trend p= 0.018). This neoplasm occurred in 10% of the matched controls. Under the conditions of the study, DDVP was not demonstrated to be carcinogenic in rats.

The study is Unacceptable Guideline and does not satisfy the guideline requirement ( series 83 2) for a carcinogenicity study in rats. Too few animals ( 10/ sex) were used as matched controls and only 2 dose levels were employed.

870.4200 ( 83 2) 94 Week Feeding/ Carcinogenicity Study in B6C3F1 Mice  TXR 007765, NCI, 1977 EXECUTIVE SUMMARY: In a 94 week feeding/ carcinogenicity study ( NCI, 1977), groups of fifty B6C3F1 mice/ sex, 35 36 days of age, were administered DDVP ( 94%) at dose levels ( timeweighted average) of 318 or 635 ppm ( 47.7 and 95.3 mg/ kg/ day by standard convention methods). The dosage levels for the low and high dose mice were 1000 and 2000 ppm ( 150 and 300 mg/ kg/ day) for the first 2 weeks, then reduced to 300 and 600 ppm ( 45 and 90 mg/ kg/ day) for the remaining 78 weeks. A matched control group of 10 mice/ sex was included. The pooled control group consisted of 100 males and 80 females. All animals were examined twice daily for signs of toxicity, weighed at regular intervals, and palpated for masses at each weighing. Gross and microscopic examination of all major tissues, organs and gross lesions were made from sacrificed animals and, where feasible, from animals found dead. The mice were sacrificed at 92 94 weeks.

Initially, mice fed DDVP exhibited severe signs of toxicity: tremors, rough coat, diarrhea and poor general appearance. After doses were reduced, the behavior and appearance of treated mice were comparable to controls. Survival was 92% and 90% in males in the low and high dose groups, respectively. Survival was 74% and 84% in females in the low and high dose groups, respectively. The body weight of male and female mice in the high dose group was generally lower after the initial growth phase than the low dose and control groups. Two squamous cell carcinomas of the esophageal epithelium occurred, 1 in a low dose male and 1 in a high dose female. Two low dose males had focal hyperplasia of the esophageal epithelium. And one high dose female had a papilloma of the esophageal epithelium. There was insufficient information to establish the association of esophageal tumors with DDVP treatment. Under the conditions of the study, DDVP was not demonstrated to be carcinogenic in mice.

The study is Unacceptable Guideline and does not satisfy the guideline requirement ( series 83 2) for a carcinogenicity study in mice. Too few animals ( 10/ sex) were used as matched controls and only two dose levels were employed.

870.4100 ( 83 1b) 52 Week Chronic Oral Toxicity Study in Dogs. MRID 41593101 Page 216 of 338 CITATION: Markiewicz, V. ( 1990) A 52 Week Chronic Toxicity Study on DDVP in Dogs: Lab Project Number: 2534/ 102. Unpublished study prepared by Hazleton Laboratories America, Inc. 431 p. MRID 41593101 EXECUTIVE SUMMARY: In a chronic oral toxicity study ( MRID 41593101), dichlorvos ( DDVP) ( purity not given but was 97.3% in the preceding range finding study; Lot No. 802097) was administered to 4 beagle dogs/ sex/ dose by capsule for 52 weeks at doses of 0, 0.1, 1.0, or 3.0 mg/ kg/ day. Due to excessive plasma cholinesterase inhibition at week 2, the low dose was changed from 0.1 to 0.05 mg/ kg/ day in both sexes on treatment day 22 to achieve a NOAEL.

