Page | 2 

field crops. There are no residential uses for oxamyl, and it is a member of the N-methyl 

carbamate (NMC) class of chemicals that share a common mechanism of toxicity and inhibit 

acetylcholinesterase. 

The Interim Reregistration Eligibility Decision (IRED) for Oxamyl was completed in 

October 2000, and the Reregistration Eligibility Decision (RED) for Oxamyl1

 was finalized in 

September 2007 upon completion of the Revised N-Methyl Carbamate Cumulative Risk 

Assessment. To evaluate dietary and drinking water exposures, the oxamyl RED used a 

combination of modeling, with the drinking water and dietary models typical of that time2

, and 

available surface and ground water monitoring data. The oxamyl RED determined that estimated 

environmental concentrations of oxamyl residues in surface and ground water were less than the 

acute drinking water level of concern (DWLOC) for the general population. Estimated 

concentrations of oxamyl residues in ground water were found to be potentially greater than the 

DWLOC for children 1 to 6 years of age, and of concern to EPA. To mitigate this potential risk 

and reduce dietary exposures for children in the ages 1 to 6 population subgroup, the registrant 

agreed to reduce the application rates for cotton and various other crops. Furthermore, the RED 

concluded that the food plus drinking water dietary assessment used conservative underlying 

assumptions (i.e., not accounting for the reversibility of cholinesterase inhibition or more refined 

food consumption patterns) which resulted in an overestimate of risk. 

 The September 2007 Revised N-Methyl Carbamate Cumulative Risk Assessment 

evaluated the effects of oxamyl together with all other NMC pesticides. The toxicological 

endpoints and modeling parameters for the cumulative assessment were different from those of 

the individual chemical risk assessments to prevent the compounding of conservative 

assumptions. For drinking water, the cumulative risk assessment relies on typical application 

rates and considers percent crop treated for the various chemicals that can be co-located in a 

watershed. No food or drinking water risk concerns were identified for oxamyl in the NMC 

cumulative assessment. 

In May 2007, DuPont Crop Protection (DuPont), the technical registrant for oxamyl, 

submitted a petition (PP6F7136) to EPA to establish a tolerance for the use of oxamyl on sugar 

beets, and in September 2007, they submitted another petition (PP7F7242) to establish a 

tolerance on wheat. In 2008, EPA received a proposed label amendment from DuPont to expand 

several existing uses of oxamyl. The above new use requests triggered the need for new risk 

assessments to determine if the requested actions would pose an unreasonable adverse effect to 

human health or the environment. The new assessments incorporated changes in methodology 

that had occurred since the previous assessment was completed for the RED. The primary 

change to the modeling was that instead of comparing a drinking water point estimate (the 

DWLOC) to estimated drinking water exposures, a 30-year distribution of drinking water 

exposure values was incorporated directly into the DEEM-FCID3

 model for dietary exposures. 

 

1

 The Oxamyl RED can be accessed at: http://www.epa.gov/pesticides/reregistration/REDs/oxamyl_red.pdf 2

 Pesticide Root Zone Model – Exposure Analysis Modeling System (PRZM-EXAMS) and Dietary Exposure 

Evaluate Model (DEEM) 3

 Dietary Exposure Evaluation Model – Food Consumption Intake Database, version 2.03 
Page | 3 

DEEM-FCID modeling currently includes exposures from food plus drinking water and accounts 

for the reversibility of acetyl cholinesterase inhibition caused by oxamyl4. 

Several rounds of drinking water and dietary risk assessments for approximately 20 use 

sites were conducted from 2009 to 2011 with increasing levels of refinement to evaluate the new 

use requests and the currently labeled uses of oxamyl. The early risk assessments identified 

several existing use sites where modeling refinements and/or mitigation measures were needed to 

address risk estimates above EPA’s level of concern. In December 2009, DuPont withdrew all 

of the new and expanded use requests until risk concerns identified with existing labeled uses of 

oxamyl were resolved. In October 2010, DuPont submitted a mitigation proposal to EPA for 

nine existing use sites. 

DuPont’s proposed mitigation, along with the Agency’s refined drinking water modeling 

and better characterization of drinking water exposure, led EPA to conclude that all dietary (food 

plus drinking water) risks of concern have been adequately addressed. Modeling conducted for 

all use site scenarios and refinements is explained in Section III of this document. Because 

exposure from food alone occupies only 13% of the acute dietary risk cup (i.e., aPAD) for 

infants and 16% for children ages 1 to 2, refinements focused on the drinking water exposure 

assessment. 

 A chronic dietary assessment is not required for oxamyl because, as is typical for Nmethyl carbamate pesticides, reactivation of the enzyme, and therefore, of acetyl cholinesterase 

activity, occurs within a period of hours. Therefore, acute inhibition of the acetyl cholinesterase 

enzyme is the exposure duration of concern. Further, because oxamyl is a restricted use 

pesticide and has no homeowner uses or other residential exposures, the aggregate assessment 

consists of food and drinking water exposures only. 

