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OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

July 17, 2012

PC Code: 014019

MEMORANDUM DP Barcode: 376184

SUBJECT: Thiacloprid: Update of the Drinking Water Exposure Assessment for Section 3 

New Uses on Stone Fruits and Peppers

FROM: Greg Orrick, Environmental Scientist

Environmental Risk Branch II

Environmental Fate and Effects Division (7507P)

THRU: R. David Jones, Ph.D. Senior Agronomist

Brian Anderson, Chief 

Environmental Risk Branch II

Environmental Fate and Effects Division (7507P)

TO: Elizabeth Holman, Chemist

Christina Swartz, Chief

Risk Assessment Branch II

Health Effects Division (7509P)

Andrew Ertman, Risk Manager

Barbara Madden, Minor Use Team Leader, RM Team 5

Risk Integration Minor Use and Emergency Response Branch

Registration Division (7505P)

Marianne Lewis, Risk Manager

Venus Eagle, Product Manager, Team Leader, RM Team 1

Insecticide-Rodenticide Branch

Registration Division (7505P)

This Environmental Fate and Effects Division (EFED) memorandum updates the 2010 

drinking water exposure assessment (DP barcode 376181; USEPA, 2010) for proposed Section 3 

new use registrations of thiacloprid on the stone fruits crop group (12) and on peppers (both bell 

and non-bell). Bayer CropScience (Bayer) submitted comments on the 2010 drinking water 

assessment in a position paper titled, “Bayer CropScience Refinement of the EPA Cancer 

Assessment for Thiacloprid” (MRID 48658203). The position paper proposed three refinements 

to EFED’s drinking water assessment concerning unextracted residues, water treatment effects, 

and percent cropped area (PCA) factors.
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EFED concluded the following, based on Bayer’s comments:

1. Thiacloprid and its amide are the only residues of concern in untreated drinking water. 

Following drinking water treatment, thiacloprid is the only residue of concern expected to be 

potentially present. This is because the study data indicate that 1) coagulation does not 

remove thiacloprid or thiacloprid-amide from source water, 2) a typical oxidant (sodium 

hypochlorite) removes thiacloprid-amide (but not thiacloprid), and 3) HED has determined 

that the four major treatment products of thiacloprid-amide are not residues of concern. 

Because surface water sourced drinking water is typically treated, thiacloprid is the only 

compound of concern for surface water assessment. For assessment of untreated well water, 

thiacloprid and its amide are the residues of concern.

2. It is highly unlikely that any bioavailable unextracted residues included the parent 

compound. Also, although it was not well demonstrated that all bioavailable transformation 

products were completely extracted, it is unlikely that any unextracted transformation 

products were of toxicological concern (i.e., containing the thiazolidine ring). Therefore, 

exposure estimates of the residues of concern (whether thiacloprid alone or thiacloprid plus 

its amide) should not include unextracted residues.

3. Drinking water exposure estimates for current uses may be adjusted by a PCA factor for 

cotton and orchards/vineyards, which is 33% (occurring in the Texas Gulf regional basin 

where cotton production is concentrated; USEPA, 2012). Because thiacloprid is also 

proposed for use on peppers (and stone fruit, which doesn’t change PCA calculations that 

already include orchards) and a pepper-specific PCA is not available, drinking water 

exposure estimates for proposed uses of thiacloprid should be adjusted by the maximum PCA 

factor for all agriculture, which is 91% (USEPA, 2012).

These conclusions result in the following updated EDWCs of thiacloprid residues of 

concern (Table 1). The ground water EDWCs are unchanged, with the exception that the values 

including unextracted residues formerly included for characterization were removed. Treated 

ground water EDWCs are expected to be less due to the removal of thiacloprid-amide. The 

surface water EDWCs are less than previously reported (see Table 2) because the treated 

drinking water residues of concern no longer include thiacloprid-amide.

Table 1. Total Residue EDWCs in Surface Water and Ground Water for Use in Dietary Risk 

Assessment Based on the Use Pattern of Maximum Exposure, Pome Fruits.

