Page 2 of 19

lower-than-maximum application rates based on reported usage data for six of the ten current 

uses assessed in 2010. The remaining four current uses assessed in 2010 were not expected to 

result in risk exceedances at maximum use rates, based on a back-calculated approximate cut-off 

point of 80 μg/L provided by the Health Effects Division (HED) (email communication with 

Mohsen Sahafeyan, May 26, 2010). Reported use patterns were based on usage data collected by 

the Biological and Economic Analysis Division (BEAD) from a variety of sources (USEPA, 

2010). Ground water exposure estimates and characterization of monitoring data that were 

reported in the 2009 assessment were not impacted by comments submitted by DuPont and were 

not updated in this memorandum. 

 Surface water exposure estimates from the currently labeled maximum use patterns using 

current models and adjusted with national and regional percent cropped area (PCA) values are 

listed below in Table 1. Updated values are included. Tier I modeling was conducted for use on 

ginger root, pineapple, and yams because Tier II model scenarios (including surrogates) were not 

available with which to analyze these tropical uses that occur in Hawai’i and/or Puerto Rico. 

However, provisional Tier II modeling (described in the 2010 assessment) was also conducted 

for these uses in order to characterize the exposure; results from this characterization are 

tabulated in parentheses. Tier II modeling was conducted to estimate exposure for the remaining 

current uses. Model inputs are listed in Tables 3-5. 

Table 1. Estimated Drinking Water Concentrations (EDWC) from Maximum Use Patterns of Oxamyl 

(values >80 μg/L are bolded; provisional values are in parentheses). 

Drinking Water Source 

(model/data source) 

Use (modeled rate) PCA A 1-in-10-

Year Peak 

(μg/L)

1-in-10-Year 

Annual Mean 

(μg/L)

30-Year 

Mean 

(μg/L) 

Ginger root (8.0 lbs a.i./A/year) 100% 279 (269) 6.6 (13) -- 

Pineapple (8.0 lbs a.i./A/year) 100% 593 (351) 14 (13) -- 

Surface water (FIRST) 

Yams (4.0 lbs a.i./A/year) 100% 218 (108) 5.1 (5.0) -- 

Apples (2.0 lbs a.i./A/year) 87% 27 0.58 0.27 

Banana/plantain (4.0 lbs a.i./A/year) 100% 204 6.3 2.3 

Carrots (7.0 lbs a.i./A/year) 85% 161 5.4 3.3 

Celery (6.0 lbs a.i./A/year) 82% 138 5.2 2.7 

Citrus (6.0 lbs a.i./A/year) 38% 70 1.6 1.0 

Cotton (3.0 lbs a.i./A/year) 80% 96 2.4 1.1 

Cucumbers (6.0 lbs a.i./A/year) 67% 147 3.3 1.8 

Dry bulb onions (4.0 lbs a.i./A/year) 67% 90 1.9 0.52 

Eggplant (6.0 lbs a.i./A/year) 85% 237 9.1 3.6 

Mint (4.0 lbs a.i./A/year) 87% 12 0.40 0.24 

Non-bearing fruit (8.0 lbs a.i./A/year) 38% 124 3.1 1.5 

Peanut (4.0 lbs a.i./A/year) 87% 55 2.3 1.6 

Pear (2.0 lbs a.i./A/year) 87% 41 1.3 0.41 

Peppers (6.0 lbs a.i./A/year) 85% 256 4.7 2.2 

Potatoes (8.0 lbs a.i./A/year) 85% 243 6.4 3.1 

Sweet potato (6.0 lbs a.i./A/year) 87% 59 1.9 0.82 

Tobacco (2.0 lbs a.i./A/year) 87% 7.2 0.25 0.18 

Surface water (PE) 

Tomatoes (8.0 lbs a.i./A/year) 85% 208 4.5 2.4 

A PCA means “percent cropped area.” A PCA of 100% was applied to uses in areas outside the contiguous United 

States. The default national PCA of 87% was applied to uses within the contiguous United States with EDWCs 

<80 μg/L. Default regional PCAs were applied to the remaining uses. 
Page 3 of 19

B The modeled total annual application rate to ginger root was 8.0 lbs a.i./A at Tier I and 4.0 lbs a.i./A for Tier II 

characterization. 

Model input values are largely the same in the current update and previous drinking water 

exposure assessments, with two exceptions for uses assessed in 2010 and for the uses assessed in 

2009 that are currently being updated: 1) the aerobic aquatic metabolism half-life input was set 

to zero because degradation was not observed beyond that expected due to hydrolysis alone in 

the submitted aerobic aquatic metabolism study, and 2) a calculated Henry’s Law Constant was 

input rather than a vapor pressure. All of the uses assessed in 2009 were not updated to reflect 

these model input changes because the newer model input values do not result in substantially 

different acute exposure estimates. 

Surface water exposure estimates for use patterns based on reported usage are provided 

for characterization in Table 2. Reported use patterns were not characterized for uses in Table 1

for which 1-in-10-year peak values were less than 80 μg/L. Exposure estimates for 

bananas/plantains are not reduced in Table 2 because typical usage of oxamyl on the crop is at 

maximum rates. The 30-year daily time series of EDWCs that Tier II point estimates in Tables 1

and 2 represent will be transmitted (as comma delimited files) with this assessment to the Health 

Effects Division (HED) for modeling in support of human health dietary risk assessment. 

It is important to note that only one use pattern per crop was modeled to produce the 

results in Table 2 due to the complexity of label directions. If the specific label directions used 

for modeling are changed to eliminate potential risk exceedances, other use patterns not modeled 

in this assessment may still result in risk exceedances. For example, both use patterns for 

eggplant modeled in the 2010 DWA, one for nematodes and the other for insects, resulted in 

EDWCs >80 μg/L. If the use pattern assessed in this update is mitigated to reduce exposure, 

exposure from the use pattern not assessed in this update will not necessarily be reduced as well. 

Table 2. EDWCs from Reported Use Patterns of Oxamyl Based on Reported Usage (values >80 μg/L are 

bolded; provisional values are in parentheses). 