 Registration review is EPA’s program to periodically reevaluate pesticides to make sure 

that as the ability to assess risk evolves and as policies and practices change, products in the 

marketplace can continue to be used safely. The registration review process for oxamyl started 

in September 2010 when the initial docket was opened for public comment (EPA-HQ-OPP2010-0028) and coincided with the ongoing oxamyl registration actions. The Preliminary Work 

Plan (September 2010) and Final Work Plan (February 2011) for the registration review of 

oxamyl both stated that EPA was in the process of working with DuPont to resolve concerns 

with some existing uses. Although new human health and ecological risk assessments are 

planned as part of the registration review process, they are not expected to be completed until 

Spring 2015. Due to the length of time before the registration review risk assessments and 

regulatory decision, EPA determined it was appropriate to resolve the known oxamyl dietary risk 

concerns on an accelerated timeline. 

 

4

 The dietary modeling DEEM-FCID results were adjusted to obtain “eating occasions” results using a SAS 

algorithm to find the peak cholinesterase inhibition / exposure level in a day by accounting for the rise in exposure 

immediately upon eating and decay of the exposure to half its value after 150 minutes from ingestion. 
Page | 4 

III. RESULTS OF REFINED DIETARY (FOOD PLUS WATER) 

MODELING AND PROPOSED MITIGATION FOR ALL EXISTING 

USE SITES, EXCLUDING TROPICAL CROPS 

Results of the Agency’s refined dietary (food plus water) modeling are presented below in 

three groups: Group 1 use sites did not exceed EPA’s level of concern at the maximum labeled 

application rates and did not require mitigation; Group 2 use sites did not exceed EPA’s level of 

concern with mitigated use patterns (e.g., lower application rates); Group 3 use sites with 

mitigated use patterns resulted in aPADs greater than 100% for infants only. However, as 

discussed later in this document, EPA believes that its analyses likely overestimate oxamyl 

exposures and therefore risks, and that actual oxamyl exposures for the Group 3 use sites will be 

below the level of concern for infants and children ages 1 to 2. 

 For additional details regarding the drinking water and dietary modeling parameters and 

methodologies, please reference the following support documents located in the oxamyl 

registration review docket (EPA-HQ-OPP-2010-0028): 

- Oxamyl: Acute Aggregate (Food and Drinking Water) Dietary Exposure and Risk Assessments 

for the Currently Registered Uses And Drinking Water Residue Distributions Resulting From 

Maximum and/or Reported Rates on Banana, Carrot, Celery, Cotton, Eggplant, Ginger, Peanut, 

Pear, Pineapple, Sweet Potato, Tobacco, and Yam. M. Sahafeyan. July 15, 2010. 

- Update to Drinking Water Exposure Assessments for Current Uses of Oxamyl. G. Orrick. June 

15, 2010. 

a. GROUP 1 USE SITES 

The use sites in Table 1 were below EPA’s level of concern at the maximum labeled 

application rates using the Environmental Fate and Effects Division’s (EFED) standard Tier II 

drinking water modeling approach. These use sites did not require mitigation by the registrant 

for EPA to conclude that continued use would be “safe.” Use patterns and application rates as 

currently labeled on oxamyl products are acceptable. 

Table 1. Results of Oxamyl Acute Aggregate Dietary Risk Assessment at the 99.9th Percentile of 

Exposure Distribution for Infants and Children 1 – 2 Years Old for Existing Labeled Use Sites 

at Maximum Application Rates. 

Commodity 

%aPAD with Eating Occasions5

 Infants | Children 1 – 2 

Worst-case 

Drinking Water 

HUC-2 Region6

Percent Cropped 

Area (PCA) 

Apple 34 21 n/a7 (national default) 87

 

5

 Data source for %aPAD: Oxamyl Acute Aggregate (Food and Drinking Water) Dietary Exposure and Risk 

Assessments for the Currently-Registered Uses And Drinking Water Residue Distributions Resulting From 

Maximum and/or Reported Rates on Banana, Carrot, Celery, Cotton, Eggplant, Ginger, Peanut, Pear, Pineapple, 

Sweet Potato, Tobacco, and Yam. M. Sahafeyan. July 15, 2010. DP Barcode 378341. (pgs. 14-15). 6

 Data source for drinking water modeling: Update to Drinking Water Exposure Assessment for Current Uses of 

Oxamyl. G. Orrick. June 15, 2010. DP Barcode 378338. 
Page | 5 

Commodity 

%aPAD with Eating Occasions5

 Infants | Children 1 – 2 

Worst-case 

Drinking Water 

HUC-2 Region6

Percent Cropped 

Area (PCA) 

Citrus 75 37 Region 38 38

Mint 19 18 n/a7 (national default) 87

Onion 78 41 Region 128 67

Peanut 82 45 n/a7 (national default) 87

Pear 42 25 n/a7 (national default) 87

Sweet potato 71 39 n/a7 (national default) 87

Tobacco 19 17 n/a7 (national default) 87

b. GROUP 2 USE SITES 

The use sites listed in Table 2 resulted in dietary risks of concern (i.e., aPADs greater 

than 100%) when modeled at the maximum current labeled rates using the standard Tier II 

drinking water modeling approach. DuPont submitted a mitigation proposal to alter the use 

patterns for this group, which included lowering annual maximum application rates for certain 

states, reducing the number of applications per year, and requiring a specific soil incorporation 

depth. The proposed mitigation measures are explained in further detail following Table 2. As a 

result of proposed mitigation, aPADs for the use sites listed in Table 2 are below EPA’s level of 

concern. 

