UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

OFFICE OF CHEMICA L SAFETY AND POLLUTION PREVENTION
PC Code: I 0850 I DP Barcode: 421275 , 420012 January 

### 8 , 2015 MEMORANDUM SUBJECT:

FROM:

THRU:

TO: Drinking Water Assessment for Proposed New Uses ofPendimethalin on Caneberry Subgroup 13-07A, Bush berry Subgroup 13

- 07B, Crop Group Conversion for Tree N ut Group 14-12; and Cool- and Warm Season Forage Grasses
. Ibrahim Abdel-Saheb, Ph
. D, Env ironm ental Scientist 

## --==:--

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# 5 Environmental Risk Branch 

### V I ' Env ironmental Fate and Effects Di v i sion (7507P) 

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# r p \ -<2;-\sMark Corbin, Branch Chief**--{f~ ~**  

## \...L/' Willi.am P.

## ~eke!, Ph.D., Senio r Sc i e n ce Advisor r 

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# //i'llj - Momca, Wait, RAPL 

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.**~** o \ Environmental Risk Branch 

### VI Environmental Fate and Effects Division (7507P)

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## ~ /\5 Office of Pesticide Programs Office of Chemical Safety & Pollution Prevention Yvonne Barnes, Chemist Donna Davis, Branch Chief RAB 6 He alth Effects Division (7509P) Emi l y Schm id, Risk Manager Reviewer Kathryn Montague, Product Manager Team 23 He rbicide Branch Registration Division (7505 P) Sidney Jackson, Risk Manager Reviewer Barbara Madden, Minor Use Team Leader Product Manager 5 Minor Use and Emergency Response Branch Registration Division (7505 P)This memorandum provides estimates of human drinking water exposure to the herbicide pendimethalin from the proposed new uses on cane berry subgroup 13-07A, bush berry subgroup 13-07B , crop group conversion for tree nut gro u p 14-12, and cool- and warm season forage grasses. The pendimethalin product ( PROWL H 2 0, EPA Reg. No 241-418) assoc iated w ith the propo s ed new uses is to be applied to annual gra sses and certain broadleafweeds as they germinate
. The proposed maximum si ngle and annual app li cation rate is 6 .0 0 l b a
.i./A (caneberry subgroup 1 3-07 A and bush berry subgro up 13-078 , p l us crop group conversion for the tree nut group 14-12), and 4 lb ail A (cool- and warm season forage grasses). In the case of pendimethalin, grapes, a previously registered use, has the highes t application rate of all currently registered u s e s ites: 6 lb a.i./A (May 8 , 2007 DWA, DP barcode 334061)
. The Tier 2 (PRZMEXAMS) mode ls were used in the 2007 drinking water assessment (DWA) cited above and resulted in the following est imated drinking wate r concentrat ions (EDWCs): 77
. 7 ppb peak exposure, 6.0 ppb annua l mean, and 4
. 8 ppb f o r the 30-year average. For groundwater, the model SCI-GROW gave EDWCs for , acute and chro ni c , of 0.036 ppb. All exposures are for parent pendimetha lin only; the input parameters used indicate litt l e production of degradates. Since 2007, EFED has introduced new surface water and groundwater models [i.e Surface Water Concentration Calculator (SWCC), and PRZM-GW, respectively]. A comparison was made be tween output from current EFED mode ls for pendimethalin for the proposed u s es on caneberry subgro up 13-07 A , bush berry subgroup 13-07B , crop group conversion for tree n ut group 14-12 (6.0 lb ai /A) , and cool- and warm s e a son forage grasses (4.0 lb ai/A) with the output from the currently registe red use on grapes (6.0 lb ai /A). Results are shown in Table I (se e model input and output in Appendix 1). A pplication da te s for the proposed usse were based on information from th e proposed supplemental labe ls (EPA Reg. No. 241-418)
.



### 2

### Thus, EFED recommends that the Health Effects Division us e the follo wing surface water and groundwater EDWCs ( highlighted field s) resulting from modeling. Table 

### l. Recommended Drinking Water Exposure Estimates. (SWCC)* PRZM-GW** Surface Water ( ppb) Groundwater ( ppb) Cool- and Berries & 

### Cool- and warm season warm season Grape forage others forage grasses grasses Peak ( 1-in-1 0 yr) 96.4 21.9 Peak-ppb 4.38E-9 l.78E -10 365-day Avg (1