Drinking Water Source 

(model/data source) 

Use (modeled rate) PCA A 1-in-10-

Year Peak 

(μg/L)

1-in-10-Year 

Annual Mean 

(μg/L)

30-Year 

Mean 

(μg/L) 

Ginger root (4.0 lbs a.i./A/year) 100% 198 (266) 4.7 (6.7) – 

Pineapple (3.0 lbs a.i./A/year) 100% 120 (149) 2.8 (5.2) – 

Surface water (FIRST) 

Yams (2.5 lbs a.i./A/year) 100% 171 (108) 4.0 (3.9) – 

Banana/plantain (4.0 lbs a.i./A/year) 100% 204 6.3 2.3 

Carrots (2.0 lbs a.i./A/year) 85% 75 2.8 0.97 

Celery (3.0 lbs a.i./A/year) 82% 69 2.6 1.3 

Cotton (1.0 lbs a.i./A/year) 80% 56 0.96 0.34 

Cucumbers (2.0 lbs a.i./A/year) 67% 45 0.91 0.46 

Dry bulb onions (3.5 lbs a.i./A/year) 67% 32 1.2 0.67 

Eggplant (1.9 lbs a.i./A/year) 85% 72 2.5 1.1 

Non-bearing fruit (2.0 lbs a.i./A/year) 38% 45 0.85 0.37 

Peppers (2.0 lbs a.i./A/year) 85% 87 1.5 0.73 

Potatoes (3.0 lbs a.i./A/year) 85% 88 2.9 1.1 

Surface water (PE) 

Tomatoes (4.5 lbs a.i./A/year) 85% 159 2.6 1.1 

A PCA means “percent cropped area.” A PCA adjustment was not applied to uses in areas outside the contiguous 

United States. Default regional PCA values were applied to the remaining uses. 
Page 4 of 19

1. Exposure Modeling Input Parameters 

1.1. Tier I Modeling 

FIRST was used in the 2010 DWA to estimate screening level exposure in surface water 

from use of oxamyl on yams (labeled for Puerto Rico only), ginger root (labeled for Hawai’i 

only), and pineapple (label prohibits use in California; grown in Hawai’i and Puerto Rico). 

Other assessed uses were modeled with the Tier II PE model because PRZM scenarios or 

reasonable surrogate PRZM scenarios were available. Model input parameters used in FIRST 

are listed in Table 3. No model input parameters were changed for this DWA update. 

Table 3. FIRST Input Parameters for Oxamyl Uses on Yams, Ginger Root, and Pineapple. 

Input Parameter Value Comments Source 

Application rate 

(lbs a.i./A) 

Ginger root: 1.0 

Pineapple: 2.0 

Yams: 0.5 

Maximum labeled single application rate 

for post-plant or foliar treatment Current label 

Number of applications per 

year 

Ginger root: 8 

Pineapple: 4 

Yams: 8 

Maximum labeled number of applications 

per season (either explicit or inferred from 

the maximum seasonal application rate) 

Current label 

Re-application interval 

(days) 

Ginger root: 30 

Pineapple: 14 

Yams: 14 

Minimum labeled re-application intervals Current label 

Percent cropped area 100% Default for uses outside of the contiguous 

United States 

Effland et al., 

1999 

Organic Carbon Partition 

Coefficient (KOC) (L/kgOC) 35 Mean of five KOC values MRID 46237301 

Aerobic soil metabolism 

half-life (days) 52 Upper 90% confidence bound on the mean of six half-lives 

MRID 63012 

MRID 42820001 

MRID 45176602 

Wetted in? No Input recommended in divisional guidance USEPA, 2009c 

Method of application Ground Modeled use patterns are for foliar ground 

applications. Current label 

Depth of incorporation 

(inches) 0 Foliar applications are not incorporated. Current label 

Solubility in water (ppm) 280,000 Product chemistry data MRID 40499702 

Aerobic aquatic metabolism 

half-life (days) 0 

At the study pH levels, aqueous 

degradation was indistinguishable from 

that due to hydrolysis. 

MRID 45045305 

Hydrolysis half-life (days) 8.0 Half-life at pH 7 MRID 40606516 

Aqueous photolysis half-life 

(days) 14 Maximum environmental 

phototransformation half-life 

MRID 40606515; 

41058801 

1.2. Tier II Modeling 

Chemical Inputs 

The chemical input parameters for PE are listed in Table 4. Input values are largely the 

same in the current update and previous drinking water exposure assessments, with two 

exceptions for uses assessed in 2010 and for the uses assessed in 2009 that are currently being 

updated: 1) the aerobic aquatic metabolism half-life input was set to zero because degradation 

was not observed beyond that expected due to hydrolysis alone in the submitted aerobic aquatic 
Page 5 of 19

metabolism study, and 2) a calculated Henry’s Law Constant was input rather than a vapor 

pressure. The use of the Henry’s Law Constant is consistent with guidance and does not alter 

exposure estimates. The new aerobic aquatic metabolism input results in a small increase in 1-

in-10-year peak EDWCs and larger increases in time-averaged EDWCs because stability to 

aquatic metabolism results in less degradation over time in the index reservoir. For example, the 

1-in-10-year peak (256 μg/L), 1-in-10-year annual mean (4.7 μg/L), and 30-year mean (2.2 

μg/L) EDWCs for the maximum use pattern for peppers are increased with the new aerobic 

aquatic metabolism input to 262 μg/L, 9.0 μg/L, and 4.1 μg/L, respectively. In summary, the 1-

in-10-year peak estimates are not substantially different, while the time-averaged estimates are 

approximately doubled. All of the uses assessed in 2009 were not updated to reflect these model 

input changes because of the insubstantial difference in acute exposure estimates. 

Table 4. PE Chemical Input Parameters for Oxamyl. 

Input Parameter Value Comment Source

Molecular Mass (g/mol) 219 Product chemistry data MRID 40499702 

Henry’s Law Constant A

(atm m3

/mol) 3.9 x 10-13 Product chemistry data 

Calculated from 

MRID 42526101, 

40499702 

Solubility in Water (mg/L) 2.8 x 105 Product chemistry data MRID 40499702 

Organic Carbon Partition 

Coefficient (KOC) (L/kgOC) 35 Mean of five KOC values MRID 46237301 

Aerobic Soil Metabolism 

Half-life (days) 52 Upper 90% confidence bound on the mean of six half-lives 

MRID 63012 

MRID 42820001 

MRID 45176602 

Aerobic Aquatic Metabolism 

Half-life (days) B 0 Aqueous degradation is indistinguishable from that due to hydrolysis. MRID 45045305 

Anaerobic Aquatic 

Metabolism Half-life (days) 0 Assumed stable in the absence of data. Aqueous degradation will be dominated by hydrolysis. Not applicable 

Hydrolysis Half-life (days) 8.0 Half-life at pH 7 MRID 40606516 

Aqueous Photolysis 

Half-life (days) 14 Maximum environmental phototransformation half-life 

MRID 40606515; 

41058801 

A The Henry’s Law Constant value of 3.9 x 10-13 atm m3/mol was used to model uses assessed or updated in 2010. 