Table 2. Results of Oxamyl Acute Aggregate Dietary Risk Assessment at the 99.9th Percentile of 

Exposure Distribution for Infants and Children 1 – 2 Years Old for Existing Labeled Use Sites 

at DuPont’s Proposed Mitigated Application Rates. 

Commodity 

%aPAD with Eating Occasions Worst-case 

Drinking Water 

HUC-2 Region9

Percent Cropped 

Infants Children 1 – 2 Area (PCA) 

Cotton 80 44 Region 11 80

Cucurbits10 85 43 Region 12 67

Non-bearing fruit 74 39 Region 3 38

Peppers 72 38 Region 8 85

 DuPont proposed changes to existing labeled use sites on a regional basis depending on 

the regional areas of concern. EFED’s June 15, 2010 “Update to Drinking Water Exposure 

Assessments for Current Uses of Oxamyl” calculated 1-in-10-year peak estimated drinking water 

concentrations (EDWCs) for each crop for each HUC-2 region where that crop is grown and 

 7

 National level modeling conducted for this use site. 8

 There are eighteen HUC-2 watershed basins within the contiguous United States. Where estimated drinking water 

concentrations were high for a national, screening-level assessment using a default PCA of 87%, the drinking 

water modeling was refined to a regional basis using regional PCA factors. The HUC-2 region listed in the table 

represents the worst-case scenario which is assumed to be protective of all other regions. 9

 The HUC-2 region listed in the table represents the worst-case scenario which is assumed to be protective of all 

other regions. 10 Oxamyl is labeled for use on the following cucurbit crops only: cucumber, cantaloupe, honeydew melon, 

watermelon, squash, and pumpkin. 
Page | 6 

labeled for use. Regions were identified as potentially of concern if the EDWC exceeded the 

threshold concentration of 80 μg/L. Therefore, DuPont’s proposed mitigation was targeted 

towards the HUC-2 regions identified to have 1-in-10 year peak EDWCs > 80 μg/L. Proposed 

mitigations for Group 2 use sites are listed below. 

i. General Label Statement proposed by DuPont: 

 As part of its mitigation proposal, DuPont proposed to add the following general label 

statement to specify soil incorporation to a particular depth for all soil applications, including infurrow and shank applications. This proposed additional language would apply to directions for 

use for all oxamyl applications and would allow EPA to accurately specify a soil incorporation 

depth in the PRZM-EXAMS model. 

“All applications to the soil must be incorporated immediately after application to 

a depth of at least 2 inches by mechanical means or by water. For best results, 

Vydate® should be placed in the root zone of the plant. If irrigation is used to 

water in the application, use sufficient water to move the applied Vydate® at least 

2 inches deep in the soil. However, do not apply irrigation water such that the 

water moves off the field.” 

ii. Mitigation proposed by DuPont for cotton: 

 In AR, KS, LA, MS (west of I-55), OK, and TX, apply up to 0.5 pounds active 

ingredient per acre (lbs a.i./A) of oxamyl per individual application with a 

maximum of 4 foliar applications. 

 The minimum retreatment interval between all applications is 7 days. 

 Do not apply more than 1 gallon of product (2 lbs a.i. of oxamyl) per acre per 

season. 

 For all other states, application rates stay as specified on the current product label. 

iii. Mitigation proposed by DuPont for cucurbits: 

 In AL, FL, GA, MS, NC, SC, and TX (except Rio Grande Valley), apply up to 1 lb 

a.i./A oxamyl pre-plant, at-plant, or transplant. Foliar, drip and/or soil injection 

applications can also be made. Apply up to 1 lb a.i./A oxamyl with a maximum of 

3 applications. The minimum retreatment interval between all applications is 7 

days. 

 In AL, FL, GA, MS, NC, SC, and TX (except Rio Grande Valley), up to 2 lbs a.i./A 

oxamyl pre-plant, at-plant or transplant may be applied. However, if more than 1 lb 

a.i./A is applied pre-plant, at-plant, or transplant, allow at least 14 days before 

making subsequent foliar, drip and/or soil injection applications. Foliar, drip, 

and/or soil injection applications may be applied at a rate of up to 1 lb a.i./A of 

oxamyl with a maximum of 2 applications and a minimum retreatment interval of 7 

days.. 

 Do not apply more than 2 gallons of product (4 lbs a.i. of oxamyl) per acre per 

season. 