No dogs died during the study. Clinical signs included ataxia, salivation, and dyspnea in one highdose male on one day during week 33 and emesis in three high dose females and one male and/ or female at most other doses. Cumulative body weight gains were lower than that of controls only in the high dose males, from approximately weeks 1 8. No treatment related effects were noted on the food consumption, ophthalmoscopic examination, hematology, urinalysis, gross or microscopic pathology, organ weights, or clinical chemistry except for cholinesterase ( ChE) measurements. After 2 weeks of treatment, plasma ChE levels were 21 26% lower than pretreatment values for both sexes given 0.1 mg/ kg/ day DDVP, prompting the dose decrease to 0.05 mg/ kg/ day on day 22. At subsequent test weeks ( 6, 13, 26, 39, and 52), plasma ChE levels in the low dose group were within 12% of pretreatment values. Plasma ChE levels of dogs given 1.0 and 3.0 mg/ kg/ day DDVP were decreased 39 59% and 61 74%, respectively, throughout the study in both sexes. RBC ChE levels were decreased in low dose dogs at week 6 ( 24% in males and 50% in females), likely due to effects of the earlier higher dose of 0.1 mg/ kg/ day, but were within 13% of pretreatment values at all other time points. At 1.0 or 3.0 mg/ kg/ day DDVP, RBC ChE levels in both sexes were lowered 33 65% and 67 94%, respectively, throughout the study. The % inhibition of neither plasma nor RBC ChE appeared to change with time. Brain ChE measurements taken at termination were comparable to concurrent controls for the low dose groups but were decreased at both 1.0 mg/ kg/ day ( 22%, p   0.05 in males; 7%, N. S. in females) and 3.0 mg/ kg/ day ( 47% in males and 29% in females, p   0.05 for both).

Under the conditions of this study, the NOAEL was identified as 0.05 mg/ kg/ day for both sexes. The L0EL was 1.0 mg/ kg/ day, based on the inhibition of plasma and RBC ChE levels in both sexes and the inhibition of brain ChE in males. It should be noted that the actual LOAEL could be as low as 0.1 mg/ kg/ day since plasma ChE was decreased by nearly 25% after the initial administration of this dose to the low dose group during the first two weeks.

This study was classified as acceptable ( guideline) for satisfying the guideline requirement for a chronic oral toxicity study ( 83 1b) in dogs.

870.3700 ( 83 3a) Developmental Oral Toxicity Study in SD Rats.

CITATION: Tyl, R.; Marr, M.; Myers, C. ( 1991) Developmental Toxicity Evaluation of DDVP Administered by Gavage to CD ( Sprague Dawley) Rats: Lab Project Number: 60C 4629 10/ 20. Unpublished study prepared by Research Triangle Inst. 305 p. MRID 41951501 Page 217 of 338 EXECUTIVE SUMMARY: In a developmental toxicity study ( MRID 41951501), 25 pregnant Sprague Dawley rats per group were administered Dichlorvos ( 96.86% a. i.; Lot No. 802097) by gavage at doses of 0, 0.1, 3.0, or 21.0 mg/ kg/ day on gestation days ( GD) 6 15, inclusive. On GD 20, all dams were sacrificed and all fetuses were examined for external anomalies. Approximately one half of all fetuses were examined for visceral anomalies and the remainder stained and examined for skeletal anomalies.

All animals survived until scheduled sacrifice. There was no evidence of maternal toxicity at 0.1 or 3.0 mg/ kg/ day. At the high dose, clinical signs of toxicity were indicative of cholinesterase inhibition. All high dose dams exhibited tremors at some time during the dosing period. Other anticholinesterase related signs of toxicity included prone positioning, hindlimb splay, circling, vocalization, excitability, hypoactivity, and labored respiration among others.

Absolute maternal body weights of the high dose dams were significantly ( 4 6%; p   0.05) lower than the controls on GD 9, 12, and 15 and body weight gains during the dosing period were significantly ( p   0.01) decreased by 28%. Food consumption and food efficiency of high dose dams were significantly ( p   0.01) less than the controls during the dosing interval and overall ( GD 0 20).

Therefore, the maternal toxicity LOAEL is 21 mg/ kg/ day based on clinical signs of toxicity, reduced body weight gain, and food consumption and efficiency. The maternal toxicity NOAEL is 3 mg/ kg/ day.

No treatment related effects were observed for gravid uterine weights, number of fetuses/ litter, preand post implantation loss, numbers of corpora lutea/ dam, number of implantations/ dam, resorptions/ dam, fetal body weights, or fetal sex ratios. There were no developmental malformations/ variations in any fetus that were attributed to treatment.

