Methomyl (090301): Risk Mitigation Decision for Risks Due to Drinking Water Concerns 

Summary 

This document presents the mitigation measures that methomyl technical and end user 

registrants Chemtura Corporation, E.l. DuPont de Nemours and Company (DuPont), Glades 

Formulating Corporation, Rotam Limited, and Sinon Corporation, have voluntarily agreed to 

implement in order to mitigate estimated dietary risk due to drinking water exposure. To ensure 

timely implementation of the changes to several crops regarding number of applications and 

maximum seasonal rate, EPA is taking steps to make sure that the new use restrictions appear on 

all methomyl product labels by the end of 2014. 

The mitigation measures will cancel the use of methomyl on barley, oat, and rye and 

restrict its use on wheat to Idaho, Oregon, and Washington. For celery, head lettuce, and peppers 

the number of applications will be reduced by 20% and the seasonal maximum rate will be 

reduced by 12% to 20%. For com, language will be added to labels that will change the timing of 

applications such that only two applications can occur prior to tassel push, at the 1-2 leaf stage, 

and applications will no longer be able to occur on bare soil. Additionally, the number of 

applications for leaf lettuce, field com, popcorn, and seed com will be reduced 25% to 50%. 

While Florida and California were the areas of greatest concern for risks to drinking water, the 

registrants have agreed to implement the mitigation nationwide. 

While the risk assessment phase of registration review for methomyl is only just 

beginning, this effort to mitigate a chemical's risks early in the registration review process is 

consistent with the Agency's approach to registration review. Where risks are identified early in 

the process and opportunities for early mitigation exist, the Agency will pursue those 

opportunities as they arise, rather than waiting for completion of a chemical's registration review 

in order to mitigate risks. 

Background 

Methomyl is anN-methyl carbamate insecticide currently registered for use on a wide 

variety of sites including field, vegetable, orchard crops, and on ~urf (sod farms only). Methomyl 

is generally a restricted use pesticide [based on percent active ingredient (a.i.)]. There are 

currently no homeowner uses. However, certain low percentage a.i. formulations are not 

designated as restricted use and can be used around livestock quarters, commercial premises, and 

refuse containers. Methomyl was first registered in the United States in 1968. A Reregistration 

1 
Results of the Agency's Dietary Risk Assessment 

The Agency's dietary risk assessment included drinking water exposure estimates that 

used the most refined regional percent cropped area (PCA) factors consistent with 

recommendations from the Scientific Advisory Panel's2 peer review. This resulted in a number 

of methomyl uses which caused the human health dietary assessment to indicate potential risk of 

concern. The approach used for evaluating and characterizing the drinking water exposure 

concerns for methomyl are consistent with the approach used during the mitigation of oxamyl 

drinking water risks of concern. 3 This stands in contrast to the assessment provided by DuPont4, 

which explored crop-by-crop and region-by-region PCA factors. While DuPont's analysis looked 

at PCAs on a finer scale using the available data, their approach is not currently an Agency 

approved approach nor has their approach been informed by an SAP review, and thus, could not 

be used quantitatively in the Agency's assessment. 

The Agency looked at its drinking water simulations in the context of recent methomyl 

usage data in an effort to further characterize the risk. See Appendix A for "MethomylSummary of Agency Drinking Water Assessment and Discussion of Risk Management Options", 

which lays out the risk management analysis and options for resolution. In general, methomyl's 

use, regardless of crop, appears to occur predominantly in the southeast (primarily Florida and 

Georgia), the three west coast states (California, Washington, and Oregon), the southwest (Texas 

and Arizona), and the northeast (New York, Pennsylvania, and New Jersey). More specifically, 

geographically on a state-by-state basis, methomyl's use in Florida and California significantly 

exceeds its use in any other state. In fact, methomyl's use in those two states exceeds its use in 

all the other states combined. 