 For all other states, application rates stay as specified on the current product label. 
Page | 7 

iv. Mitigation proposed by DuPont for non-bearing fruit: 

 In AL, FL, GA, IN, KY, MS, NC, OH, SC, TX (except Rio Grande Valley), and 

WV, apply up to 2 lbs a.i./A oxamyl pre-plant, at-plant, or transplant. Foliar, drip, 

and/or soil injection applications can also be made. Apply up to 1 lb a.i./A oxamyl 

with a maximum of 5 applications. The minimum retreatment interval between all 

applications is 14 days. Do not apply more than 3.5 gallons of product (7 lbs a.i. 

oxamyl) per acre per season. 

 In AR, KS, and OK, apply up to 2 lbs a.i./A of oxamyl pre-plant, at-plant, or 

transplant. Foliar, drip, and/or soil injection applications can also be made. Apply 

up to 1 lb a.i./A with a maximum of 3 applications. The minimum retreatment 

interval between all applications is 14 days. Do not apply more than 2.5 gallons of 

product (5 lbs a.i. oxamyl) per acre per season. 

 For all other states, application rates stay as specified on the current product label. 

v. Mitigation proposed by DuPont for peppers: 

 In AR, KS, LA, MS, OK, and TX (except Rio Grande Valley), apply up to 1 lb 

a.i./A oxamyl at-plant or transplant. Foliar, drip, and/or soil injection applications 

can also be made. Apply up to 0.5 lbs a.i./A oxamyl with a maximum of 4 

applications. The minimum retreatment interval between all applications is 10 

days. Do not apply more than 1.5 gallons of product (3 lbs a.i. oxamyl) per acre per 

season. 

 In NM and TX (Rio Grande Valley), apply up to 1 lb a.i./A of oxamyl at-plant or 

transplant. Foliar, drip and/or soil injection applications can also be made. Apply 

up to 0.5 lbs a.i./A of oxamyl with a maximum of 5 applications. The minimum 

retreatment interval between all applications is 7 days. Do not apply more than 

1.75 gallons of product (3.5 lbs a.i. oxamyl) per acre per season. 

 For all other states, application rates stay as specified on the current product label. 

c. GROUP 3 USE SITES 

The use sites listed in Table 3 below, resulted in dietary risks of concern (i.e., aPADs 

greater than 100%) when modeled at the maximum current labeled rates and using the standard 

Tier II drinking water modeling approach. DuPont submitted a proposal to mitigate risks by 

altering the use patterns for these crops, which included lowering annual maximum application 

rates in certain states, reducing the number of applications per year, and requiring a specific soil 

incorporation depth. The proposed mitigation measures for each use site are explained in further 

detail below. Although the mitigation measures proposed for these crops greatly reduced the 

food plus drinking water dietary exposures for both infants and children, the modeling resulted in 

aPADs greater than 100% for infants. For children ages 1-2, the proposed mitigation reduced all 

modeled exposures to less than 100% of the aPAD, but for infants, the calculated aPADs were 

greater than 100%. See the modeling results in Table 3 below. 
Page | 8 

Table 3. Results of Oxamyl Acute Aggregate Dietary Risk Assessment at the 99.9th Percentile of 

Exposure Distribution for Infants and Children 1 – 2 Years Old for Existing Labeled Use Sites 

at DuPont Proposed Mitigated Application Rates. 

Commodity 

%aPAD with Eating Occasions 

 Infants | Children 1 – 2 

Worst-case 

Drinking Water 

HUC-2 Region11

Percent Cropped 

Area (PCA) 

Carrot 105 53 Region 8 85

Celery 121 64 Region 5 82

Eggplant 132 70 Region 8 85

Potato 102 54 Region 8 85

Tomato 143 77 Region 7 85

i. Mitigation proposed by DuPont for carrots: 

 In AR, CO, IA, IL, KS, LA, MN, MO, MS, MT, ND, NE, OK, SD, TN, TX (except 

Rio Grande Valley), WI and WY, apply up to 2 lbs a.i./A oxamyl pre-plant, at-plant 

or prior to emergence. All applications to the soil must be incorporated 

immediately to a minimum depth of 2 inches either by mechanical means or water. 

 Foliar applications can be made. In AR, CO, IA, IL, KS, LA, MN, MO, MS, MT, 

ND, NE, OK, SD, TN, TX (except Rio Grande Valley), WI and WY, apply up to 1 

lb a.i./A oxamyl with a maximum of 3 foliar applications. 

 The minimum retreatment interval between all applications is 14 days. 

 Do not apply more than 2.5 gallons of product (5 lbs a.i. oxamyl) per acre per 

season. 

 For all other states, application rates stay as specified on the current product label 

(except California, where use on carrots is not registered). 

ii. Mitigation proposed by DuPont for celery: 

 In MI, OH, PA, and TX (except Rio Grande Valley), apply up to 2 lbs a.i./A 

oxamyl pre-plant, at-plant or transplant. All applications to the soil must be 

incorporated immediately to a minimum depth of 2 inches either by mechanical 

means or water. Allow at least 14 days prior to making foliar applications. 

 Foliar applications can be made. In MI, OH, PA, and TX (except Rio Grande 

Valley), apply up to 1 lb a.i./A oxamyl with a maximum of 4 foliar applications. 