The remaining uses assessed in 2009 were modeled with a vapor pressure input (3.8 x 10-7 torr) instead. 

B The aerobic aquatic metabolism half-life model input was updated to zero for uses assessed or updated in 2010. 

For the remaining uses that were assessed in 2009, the aerobic aquatic metabolism half-life was 6.6 days.

Use Pattern Inputs 

 The model input parameters used in PRZM to simulate oxamyl application and crop 

management practices are provided in Table 5. Explanations of the selected model input values 

and scenarios are provided in the previous assessments. Updates to the model input parameters 

in this assessment relative to previous assessments include: 1) the removal of the South Texas 

vegetable scenario for modeling use on carrots (due to the poor drainage of the heavy clay soil of 

the scenario), 2) an initial application date of August 9th rather than September 7th for modeling 

use on cotton with the Mississippi cotton scenario (in order to be consistent with the modeled 

crop timing), and 3) an initial application date of October 25th rather than April 1st for modeling 

use on eggplant with the Florida pepper scenario (also to be consistent with the modeled crop 

timing). Furthermore, whereas the 2010 DWA assessed two different use patterns for single 

PRZM scenarios for uses on celery and eggplant, this update restricts all use and PRZM scenario 
Page 6 of 19

combinations to one use pattern each, whichever use pattern results in the highest exposure 

estimates. This means that 1) the aerial use pattern for the Florida cabbage scenario used to 

assess use on celery and 2) the nematode-control use pattern with two initial applications of 2.0 

lbs a.i./A followed by two applications of 1.0 lb a.i./A used to assess use on eggplant in the 2010 

DWA have been removed. 

Table 5. PRZM Scenarios and Input Parameters Describing Maximum Oxamyl Use Patterns. 

Uses Scenario

Date of 

Initial 

App. 

App. Rate

(lbs 

a.i./A) 

App. 

per 

Year

App. 

Interval 

(days) 

CAM 

Input

IPSCND 

Input 

Application 

Efficiency/ 

Spray Drift

PA apple STD 

NC apple STD 

OR apple STD 

Apple (bearing fruit) 

CA fruit STD 

Apr. 1 2.0 1 N/A 2 3 0.99/0.064

Banana/plantain PR coffee STD Sep. 1 4.0 1 N/A 1 3 0.99/0.064

CA row crop RLF Jan. 11 1.0, 4.0 A 14, 309 A

Carrot PA vegetable NMC May 7

FL carrot STD Oct. 13

4.0, 1.0 B 4 14 

2 1 0.99/0.064

CA row crop RLF 1.0 6 5 0.95/0.16 Celery 

FL cabbage STD 

Jan. 15

2.0 3 21 

2 1 

0.99/0.064

CA citrus STD Oct. 1 2.0 3 30 2 3 0.99/0.064

Citrus (bearing fruit) STX grapefruit NMC

FL citrus STD 

Apr. 1 1.0 6 15 2 3 0.95/0.16 

CA cotton STD Sep. 20 1.0 3 

NC cotton STD Aug. 1

TX cotton OP Sep. 15

STX cotton NMC Jul. 20

Cotton 

MS cotton STD Aug. 9

0.50 6 

6 2 1 0.95/0.16 

CA melons RLF May 16

STX melon NMC Feb. 1

MO melon STD Apr. 10

MI melon STD Apr. 30

FL cucumber STD Oct. 16

Cucumber 

NJ melon STD May 1

1.0 6 7 2 1 0.95/0.16 

CA onion STD Jan. 16 14 

WA onion NMC Jun. 15

2.0, 0.5 C 3 

5 D

PA vegetable NMC May 24

Dry onion 

GA onion STD Oct. 1

2.0 2 14 

2 1 0.99/0.064

CA row crop RLF Jan. 15

CA tomato STD Jul. 15

Eggplant 

FL tomato STD Apr. 1

1.0 6 7 2 1 0.99/0.064
Page 7 of 19

Table 5. PRZM Scenarios and Input Parameters Describing Maximum Oxamyl Use Patterns. 

Uses Scenario

Date of 

Initial 

App. 

App. Rate

(lbs 

a.i./A) 

App. 

per 

Year

App. 

Interval 

(days) 

CAM 

Input

IPSCND 

Input 

Application 

Efficiency/ 

Spray Drift

FL pepper STD Oct. 25

PA tomato STD Jul. 15

PA vegetable NMC Aug. 1

STX vegetable NMC Jan. 15

Mint OR mint STD Apr. 15 2.0 2 21 2 1 0.99/0.064

CA fruit STD 

CA citrus STD 

FL citrus STD 

GA peach STD 

Mar. 1

MI cherry STD May 1

NC apple STD 

OR apple STD 

Orchard BSS 

WA orchard NMC 

Apr. 1

PA apple STD Apr. 16

Non-bearing fruit 

STX grapefruit NMC Mar. 16

1.0 8 7 2 3 0.95/0.16 

Peanut NC peanut STD May 30 0.5 8 14, 5 E 2 1 0.95/0.16 

PA apple STD 

NC apple STD 

OR apple STD 

WA orchard NMC 

Pear (bearing fruit) 

TX orchard BSS 

Mar. 1 2.0 1 N/A 2 3 0.99/0.063

CA row crop RLF Jan. 1 

STX vegetable NMC Oct. 1

PA vegetable NMC May 10

Pepper 

FL pepper STD Sep. 1

1.0 6 7 2 1 0.95/0.16 

CA potato RLF Apr. 15

IDN potato STD Aug. 1

WA potato NMC Jul. 15

FL potato NMC Mar. 1

8 

Potato 

ME potato STD Jun. 15

1.0 

6 

5 2 1 0.95/0.16 

FL potato NMC Dec. 13 Sweet potato 

NC sweet potato STD Apr. 26

2.0, 4.0 F 2 5 F 4 F 1 0.99/0.064

Tobacco NC tobacco STD Apr. 15 2.0 1 N/A 4 G 2 0.99/0.064

Tomato CA tomato STD Apr. 1

STX vegetable NMC Nov. 15

1.0 8 5 2 1 0.95/0.16 
Page 8 of 19

Table 5. PRZM Scenarios and Input Parameters Describing Maximum Oxamyl Use Patterns. 

