### 2 DRINKING WATER EXPOSURE ASSESSMENT

This memorandum addresses potential drinking water exposure related to pirimiphos-methyl existing uses. Pirimiphos-methyl post-harvest tr eatments to stored corn and sorghum grain commodities, eartag uses, and fogger treatments to Gladiola and Iris bulbs encompass all of the currently registered uses and are all being evaluated under Registration Review.

For stored corn and sorghum grain commodities , drinking water e xposure can occur as harvested grain treated with pirimiphos-methyl is re-planted back into th e soil during the next growing season, usually 6 -7 months after treatme nt. Estimated drinking water concentrations (EDWCs) in surface water were previously provided and estimated using the Food Quality Protection Act (FQPA) Index Reservoir Screen ing Tool, aka the FIRST model (DP Barcode 328151, Dated Feb. 22, 2007). These results for the st ored grain uses are still applicable and provided in Table 1 below. However, EDWCs in ground water for pirmiphos-methyl stored grain uses are updated in this memorandum w ith the recent implementation of the PRZMGW model, and also provided in Table 1 below. Generally, very minimal exposures in both surface and ground water is expected associated with re-planted stored grain treated with pirimiphos-methyl.

Table 1. Summary of upper-bound EDWC s for surface water and ground water associated with the post-harvest stored grain treatments with pirimiphos-methyl. Surface Water (ppb)
Acute 1 

### Chronic and Cancer 1



### <0.01 <0.01 Ground Water (ppb)
Acute 2 

### Chronic and Cancer 2



### <0.01 <0.01

1. Upper-bound EDWCs in surface water calculated from FIRST model (see memo DP Barcode 328151, datedFeb. 22, 2007 for exact results). EDWCs conservatively include TTRs furfural and its organophosphate demethylated degradate, produced by aci dic-catalyzed hydrolysis, by assuming that 100 percent of residues are stable to hydrolysis (see Table A-2 in this assessment for information regarding the formation and decline of this degradate in the environment).

2 Upper-bound EDWCs in ground water based on PRZM-GW FL Citrus scenario presented in this assessment (see Table B-1 and Table B-2 in this assessment). EDWCs include TTRs pirimiphos-methyl and its demethylated organosphosphate degradate (see Table A-2 in this assessment for information regarding the
formation and decline of this degradate in the environment).



### For eartag uses , definitive EDWCs are not calculated in this memora ndum due to uncertainties with pirimiphos-methyl loading in the environmen t resulting from the eartag use. With eartag uses, drinking water exposure can occur with washoff and subsequent runoff and leaching of pirimiphos-methyl residues with rainfall on treat ed cattle. The uncertainties stem from limited
information on simultaneous cattle treated with pirimiphos-methyl eartags, and the maximum amount of pirimiphos-methyl available for washoff and runoff/leaching from treated cattle at use sites. Given these uncertainties, prelim inary pirimiphos-methyl estimated exposure

### 3 concentrations 1 

### (EECs) in surface water are calculate d using the FIRST model with results normalized to one-hundred percent of pirimiphos-m ethyl washing off from one head of cattle. The resulting preliminary normalized concentrati ons are then extrapolated to calculate the
number of treated cattle causi ng concern based on a derived dr inking water concentration level of concern (DWLOC). An acute DWLOC of 3,600 ppm (36,000,000 ppb) is calculated based on
the acute rat LD 50 

### = 2,400 mg/kg-bw (pirimiphos-methyl Reregistration Eligibility Decision
document 2 

### ) assuming a standard assumption that a 15 kg ch ild drinks 1L of water. Based on this DWLOC and preliminary normalized surface water concentrations from FIRST described above, the number of treated cattle expect ed to cause a toxicologically-rele vant concern is presented in
Table 2 below. Even with 100 percent of applied pi rimiphos-methyl washing off, over 5
trillion head of cattle treated simultaneo usly are necessary to result exceeding the DWLOC, which is well beyond any expected dens ity of cattle at any pastureland use site
nationwide 3



### . Impacts to ground water were also evaluated using PRZMGW, but acute ground water concentrations indicate much smal ler relative concentrations than estimated in surface water, and therefore an even higher amount of treated cattle would be expected
to result in the exceedance DWLOC

.

Table 2. Head of Treated Cattle Causing Concern Given Washoff Fractions (number of cattle) for pirimiphos-methyl eartag uses.

Drinking Water Exposure Source Pirimiphos -Methyl
DWLOC

(  g/L) 1 100% 20% 10% 5% 1%

Reservoir (Surface Water) 2 36,000,000 5.4 x 10 9 2.7 x 10 10 5.4 x 10 10 1.0 x 10 11 5.4 x 10 11

Well (Ground Water) 3 > 5.4 x 10 9 > 2.7 x 10 10 > 5.4 x 10 10 > 1.0 x 10 11 > 5.4 x 10 11

1 Calculated based on acute rat LD 50 = 2,400 mg/kg-bw (pirimiphos-methy l Reregistration Eligibility Decision

document) assuming a standard assumption that a 15 kg child drinks 1L of water.