The minimum retreatment interval between foliar applications is 7 days. 

 Do not apply more than 3 gallons of product (6 lbs a.i. oxamyl) per acre per season. 

 For all other states, application rates stay as specified on the current product label. 

iii. Mitigation proposed by DuPont for eggplant: 

 In AL, CO, FL, GA, IA, IL, IN, KS, KY, MI, MN, MO, MS, MT, NC, ND, NE, 

OH, SC, SD,TN, WI, WV, and WY, apply up to 1 lb a.i./A oxamyl as a foliar, drip, 

or soil injection application with a maximum of 4 foliar applications. Do not apply 

more than 2 gallons of product (4 lbs a.i. oxamyl) per acre per season. 

 

11 The HUC-2 region listed in the table represents the worst-case scenario which is assumed to be protective of all 

other regions. 
Page | 9 

 In AR, KS, LA, OK, and TX (except Rio Grande Valley), apply up to 1 lb a.i./A 

oxamyl as a foliar, drip, or soil injection application with a maximum of 3 foliar 

applications. Do not apply more than 1.5 gallons of product (3 lbs a.i. oxamyl) per 

acre per season. 

 The minimum retreatment interval between all applications is 10 days. 

 For all other states, application rates stay as specified on the current product label. 

iv. Mitigation proposed by DuPont for potato: 

 In AL, AR, FL, GA, KS, LA, MS, NC, OK, SC and TX (except Rio Grande 

Valley), apply up to 2 lbs a.i./A oxamyl at planting. Incorporate to a minimum 

depth of 2 inches either by mechanical means or water. 

 Foliar applications can be made. Apply up to 1 lb a.i./A oxamyl with a maximum 

of 4 applications. 

 The minimum retreatment interval between all applications is 14 days. 

 Do not apply more than 3 gallons of product (6 lbs a.i. oxamyl) per acre per season. 

 For all other states, application rates stay as specified on the current product label. 

v. Mitigation proposed by DuPont for tomato: 

 In AL, AR, DE, FL, GA, IA, IL, IN, KY, LA, MD, MI, MN, MS, NC, NJ, NY, OH, 

PA, SC, TN, TX (except Rio Grande Valley), WV, VA, and WI, apply up to 2 lbs 

a.i./A oxamyl at-plant or transplant. Incorporate to a minimum depth of 2 inches 

either by mechanical means or water. 

 Foliar, drip and/or soil injection applications can be made. Apply up to 1 lb a.i./A 

oxamyl with a maximum of 7 applications. 

 The minimum retreatment interval between all applications is 7 days. 

 Do not apply more than 4 gallons of product (8 lbs a.i. oxamyl) per acre per season. 

 For all other states, application rates stay as specified on the current product label. 

For several reasons, discussed in further detail below, EPA believes that actual dietary 

exposures of infants to oxamyl residues on carrots, celery, eggplant, potato, and tomato are less 

than 100% of the aPAD and below EPA’s level of concern. Sensitivity analyses and the weightof-evidence suggests that, provided mitigation is incorporated into oxamyl product labels, actual 

exposures to infants are expected to be less than 100% of the aPAD. Specifically, the registrant 

conducted an assessment (MRID 48462501), which includes proposed mitigations (i.e. reductions in label guidance for both rates and numbers of applications on selected crops and regions) 

and regional PCA refinements excluding major crops (i.e., corn, soybeans, and wheat) to 

demonstrate that the exposures to infants for Group 3 use sites are expected to be less than 100% 

of the aPAD. DuPont will submit revised oxamyl product labels with the proposed mitigation, 

and once an on-going project to revise EPA’s PCA policy is completed, modeling for use of 

oxamyl on carrots, celery, eggplant, potato, and tomato will be reevaluated to confirm that 

aPADs are below the level of concern. 

There are three major factors in EPA’s drinking water modeling that influence the 

amount of a pesticide active ingredient and the estimated drinking water concentrations (EDWC) 

in a given watershed. The three factors are the application rate, estimates of the percent of the 

crop treated in a watershed (PCT), and the estimated percent of the cropped area in a watershed 
Page | 10 

(PCA). For screening-level drinking water modeling, EPA makes certain assumptions about 

each of these factors which are intended to be conservative and protective of all scenarios. 

However, application of these standard parameters to the oxamyl case likely overestimates 

drinking water exposures and thus risk, due to the relatively small acreage of most of the crops 

for which oxamyl is registered for use. 

EPA models all applications of a pesticide at the maximum labeled application rate 

because that rate may be legally applied by pesticide users. The Agency acknowledges that 

actual application rates are dependent on pest pressure, weather, and other factors, and that rates 

lower than the maximum are frequently used to control pests. For oxamyl, EPA has survey data 

indicating that rates lower than the legally-allowed maximum are often applied by growers, but 

these data are difficult to convert to a national or regional value that can be input to the drinking 

water model. For all of these reasons, EPA models all applications, for oxamyl and other single 

chemical assessments, at the maximum rate. 