Therefore, the developmental toxicity NOAEL is   21 mg/ kg/ day and the developmental toxicity LOAEL was not identified.

This study is classified as Acceptable ( guideline) and satisfies the guideline requirements for a developmental toxicity study ( 83 3a) in rats.

870.3700 ( 83 3b) Developmental Oral Toxicity Study in New Zealand Rabbits.

CITATION: Tyl, R.; Marr, M.; Myers, C. ( 1991) Development Toxicity Evaluation of DDVP Administered by Gavage to New Zealand White Rabbits: Lab Project Number: 60C 4629 30/ 40. Unpublished study prepared by Research Triangle Institute. 247 p. MRID No. 41802401 EXECUTIVE SUMMARY: In a developmental ( teratology) toxicity study ( MRID 41802401), 16 pregnant New Zealand rabbits per group were administered Dichlorvos ( 97% purity; Lot No. 802097) by gavage at doses 0, 0.1, 2.5, or 7.0 mg/ kg/ day on gestation days ( GD) 7 19. ( Dose selection was based on a range finding study in which maternal toxicity, including increased Page 218 of 338 mortality ( 5/ 8 died), decreased weight gain, and clinical signs, were manifested at the highest tested dose of 10 mg/ kg/ day.) At study termination ( GD 30), the number of does with live fetuses was 14, 12, 11, and 9 in each of the control, 0.1, 2.5, and 7.0 mg/ kg/ day group, respectively. On GD 30, all surviving dams were euthanized and all fetuses were weighed and examined for external, skeletal, and visceral anomalies.

Maternal toxicity ( dose dependent) was evident in the form of dose dependent increased mortality ( four and two died in the high and mid dose groups, respectively), decreased mean body weight gain and typical anticholinesterase related clinical observations. Mean body weight gain during the dosing period ( GD 7 19) was 67% and 58% below control in the mid and high dose groups, respectively. Mean body weight gain during the entire gestation period ( corrected for gravid uterine weight) was variable where, compared to the control group, it was higher in the low and mid dose groups ( by 140% and 45%, respectively) and lower ( 54%, p< 0.05) in the high dose group. There were no abortions but two does in the low dose group had premature deliveries ( GD 23 and 30).

Therefore, based on mortality, and other effects, the maternal toxicity LOAEL is 7.0 mg/ kg/ day; the maternal toxicity NOAEL is 2.5 mg/ kg/ day. There were no statistically significant treatment related differences in the number ( per doe) of corpora lutea, implantations, live fetuses, resorptions, or dead fetuses. Though not indicated to be significantly different than the control group, the low dose group had fewer implantations/ doe ( 4.9 ± 0.8 vs. 7.0 ± 0.8) and fewer live fetuses/ doe ( 4.8 ± 0.8 vs. 6.5 ± 0.8). There were no apparent developmental malformations or variations that could be attributed to treatment.

Therefore, the developmental toxicity NOAEL is > 7 mg/ kg/ day and the developmental toxicity LOAEL was not identified.

This study was classified as Core Minimum where all criteria were satisfied except for the minimum number ( 12) of available does/ group which, due to mortality in the mid and high dose groups, were 11 and 9, respectively. The reviewer of this study also indicated that individual data on corpora lutea were not submitted.

870.3800 ( 83 4) Two Generation Reproduction Study in SD Rats. MRID No. 42483901 CITATION: Tyl, R.; Myers, C.; Marr, M. ( 1992) Two Generation Reproductive Toxicity Study of DDVP Administered in Drinking Water to CD ( Sprague Dawley) Rats: Final Report: Lab Project Number 60C 4629 170. Unpublished study prepared by Research Triangle Institute. 1225 p. MRID No. 42483901 EXECUTIVE SUMMARY: In a 2 generation reproduction study ( MRID 42483901) DDVP ( 96.86%) was administered to 30 CD ( Sprague Dawley) rats/ sex/ dose in their drinking water at concentrations of 0, 5, 20 and 80 ppm. Equivalent dosages were the following:

Table 10.