Use (maximum 

rate) Source PCA (%)

1-in-10-year 

Peak Exposure 

(ppb)

1-in-10-year 

Annual Mean 

Exposure (ppb)

30-year Mean 

Exposure 

(ppb)

Pome fruits

(0.50 lbs a.i./A/year)

Surface water (treated) 91 18 2.3 1.2

Ground water (untreated) N/A 0.25 0.25 <0.25

Table 2. EDWCs Reported in the Previous (2010) Drinking Water Exposure Assessment

Pome fruits

(0.50 lbs a.i./A/year)

Surface water (treated) 91 26 6.8 4.4

Ground water (untreated) N/A 0.25 0.25 <0.25
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SCI-GROW model inputs (and outputs) from the 2010 assessment (see Appendix A) 

were not updated:

Table 3. SCI-GROW Input Parameters for Thiacloprid Residues of Concern.

Input Parameter Value Source

Application Rate 0.25 lbs a.i./A Current labels

Applications per Year 2 Current labels

Organic Carbon Partition 

Coefficient (KOC) 

166 L/kgOC MRID 44927909

Aerobic Soil Metabolism

Half-life

69 days MRID 44927916

PRZM use pattern inputs were not updated:

Table 4. PRZM Scenarios and Input Parameters Describing Proposed and Current Maximum Use 

Patterns of Thiacloprid.

Use Scenario

Date of 

Initial 

App.

App. Rate in 

lbs a.i./A

(kg a.i./ha)

App. 

per 

Year

App. 

Interval 

(days)

CAM 

Input

IPSCND 

Input

Application 

Efficiency/ 

Spray Drift

Pome fruits

NC apple Aug. 1

0.25 (0.28) 2 7 2 3 0.95/0.16 PA apple Sep. 1

OR apple Oct. 1

CA fruit May 15

Stone fruits

MI cherry Jul. 1

0.25 (0.28), 

0.13 (0.14) GA peach May 15 A 2 7 2 3 0.95/0.16

CA fruit May 15

Peppers FL pepper Oct. 15 0.094 (0.11) 3 7 2 1 0.95/0.16

Cotton

MS cotton Sep. 1

NC cotton Sep. 15 0.088 (0.099) 3 7 2 1 0.95/0.16

CA cotton Oct. 1

A A second application of 0.13 lbs a.i./A was modeled to reach the labeled seasonal maximum application rate.

Three PE chemical inputs were updated to represent thiacloprid alone rather than the 

residues of concern defined in the previous assessment (tabulated in bold). The aerobic soil 

metabolism and aerobic aquatic metabolism half-life input values were substantially reduced:

Table 5. PE Chemical Input Parameters for Thiacloprid.

Input Parameter Value Justification Source

Molecular Mass (g/mol) 252.73 Product chemistry data (Calculated)

Henry’s Law Constant 

(atm m3/mol) 4.7 x 10-15 Ratio of vapor pressure to water solubility

(Calculated from 

MRID 44927602)

Solubility in Water 

(mg/L) 185 Study value for thiacloprid MRID 44927602
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Input Parameter Value Justification Source

Organic Carbon Partition 

Coefficient (KOC) 

(L/kgOC)

572 Mean value for thiacloprid MRID 44927905

Aerobic Soil Metabolism 

Half-life (days) 5.5 (was 144) 90th percentile confidence bound on the mean half-life of thiacloprid in four soils MRID 44927916

Aerobic Aquatic 

Metabolism Half-life 

(days)

28 (was 139)

90th percentile confidence bound on the 

mean half-life of thiacloprid in two 

sediment systems

MRID 44927920

Anaerobic Aquatic 

Metabolism Half-life 

(days)

945 (was 

stable)

90th percentile confidence bound on the 

mean half-life of thiacloprid in three 

sediment systems

MRID 44927935

Hydrolysis Half-life at pH 

7 (days) Stable Study value for thiacloprid MRID 44927917

Aqueous Photolysis

Half-life (days) 381 Study value for thiacloprid MRID 44927918; 45159309

Updated thiacloprid surface water exposure estimates per use are listed in Table 6. 