The usage data also suggested that the application rate, retreatment intervals, and number 

of applications could be reduced below that on currently registered product labels in order to 

reduce drinking water exposure. In addition, the usage data indicated that methomyl has very 

1 Available at http://www.epa.gov/oppsrrd l/REDs/0028red.pdf. 

2 U.S. EPA (I 999). Scientific Advisory Panel Report- Sets of Scientific Issues Being Considered by the 

Environmental Protection Agency Regarding: Session III- Use of Watershed-derived Percent Crop Areas as a 

Refinement Tool in FQPA Drinking Water Exposure Assessments for Tolerance Reassessment. Available at 

http:/ /www.epa. gov/scipo I y/sap/meetings/ 1999/ma y/final.pdf. 

3 U.S. EPA (2011) Oxamyl Mitigation of Dietary (Drinking Water) Risks of Concern for Certain Use Sites. 

Available at http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-20 I 0-0028-0021 . 

4 N. Snyder, A. Klemens, K. Wright, S. Zelonis. Sponsored by E. I. duPont de Nemours and Company. Tier 2 

Dietary and Drinking Water Risk Assessment for Methomyl Under Current Use Guidance. June 7, 2012. MRID 

48859101. 

2 
some crops, drinking water concerns have been sufficiently mitigated at this time. While Florida 

and California were identified as the areas where we were most concerned about drinking water 

risk because most of the methomyl use occurs in those two states, the registrants have agreed to 

implement the mitigation nationwide. See Appendix B for the Agency's complete analysis 

supporting the sufficiency of the mitigation to address drinking water cmwems in Florida and 

California. 

T a e bl 1 A . .gree d t - o Mit' Iga f IOn or M e I R C th omy1 on ow rops 

Labeled Crop Mitigation 

Barley Cancel Use 

Oats Cancel Use 

Rye Cancel Use 

Wheat Cancel Use Except in ID, OR, and WA 

Number of Applications 

Current* Proposed 

Com, Field 10 5 Com, Pop 10 5 

Com, Seed 10 5 

Timing of applications: Do not make more than two 

Com, Sweet, applications to com prior to tassel push. Make 1 

Field, Pop, and application when com is at 1-2 leaf stage for control 

Seed of early season pests; make a second application, if 

needed, 5-7 days later. 

T bl 2 . A a e lgree d - 0 t Mif Iga f IOn or M e th omyl I V on egeta bl es 

Crop Number of Applications Seasonal Maximum Rate Obs a.iJ Acre) Current* Proposed Current* Proposed 

Celery 10 8 7.2 6.3 

Head Lettuce 15 12 7.2 6.3 

Leaf Lettuce 8 6 3.6 3.6 

Peppers 10 8 4.5 3.6 

*Currently on labels. 

Conclusion 

This document presents the mitigation measures being taken voluntarily by registrants in 

order to mitigate estimated dietary risk due to drinking water exposure from methomyl. The 

Agency believes that these reductions in the maximum seasonal label rates for methomyl 

3 
Richard P. Keigwin, 

Jr. 

Director 

Pesticide Re-evaluation Division 

4 
WASHINGTON, D.C. 20460 

SENT VIA EMAIL 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

To: Patricia G. Devine, Product Registration Manager 

DuPont Crop Protection 

Re: Methomyl- Summary of Agency Drinking Water Assessment and Discussion of Risk 

Management Options 

Date: March 20,2013 

This document highlights results of EPA's dietary risk assessment for methomyl as it relates to 

specific crops and areas of the country. It is our effort to note the differences between DuPont's 

drinking water assessment and the Agency's assessment because these differences result in a 

number of dietary risk levels-of-concern exceedances in EPA's assessment. At the same time, 

from a risk management perspective, possible options for mitigating the risks are discussed. 