Uses Scenario

Date of 

Initial 

App. 

App. Rate

(lbs 

a.i./A) 

App. 

per 

Year

App. 

Interval 

(days) 

CAM 

Input

IPSCND 

Input 

Application 

Efficiency/ 

Spray Drift

FL tomato STD Mar. 24

PA tomato STD Aug. 15

A Because the initial application occurs in December, this use pattern was modeled with 3 applications at 1.0 lb 

a.i./A, 14 days apart, beginning January 11th and followed 309 days later, in December, by the next season’s 

initial application of 4.0 lbs a.i./A. 

B The initial application is 4.0 lbs a.i./A, followed by 3 applications at 1.0 lb a.i./A. 

C The initial two applications are 2.0 lbs a.i./A, followed by one application at 0.5 lbs a.i./A. 

D Interval is assumed in the absence of a labeled value. 

E Interval of 14 days is labeled for the second application. Interval of 5 days is assumed for following applications 

in the absence of a labeled value. 

F The initial application is 2.0 lbs a.i./A incorporated to a 10-cm-depth, followed by an application at 4.0 lbs a.i./A 

applied in-furrow at transplant (CAM value set to 4 for all applications). Interval of 5 days is assumed in the 

absence of a labeled value. 

G Application is incorporated to a 10-cm depth. 

 PE exposure estimates for uses within the contiguous United States were multiplied by 

the default national percent cropped area factor (PCA), which is 87% (Effland et al., 1999). PE 

exposure estimates for uses constrained to Hawai’i and/or Puerto Rico were not adjusted by a 

PCA value because PCA values are not available for these areas. 

Regional PCA Refinement 

A previous dietary risk assessment determined that dietary levels of concern (for food 

plus water and accounting for number of eating occasions per day) were not exceeded when 

EDWC time series were represented by a 1-in-10-year peak value below approximately 80 μg/L 

(personal communication with Sheila Piper, Nov. 19, 2008). This back-calculated point estimate 

used to evaluate probabilistic distributions was revisited recently due to a reevaluation of toxicity 

data upon which the FQPA factor is based. Although the reevaluation resulted in a reduction of 

the FQPA factor, this cut-off point could not be raised to a higher value with certainty because of 

variability in the drinking water distributions for different crops (email communication with 

Mohsen Sahafeyan, May 26, 2010). Therefore, the cut-off point of 80 μg/L was retained as an 

approximate level of concern. 

As with past drinking water exposure assessments, this assessment update applies 

regional PCA refinements for uses within the contiguous United States for which initial acute 

exposure estimates (adjusted by the national default PCA) exceed 80 μg/L. These uses were 

refined by applying default regional PCA values that account for the highest extent of HUC-8 

watershed in the HUC-2 regions on which agricultural crops are grown (Effland et al., 1999). 

Figure 1 displays the 18 regions (or HUC-2 watershed basins) of the contiguous United States 

for which regional PCA factors were calculated. This refinement could not be conducted with 

exposure estimates for uses constrained to Hawai’i and/or Puerto Rico because PCA values, 

including regional PCA values, are not available for these areas. Further explanation of this 

refinement process is contained in the previous drinking water exposure assessments. 
Page 9 of 19

Figure 1. The Eighteen HUC-2 Watershed Basins of the Contiguous United States. 

Table 6 lists the PRZM scenarios assigned to each use-PCA region combination where 

oxamyl might be applied. The only update in Table 6 relative to the previous assessments is 

that, for carrots, the Florida carrot scenario replaced the South Texas vegetable scenario 

assignment for PCA regions 8, 11, 12, and 13. 
Page 10 of 19

Table 6. Scenario assigned to each combination of use and major basin (HUC-2 region). 

Major 

Basin # 

Basin 

Name 

Regional 

PCA Carrot Celery Citrus Cotton Cucumber Dry bulb onion Eggplant Non-bearing fruit 

East of Eastern Divide

1 New England 14 PA vegetable NMC – – – NJ melon STD – PA tomato STD PA apple STD PA 2 Mid Atlantic 46 PA vegetable NMC FL cabbage STD – NC cotton STD NJ melon STD – PA tomato STD PA apple STD PA 3 South Atlantic 38 FL carrot STD FL cabbage STD FL citrus STD MS cotton STD FL cucumber STD – FL pepper STD FL citrus STD FL p

Mid-Continent (Mississippi River Basin)

4 Great Lakes 77 PA vegetable NMC FL cabbage STD – – MI melon STD PA vegetable NMC PA tomato STD MI cherry STD PA 5 Ohio 82 PA vegetable NMC FL cabbage STD – – MO melon STD – PA tomato STD PA apple STD PA 6 Tennessee 38 PA vegetable NMC – – MS cotton STD MO melon STD – FL pepper STD NC apple STD PA 7 Upper Mississippi 85 PA vegetable NMC – – – MI melon STD – PA tomato STD MI cherry STD PA 8 Lower Mississippi 85 FL carrot STD – STX grape- fruit NMC MS cotton STD MO melon STD – STX vegetable NMC GA peach STD STX 9 Souris 83 PA vegetable NMC – – – – – PA tomato STD – PA 

10 Missouri 87 PA vegetable NMC – – – MO melon STD – PA tomato STD MI cherry STD PA 11 Arkansas 80 FL carrot STD FL cabbage STD – TX cotton OP MO melon STD WA onion NMC STX vegetable NMC Orchard BSS STX 12 Texas Gulf 67 FL carrot STD FL cabbage STD STX grape- fruit NMC STX cotton NMC STX melon NMC GA onion STD STX vegetable NMC Orchard BSS STX 13 Rio Grande 28 FL carrot STD FL cabbage STD – TX cotton OP – CA onion STD STX vegetable NMC CA citrus STD STX 

West of Western Divide

14 Upper Colorado 7 CA row crop RLF CA row crop RLF – – – – CA tomato STD OR apple STD CA 15 Lower Colorado 11 CA row crop RLF CA row crop RLF CA citrus STD CA cotton STD – CA onion STD CA tomato STD CA citrus STD CA 16 Great Basin 28 CA row crop RLF CA row crop RLF – – – – CA tomato STD OR apple STD CA 17 Pacific Northwest 63 CA row crop RLF – – – CA melon RLF WA onion NMC CA tomato STD OR apple STD CA 18 California 56 – CA row crop RLF CA citrus STD CA cotton STD CA melon RLF CA onion STD CA tomato STD CA fruit STD CA 
Page 11 of 19

2. Exposure Modeling Results 

2.1. Tier I Results 

Tier I modeling results of the 2010 DWA did not change in this assessment update 

because model input parameters were not updated. Screening acute and chronic exposure 

estimates in surface water drinking water sources from FIRST are listed in Table 7. Use on 

pineapple resulted in the highest estimated peak exposure (593 μg/L). 