- 9.73 1.47 Post**Incomplete~** 

### Incomplete in

- 1 0 yr) Br eakthrough Avg-ppb

0

-- 

### Entire Simu lat ion 8.16 1.25 S imulation 3.09E-13 1.88£-13 Mean Avg-ppb *:For the SWCC mode l The NY grape scenario was used to represent berr ies. The CArangela ndhay, and the ORgrassseed scenarios were used to represent forage gra!Ses. The ORgrassseed scenario resulted in higher EECs than theCA scena r io; and it is presented here. ** : For the PRZM-GW model ; the following available scenarios were used to represent ornamentals and turf : Flpotato, GAcoastal, NCcoastal, and Wlsand. The NC scenario gave the highest EDWCs. ¥ : The chemical did not r each groun dwater even after running the model with an extended 100-year weather file

3

# Appendix .I SWCCModel
Table 

### 1. Estimated Drinking Water Concentrations (ppb) for pendimethalin.

Peak ( 1 -in- 10 yr) 96.4 4-day Avg ( 1-in-10 yr) 58.8 21-day Avg ( 1

- in-10 yr) 28.1 60-day A vg (1-in-1 0 yr) 19.7 365-day Avg (1-in-l 0 yr) 9.73 Enti re Simulation Mean 8.16 

### Table 2. Summary of Model Inputs for pendimethalin.

Scenario NYGrapesSTD Cropped Area Frac t ion 1.0 Koc ( mllg ) 19768 Water Half-Life (days) @ 25 °C 344 Benthic Half-Life (days ) @ 25 °C 68 Photolysis Half-Life (days)@ 40 17 0 

### Lat Hydrolysis Half-Life (days) 0 Soil Half-Life (days) @ 22 

# oc 172 Foliar Half-Life (days) 35 Molecular Wt 281 Vapor Pre ss ure (torr ) 3E-5 Solubi li ty (m g/ 1) 3.75

4

### Table 3. Application Schedule for pendimethalin. 

### Date (Days Type Amount 

### (kg/ha) 

### Eff. Drift Since Emergence) 

# .. 5 Ground 6.72 0.99 0.066


### Figure 1. 

### Yearly Peak Concentr ation s
pendimethalin, NYGrapesSTO
. Res ervo ir 120 

# • 100 :0 0. 

### .e. 80 c**~** 

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# • • 

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# •**~** 40 c 

### 8 20 

### -1-----ec - --- _.___!1

--------- --- - 

# • 

# . . 

# . . . . . 

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# .. . • • 

# • • • 0 0 5 10 15 20 25 30 Year 

# PRZM GW Model Berries
Sc en ario 10 Peak(ppb) PDT A'• g( pp b) S imAvg BT(d) Thro ug hput s 90 -d ay Avg DELMARVA

_ ST O.SCN 2.78[- 1 0 Incomplete 2
.96£

- 1 1 In co mp l e te 0. 1 995277 2.7[-10 flPOTATO

_STO.SCN 0.00000 In co mpl ete 0.000000 In co mp lete 0.053 92589 0.000000 GACOASTAL

_ST O.SCN 2.22 [- 16 In co mpl e te 1.28[ -17 Incomplete 0
. 1 450981 2. 1 9[- 16 NCCOASTAL

_S TD.SCN 4.38[

-9 In complete 5. 79 [
- 10 Inc o mplete 0 .252 9869 4.3[-9 W 1SA N DS

_ST D .SCN 5.39£

- 1 2 I ncomplete 3.09[-13 In comp l e te 0.178004 5 .38£

- 12 

# Grasses
P ea k( ppb) PBT Avg(ppb) SimAvg BT(d) Tl\roug hp uts 90 -da y Avg

DELMARVA exte nd e d. SCN 1.78£- 10 I ncomp l ete I.89E- ll In complete 0.1995277 1. 73£

- 10 

### 5Flpotato extended.SCN GAcoasta l extended.SCN NC coas tal cxtended.SCN Wlsand e xtended .SCN 3 0 Incomp lete 1.48 E- 1 6 Incomplete J.O:Z E- 09 Incomplete 3.29 E- 12 In co mpl ete 0 Incomplete 8.53£-18 In co mpl et e 4 .06E-1 0 Incompl e te .1.88E-13 In co mplet e Chemical Properties for Groundwater Modeling of pendimethalin.

Koc (ml/g) 

### 15000 Su rface Soil Half Life (days) 

### 172 Hydrolysis Half Life (days) 

### 0 Diffus ion Coefficie n t Air (cm2/day) 

### 0.0 Henry's Constant 

### 0.0 Enthalpy (kcal/mol) 

### 0.0

6 0.05392589 0.1450981 0.2529869 0.178004 0 1 .46 E- 1 6 3.0:ZE-09 3.20E

- 1 1