2 Calculated based on FIRST acute EDWC of 0.0066 ppb per head of cattle at 100 percent of applied washed off.

Results extrapolated to 20, 10, 5, and 1 percent washoff fraction via linear proportional scaling with application

rate.

3 Non-definitive values due to very low EDWCs per head of cattle <<0.01 ppb including levels up to 100 percent

residues washed off. Values for he ad of treated cattle causing concern e xpected greater than found for surface water exposure scenario.



### No drinking water exposure is anticipated with indoor fogger treatments of Gladiola and
Iris bulbs.

1 EDWCs include TTRs pirimiphos-methyl and its de-methylated organophosphate degradate 2(diethylamino)-4- hydroxy-6-methyl pyrimidine (see Table A-2 in this assessment for informati on regarding the formation and decline of this degradate in the environment).

2 Available on-line at: http://www.epa.gov/pesticid es/reregistration/REDs/p irimiphos_methyl_red.pdf

3 Based on release from a relatively sma ll 25-acre or 10 hectare pasture field site. However, pirimiphos-methyl loading is

expected to be similar per unit area for larg er pastures possessing larger cattle populations.

### 4 Complete and detailed descriptions on the Us e Characterization and Environmental Fate of pirimiphos-methyl is provided in Appendix A. Details on the complete exposure assessment and a description of the analysis sup porting the above results is provided in Appendix B.

REFERENCES

Kentucky (State of), University of Kentucky. Horn Flies and Cattle. Available online at http://www2.ca.uky.edu/entomology/entfacts/ef509.asp Accessed December 2015.

Mississippi (State of), Mississi ppi State University. Horn Flies on Cattle: Biology and Management. Available on-line at http://store.msuextension.org/publicati ons/AgandNaturalResources/MT200912AG.pdf
Accessed December 2015.

Nebraska (State of), University of Nebraska. Controlling Flies on Pastured Cattle in Nebraska.
Available on-line: http://newsroom.unl.edu/announce/beef/3199/18423 Accessed 2015.

### 5 

## Appendix A. Pirimiphos-Methyl Use and Environmental Fate
Characterization

Use Characterization

Pirimiphos-methyl uses encompass six active regi strations. The labels by FIFRA classification
are summarized below:

 Four Section 3 labels, and

 Two Special Local Needs (Section 24c) labels

Uses for the Section 3 pirimiphos-methyl registrations include cattle eartag uses (for lactating and beef cattle) and post-harvest stored grain seed treatments for corn and sorghum seeds. Eartags contain up to 3.84 grams a.i. per animal (or 1.92 gram s a.i. per eartag). There are no restrictions related to the quantity of cattle treated or the frequency of application per use site. For post-harvest seed treatments, up to 0.48 lbs a. i. per 300 tons of grain may be a pplied. There ar e no restrictions for where pirimiphos-methyl can be used nationwide.

Special Local Needs uses include indoor f ogger treatments using pirimiphos-methyl for ornamental bulbs in Washington State and Michiga n. Up to 0.224 lbs. a.i. per 1,000 cubic feet of space may be applied for these uses.

For eartag uses, the labels are no t restrictive of pirimiphos-methyl’s use at any given use site. However, given pirimiphos-methyl’s intended use to control horn flies and face flies, it is most likely to be used exclusively use sites such as pa sture lands and range land. Infestations are most prevalent at sites such as th ese since these insects thrive with excrement on ground surfaces which are not subject to disturbance and agitation. Other sites containing cattle such as feedlots are not likely to encumber infestations of horn f lies and face flies since hi ghly concentrated cattle populations likely provide ample agitation of th e ground, thus limiting suitable living conditions
for these insects to thrive.

Pasture land use sites with piri miphos-methyl are anticipated to c ontain much less inventories of cattle than at feedlots, but may be more variable in size. However, pirimiphos-methyl loading due to washoff and runoff/leaching processes are not anticipated to be higher than concentrated feeding operations at feedlots. This informa tion is conveyed by multiple state agricultural extension services (e.g., Alabama, Mississippi, Kentucky, and Nebraska) where eartag usage is common or where feedlots are present.

Environmental Fate and Transport Characterization

Registrant-submitted data defini ng the physical, chemical, fate and transport characteristics associated with pirimiphos-methyl are summarized in Table A-1 . As part of registration review, available environmental fate studies for pirimip hos-methyl have been reevaluated. The fate and

### 6 transport of pirimiphos-methyl in the environment is discussed below.

Table A-1. General physical-chemical and envi ronmental fate properties of pirimiphosmethyl.

