UNITED STATES ENVIRONMENTAL PROTECTION 

AGENCY 

OFFICE OF CHEMICAL 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 13-07 A, Bush berry Subgroup 13-07B, Crop Group Conversion for Tree Nut 

Group 14-12; and Cool- and Warm Season 

Forage Grasses. 

Ibrahim Abdel-Saheb, Ph.D, Environmental Scientist --==:--~ ' / )!. / / 5 

Environmental Risk Branch VI ' 

Environmental Fate and Effects Division (7507P) 

,. , n j r p \ -<2;-\sMark Corbin, Branch Chief --{f~ ~ \...L/' 

Willi.am P. ~eke!, Ph.D., Senior Science Advisor r /1 A I 71 'f c> " /) //i'llj - Momca, Wait, RAPL "'fiJI {,/[/t(/v- . ~ o \ 

Environmental Risk Branch VI 

Environmental Fate and Effects Division (7507P) ~ W C...:A:. \I ~ /\5 

Office of Pesticide Programs 

Office of Chemical Safety & Pollution Prevention 

Yvonne Barnes, Chemist 

Donna Davis, Branch Chief 

RAB 6 

Health Effects Division (7509P) 

Emily Schmid, Risk Manager Reviewer 

Kathryn Montague, Product Manager Team 23 

Herbicide 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 13-07 A, bush berry subgroup 13-07B, crop group 

conversion for tree nut group 14-12, and cool- and warm season forage grasses. 

The pendimethalin product (PROWL H20, EPA Reg. No 241-418) associated with the proposed new uses 

is to be applied to annual grasses and certain broadleafweeds as they germinate. The proposed maximum 

single and annual application rate is 6.00 lb a. i./A (caneberry subgroup 13-07 A and bush berry subgroup 

13-078, plus 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 highest application rate of all 

currently registered use sites: 6 lb a.i./A (May 8, 2007 DWA, DP barcode 334061). The Tier 2 (PRZMEXAMS) models were used in the 2007 drinking water assessment (DWA) cited above and resulted in the 

following estimated drinking water concentrations (EDWCs): 77.7 ppb peak exposure, 6.0 ppb annual 

mean, and 4.8 ppb for the 30-year average. For groundwater, the model SCI-GROW gave EDWCs for, 

acute and chronic, of 0.036 ppb. All exposures are for parent pendimethalin only; the input parameters 

used indicate little 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 between 

output from current EFED models for pendimethalin for the proposed uses on caneberry subgroup 13-07 A, 

bush berry subgroup 13-07B, crop group conversion for tree nut group 14-12 (6.0 lb ai/ A), and cool- and 

warm season forage grasses (4.0 lb ai/A) with the output from the currently registered use on grapes (6.0 

lb ai/A). 

Results are shown in Table I (see model input and output in Appendix 1). Application dates for the proposed 

usse were based on information from the proposed supplemental labels (EPA Reg. No. 241-418). 

2 
Thus, EFED recommends that the Health Effects Division use the following surface water and groundwater 

EDWCs (highlighted fields) 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) Breakthrough 

Avg-ppb 

0 --

Entire Simulation 8.16 1.25 Simulation 3.09E-13 1.88£-13 

Mean Avg-ppb 

*:For the SWCC model 

The NY grape scenario was used to represent berries. 

The CArangela ndhay, and the ORgrassseed scenarios were used to represent forage gra!Ses. The 

ORgrassseed scenario resulted in higher EECs than theCA scenario; 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 groundwater 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 

Entire Simulation Mean 8.16 

Table 2. Summary of Model Inputs for pendimethalin. 

Scenario NYGrapesSTD 

Cropped Area Fraction 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 Pressure (torr) 3E-5 

Solubility (mg/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 Concentrations 

pendimethalin, NYGrapesSTO. Reservoir 

120 

• 

100 

:0 

0. 

.e. 80 c 

~ 

• a 

• • 

• - u • • r----= ----• ---• 

• • • • • f! so 

c • ~ c 40 

8 

20 -1-----ec- ---_.___!1------------- • . . . . . . . . . . . 

• • • • • 

0 

0 5 10 15 20 25 30 

Year 

PRZM GW Model 

Berries 

Scenario 10 Peak(ppb) PDT A'•g(ppb) SimAvg BT(d) Throughputs 90-day Avg 

DELMARVA_ST O.SCN 2.78[-10 Incomplete 2.96£-11 Incomplete 0.1995277 2.7[-10 

flPOTATO_STO.SCN 0.00000 Incomplete 0.000000 Incomplete 0.05392589 0.000000 

GACOASTAL_STO.SCN 2.22[-16 Incomplete 1.28[-17 Incomplete 0.1450981 2.19[-16 

NCCOASTAL_STD.SCN 4.38[-9 Incomplete 5.79[ -10 Incomplete 0.2529869 4.3[-9 

W1SANDS_STD.SCN 5.39£-12 Incomplete 3.09[-13 Incomplete 0.178004 5.38£-12 

Grasses 

Peak(ppb) PBT Avg(ppb) SimAvg BT(d) Tl\roughputs 90-day Avg 

DELMARVA extended.SCN 1.78£-10 Incomplete I.89E-ll Incomplete 0.1995277 1.73£-10 

5 
Flpotato extended.SCN 

GAcoastal extended.SCN 

NCcoastal cxtended.SCN 

Wlsand extended.SCN 3 

0 Incomplete 

1.48E-16 Incomplete 

J.O:ZE-09 Incomplete 

3.29E-12 Incomplete 

0 Incomplete 

8.53£-18 Incomplete 

4.06E-10 Incomplete 

.1.88E-13 Incomplete 

Chemical Properties for Groundwater Modeling of pendimethalin. 

Koc (ml/g) 15000 

Surface Soil Half Life (days) 172 

Hydrolysis Half Life (days) 0 

Diffusion Coefficient 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 

1.46E-16 

3.0:ZE-09 

3.20E-11