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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

OFFICE OF

PREVENTION, PESTICIDES AND

TOXIC SUBSTANCES

PC Code 129099

DP Barcode D367105

Date August 4, 2009

MEMORANDUM

SUBJECT: Tier I Estimated Environmental Concentrations of Imidacloprid for the 

Use in the Human Health Risk Assessment, Registration of a New Product 

for Seed Treatment, Sepresto 75WS, and New Use on Bulb Vegetables 

(Crop Group 3) for GAUCHO 550SC

FROM: José L. Meléndez, Chemist

Environmental Risk Branch V

Environmental Fate and Effects Division (7507P) 

THROUGH: Mah T. Shamim, Branch Chief

Environmental Risk Branch V

Environmental Fate and Effects Division (7507P)

TO: Kable Davis, Risk Manager Reviewer

Venus Eagle, Risk Manager #1

Insecticide-Rodenticide Branch

Registration Division (7505P)

AND: Jennifer R. Tyler, Risk Assessor

Dana Vogel, Branch Chief

Registration Action Branch I

Health Effects Division (7509P)

This memo presents the Tier I Estimated Surface Drinking Water Concentrations and 

Estimated Ground Water Concentrations (EDWCs) for Imidacloprid, calculated using the 

Tier I aquatic models FIRST and SCI-GROW, respectively, for use in the human health 

risk assessment. It was found that caneberries and citrus are still the uses with the major 

exposure, with an application rate of 0.5 lb a.i./A, and the highest percent crop area 

(PCA=0.87), and, therefore, the drinking waters assessment results do not change from 

the previous ones. The previous Drinking Waters Assessment (DWA) still applies. An 

electronic copy of the previous assessment is attached.
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The Estimated Drinking Water Concentrations (EDWCs) for imidacloprid were 

calculated based on a maximum application rate of 0.5 lb a.i./A/season. The acute 

drinking water concentration in surface water is 36.0 ppb of imidacloprid, based on 

applications of the chemical to citrus. The cancer/chronic surface drinking water 

concentration is 17.2 ppb (based on applications to citrus). The SCI-GROW generated 

EDWC is 2.09 ppb of imidacloprid, which is recommended for use, both for acute and 

chronic exposures. Table I provides a summary of the Tier I modeled drinking water 

concentrations. Should there be a need for additional refinements, the EFED can perform 

a Tier II aquatic assessment, for surface waters.

Data Gaps and Uncertainties:

The environmental fate database is substantially complete. An aerobic aquatic 

metabolism (Guideline No. 835.4300) study has been required.

Table 1. Maximum Tier I Estimated Drinking Water Concentrations (EDWCs) for 

drinking water risk assessment based on ground application of imidacloprid (for 

additional details, refer to Attachment A).

DRINKING WATER 

SOURCE (MODEL 

USED) USE (rate modeled)

MAXIMUM ESTIMATED DRINKING 

WATER CONCENTRATION (EDWC) (ppb)

Groundwater 

(SCI-GROW) Citrus (0.5 lb a.i./A) Acute and chronic 2.09

Surface water 

(FIRST)

Citrus (0.5 lb a.i./A) Acute 36.0

Citrus (0.5 lb a.i./A) Chronic 17.2

Use Characterization

Table 2 is a summary of all agricultural use patterns for imidacloprid in the proposed 

labels. Uses were arranged according to crop groups. The uses shaded gray are the 

proposed new ones under Pesticide Amendment for GAUCHO 550SC (new use added to 

the label), or Registration Application for Sepresto 75WS (a proposed new product for 

seed treatment, containing imidacloprid and clothianidin as active ingredients). The use 

information was obtained from the proposed labels for GAUCHO® 550SC (EPA Reg. 

No. 264-827) and Sepresto 75WS (EPA Reg. No. 264-XXX, Proposed New Product).