Chemical/Fate parameter Value Source (MRID) Study Acceptability

Physical Chemical Properties

Chemical Structure and SMILES
Code

CCN(CC)c1nc(C)cc(OP(=S) (OC)OC)n1 Product Chemistry

(MRID
00129333 N/A

Molecular Weight (g/mol) 305 Product Chemistry

(MRID 00129333) N/A

Vapor Pressure (torr at 30°C) 1.1 x 10 -4 Product Chemistry

(MRID 00129333) N/A

Octanol-water Partition Coefficient (Log K OW at 20°C) 4.2 Product Chemistry

(MRID 92147003) N/A

Octanol-air Partition Coefficient (Log K OA ) 8.743 EPI Suite (KOAWIN v. 1.1 estimate) N/A

Water Solubility (mg/L; at 20°C) 9.9 mg/L at pH 5.2 8.6 mg/L at pH 7.3 9.3 mg/L at pH 9.3 Product Chemistry

(MRID 92147003) N/A

Henry's Law Constant (atm-m 3

mol -1 ) 5.105 x 10 -6 EPI Suite (HENRYWIN v. 3.10) N/A

### 7 Table A-1. General physical-chemical and envi ronmental fate properties of pirimiphosmethyl.

Chemical/Fate parameter Value Source (MRID) Study Acceptability

Soil-water partition coefficients (K d ) England Soils 5 : LS1: 15.6 mL/g (OC = 1.60%) LS2: 27.4 mL/g (OC = 1.69%) LS3: 32.7 mL/g (OC = 2.97%) S: 11.6 mL/g (OC = 0.29%) SiCL: 161.9 mL/g (OC = 1.63%) SL: 45 mL/g (OC = 1.92%) MRID 48355601 Supplemental:

 Significant degradation was observed in low pH soils (S, SiCL, SL)

Abiotic Degradation 1

Hydrolysis half=lives (days) 7.3 days at pH 5 79 days at pH 7 54 – 62 days at pH 9 2 MRID 42982401
MRID 43177601 Acceptable

Aqueous photolysis half-life (days at 20°C) 3 0.2 days
IUPAC Pesticide Properties
Database 6 N/A

Photolysis in air half-life (hours at 25°C) 2.4 hours
0.802 hours SRC Database
EPI Suite (AopWIN v. 1.92) N/A

Soil Photolysis half-life (days) No Data Available - N/A

Biotic Degradation 1

Aerobic Soil Metabolism half-life (t 1/2 in days) England Soils 5 :

SL1: 33.6 days (OC = 3.70%, pH7.1) SL2: 28.7 days (OC = 1.00%, pH6.6) L: 42.7 days (OC = 6.0%, pH7.5) P: 31.5 days (OC = 36.2%, pH6.0) MRID 135358 Supplemental:

 Potential degradation

associated with the extraction procedures
not addressed.

 Pertinent test

conditions (e.g., temperature and moisture content) throughout the studies not reported.Anaerobic Soil Metabolism halflife (days) 4 England Soils 5 :

SL1: 36.4 days (OC = 3.7%, pH7.1) L: 31.5 days (OC = 6.0%, pH7.5)

Aerobic Aquatic Metabolism halflife (days) No Data Available - N/A

### 8 Table A-1. General physical-chemical and envi ronmental fate properties of pirimiphosmethyl.

Chemical/Fate parameter Value Source (MRID) Study Acceptability

Anaerobic Aquatic Metabolism half-life (days) No Data Available - N/A

Field Studies

Terrestrial Field Dissipation No Data Available - N/A

Bioaccumulation

BCF Fish 274X SRC Database
EPI Suite (WSKOW v. 1.42) N/A

1 Half-lives based on first order rate constant, k (t 1/2 = ln2/k) derived from Time – Ln(Concentration) regression.

2 Half-life range at pH9 among multiple replicates reported.

3 Estimated based on DT-50 value.

4 Half-life ranges based on replicates with flooded water soil atmosphere reported.

5 Soil texture identifiers: SLn: Sandy lo am replicate, LSn: Loamy sand replicat e, L: Loam, P: Peat, SiCL: Silty

Clay Loam

6 Available on-line: http://sitem.herts.ac.uk/aeru/iupac/



### The measured soil-water partition coefficients (K d 

### ) for pirimiphos-methyl residues range between 11.6 mL/g to 161.9 mL/g. These measured partition coefficients in soil are poorly correlated to orga nic carbon content (r 2 

### = 0.012). The water solubi lity limit of pirimiphosmethyl ranges between 8.6 to 9.9 mg/L. Both pi rimiphos-methyl’s values of solubility and sorption coefficients indicate that pirimiphos-met hyl residues will partition both to the sorbed phase and dissolved phase in soil and aquatic sediment. Therefore, pirimiphos-methyl can be transported to offsite water bodi es via runoff and eros ion processes. Furthermore, pirimiphosmethyl has the potential for leaching in to ground water given its high mobility.

