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OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

PC Code: 101702

DP Barcode: 425825

Date: March 19, 2015

MEMORANDUM

SUBJECT: Drinking Water Exposure Assessment in support of the new use registration 

of zoxamide formulated product Gravel 75DF on ginseng, tomato subgroup 

(Subgroups 8-10A), small fruit vine climbing except fuzzy kiwifruit 

(Subgroup 13-07F), and tuberous and corm subgroup (Subgroup 1C)

TO: Vincent Chen, Risk Assessor

Meheret Negussie

Nancy Keller

Barry O’Keefe

Christine Olinger, Branch Chief

Risk Assessment Branch 3

Health Effect Division (7509P)

Andrew Ertman, Risk Manager Reviewer

Barbara Madden, Minor Use Team Leader

Marion Johnson, Branch Chief

Risk Integration Minor Use, and Emergency Response Branch

Registration Division (7505P)

FROM: Edom Seifu, Environmental Science Trainee

Stephen Wente, Ph.D., Biologist

Environmental Risk Branch I

Environmental Fate and Effects Division (7507P)

APPROVED

BY: Sujatha Sankula, Ph.D., Branch Chief

Environmental Risk Branch I

Environmental Fate and Effects Division (7507P)

This assessment provides estimated drinking water concentrations (EDWCs) of zoxamide alone 

(parent only) as well as zoxamide and its major metabolites, RH-150721, RH-24549, RH141288, RH-129151 and RH-139432 (total toxic residues) in surface water and groundwater in
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support of human health risk assessment. The previous drinking water assessment (DWA) from 

January 17, 2014 (USEPA 2014; D417061) provided surface water EDWCs based on zoxamide 

use on grapes at a maximum annual application rate of 1.60 lbs ai/A (Table 1).

Table 1. Recommended EDWCs Based on Parent Only and Total Toxic Residues of Zoxamide

Drinking 

Water Source Crop Scenario Peak Exposure(μg/L)

Annual Mean

Exposure (μg/L)

Average Annual

Exposure (μg/L)

Zoxamide (Parent only)

Surface water NY Grape STD Scenario1 17.55 2.49 0.91

Ground water FL Citrus Scenario2 1.83E-03 NA 6.84E-04

Total Toxic Residue (Parent +RH-150721, RH-24549, RH-141288, RH-129151 and RH-139432)

Surface water NY Grape STD Scenario1 81.3 54.48 22.84

Ground water WI Sands Scenario2 83.5 NA 65.8

1 Reported EDWCs generated using PRZM/EXAMS model for aerial application (US EPA 2000) and these 

values are revised with recommended current PCA factor of 0.91.

2 Highest EDWCs generated using PRZM-GW model based on 1.60 lbs ai/A for grape and potato [Gavel 80 WP 

(EPA Reg. No.10163-6413)].

Three of the four “new” uses on the proposed label are crop group conversions [tomato subgroup 

(Subgroups 8-10A), small fruit vine climbing except fuzzy kiwifruit (Subgroup 13-07F), and 

tuberous and corm subgroup (Subgroup 1C)] and have previously been assessed by the Agency. 

These three previously assessed uses produced EDWCs that were lower than the grape EDWCs 

provided in Table 1.

The fourth use on the proposed label, ginseng, is the only use that has not previously been 

assessed by the Agency. However, ginseng is restricted on the proposed label to a seasonal 

application rate of 0.96 lbs ai/A, which is approximately 2/3rd the grape use annual application 

rate. Because the ginseng seasonal application rate is much lower than the grape use annual 

application rate, the Environmental Fate and Effects Division (EFED) does not believe the 

ginseng EDWCs would exceed the currently recommended EDWCs. Therefore, EFED 

recommends that the human health risk assessment be based on the previously 

recommended EDWCs provide in Table 1.

Uncertainties

The proposed label provides maximum seasonal application rates rather than maximum annual

application rates. The Agency’s label checklist requires maximum annual application rates

(maximum seasonal application rates are optional) in order to avoid any confusion on the 

interpretation of the term “seasonal”. If the maximum annual application rates are actually higher 

than the seasonal rates provided on the label, the EDWCs provided in this memo may not 

represent conservative estimates of the expected EDWCs.

References

US EPA. 2014. Drinking Water Exposure Assessment in support of the new use registration of 

zoxamide formulated product Gravel 75DF on onions (dry bulb), garlic and shallots. January 17, 

2014. (D417061)