Table 7. Tier I Estimated Drinking Water Concentrations (EDWCs) from 

Use of Oxamyl on Ginger Root, Pineapple, or Yams (values >80 μg/L are 

bolded). 

Use (modeled rate) Peak (μg/L) Annual Mean (μg/L)

Ginger root (8.0 lbs a.i./A/year) 279 6.6 

Pineapple (8.0 lbs a.i./A/year) 593 14 

Yams (4.0 lbs a.i./A/year) 218 5.1 

Exposure Characterization with Provisional PE Scenarios 

 Because Tier I modeling of the uses on ginger root, pineapple, and yams produced peak 

exposure estimates >80 μg/L, a provisional Tier II modeling approach was used to characterize 

potential refinement of these estimates. Unrelated scenario and metfile data were paired for 

modeling because surrogate PRZM scenarios were not available for these uses in Hawai’i or 

Puerto Rico but meteorological data (i.e., “metfiles”) were available for locations near where the 

modeled crops are grown. Modeling local metfiles was expected to increase the 

representativeness of modeled surrogate scenarios because the PE model is sensitive to 

precipitation. Therefore, the metfile for Hilo, Hawai’i (w21504) was used to model use on 

ginger root grown in Hawai’i, since it is near where most ginger root is grown on the Hawaiian 

Islands (USDA, 2010e). The metfile for San Juan, Puerto Rico was used for yams grown in 

Puerto Rico because it is the only metfile available for the Territory. And lastly, because 

pineapple is grown in both Puerto Rico and Hawai’i (but mostly on Oahu and Maui), metfiles for 

San Juan, Puerto Rico; Honolulu, Hawai’i; and Kahului, Hawai’i were used to model use on 

pineapple. This provisional approach was not changed in this assessment update. 

 Surrogate PRZM scenarios were selected for this provisional modeling refinement based 

on crop similarity and without regard to location because local surrogate scenarios were not 

available. More specifically, the Florida potato scenario was used to model use on ginger root 

and yams and the Florida cabbage scenario was used to model use on pineapples. These 

surrogate scenarios were selected for modeling rather than other potato or row crop scenarios 

because their vulnerability to runoff is higher than that of other scenarios (with the exception of 

that of the South Texas vegetable scenario). 

Table 8 lists the PRZM scenarios, metfiles, and input parameters that were used for this 

provisional refinement. Two use patterns were modeled for use on ginger root in order to 

evaluate exposure from different application methods and timing. The first use pattern is a perplant application of 4.0 lbs a.i./A that is incorporated to a depth of 5 cm. The second use pattern 
Page 12 of 19

is eight foliar (post-emergent) applications of 1.0 lb a.i./A, 30-days apart. Updates with respect 

to the previous assessment include changes in the initial application dates for yams and ginger 

root. The initial application date for yams was pushed forward from January 1st to February 15th

in order to occur approximately two months after planting, as directed by the label, consistent 

with the PRZM scenario. The initial application date for post-emergent foliar applications to 

ginger root was changed from January 15th to April 4th in order to better approximate the 

application timing that may occur in the spring. The initial application date for pre-plant 

incorporated applications was not changed to the spring because it should not occur after the 

crop emergence date in the PRZM scenario, which is January 1st

. 

Table 8. PRZM Scenarios, Meteorological Files, and Input Parameters for Tier II Characterization of Tier I 

Modeled Use Patterns. 

Use Scenario Metfile 

Location

Date of 

Initial 

App. 

App. Rate

(lbs 

a.i./A) 

App. 

per 

Year

App. 

Interval 

(days) 

CAM 

Input

IPSCND 

Input 

Application 

Efficiency/ 

Spray Drift

Dec. 15 4.0 1 None 4A

Ginger root FL potato NMC Hilo, HI 

Apr. 4 1.0 8 30 2 

1 0.99/0.064

Honolulu, HI

Pineapple FL cabbage STD Kahului, HI 

San Juan, PR

Oct. 16 2.0 4 14 2 1 0.99/0.064

Yams FL potato NMC San Juan, PR Feb. 15 0.5 8 14 2 1 0.99/0.064

A Application is pre-plant at 4.0 lbs a.i./A, incorporated (CAM 4) to a 5-cm minimum depth. 

Exposure estimates from this provisional refinement are listed for characterization in

Table 9. The results indicate that the Tier I exposure estimates were conservative, but not 

unreasonable. With respect to Tier I values, this provisional refinement approach reduces peak 

EDWCs from 218 μg/L to 108 μg/L for use on yams, from 593 μg/L to 351 μg/L for use on 

pineapple, and from 279 μg/L to 269 μg/L for use on ginger root. Updates with respect to the 

previous assessment include a decrease in the peak EDWC for post-emergent foliar applications 

to ginger root from 392 μg/L to 269 μg/L and an increase in the peak EDWC for use on yams 

from 87 μg/L to 108 μg/L (both changes were caused by updated application dates for the uses). 

Table 9. Tier II Characterization of EDWCs from Use of Oxamyl on Ginger Root, Pineapple, or Yams 

(values >80 μg/L are bolded). A

Use (modeled rate) PCA B PRZM Scenario/ Metfile 

1-in-10 

Year Peak 

(μg/L)

1-in-10-Year 

Annual Mean 

(μg/L)

30-Year 

Mean 

(μg/L) 

Ginger root (4.0 lbs a.i./A/year) C 266 6.7 2.2 

(8.0 lbs a.i./A/year) C 100% FL potato NMC/ Hilo 269 13 6.6 

FL cabbage STD/ Honolulu 351 13 5.2 

Pineapple (8.0 lbs a.i./A/year) 100% FL cabbage STD/ Kahului 167 7.3 3.0 

FL cabbage STD/ San Juan 177 7.1 3.7 

Yams (4.0 lbs a.i./A/year) 100% FL potato NMC/ San Juan 108 5.0 2.8 

A Each table row corresponds to the same row, in order, in Table 8. 

B The PCA for uses outside of the contiguous United States is 100%. 