The vapor pressure of 1.1 x 10 -4 

### torr suggests that pirimiphos-m ethyl can exist in the vaporphase. However, the photolysis in air half-l ife of between 0.802 and 2.4 hours suggests that the residence time of pirimiphos-methyl vapors in air will be limited. Furthermore, no VOCs (including vapor-phase pirimiphos-m ethyl) were detected in any vol atile trap in the aerobic and
anaerobic soil metabolism st udies summarized above in Table A-1

.

The major degradation pathway for pirimiphos-m ethyl O-(2-Diethylamino-6-methylpyrimidin-4- yl) O,O-dimethyl phosphorothioa te) is hydrolysis, especially in acidic environments. Hydrolysis half-lives from laborat ory studies ranged from 7.3 days at pH 5, to 79 days at pH 7 with a half-life of 54 – 62 days at pH 9. In acidic environments, the major degradate was 2(diethylamino)-4-hydroxy-6-methyl pyrimidine (hereafter degradate no. 1). In the pH 5

### 9 solution, degradate no. 1 reached maximum levels up to 87.3 days post treatment of the overall
material balance. In neutral and alkaline envi ronments, degradate no. 1 was also found at major levels along with the degradate O-2 diet hylamino-6-methylpyrimidin-4-yl o-methylphosphorothioate (hereafter degradate no. 2). In the pH 7 solution, degradate nos. 1 and 2
reached maximum levels of 22.5 % and 26.5% of the overall material balance at 90 days posttreatment, respectively. In th e pH 9 solution, degradate no. 1 a nd 2 reached levels of 21.0 and 18.2%, respectively of the overall material bala nce. Degradate no. 1 did not retain the organophosphate (P=S bond) linkage, whereas degrad ate no. 2 did in a demethylated form. With degradate no. 2 retaining the organophosphate linkage, all exposure estimates presented in this assessment include this degr adate as part of total toxic residues evaluated.

Pirimiphos-methyl degradation in soil occurs at similar rates and appears to be mediated by hydrolysis, with half-lives ranging between 28.7 – 42.7 days in four soils. The major metabolite
from aerobic and anaerobic soil metabolism is de gradate no. 1 (defined above) which formed at levels up to between 37 – 66% of applied. Major levels of unextractable residues consistently occurred throughout all tested so ils, in the range of up to 28.2 – 66.3% of the applied material, and a nonpolar extraction solvent was not used to extract residues pa rtitioned to soil. However, given pirimiphos-methyl’s high sorption to soil (see Section 3.1 above) and partially thorough extraction method utilizing acetone followed by metha nol extraction solvents, residues appear to be bound to sediment. No Agency guideline st udies have been conducted to determine the biodegradation of pirimiphos-methyl in wa ter or its dissipation in the field.

Degradate no. 1 did not maintain the organophosphate moiety (P=S bond) and is not expected to possess toxicity exceeding that of parent pirimiphos-methyl. However the organophosphate moiety was maintained with degradate no. 2. Ther efore, the potential for toxicity exists with degradate no.2. Refer to Table A-2 for further information on the formation of degradates,

A log K ow 

### of 4.2 indicates that pirimiphos-methyl is sufficiently hydrophobic for binding to fatty tissue for aquatic organisms as well as availabl e sediment. While there are no BCF in fish studies available, a regression K ow 

### –based model suggests that the BCF value for pirimiphosmethyl is approximately 274X in aquatic orga nisms. This BCF further indicates the high potential for pirimiphos-methyl residues to build up in the tissues of aquatic biota.

### 10 Table A-2. Pirimiphos-methyl de gradation products identified in environmental fate studies.

Degradate Identity Structure Max% of Applied and Days
Post Application Comments

Hydrolysis (MRID Nos. 42982401 and 43177601)



### 2(diethylamino)-4- hydroxy-6-methyl pyrimidine

( Non-OP degradate ) 87.25%, 30 days (pH5)

22.51%, 90 days (pH7)

29.97%, 60 days (pH9) pH5 study
terminated at 30 days.

pH7 study
terminated at 90 days.

pH9 study
terminated at 60 days.



### O-2 diethylamino-6-methylpyrimidin-4-yl omethyl-phosphorothioate

( OP Demethylated degradate ) 4.99%, 21 days (pH5)

26.54%, 90 days (pH7)

18.17%, 60 days (pH9) pH5 study
terminated at 30 days.

pH7 study
terminated at 90 days.

pH9 study
terminated at 60 days.

Aerobic Soil Metabolis m (MRID No. 135358)



### 2(diethylamino)-4- hydroxy-6-methyl pyrimidine

( Non-OP degradate ) 42.08%,,

Peartree Sandy Loam (SL1) at 70 days

55.58%,,
Frensham Sandy Loam (SL2) at 14 days

37.22%,,
Gore Loam (L) at 14 days

66.28 %,, Blackborough Peat (P) at 210 days Studies in all soils
terminated at 210 days. N N CH 3

N

C H 2 C H 2 C H 3 CH 3 O H

N N CH 3

N

C H 2 C H 2 C H 3 CH 3 O H

### 11 Table A-2. Pirimiphos-methyl de gradation products identified in environmental fate studies.

Degradate Identity Structure Max% of Applied and Days
Post Application Comments

Anaerobic Soil Metabolism (MRID No. 135358)



### 2(diethylamino)-4- hydroxy-6-methyl pyrimidine

( Non-OP degradate ) 61.4%,,

Peartree Sandy Loam (SL1) at 14 days

37.22%,,
Gore Loam (L) at 14 days Studies in all soils
terminated at 210 days.