 For the second factor, percent crop treated in a watershed, the Agency’s drinking water 

assessment assumes 100 percent of the cropped area is treated with the particular pesticide of 

interest. Although EPA knows that realistically less than 100% of planted acres of the Group 3 

crops are likely treated with oxamyl at the large HUC-2 watershed level, EPA lacks the data to 

confidently quantify the PCT on a small watershed scale. Thus, the default assumption of 100% 

is used in drinking water modeling. However, national survey data indicates that the percent of 

the crop treated for Group 3 use sites is significantly less than 100%. For a five year period from 

2006 to 2010, the average PCT for celery treated with oxamyl was approximately 40%; for 

potatoes, less than 20%; and for carrots and tomatoes, less than 5% of the crop was treated 

(Source: GfK Kynetec, 2006-2010). While the PCT does vary regionally, the highest PCT 

reported at the state level in the survey data for any of the Group 3 use sites was 52%. 

 The third major factor that affects drinking water modeling, PCA, represents the 

percentage of total agricultural land area within a watershed, and except for four main crops, 

PCAs do not distinguish between different crops grown within that area. The national default 

PCA of 87% is used as a conservative screening-level estimate for national-level drinking water 

assessments. This represents the HUC-8 watershed with the maximum amount of agriculture in 

the nation. At the next level of refinement, EPA uses regional default PCAs for each of the 18 

largest hydrologic regions (HUC-212) in the contiguous United States13. Because PCAs for the 

HUC-2 regions are selected from the highest PCA observed in any of its constituent HUC-8 

watersheds, they are the highest estimates for the entire region. 

To date, EPA has determined crop-specific PCAs only for four major field crops: corn, 

soybeans, wheat, and cotton. However, when modeling any crop other than corn, soybeans, 

wheat, or cotton, a default PCA, comprised of all agricultural land, is used. In 1999, the Federal 

Insecticide, Fungicide, and Rodenticide Act (FIFRA) Scientific Advisory Panel (SAP) 

determined that EPA did not have enough data to select crop-specific PCAs for crops other than 

the four field crops mentioned above. Out of the four major field crops, oxamyl is registered for 

use on cotton only. All other use sites for oxamyl are smaller acreage crops such as vegetables 

 

12 HUC-2 = 2-digit hydrological unit codes, HUC8 = 8-digit hydrological unit codes (smaller watershed area) 

13 See the HUC-2 map provided in Attachment 1. 
Page | 11 

and fruits. Because the majority of crops labeled for oxamyl use are relatively small acreage 

specialty crops rather than high acreage field crops, EPA believes that it is unlikely that 87% of 

any HUC-2 watershed will be dedicated to the smaller acreage fruit and vegetable crops of 

Group 3 use sites. Consequently, the standard PCAs can be expected to overestimate the land 

area to which oxamyl can be applied. 

Carrots: The default PCA for HUC-2 Region 8 is 85%, and this region represents the 

worst-case modeling scenario for carrots, resulting in the highest EDWC. Due to similar soil and 

weather patterns, HUC-2 Regions 11 and 12 also had similarly high EDWCs. HUC-2 Regions 8, 

11, and 12 are made up of Oklahoma, Louisiana, Arkansas, most of Texas, and smaller parts of 

Kansas, Mississippi, and several other neighboring states. Although EPA has not determined a 

specific PCA for carrots, carrot acreage in these regions is extremely small and limited to several 

counties, and oxamyl treated carrot acreage is even smaller (MRID 48462501). The major crops 

grown in HUC-2 Regions 8, 11, and 12 are soybeans, corn, cotton, rice, small grains, and 

pastureland, with carrots occupying only a very small portion of available cropland. As 

mentioned earlier, out of four major field crops, oxamyl is registered for use on cotton only, but 

all four major crops contribute to the default regional PCA. From what is known about carrot 

and other crop acreage and usage of oxamyl in these regions, EPA believes that the actual PCAs 

for oxamyl-registered crops based on HUC-8 watersheds are well below the currently used 85% 

PCA adjustment factor. 

EPA conducted a sensitivity analysis for HUC-2 Region 8, using a PCA of 65% to 

determine whether the estimated PCAs would need to be significantly lower for dietary 

exposures to be below EPA’s level of concern; this number was originally proposed by the 

oxamyl technical registrant, and while EPA cannot definitively confirm this figure, the lower 

number is not inconsistent with the national average and other available crop-specific 

information. Based on this analysis, dietary exposure to infants was calculated to be 80% of the 

aPAD. With DuPont’s proposed mitigation for use of oxamyl on carrots and actual use intensity 

of oxamyl on carrots and other crops, EPA believes that exposure in drinking water would be 

lower than the assumed threshold concentration of 80 μg/L and would have a low potential to 

exceed dietary risks of concern from oxamyl use on carrots. EPA will confirm that the aPAD for 

carrots is below the level of concern once ongoing revisions to EPA’s PCA policy have been 

completed. 