C The first use pattern for ginger root is one incorporated application of 4.0 lbs a.i./A. The second use pattern is 

eight foliar applications of 1.0 lb a.i./A, 30-days apart. 
Page 13 of 19

Refined EDWCs for each use remained above 80 μg/L. If surface water drinking water 

intakes in Hawai’i and Puerto Rico are located in streams rather than reservoirs down-gradient 

from these uses, these EDWCs may underestimate the potential peak exposure and overestimate 

the potential time-averaged exposure resulting from these uses because less dilution will occur in 

the lower-volume streams that also provide less residence time than the modeled index reservoir. 

The relevance of the index reservoir to these situations is uncertain. 

2.2. Tier II Results 

Acute and chronic exposure estimates in surface water drinking water sources from PE 

are listed in Table 10. Only one PRZM scenario is listed per use. The listed scenario is the 

scenario from Table 5 that resulted in the highest 1-in-10-year peak EDWC (accounting for PCA 

adjustments). 

Exposure estimates for uses within the contiguous United States were adjusted by the 

default national PCA (87%) where exposure from that use was initially below 80 μg/L. 

Exposure estimates for the remainder of uses within the contiguous United States were adjusted 

by the default regional PCA associated with the maximum EDWC for the use listed in Table 12

(this was not done for the uses on celery and eggplant in the 2010 DWA). Exposure estimates 

for uses in other areas were not adjusted by PCA values (i.e., PCA=100%) because PCA values 

for areas outside of the contiguous United States are not available. 

Based on the updated input values, reported estimates in Table 10 for carrots and cotton 

have changed with respect to those of the previous assessments. The PRZM scenario and 

regional PCA listed for cotton have changed from Mississippi cotton and 85% to Texas cotton 

and 80% because the updated exposure estimates for the Mississippi scenario were below those 

of the Texas scenario. Also, unlike the previous DWA, multiple rows of EDWCs are not 

reported for uses on celery and eggplant. Oxamyl use on bananas/plantains, carrots, celery, 

cotton, cucumbers, dry bulb onions, eggplant, non-bearing fruit, peppers, potatoes, and tomatoes 

resulted in 1-in-10-year peak exposure estimates greater than 80 μg/L. 

Table 10. Tier II Estimated Drinking Water Concentrations (EDWCs) Adjusted by Maximum PCAs 

Resulting from Application of Oxamyl. 

Use 

(modeled rate) PCA A PRZM Scenario 1-in-10 Year Peak (μg/L)

1-in-10-Year 

Annual Mean 

(μg/L)

30-Year 

Mean 

(μg/L) 

Apples (2.0 lbs a.i./A/year) 87% PA apple 27 0.58 0.27 

Banana/plantain (4.0 lbs a.i./A/year) 100% PR coffee 204 6.3 2.3 

Carrots (7.0 lbs a.i./A/year) 85% FL carrot 161 5.4 3.3 

Celery (6.0 lbs a.i./A/year) 82% FL cabbage 138 5.2 2.7 

Citrus (6.0 lbs a.i./A/year) 38% FL citrus 70 1.6 1.0 

Cotton (3.0 lbs a.i./A/year) 80% TX cotton 96 2.4 1.1 

Cucumbers (6.0 lbs a.i./A/year) 67% STX melon 147 3.3 1.8 

Dry bulb onions (4.0 lbs a.i./A/year) 67% GA onion 90 1.9 0.52 

Eggplant (6.0 lbs a.i./A/year) 85% STX vegetable 237 9.1 3.6 

Mint (4.0 lbs a.i./A/year) 87% OR mint 12 0.40 0.24 
Page 14 of 19

Table 10. Tier II Estimated Drinking Water Concentrations (EDWCs) Adjusted by Maximum PCAs 

Resulting from Application of Oxamyl. 

Use 

(modeled rate) PCA A PRZM Scenario 1-in-10 Year Peak (μg/L)

1-in-10-Year 

Annual Mean 

(μg/L)

30-Year 

Mean 

(μg/L) 

Non-bearing fruit (8.0 lbs a.i./A/year) 38% FL citrus 124 3.1 1.5 

Peanut (4.0 lbs a.i./A/year) 87% NC peanut 55 2.3 1.6 

Pear (2.0 lbs a.i./A/year) 87% NC apple 41 1.3 0.41 

Peppers (6.0 lbs a.i./A/year) 85% STX vegetable 256 4.7 2.2 

Potatoes (8.0 lbs a.i./A/year) 85% FL potato 243 6.4 3.1 

Sweet potato (6.0 lbs a.i./A/year) 87% NC sweet potato 59 1.9 0.82 

Tobacco (2.0 lbs a.i./A/year) 87% NC tobacco 7.2 0.25 0.18 

Tomatoes (8.0 lbs a.i./A/year) 85% PA tomato 208 4.5 2.4 

A Percent Cropped Area (PCA) values were used to adjust EDWCs. PCA values are the default national PCA 

(87%) for initial exposure estimates <80 μg/L for uses within the contiguous United States, the default regional 

PCA associated with the maximum EDWC for the use in Table 12 for other uses within the contiguous United 

States, and 100% for areas outside of the contiguous United States. 

Guidance indicates that the hydrolysis rate at pH 7 (half-life of 8.0 days for oxamyl) 

should be modeled, which was done for exposure estimation. However, oxamyl is relatively 

stable to hydrolysis in acidic water bodies. Therefore, exposure estimates in acidic water bodies 

are expected to be higher than those modeled in this assessment. As an example, use on 

plantains and bananas (crops that are mainly grown on soils of pH 4.5-5.5 in Puerto Rico; 

USDA, 2010) is considered. If exposure is estimated using hydrolysis rates at pH 5 or 6, 

exposure estimates increase as shown in Table 11. These estimates were not changed in this 

assessment update. 

Table 11. Exposure Estimates for Oxamyl Use on Plantains and Bananas Using Hydrolysis 

Half-lives for Environments at pH 5, 6, or 7. 