Water Conc. F0 & F1   ( µ g/ kg/ day) F0 & F1   prebreeding F0 & F1   gestation F0 & F1   lactation Page 219 of 338 ( ppm) ( µ g/ kg/ day) ( µ g/ kg/ day) ( µ g/ kg/ day)

5.0 476 500 650 660 564 590 930 1176 20.0 1923 1952 2432 2673 2124 2420 4280 4596 80.0 6897 7528 9370 9472 7035 8150 13238 17468 After at least 10 weeks of continuous exposure, rats were randomly mated within treatment groups to produce the F1 generation; after mating the F0 males were necropsied. F1 litters were culled to 8 pups ( 4   , 4   when possible) on post natal day 8 and weaned on day 21. Ten weanlings/ sex/ dose were necropsied and 30 weanlings/ sex/ dose were selected as F1 parents with at least 11 week prebreeding exposure to DDVP in their water. These rats were about 14 17 weeks old when mated and their F2( a) litters were culled to 8 pups/ litter on post natal day 8. At weaning, 10 F2( a) weanlings/ sex/ dose level were necropsied.

Due to poor reproductive performance ( not treatment or dose related), F1 females were evaluated for vaginal estrus cyclicity and then rebred with untreated males to produce F2( b) litters which were culled on PND 8 ( 8 pups/ litter) and necropsied ( 10/ sex/ dose) after weaning.

Systemic toxicity: A NOAEL for cholinesterase inhibition in parental animals was not observed. Cholinesterase levels were dose dependently decreased in plasma ( by 3.6 to 57.4%), erythrocytes ( by 7.0 to 60.5%), and brain ( by 1.1 to 60.3%) from F0 and F1 animals and, overall, females were more sensitive than males. No ChE measurements were done on the F2( a) or F2( b) progeny. Water consumption was also reduced in the 80 ppm dosed animals.

Reproductive toxicity: No effects on reproductive parameters were observed in the F0 mating, although mean pup body weight in the 80 ppm group at weaning ( day 21) was significantly lower than controls ( 57.02 vs. 62.29 g). In the first mating of the F1 animals, incidences of pregnancies were low ( controls: 17/ 30; 5 ppm: 14/ 30; 20 ppm: 16/ 30; 80 ppm: 11/ 30). Mean pup body weight in the 80 ppm group at weaning was noticeably ( not significantly) lower than controls ( 52.22 vs. 57.43 g). As stated in the report conclusions: " Parental reproductive parameters were slightly affected in F1 animals at 80 ppm, although these changes did not achieve statistical significance. Offspring survival was also slightly reduced at 80 ppm, associated with accompanying maternal toxicity seen at this dose level."

Results of the estrous cyclicity assessment showed that in the 80 ppm F1 group, there was a statistically significant decrease in the percent of females cycling ( 63.3%, control 86.2%) accompanied by increased abnormal cycling ( 68.4%, control 16%).

In the F2( b) mating, incidences of pregnancies were still relatively low ( controls: 19/ 29; 5 ppm: 19/ 30; 20 ppm: 17/ 30; 80 ppm: 13/ 30); in terms of pregnancies/ confirmed copulations incidences were: controls: 19/ 25 ( 76%); 5 ppm: 19/ 27 ( 70.4%); 20 ppm: 17/ 27 ( 63%); 80 ppm: 13/ 26 ( 50%). Page 220 of 338 The LOAEL for systemic toxicity [ drinking water administration] is 5 ppm ( 488 µ g/ kg/ day in males, 577 µ g/ kg/ day in females), based on RBC and plasma cholinesterase inhibition. The NOAEL is < 5 ppm (< 488 µ g/ kg/ day in males, < 577 µ g/ kg/ day in females).

The reproductive LOAEL [ drinking water administration] is 80 ppm ( 7592 µ g/ kg/ day) based on the lack of cycling and abnormal cycling due to persistent or prolonged estrus. In addition, parental reproductive parameters ( decreased pregnancy and fertility, and decreased live litters and survival) were slightly affected in F1 animals at 80 ppm, although these changes did not achieve statistical significance. Offspring survival was also slightly reduced. The reproductive NOAEL is 20 ppm ( 4438 µ g/ kg/ day).