Findings from
flooded water soil atmosphere reported. N N CH 3

N

C H 2 C H 2 C H 3 CH 3 O H

### 12 

## Appendix B. Detailed Exposure Analys is Description for Pirimiphos-Methyl
Current Uses

Post-harvest stored grain seed treatments

Surface water EDWCs using the FIRST model are estimated in the previous drinking water assessment for new use on post-harvest stored gr ain seed treatments. The maximum application rate of 0.48 lbs. a.i. per 300 tons of grain was ev aluated. The analysis an d results are provided in the previous drinking water memo (DP Barcode 328151, Dated Feb. 22, 2007). FIRST EDWCs in surface water for pirimiphos-methyl 4 

### post-harvest stored grain treatments are very minimal at << 0.1 ppb.

Ground water EDWCs are updated in this memo using the PRZMGW model ( version 1.07), dated . Table B-1 below shows the PRZMGW input parameters for seed treatment applications, and results are shown in Table B-2. PRZMGW EDWCs for the post-harvest grain treatment uses for pirimiphos-methyl 4 

### are also very minimal at <<0.1 ppb, and is consistent with the previous EDWCs from SCIGROW provided in the previous drinking

water memo. Sample documentation of the PRZMGW model simulations are provided in Appendix C.

Table B-1. PRZM-GW input parameter val ues for physical chemical and fate properties used for pirimiphos-methyl post-h arvest stored grain treatments surface water aquatic exposure estimation. PRZM/EXAMS Input
Parameter Input Value and Unit Source

Pesticide Properties Hydrolysis at pH7 (t 1/2 

### ) 198 days TTR half-life of pirimiphosmethyl and its demethylated OP degradate (degradate no. 2)

MRID Nos. 42982401 &
43177601 

### Surface soil metabolism (t 1/2 

### ) at
25°C 39.1 days MRID 48604492 & 48604493

EFED Input Parameter Guidance

90 th percentile on the upper
confidence bound half-life from n=4 soils (refer to Table A-1 )

4 EDWCs include TTRs pirimiphos-methyl and its de-methylated organophosphate degradate 2(diethylamino)-4- hydroxy-6-methyl pyrimidine. (see Table A-2 in this assessment for information regarding the formation and decline of this degradate in the environment).

### 13 Table B-1. PRZM-GW input parameter val ues for physical chemical and fate properties used for pirimiphos-methyl post-h arvest stored grain treatments surface water aquatic exposure estimation. PRZM/EXAMS Input
Parameter Input Value and Unit Source

Soil-Water Partition Coefficient (K oc 

### ) (mL/g) 49.03 MRID 48355601

EFED Model Input Parameter
Guidance

Average value from n=6 soils (refer to Table A-1 )

MRID 48355601



### Application Methods and Crop Management Input Parameters Crop Scenarios, Application

Date 5 

### , and Weather WI Sands: Jul. 20, w14920 (La Crosse, WI) NC Coastal: Feb. 1, w13722 (Raleigh, NC) GA Coastal: June 15, w93805 (Tallahasse, FL) Delmarva Peninsula: July 10, w13781 (Wilmington, DE) FL Citrus: Aug. 10, w12842 (Tampa, FL) FL Potato: Sept. 5, w13889 (Jacksonville, FL)

Application Rate 8.96 x 10 -5 

### kg/ha Equivalent maximum single application rate for seed treatment with corn and sorghum grain, maximum seasonal application rate at one application for seed treatment. No degradation of residues before planting assumed. 

### Number of Applications and
Retreatment Interval 1 applications

Application Methods Soil Incorporated
at 4 inches Appropriate for seed treatment and information from product
labels

### 14 Table B-2. PRZM-GW estimated upper bound concentrations in ground water (ppb) for pirimiphos-methyl 1 

### post-harvest corn and sorghum grain

treatment uses.

Tier I Scenario Highest Daily Value (Acute) Post-Breakthrough Average (Chronic and Cancer)
WI Sands

<0.01 NC Coastal

GA Coastal
FL Citrus

FL Potato
Delmarva Peninsula

1 EDWCs include TTRs pirimiphos-methyl and its demethylated organosphosphate degradate (see Table A-2 in this assessment for information regarding the formation and decline of this degradate in the environment).



### Eartag Uses

Since runoff and leaching of pirimiphos-methyl is being evaluated, drinking water exposure can be estimated using routine fate and transport mo dels to evaluate the amount of pirimiphos-methyl applied that would be required to runoff and leaching in sufficien t quantities to trigger adverse impacts.