Celery: HUC-2 Region 5, comprised of large parts of Ohio, Indiana, Kentucky, 

Pennsylvania, and West Virginia and small parts of Illinois, Tennessee, and other surrounding 

states, was the worst-case modeling scenario, with the highest EDWC for celery. The default 

PCA for this region is 82%. HUC-2 Regions 4 (Michigan) and 11 (Oklahoma and parts of 

Texas, Kansas, and Arkansas) also had high EDWCs. The major agricultural uses in HUC-2 

Regions 4, 5, and 11 are corn, soybeans, small grains, and pastureland with celery occupying 

only a very small portion of available cropland. All major crops, however, contribute to the 

default regional PCA. From what is known about celery and other oxamyl-registered crops in 

these regions, actual PCAs based on HUC-8 watersheds are expected to be well below the 

currently used 82% PCA adjustment factor. 
Page | 12 

EPA conducted a sensitivity analysis for HUC-2 Region 5 using a PCA of 53%. This 

number was proposed by the technical registrant, and while EPA cannot definitively confirm this 

figure, it is not inconsistent with the national average and other available information. Based on 

this analysis, dietary exposure to infants from celery was calculated to be 78% of the aPAD. 

With DuPont’s proposed mitigation for use of oxamyl on celery and the actual use intensity of 

oxamyl on celery and other crops in the region, EPA believes that exposure in drinking water 

would be lower than the assumed threshold concentration of 80 μg/L and has a low potential to 

exceed dietary risks of concern from oxamyl uses on celery. EPA will confirm that the aPAD for 

celery is below the level of concern once ongoing revisions to EPA’s PCA policy have been 

completed.

Eggplant: HUC-2 Region 8, with a default PCA of 85%, resulted in the worst-case 

modeling scenario for eggplant. HUC-2 Regions 11 and 12 also had notably high EDWCs. 

Eggplant production in these regions is limited to a few counties and encompasses extremely low 

acreage (MRID 46482501). Again, the major agricultural uses in these regions, which consume 

a large share of available cropland and contribute to the default regional PCA, are soybeans, 

corn, cotton, rice, small grains, and pastureland. From what is known about eggplant and other 

oxamyl-registered crop acreage, actual PCAs based on HUC-8 watersheds are expected to be 

well below the currently used 85% PCA adjustment factor. 

EPA conducted a sensitivity analysis for HUC-2 Region 8 using a PCA of 44%, and 

dietary exposure to infants from eggplant was calculated to be 69% of the aPAD. The PCA 

adjustment factor used in the sensitivity analysis was estimated by removing the major field 

crops corn, soybeans, and wheat from the calculation because they are not registered use sites for 

oxamyl. With DuPont’s proposed mitigation for use of oxamyl on eggplant and the actual use 

intensity of oxamyl on eggplant, EPA believes that exposure in drinking water would be lower 

than the assumed threshold concentration of 80 μg/L and has a low potential to exceed dietary 

risks of concern from oxamyl uses on eggplant. EPA will confirm that the aPAD for eggplant is 

below the level of concern once ongoing revisions to EPA’s PCA policy have been completed.

Potato14: For potato, HUC-2 Region 8, with a default PCA of 85%, resulted in the 

worst-case modeling scenario. Due to similar soil and weather patterns in HUC-2 Regions 11 

and 12, these regions also had high calculated EDWCs. Again, the major agricultural uses in 

these regions, which consume a large share of available cropland, are soybeans, corn, cotton, 

rice, small grains, and pastureland. Potatoes are not a major crop produced in these regions, and 

account for only a very small portion of available cropland (MRID 48462501). However, 

presence of major crops like corn, soybean, and small grains contribute to the default regional 

PCA calculations and consequently, higher EDWCs. From what is known about potato and 

other oxamyl-registered crops in these regions, actual PCAs based on HUC-8 watersheds are 

expected to be well below the currently used 85% PCA adjustment factor. 

EPA conducted a sensitivity analysis for HUC-2 Region 8 using a PCA of 69%. This 

number was proposed by the technical registrant, and while EPA cannot definitively confirm this 

 

14 HUC-2 Region 17 for the Pacific Northwest, including Idaho, had an estimated drinking water concentration 

below the 80 μg/L threshold based on currently labeled use directions, and thus is not expected to be of risk 

concern. 
Page | 13 

figure, it is not inconsistent with the national average, and other available information. Based 

on this analysis, dietary exposure to infants from potato was calculated to be 83% of the aPAD. 

With DuPont’s proposed mitigation for use of oxamyl on potatoes and the actual use intensity of 

oxamyl in these regions, EPA believes that exposure in drinking water would be lower than the 

assumed threshold concentration of 80 μg/L and has a low potential to exceed dietary risks of 

concern from oxamyl uses on potato. EPA will confirm that the aPAD for potatoes is below the 

level of concern once ongoing revisions to EPA’s PCA policy have been completed.