From Table 2 it is noted that of the new uses, only bulb vegetables (Crop Group 3-07, 

e.g. onion & garlic) could involve the highest use rate for a single application at 0.5 lb 

a.i./A, applied foliarly. This rate was assessed for caneberries, using FIRST, in 

memorandum dated 4/13/07 from R.D. Parker to J.R. Tyler and B. Madden (Attachment 

A). Therefore, a new assessment is not required.
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Table 2. Summary use information for imidacloprid, including proposed (shaded gray) and current (not shaded) 

uses [labels for GAUCHO® 550SC (EPA Reg. No. 264-827) and Sepresto 75WS (EPA Reg. No. 264-XXX, 

Proposed)].

PURPOSE/ 

SOURCE USE

a.i. oz/

1000 seed

APP. RATE 

max. lb a.i./ 

A/applic.

APP. RATE 

lb. a.i./ 

A/season

LABELED 

METHODS OF 

APPLICATION4

COMMENTS

Sepresto 75WS Root & Tuber 

veg. (CG 1) 0.00525 0.305

0.5 Seed treatment

GAUCHO 550SC

Root veg. 

(CSG 1B except 

sugarbeet + kava)

N/A 0.38 0.38 Seed treatment, 

soil, foliar

GAUCHO 550SC

Tuberous & 

Corm veg. 

(CSG 1C)

N/A 0.38 0.38 Seed treatment, 

soil, foliar

GAUCHO 550SC Sugarbeet 

(CA only) N/A 0.18 0.18 Seed treatment, soil

Sepresto 75WS Potato Seed 

pieces N/A 0.092

0.092Seed treatment

0.35 oz prod/100 

lb seed; 7.7 oz

prod/A2

GAUCHO 550SC

Potato & 

Potato Seed 

Piece Treatment

NA 0.31 0.31 Seed treatment, 

soil, foliar

Sepresto 75WS Leafy Greens 

veg. (CSG 4A) 0.0094 0.0256

0.5 Seed treatment

GAUCHO 550SC

Leafy veg. 

(CSG 4A plus 

watercress)

N/A 0.38 0.38 Seed treatment, 

soil, foliar

Sepresto 75WS Brassica (Cole) 

Leafy veg (CG 5) 0.01387 0.0387

0.5 Seed treatment

GAUCHO 550SC Brassica (Cole) 

Leafy veg (CG 5) N/A 0.38 0.38 Seed treatment, soil, foliar

Sepresto 75WS Fruiting veg. 

(CG 8) 0.00581 0.000358

0.5 Seed treatment

GAUCHO 550SC

Fruiting veg.

(CG 8) (except 

pepper & okra)

N/A 0.38 0.38 Seed treatment, 

soil, foliar

Additional use 

for planthouses

Pepper & Okra N/A 0.5 0.5

Sepresto 75WS Cucurbit veg. 

(CG 9) 0.011 0.0459

0.5 Seed treatment
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Table 2. Summary use information for imidacloprid, including proposed (shaded gray) and current (not shaded) 

uses [labels for GAUCHO® 550SC (EPA Reg. No. 264-827) and Sepresto 75WS (EPA Reg. No. 264-XXX, 

Proposed)].

PURPOSE/ 

SOURCE USE

a.i. oz/

1000 seed

APP. RATE 

max. lb a.i./ 

A/applic.

APP. RATE 

lb. a.i./ 

A/season

LABELED 

METHODS OF 

APPLICATION4

COMMENTS

GAUCHO 550SC Cucurbit veg. 

(CG 9) N/A 0.38 0.38 Seed treatment, soil, foliar

Addl use for 

planthouses

Sepresto 75WS Bulb veg. (CG 3) 0.0024 0.06410 0.5 Seed treatment

GAUCHO 550SC Bulb veg. 

(CG 3-07) N/A 0.5 0.5

Seed treatment, 

soil, foliar

Sepresto 75WS Cereal Grain (CG 

15 w/o rice) N/A 0.031

0.031Seed treatment 2.0 oz/100 lb 

seed; 2.6 oz/A1

GAUCHO 550SC Cotton N/A 0.33 0.5 Seed treatment, 

soil, foliar

Max. 6 applics. 

a.i./ season

GAUCHO 550SC Peanut N/A 0.38 0.38 Seed treatment, 

soil, foliar

GAUCHO 550SC Tobacco N/A NS 0.5 Soil, foliar Max. 1.2 oz 

prod/ 1000 plants

GAUCHO 550SC Greenhouse veg. 