 Surface Water

To evaluate impact on surface water resources, the screening Tier I drinking water exposure model FIRST (one generic upper-bound watershed exposur e scenario, version 1.1.1) is used for this evaluation given that it addresses contaminant runoff in a watershed feeding into a reservoir. An adverse impacts analysis then incorporates th e FIRST estimated drinking water concentrations (EDWCs) normalized to one head of treated cattle and available acute toxicity data and exposure dose drinking scenario (e.g., a 15 kg child drinks 1L of water for human exposure scenario) to
determine the number of treated cattle exceeds th e resulting exposure dose level of concern for drinking water.

The exposure analysis for feedlo t and pasture pirimiphos-methyl ap plications will evaluate the potential exposure which occurs from heads of cat tle treated simultaneousl y. It will be assumed that each head of cattle possesse s two eartags containing 1.92 gram s a.i. each for a total of 3.84 grams (8.47 x 10 -3 

### lbs.) total of pirimiphos-methyl as permitted by the label. From this scenario, an application rate can be calculated with the in itial assumption that the total amount of pirimiphosmethyl washes off from the treated cattle, is availa ble for runoff, and that th e resulting residue will be evenly distributed with the 10-hectare treated pastures. From these assumptions, an equivalent application rate normalized to one head of treat ed cattle can be calcula ted considering the 3.84 grams (8.47 x 10 -3 

### lbs.) of pirimiphos load with each head of cattle and the 10-ha treated area. The resulting equivalent app lication rate is 3.43 x 10 -4 

### lbs./A per head of cattle [8.47 x 10 -3 

### lbs. ÷ (10 ha x 2.47 A/ha)]. Pasture land a nd ranches larger than 10 hectares are not evaluated since the

### 15 loading of pirimiphos-methyl is ex pected to the same per unit area with larger cattle populations residing at larger properties. T hus, the effective application rate should not be impacted.

However, the major uncertainty is the fraction of pirimiphos-methyl that could potentially wash
off from treated cattle. The 3.43 x 10 -4 

### lbs./A value is a high-end application rate assuming 100% of pirimiphos-methyl residues wash es off. Therefore, this dri nking water exposure analysis will use a bounding technique, where the equivalent application rate is linearly proportional to the amount that washes off. Accordingly, the app lication rates for each of the washoff fractions (evaluated for 100%, 20%, 10%, 5%, and 1%) from treated cattle are shown in Table B-4.

The remaining parameterization for FIRST is co mposed of the physical chemical and fate properties of pirimiphos-methyl utilizing EFED Model Input Parameter Guidance 5 

### . All input parameter values for the aquatic exposure assess ment for pirimiphos-methyl cattle eartags are
shown in Table B-3.

Table B-3. Input parameter values used in FIRST for pirimiphos-methyl adverse impacts analysis for cattle ear tag us es at feedlot and pasture use sites.

FIRST Input Parameter Input Value and
Unit Comment Source

Application Rate (lbs. a.i./A per head of treated cattle) See Table B-4 Based on 3.84 gramsof pirimiphosmethyl per head of
treated cattle and 10-
hectare feedlot size for specified
washoff fraction Product label and
standard runoff exposure scenario
evaluated

Application Method Broadcast 1 No Spray Drift, Incorporated to Surface Only Consistent with washoff scenario for eartag use

Hydrolysis (t 1/2 ) 198 days TTR half-life of pirimiphos-methyl and its demethylated OP degradate (degradate no. 2)

MRID Nos. 42982401
& 43177601 Aerobic soil metabolism (t 1/2 ) 39.1 days 90 th percentile on the upper confidence
bound half-life from n=4 soils (refer to
Table A-1 ) MRID 135358

EFED Model Input
Parameter Guidance

5 Available on-line: http://www.epa.gov/oppefe d1/models/water/input_parameter_guidance.htm

### 16 Table B-3. Input parameter values used in FIRST for pirimiphos-methyl adverse impacts analysis for cattle ear tag us es at feedlot and pasture use sites.

FIRST Input Parameter Input Value and
Unit Comment Source

Aerobic aquatic metabolism (t 1/2 ) Stable Conservative assumption -

Solubility in Water at 20oC 8.6 mg/L Product Chemistry Product Chemistry (MRID 92147003) Soil-Water Partition Coefficient (K d ) 49.03 mL/g Average value from n=6 soils (refer to
Table A-1 ) MRID 48355601

EFED Model Input
Parameter Guidance Aqueous Photolysis (t 1/2 ) 0.2 days DT-50 value IUPAC Pesticide Properties Database 2

1 Broadcast application method consistent with chemi cal distribution associated washoff scenario evaluated.

2 Available on-line: http://sitem.herts.ac.uk/aeru/iupac/



### Table B-4. Pirimiphos-methyl surface wat er EDWCs at equivalent application rates
normalized to one head of treated cattle for certain washoff fractions.