Tomato: HUC-2 Region 7, with a default PCA of 85%, resulted in the worst-case 

modeling scenario for tomato, although Regions 3, 4, and 5 also had high EDWCs. The regions 

are made up of the southeastern and Great Lakes states along with parts of Kentucky, West 

Virginia and several other states. The major agricultural uses in these regions are pastureland, 

soybeans, corn, cotton, and small grains with tomatoes accounting for only a very small portion 

of available cropland. From what is known about tomato and other oxamyl-registered crop 

acreage, actual PCAs based on HUC-8 watersheds are expected to be well below the currently 

used 85% PCA adjustment factor. 

EPA conducted a sensitivity analysis for HUC-2 Region 7 using a PCA of 56%, and 

dietary exposure to infants from tomatoes was calculated to be 94% of the aPAD. The PCA 

adjustment factor used in the sensitivity analysis was estimated by removing the major field 

crops corn, soybeans, and wheat from the calculation because they are not registered use sites for 

oxamyl. With DuPont’s proposed mitigation for use of oxamyl on tomato and actual use 

intensity of oxamyl in these regions, EPA believes that exposure in drinking water would be 

lower than the assumed threshold concentration of 80 μg/L and has a low potential to exceed 

dietary risks of concern from oxamyl uses on tomato. EPA will confirm that the aPAD for 

tomatoes is below the level of concern once ongoing revisions to EPA’s PCA policy have been 

completed.

 EPA’s default assumptions for application rate, PCT, and PCA within the oxamyl 

modeling generated upper-bound concentrations of oxamyl in drinking water for the five use 

sites discussed above. With DuPont’s proposed mitigation for use of oxamyl on the Group 3 use 

sites and considering the actual use intensity of oxamyl in various HUC-2 regions, EPA believes 

that dietary exposure of infants to oxamyl residues in drinking water would be lower than the 

threshold concentration of 80 μg/L and below EPA’s level of concern. Furthermore, EPA will 

confirm this conclusion, once an on-going project to develop a vegetable-specific PCA factor is 

completed by the Office of Pesticide Program’s Environmental Fate and Effects Division. 

IV. TROPICAL CROPS GROWN IN HAWAII AND PUERTO RICO 

For additional details regarding the use of oxamyl on certain tropical crops grown in 

Hawaii (HI) and Puerto Rico (PR) (bananas/plantains, ginger, pineapple, and yams), please see 

the following document in the oxamyl docket (EPA-HQ-OPP-2010-0028): 
Page | 14 

- Review of Assessment of the Potential Oxamyl Exposure to Surface Water Drinking Water 

Supplies in the United State, Hawaii and Puerto Rico Under Current and Proposed Mitigation 

Use Guidance. F. Khan. June 29, 2011. 

Except for a few particular cases, EPA has only developed PCA adjustment factors and 

Tier II drinking water modeling for scenarios that occur within the continental United States. 

For most scenarios modeled outside of the continental US, such as oxamyl scenarios for yams 

and pineapple grown in PR and ginger and pineapple grown in HI, Tier I modeling using the 

FIRST15 model is typically conducted. FIRST is a screening-level model which simulates upperend exposures and makes conservative assumptions. For bananas/plantains grown in PR, more 

refined Tier II modeling was conducted, but it used a very conservative 100% PCA adjustment 

factor. 

Drinking water modeling for ginger, pineapple, and yams scenarios in HI and PR, 

conducted with the FIRST model, resulted in dietary exposures above EPA’s level of concern. 

Due to the conservative nature of this basic model, further refinement of these scenarios was 

used to more accurately assess real-world conditions relative to oxamyl use on these crops. Tier 

II drinking water modeling for bananas/plantains also resulted in dietary exposures above EPA’s 

level of concern due to the conservative assumption that 100% of land area is cropped. 

EPA used a simplified version of the Agency’s standard procedures for calculating PCA 

adjustment factors for HI and PR and determined that the EDWCs would be lower than the 

threshold concentration of 80 μg/L for bananas/plantains, ginger, pineapple, and yams and would 

have low potential to exceed dietary risks of concern. EPA previously determined that EDWCs 

of 80μg/L or lower would result in aPADs below 100%, and thus not be of concern. 

V. SUMMARY OF RISKS / DECISION 

Based on refinements to the drinking water exposure assessment, characterization of the 

use of oxamyl on specific crops, and mitigation measures proposed by DuPont, the risks of 

concern associated with use of oxamyl on existing use sites have been adequately addressed, 

provided that labels are revised as agreed upon with DuPont and submitted to the Agency for 

approval. 

Once an on-going project to develop a vegetable-specific PCA factor is completed by the 

Office of Pesticide Program’s Environmental Fate and Effects Division, drinking water and 

dietary modeling for use of oxamyl on carrots, celery, eggplant, potato, and tomato will be 

reevaluated to confirm that aPADs are below the level of concern. A weight-of-evidence 

approach, as discussed in this document, supports the finding that that actual dietary exposures of 

infants and children ages 1 – 2 to oxamyl are below EPA’s level of concern. 

 

15 FIRST = FQPA Index Reservoir Screening Tool 
Page | 15 

Attachment 1 

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

Source: G. Orrick. Update to Drinking Water Exposure Assessments for Current Uses of 

Oxamyl. June 15, 2010. DP Barcode 378338.