81 8ss Acute Oral Neurotoxicity Study in Rats.

CITATION: Lamb, I. ( 1993) An Acute Neurotoxicity Study of Dichlorvos in Rats: Final Report ( Text and Summary Data): Lab Project Number: WIL 188003. Unpublished study prepared by WIL Research Labs., Inc. 984 p. MRID 42655301 EXECUTIVE SUMMARY: In an acute oral neurotoxicity study ( MRID 42655301), a single gavage dose of dichlorvos ( 97.8% a. i., lot # 80209) was administered in deionized water to 12 Sprague Dawley rats/ sex/ group at 0, 0.5, 35, or 70 mg/ kg. The animals were observed for up to 14 days. Functional Observational Battery ( FOB) tests were done pretest and on study days 0 ( 15 minutes after compound administration), 7 and 14. Animals surviving to study termination were sacrificed and perfused in situ for neurohistopathological evaluation. All animals were necropsied.

Two high dose males and five high dose females died within four hours of compound administration. All other animals survived until study termination. No body weight effects were observed. The FOB and motor activity effects ( described below) of dichlorvos were most prevalent 10 20 minutes post dosing and had essentially resolved by days 7 and 14. Statistically significant ( p< 0.05) postural alterations, tremors, salivation, and changes in fur appearance and skin color were observed in mid and high dose males and females. High dose males exhibited an increased incidence ( p< 0.05) of exophthalmus. Group mean time to first step was significantly ( p< 0.01) increased in high dose males ( 31.7 sec) and females ( 18.3 sec). Treatment related ( p< 0.05) decreased group mean rearing, impaired mobility, abnormal gait, and decreased arousal level were also observed in mid and high dose males and females. Dose related ( p< 0.05) alterations of touch, tail pinch, pupil response and air righting reflex were observed in mid and high dose males and in high dose females. Dose related decreased hindlimb resistance ( mid and high dose, p< 0.05), grip strength ( high dose, p< 0.01), and rotarod performance ( mid and high dose, p< 0.01) were observed in male and female rats. Decreased ( p< 0.01) mean body temperature was observed in mid and high dose males and females, and increased ( p< 0.01) group mean catalepsy values were observed in high dose animals of both sexes. No brain weight, brain dimension, or neurohistopathological effects were observed.

Under the conditions of this study, the LOAEL for dichlorvos is 35 mg/ kg and the NOAEL is 0.5 mg/ kg based on changes in the FOB, decreased motor activity, and decreased body temperature. This study is classified as acceptable ( guideline) for an acute neurotoxicity study in rats ( 81 8ss). Page 221 of 338 81 8ss Subchronic Oral Neurotoxicity Study in Rats.

CITATION: Lamb, I. ( 1993) A Subchronic ( 13 Week) Neurotoxicity Study of Dichlorvos in Rats: Final Report: Lab Project Number: WIL 188004. Unpublished study prepared by WIL Research Labs, Inc. 1199 p. MRID 42958101.

EXECUTIVE SUMMARY: In a subchronic oral neurotoxicity study ( MRID 42958101), dichlorvos ( 97.87% a. i., lot No. 802097) was administered in deionized water to 15 Sprague Dawley rats/ sex/ group at gavage doses of 0, 0.1, 7.5, or 15.0 mg/ kg/ day for 90 days. Within each dose group, 10 rats/ sex were allocated for brain cholinesterase determination and 5 rats/ sex were allocated for neuropathology evaluation. Additionally, blood samples were collected for cholinesterase measurements prestudy and on study weeks 3, 7, and 13. Five rats/ sex/ dose from the cholinesterase group and 5/ sex/ dose from the neuropathology group were evaluated with the Functional Observational Battery ( FOB) and motor activity tests pretest and on study weeks 3, 7, and 12. Body weight and food consumption were measured weekly.