Input/Output Variable Washoff Fraction
100% 20% 10% 5% 1% Equivalent Application Rate (lbs. a.i./A per head of treated cattle) a,b 3.43 x 10 -4 6.85 x 10 -5 3.43 x 10 -5 1.71 x 10 -5 3.43 x 10 -6

Preliminary FIRST Surface
Water EDWCs (μg/L per head of treated cattle) 0.0066 0.0013 0.0006 0.0003 0.00006

a For calculation of the equivalent application rate, please refer to the discussion above Table B-4.

b Based on 10-hectare sized pasture.



### The surface water EDWCs normalized to one head of treated cattle for each washoff fraction,
shown in Table B-4 , are used along with a DWLOC to co mpute the number of treated cattle leading to adverse impacts resulting from eartag use. The acute DWLOC of 3,600 ppm (36,000,000 ppb) is calculated based on the acute rat LD 50 

### = 2,400 mg/kg-bw (pirimiphos-methyl Reregistration Eligibility Decision document 6 

### ) assuming a standard assumption that a 15 kg child
drinks 1L of water. Based on this DW LOC and preliminary normalized surface water concentrations from FIRST (generic upper-bound watershed exposure scenario) described above, the number of treated cattle expect ed to cause a toxicologically-rele vant concern is presented in
Table B-5 below. Sample documentation of the FI RST model simulations are provided in Appendix C

.

6 Available on-line at: http://www.epa.gov/pesticid es/reregistration/REDs/p irimiphos_methyl_red.pdf

### 17 Table B-5. Head of Treated Cattle Caus ing Concern due to Drinking Water Exposure from Surface Water Given Washoff Fractions (number of cattle) based on FIRST model results (generic upper-bound wate rshed exposure scenario) and DWLOC. 2,3

PirimiphosMethyl
DWLOC

(  g/L) 1 100% 20% 10% 5% 1%

36,000,000 5.4 x 10 9 2.7 x 10 10 5.4 x 10 10 1.0 x 10 11 5.4 x 10 11

1 Calculated based on acute rat LD 50 = 2,400 mg/kg-bw (pirimiphos-methy l Reregistration Eligibility Decision

document) assuming a standard assumption that a 15 kg child drinks 1L of water.

2 Calculated based on FIRST acute EDWC of 0.0066 ppb per head of cattle at 100 percent of applied washed off.

Results extrapolated to 20, 10, 5, and 1 percent washoff fraction via linear proportional scaling with application

rate.

3 Population size on 10-hectare lot assumed.



###  Ground Water

A similar approach can be used to evaluate impact on ground water resources, except using the PRZMGW model (version 1.07) . PRZMGW input parameter values shown in Table B-1 for post-harvest stored grain uses can be used is applicable to the an alysis for eartag uses except for 1.) The equivalent broadcast pesticide applicat ion method appropriate to evaluate the washoff scenario and 2.) The equivalent application rate to evaluate the various washoff scenarios. Refer

to Table B-3 regarding the pesticide app lication method simulated and Table B-4 regarding the equivalent application rates modeled for the diffe rent washoff fractions. The number of treated cattle expected to cause a t oxicologically-relevant concer n for ground water exposure is presented in Table B-6 below for each PRZMGW screening scenario. The FL Potato scenario possesses the most vulnerable resu lts; modeling simulations with other scenarios indicate that a much larger amount of treated cattle which would lead to toxicologically-relevant concerns. The
results for other scenarios are non-definitive due to EDWCs per head of cattle <<0.01 ppb. Sample documentation of the PRZMGW model simulations are provided in Appendix C

.

### 18 Table B-6. Head of Treated Cattle Causing Con cern due to Drinking Water Exposure from Ground
Water Given Washoff Fracti ons (number of cattle) based on PRZMGW model results (six screening scenarios) and DWLOC. 2,3

PirimiphosMethyl
DWLOC

(  g/L) 1 PRZMGW
Scenario 100% 20% 10% 5% 1%

36,000,000 FL Potato

>5.4 x 10 9 >2.7 x 10 10 >5.4 x 10 10 >1.0 x 10 11 >5.4 x 10 11 FL Citrus

WI Sands

Georgia Coastal

North Carolina
Coastal

Delmarva

1 Calculated based on acute rat LD 50 = 2,400 mg/kg-bw (pirimiphos-methy l Reregistration Eligibility Decision

document) assuming a standard assumption that a 15 kg child drinks 1L of water.

2 The results for other PRZMGW scenarios are non-definitive due to EDWCs per head of cattle <<0.01 ppb

including levels up to 100 percent residues washed off. Values for head of treated cattle causing concern expected greater than found for surface water exposure scenario.

3 Population size on 10-hectare lot assumed.

### 19 

## Appendix C. Drinking Water Exposure Model Simulation Documentation

Figure C-1. Sample PRZMGW model simulation file for postharvest corn and sorghum grain treatment use.