Exposure estimates were adjusted by the default national percent cropped area (PCA) value 

(91%) that accounts for the maximum area within any watershed that may be in agriculture 

(USEPA, 2012). Multiple PRZM scenarios are listed for use on cotton because a single scenario

did not produce maximum values for all three exposure durations. Input and output files are 

attached in Appendix B.

Table 6. EDWCs in Surface Water from Proposed and Current Uses of Thiacloprid. A

Use PRZM Scenario 1-in-10-year Peak 

Exposure (μg/L)

1-in-10-year Annual 

Mean Exposure (μg/L)

30-year Mean 

Exposure (μg/L)

Proposed Uses

Stone fruits MI cherry 4.0 0.88 0.59

Peppers FL pepper 8.2 0.62 0.37

Current Uses

Cotton MS cotton/ NC cotton 9.0 0.93 0.51

Pome fruits NC apple 18 2.3 1.2 A

 Maximum values are in bold.

References

USEPA. 2010. Orrick, G. Thiacloprid: Drinking Water Exposure Assessment for Section 3 New 

Uses on Stone Fruits and Peppers. DP barcode 376181. U.S. Environmental Protection 

Agency, Office of Chemical Safety and Pollution Prevention. Memorandum from the 

Environmental Fate and Effects Division to the Health Effects Division and the 

Registration Division. Oct. 18, 2010.
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USEPA. 2012. Guidance on Development and Use of Percent Cropped Area and Percent Turf 

Area Adjustment Factors in Drinking Water Exposure Assessments: 2012 Update. 

Internal Environmental Fate and Effects Division memorandum. U.S. Environmental 

Protection Agency, Office of Chemical Safety and Pollution Prevention. Mar. 16, 2012.

MRID 48658203. Arthur, E., D. Dyer, R. Heintzelman, and G. Sabbagh. Bayer CropScience 

Refinement of the EPA Cancer Assessment for Thiacloprid. Bayer report number 

US0250. Position paper prepared and submitted by Bayer CropScience, Research 

Triangle Park, NC. Nov 14, 2011. 11 p.

Appendix A. SCI-GROW Input/Output Data.

SCI-GROW Input/Output File.

SciGrow version 2.3

chemical:Thiacloprid

time is 10/ 7/2010 15:19:49

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

 Application Number of Total Use Koc Soil Aerobic

 rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

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

 0.250 2.0 0.500 1.66E+02 69.0

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

groundwater screening cond (ppb) = 2.54E-01 

************************************************************************

Appendix B. PE Input/Output Files.

Example Input File (Use on Pome Fruits)

Output File: Thia_pome_NC_p

Metfile: w03812.dvf

PRZM scenario: NCappleSTD.txt

EXAMS environment file: ir298.exv

Chemical Name: Thiacloprid

Description Variable Name Value Units Comments

Molecular weight mwt 252.73 g/mol

Henry's Law Const. henry 4.7e-15 atm-m^3/mol

Vapor Pressure vapr torr

Solubility sol 185 mg/L

Kd Kd mg/L

Koc Koc 572 mg/L
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Photolysis half-life kdp 381 days Half-life

Aerobic Aquatic Metabolism kbacw 28 days Halfife

Anaerobic Aquatic Metabolism kbacs 945 days Halfife

Aerobic Soil Metabolism asm 5.5 days Halfife

Hydrolysis: pH 7 0 days Half-life

Method: CAM 2 integer See PRZM manual

Incorporation Depth: DEPI cm

Application Rate: TAPP 0.28 kg/ha

Application Efficiency: APPEFF 0.95 fraction

Spray Drift DRFT 0.16 fraction of application rate applied to pond

Application Date Date 01-08 dd/mm or dd/mmm or dd-mm or dd-mmm

Interval 1 interval 7 days Set to 0 or delete line for single app.

app. rate 1 apprate kg/ha

Record 17: FILTRA

IPSCND 3

UPTKF

Record 18: PLVKRT

PLDKRT

FEXTRC 0.5

Flag for Index Res. Run IR Reservoir

Flag for runoff calc. RUNOFF total none, monthly or total(average of entire run)