Environmental pH Hydrolysis Half-life (days) 1-in-10 Year 

Peak (μg/L)

1-in-10-Year 

Annual Mean 

(μg/L)

30-Year Mean 

(μg/L) 

7 8.0 204 6.3 2.3 

6 63 209 31 12 

5 Stable 222 69 28 

Regional PCA Refinement 

 Regional PCA-adjusted 1-in-10-year peak EDWCs were tabulated for each combination 

of use and HUC-2 watershed basin for uses within the contiguous United States for which initial 

EDWCs exceeded 80 μg/L (Table 12). This refinement indicated that exceedances of 80 μg/L 

do not occur in the New England PCA region (Major Basin 1) or any PCA region west of the 

Continental Divide. Updates to input parameters resulted in updated EDWCs in Table 12 with 

respect to those in previous assessments, including values for carrots in PCA regions 8, 11, 12, 

and 13; for cotton in PCA region 8; and for eggplant in PCA regions 3 and 6. 
Page 15 of 19

Table 12. Regional PCA-refined 1-in-10-year Peak EDWCs for Oxamyl Uses Initially Exceeding 80 μg/L (values greater than 80 μg/L in 

Major 

Basin # Basin Name Regional PCA Carrot Celery Citrus Cotton Cucumber Dry bulb onion Eggplant Non-bearing fruit P

East of Eastern Divide

1 New England 14 13 – – – 7 – 22 14 2 Mid Atlantic 46 44 77 – 72 23 – 73 47 3 South Atlantic 38 71 64 70 55 105 – 124 124 

Mid-Continent (Mississippi River Basin)

4 Great Lakes 77 74 129 – – 29 52 122 38 5 Ohio 82 79 138 – – 68 – 130 84 6 Tennessee 38 37 – – 55 32 – 124 41 7 Upper Mississippi 85 82 – – – 32 – 134 42 8 Lower Mississippi 85 161 – 53 94 71 – 237 26 9 Souris 83 80 – – – – – 131 – 

10 Missouri 87 84 – – – 73 – 138 43 11 Arkansas 80 152 134 – 96 67 15 223 121 12 Texas Gulf 67 127 112 41 94 147 90 187 101 13 Rio Grande 28 53 47 – 34 – 4.3 78 9.0 

West of Western Divide

14 Upper Colorado 7 7.2 5.5 – – – – 4.5 2.6 15 Lower Colorado 11 11 8.6 3.4 5.1 – 1.7 7.1 3.5 16 Great Basin 28 29 22 – – – – 18 10 17 Pacific Northwest 63 65 – – – 7.7 12 41 23 18 California 56 – 44 17 26 6.8 8.7 36 28 
Page 16 of 19

Exposure Characterization for Reported Rates

In order to characterize reductions in exposure estimates resulting from potential changes 

to the proposed and currently labeled use patterns, usage data were requested from the Biological 

and Economic Analysis Division (BEAD) for the uses in Tables 9 and 12 for which EDWCs 

exceeded 80 μg/L. BEAD provided the requested usage data at the state-level (listed per crop 

stage for cotton) for the 2009 DWAs using data from 2003 to 2007 (DP barcode 359723; 

USEPA, 2009). Requested usage data at the state-level were also provided for the uses assessed 

in 2010 using data from 2004-2008 for celery and eggplant and direct communication with 

USDA personnel for the tropical uses bananas/plantains, ginger root, pineapple, and yams (DP 

barcode 377411; USEPA, 2010). Based on these data, “reported” or “actual” use patterns were 

identified (Table 13; analysis) for modeling with PRZM/EXAMS to estimate their resulting 

exposure and to explore whether the exposure would remain at levels expected to exceed 80 

μg/L. 

Updates to the 2009 assessments include 1) removal of the South Texas vegetable 

scenario for modeling use on carrots, 2) an increase in the re-application interval for use on 

carrots from 5 to 14 days in order to conform to label directions, and 3) an initial application date 

of August 9th rather than September 7th for modeling use on cotton with the Mississippi cotton 

scenario. Reported use patterns were not modeled for the uses assessed in the 2010 DWA; 

therefore, the reported use patterns listed for celery and eggplant in Table 13 are newly assessed 

in this DWA update. Reported use patterns are less than the maximum use patterns for each crop 

except for bananas/plantains, for which reported usage was at the maximum rate. 

Table 13. PRZM Input Parameters Describing “Reported” Oxamyl Use Patterns. 

Uses Scenario

Date of 

Initial 

App. 

App. Rate

(lbs 

a.i./A) 

App. 

per 

Year

App. 

Interval 

(days) 

CAM 

Input

IPSCND 

Input 

Application 

Efficiency/ 

Spray Drift

Banana/plantain PR coffee STD Sep. 1 4.0 1 N/A 1 3 0.99/0.064

PA vegetable NMC May 24 Carrot 

FL carrot STD Oct. 30

1.0 2 14 2 1 0.99/0.064

Celery FL cabbage STD Jan. 15 1.0 3 21 2 1 0.99/0.064

TX cotton OP Sep. 15

Cotton STX cotton NMC Jul. 20

MS cotton STD Aug. 9

0.50 2 6 2 1 0.95/0.16 

STX melon NMC Feb. 1 Cucumber 

FL cucumber STD Oct. 16

1.0 2 7 2 1 0.95/0.16 

Dry bulb onion GA onion STD Sep. 1 0.50 7 5 2 1 0.95/0.16 

FL pepper STD Oct. 25

Eggplant PA tomato STD Jul. 15

STX vegetable NMC Jan. 15

0.38 5 7 2 1 0.99/0.064
Page 17 of 19

Table 13. PRZM Input Parameters Describing “Reported” Oxamyl Use Patterns. 

Uses Scenario

Date of 

Initial 

App. 

App. Rate

(lbs 

a.i./A) 

App. 

per 

Year

App. 

Interval 

(days) 

CAM 

Input

IPSCND 

Input 

Application 

Efficiency/ 

Spray Drift

FL citrus STD Mar. 1

Non-bearing fruit PA apple STD Apr. 16

Orchard BSS Apr. 1

1.0 2 7 2 3 0.95/0.16 

Pepper STX vegetable NMC Oct. 1 1.0 2 7 2 1 0.95/0.16 

Potato FL potato NMC Jan. 1 1.5 2 7 2 1 0.99/0.064

STX vegetable NMC Nov. 15

Tomato FL tomato STD Mar. 24

PA tomato STD Aug. 15

1.5 3 5 2 1 0.99/0.064

The regional PCA-adjusted 1-in-10-year peak exposure estimates in surface water 

drinking water sources resulting from reported usage rates for crops within the contiguous 

United States are listed in Table 14 for the use-watershed region combinations that exceeded 80 

μg/L for the maximum labeled use patterns (cells with highlighted values in Table 12). Updates 

with respect to these values in previous assessments include reduced values for carrots in PCA 

regions 8, 11, 12, and 13 and for cotton in PCA region 8 and new values for celery and eggplant 

in the relevant PCA regions. 