## Groundwater Analysis for Pirimi phos-methyl and the FLORIDA - Potato - Met File (13889 .Dvf) Jacksonville Scenario
Estimated groundwater concentrations and breakthrough times for Pirimiphos-methyl are presented in Table 1 for the FLORIDA - potato - Met File (13889.dvf) Jacksonville groundwater scenario. A graphical presentation of the daily concentrations in the aquifer is presented in Figure 1. These values were generated with the PRZM-GW (Version 1.07). Critical input values for the model are summarized in Tables 2 and 3.

Table 1. Groundwater Results for Pirimiphos- methyl and the FLORIDA - potato - Met File (13889.dvf) Jacksonville Scenario.

Peak Concentration (ppb) 1.12E-13

Post-Breakthrough Mean Concentration (ppb) Incomplete

Entire Simulation Mean Concentration (ppb) 1.85E-14

Average Breakthrough Time (days) Incomplete

Throughputs 0.04941383

Table 2. Chemical Propertie s for Groundwater Modeling of Pirimiphos-methyl.

Kd (ml/g) 49.03

Surface Soil Half Life (days) 39.1

Hydrolysis Half Life (days) 198

Diffusion Coefficint Air (cm2/day) 0.0

Henry's Constant 0.0

Enthalpy (kcal/mol) 0.0

### 20 Table 3. Pesticide application scheme used for Pirimiphos-methyl. This application scheme was applied every year of the simulation.

Application Date
(Month/Day) Application Method Application Rate
(kg/ha)
09/05 All pesticide placed at 10.16 cm
below surface 1.12

Figure 1. Aquifer Breakthrough Curve fo r Pirimiphos-methyl and the FLORIDA - Potato - Met File (13889.Dvf) Jacksonville Scenario

* Simulation of scenario with highest EDWC shown

Notes:

1. Results scaled to equivalent maximum single application rate for seed treatment with corn and sorghum grain, as shown in Table B-1. No degradation of residues before planting assumed.

2. Pirimiphos-methyl and its demethylated OP degradate included as TTRs in this analysis.

### 21 Figure C-2. FIRST model simulation for eartag uses.

Notes:

1. First-guess unit application rate of 1 lbs. a.i./A show n here. Results in Table B-4 scaled using equivalent application rate considering initial loading as per ma ss of a.i. on eartag along with washoff fraction.

2. Granular application type equivalent to broadcast application method which mimics washoff scenario.

3. Pirimiphos-methyl and its demethylated OP degradate included as TTRs in this analysis.

### 22 Figure C-3. Sample PRZMGW model simulation file for eartag use.



## Groundwater Analysis for Pirimiphos-methyl and the
FLORIDA - Potato - Met File (13889.Dvf) Jacksonville
Scenario
Estimated groundwater concentrations and breakthrough times for Pirimiphos-methyl are presented in Table 1 for the FLORIDA - potato - Met File (13889.dvf) Jacksonville groundwater scenario. A graphical presentation of the daily concentrations in the aquifer is presented in Figure 1. These values we re generated with the PRZM-GW (Version 1.07). Critical input values for the model are summarized in Tables 2 and 3.

Table 1. Groundwater Results for Pirimipho s-methyl and the FLORIDA - potato - Met File (13889.dvf) Jacksonville Scenario.

Peak Concentration (ppb) 7.32E-19

Post-Breakthrough Mean Concentration (ppb) Incomplete

Entire Simulation Mean Concentration (ppb) 1.12E-19

Average Breakthrough Time (days) Incomplete

Throughputs 0.04941383

Table 2. Chemical Propertie s for Groundwater Modeling of Pirimiphos-methyl.

Kd (ml/g) 49.03

Surface Soil Half Life (days) 39.1

Hydrolysis Half Life (days) 198

Diffusion Coefficint Air (cm2/day) 0.0

Henry's Constant 0.0

Enthalpy (kcal/mol) 0.0

### 23 Table 3. Pesticide application scheme used for Pirimiphos-methyl. This application scheme was applied every year of the simulation.

Application Date
(Month/Day) Application Method Application Rate
(kg/ha)
09/05 Ground application with mass distribution increasing proportionally with depth to 4 cm 1.12

Figure 1. Aquifer Breakthrough Curve fo r Pirimiphos-methyl and the FLORIDA - Potato - Met File (13889.Dvf) Jacksonville Scenario

* Simulation of scenario with highest EDWC shown

Notes:

1. Results using first-guess unit application rate of 1 lbs. a.i./A shown here. Results in Table B-4 arrived at by scaling results above with the equivalent application ra te (also shown in Table B-4) as determined by the amount of a.i. per eartag, and washoff fraction. Equivalent application rate shown in Table B-4 depicts
release from 25 acre or 10-ha area.

2. Pirimiphos-methyl and its demethylated OP degradate included as TTRs in this analysis.