(cucumber & tomato)

N/A NA NA3Foliar 0.6 oz product/ 

1000 plants

GAUCHO 550SC Globe Artichoke N/A 0.5 0.5 Seed treatment, 

soil, foliar

GAUCHO 550SC Herbs (CS 19A) N/A 0.38 0.38 Seed treatment, 

soil, foliar

GAUCHO 550SC Leafy Petiole 

veg. (CSG 4B) N/A 0.38 0.38 Seed treatment, soil, foliar

GAUCHO 550SC

Legume veg. 

(CG 6 except 

dry soybean

N/A 0.38 0.38 Seed treatment, 

soil, foliar

GAUCHO 550SC

Strawberry N/A 0.5 0.5 Soil, foliar Do not use both 

app. methods in 

Use Post-Harvest N/A 0.38 0.38 Soil, foliar the same season.
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Table 2. Summary use information for imidacloprid, including proposed (shaded gray) and current (not shaded) 

uses [labels for GAUCHO® 550SC (EPA Reg. No. 264-827) and Sepresto 75WS (EPA Reg. No. 264-XXX, 

Proposed)].

PURPOSE/ 

SOURCE USE

a.i. oz/

1000 seed

APP. RATE 

max. lb a.i./ 

A/applic.

APP. RATE 

lb. a.i./ 

A/season

LABELED 

METHODS OF 

APPLICATION4

COMMENTS

NA = Not Available; N/A = Not Applicable; NS = Not Specified; For GAUCHO 550SC, seed treatment is in the field at 

planting or shortly thereafter.

1. Seeding rate 131 lb seeds/A for wheat (representative crop); Source: http://www.uky.edu/Ag/Wheat/seedrate.html

2. Seeding rate 1600-2200 lb seeds/A 

Source: http://aggie-horticulture.tamu.edu/extension/vegetable/cropguides/potato.html

3. Greenhouse uses are not assessed by EFED.

4. General instructions for GAUCHO 550SC: Aerial applications of GAUCHO 550SC are not allowed. The product 

may be applied with ground equipment or via chemigation. Applications of GAUCHO 550SC should direct product into 

the seed or root zone of crop. Broadcast foliar applications are only recommended to seedling flats or trays, or where 

product is intended to be washed from foliage to soil prior to drying on foliage.

5. Carrots, representative crop, source for approximate seeding rate: 

http://pmep.cce.cornell.edu/piap/carrot96/agpractices.html - and http://aggiehorticulture.tamu.edu/extension/vegetable/cropguides/carrot.html (23000 seeds/oz and 2-2.5 lb seeds/A => 920,000 

seeds/A; app rate for carrots 0.00525 oz/1000 seeds => 0.30 lb a.i./A)

6. Lettuce, representative crop, source of approximate seeding rate: 

http://www.ipmcenters.org/cropprofiles/CP_form.cfm (ultimately, 43000 plants/A => 0.025 lb a.i./A

7. Same source as above (6). In CA about 44,000 plants cabbage /A => 0.0038 lb a.i./A

8. Same source as above (6): In FL, maximum plant density of tomatoes is around 4,840/A; for tomatoes, the max. 

application rate is 0.00116 oz a.i./1000 seed => 0.00035 lb a.i./A (note, transplants are not considered)

9. Same source as above (6), in FL, cucumbers maximum plant population is 21,780/A => 0.015 lb a.i./A

10. Onions, representative crop, source for approximate seeding rate: http://www.ag.ndsu.edu/pubs/alt-ag/onions.htm 

(8000 seeds/oz and 2-4 lb/A => 512000 seeds/A; app. rate for onions 0.0020 oz a.i/1000 seeds. => 0.064 lb a.i./A)