The 1-in-10-year peak exposure estimate for use on bananas (204 μg/L) was unchanged 

from the estimate in Table 10 because reported usage on bananas was at the maximum labeled 

rate. 

Table 14. EDWCs (μg/L) from Reported Use Patterns by Use and by Regional PCA Specific to each Major 

Watershed Basin Where That Use May Occur (values >80 μg/L in bold).

Major 

Basin # Carrot Celery Cotton Cucumber Dry bulb onion Eggplant Non-bearing fruit Pepper Potato Tomato

2 – – – – – – – – – 86 

3 – – – 33 – 47 45 – 39 72 

4 – 65 – – – 35 – – – 144 

5 – 69 – – – 37 21 – – 153 

6 – – – – – 47 – – – 71 

7 29 – – – – 38 – – – 159 

8 75 – 32 – – 72 – 87 88 125 

9 29 – – – – 37 – – – –

10 30 – – – – 39 – – – –

11 71 67 56 – – 68 28 82 83 –

12 59 56 55 45 32 57 23 69 69 98 

13 25 – – – – – – 29 – – 

 These results indicate that reported application patterns reduce exposure estimates for 

most uses below target values. At the reported application patterns modeled for uses on carrots, 

celery, cotton, cucumbers, dry bulb onions, eggplant, and non-bearing fruit, estimated drinking 
Page 18 of 19

water exposure from any major basin does not exceed 80 μg/L (celery and eggplant analyses are 

new). However, use on tomatoes at reported application rates results in EDWCs that exceed 80 

μg/L in six watershed regions. Reported application rates for use on peppers and potatoes 

resulted in EDWCs that exceeded 80 μg/L by 10% or less in the Lower Mississippi and Arkansas 

watershed regions. Relative to the previous assessments, exposure estimates for reported 

application rates on carrots no longer exceed 80 μg/L. 

Table 15 lists reported use patterns for the tropical crops for which Tier I exposure was 

estimated and provisionally characterized with Tier II models in the 2010 DWA. Reported use 

patterns are less than the maximum use patterns for each crop except for the pre-plant application 

to ginger root (at 4.0 lbs a.i./A), for which reported usage was at the maximum rate. Because 

FIRST cannot model different application rates throughout the season, the ginger root use pattern 

of 4.0 lbs a.i./A pre-planting followed by four ground or foliar applications of 0.5 lbs a.i./A every 

30 days was approximated with two ground applications of 4.0 lbs a.i./A each, 60 days apart, and 

incorporated to a 5-cm depth. Because PE cannot model different application methods 

throughout the season, only the pre-plant application (at 4.0 lbs a.i./A) to ginger root was 

modeled (i.e., post-emergent applications were not modeled as well). 

Table 15. Tier I Input Parameters Describing “Reported” Oxamyl Use Patterns and Tier II PRZM 

Scenarios, Meteorological Files, and Input Parameters for Characterization of Tier I Modeled Use Patterns. 

Use Scenario Metfile 

Location

Date of 

Initial 

App. 

App. Rate

(lbs 

a.i./A) 

App. 

per 

Year

App. 

Interval 

(days) 

CAM 

Input

IPSCND 

Input 

Application 

Efficiency/ 

Spray Drift

Tier I Use Patterns 

Ginger root – 4.0 1 30 Ground app. incorp. to 5 cm 

Pineapple – 1.0 3 120 Ground app. 

Yams – 0.5 5 14 Ground app. 

Tier II Input Parameters 

Ginger root FL potato NMC Hilo, HI Dec. 15 4.0 1 None 4A 1 0.99/0.064

Pineapple FL cabbage STD Honolulu, HI Mar. 1 1.0 3 120 2 1 0.99/0.064

Yams FL potato NMC San Juan, PR Feb. 15 0.5 5 14 2 1 0.99/0.064

A Application is pre-plant at 4.0 lbs a.i./A, incorporated (CAM 4) to a 5-cm depth. 

Tier I exposure estimates in surface water drinking water sources resulting from reported 

usage rates for the tropical crops ginger root, pineapple, and yams are listed in Table 16. Tier II 

results from provisional modeling are provided in parentheses for characterization. Exposure 

resulting from reported rates has not been estimated prior to this DWA update. The results 

indicate that reported application patterns do not reduce exposure estimates for these uses below 

80 μg/L. 
Page 19 of 19

Table 16. EDWCs (μg/L) from Reported Use Patterns of ginger root, pineapple, and yams (values >80 μg/L 

in bold; provisional Tier II values are in parentheses). 

Use (modeled rate) PCA A (PRZM Scenario/ Metfile) 1-in-10 Year Peak 

(μg/L)

1-in-10-Year 

Annual Mean (μg/L)

Ginger root (4.0 lbs a.i./A/year) 100% (FL potato NMC/ Hilo) 198 (266) 4.7 (6.7) 

Pineapple (3.0 lbs a.i./A/year) 100% (FL cabbage STD/ Honolulu) 120 (149) 2.8 (5.2) 

Yams (2.5 lbs a.i./A/year) 100% (FL potato NMC/ San Juan) 171 (108) 4.0 (3.9) 

A The PCA for uses outside of the contiguous United States is 100%. 

3. References 

Effland, W. R., N. C. Thurman, I. Kennedy. 1999. Proposed Methods for Determining 

Watershed-derived Percent Crop Areas and Considerations for Applying Crop Area 

Adjustments to Surface Water Screening Models. Presentation to the FIFRA Science 

Advisory Panel, May 27, 1999. Online at: 

http://www.epa.gov/scipoly/sap/1999/index.htm

USEPA. 2009. Stebbins, K. State-Level Pesticide Usage Data Package in Support of EPA’s 

Drinking Water Risk Analysis for Existing and Pending Oxamyl Uses. DP Barcode 

359723. U.S. Environmental Protection Agency, Office of Prevention, Pesticides and 

Toxic Substances, Biological and Economic Analysis Division. Memorandum to the 

Environmental Fate and Effects Division, Special Review and Reregistration Division, 

and Registration Division. Feb. 3, 2009. 

USEPA. 2010. Stebbins, K. and C. Chen. Pesticide Usage Data in Support of EPA’s Drinking 

Water Exposure Assessment for Oxamyl. DP barcode 377411. U.S. Environmental 

Protection Agency, Office of Chemical Safety and Pollution Prevention, Office of 

Pesticide Programs. Memorandum from the Biological and Economic Analysis Division 

to the Environmental Fate and Effects Division and Pesticide Re-evaluation Division. 

May 19, 2010.