Results of the Agency's Dietary Risk Assessment 

Our risk assessors evaluated the potential dietary risk of methomyl using PRZMIEXAMS to 

simulate drinking water exposure, and DEEM to combine exposure through residues on food 

with drinking water exposure. The team ran PRZMIEXAMS simulations for most methomyl 

crops using the representative standard scenario for a national assessment, as well as a number of 

additional regional assessments. In addition, drinking water exposure was calculated for a 

number of scenarios using the lowest regional percent crop treated (PCA) for regions east of the 

eastern divide and west of the western divide (0.13), and using the lowest regional PCA for midcontinent regions (0.35). These were considered lower-bound values to compare with the 

representative scenarios and PCAs shown in Table 1, below. 

EPA's approach to the methomyl drinking water assessment uses the same inputs (rates, number 

of applications and retreatment intervals) as DuPont used in its assessment (June 7, 2012), but 

did not calculate crop and watershed-specific PCA factors. EPA's use ofPCAs in its drinking 

water assessment is consistent with the approach discussed in the 1999 Scientific Advisory 

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Table 1 Representative Scenario 

States with highest 

methomyl use, descending Peak ppb& Peak ppb & 

Crop order Scenario* PCAGround PCAAerlal 

Lettuce CA,AZ CA lettuce STD 99.31 (0.6i) --

Onion OR, WA, CA, 10, NY, TX, CO GAOnion WirrigSTD 39.80 (0.41) 38.89 (0.41) 

FL, GA, CA, NY, PA, NJ, OH, 127.54 

Sweet Corn MI,IL,WI KS Corn STD (0.87) 124.93 (0.87) 

Tomatoes CA, FL FL tomato STD 37.50 (0.41) 36.82 (0.41) 

Potatoes WA,CA,OR,NY,PA,NC ME potato STD 3.95 (0.13) 4.06 (0.13) 

Peppers FL, AZ, CA, NJ, GA, NC, OH FL pepper STD 50.79 (0.41) 49.22 (0.41) 

FL, NC, NY, TX, CA, CO, AR, 

Cabbage Ml Brownsville TX 74.24 (0.69) --

Apples VA, Ml, WV, PA, NY, OH, NC PA apples STD V2 8.38 (0.34) 8.52 (0.34) 

ground TX alfalfaOP; 

Alfalfa CA,CO aerial NC alfalfa OP 81.08 (0.69) 11.81 (0.41) 

Beans (Snap, Bush, 

Pole, String) FL, TX, GA, CA, PA, WI Ml beansSTD 72.28 (0.81) 71.15 (0.81) 

Peaches NJ, AL, PA, Ml, CA GA Peaches STD 11.23 (0.41) 11.62 (0.41) 

Celery CA,MI CA cole crop RLF v2 86.68 (0.61) --

*Where there is a ground and aerial peak ppb and PCA, unless indicated, the scenario is for both ground and aerial 

The consideration of default regional PCAs represents the extent of refinement that could be 

done for the drinking water exposure assessment, given the wide variety of crops on methomyl 

labels and the fact that there are no geographical limitations for the use of methomyl. However, 

we have taken a closer look at where methomyl appears to actually be used (geographically and 

crop specific) based upon our use and usage information from the most recent available 5-year 

period. Upon this closer evaluation of methomyl' s apparent geographical use and predominant 

crop specific use, there may be options for moving forward to mitigate the issues driving the 

failure of certain crops. 

5 U.S. EPA (1999). Scientific Advisory Panel Report- Sets of Scientific Issues Being Considered by the 

Environmental Protection Agency Regarding: Session III- Use of Watershed-derived Percent Crop Areas as a 

Refinement Tool in FQPA Drinking Water Exposure Assessments for Tolerance Reassessment. Available at 

http://www .epa. gov/scipo I y/sap/meetings/ 1999/may/final. pdf. 

6 
In addition, the use of methomyl appears to be insignificant for major crops which account for 

much of the area in default PCA calculations. For instance, the average percent crop treated for 

spring and winter wheat for the last five years has been 0.0, according to our analysis. The same 

is true for both soybeans and field com. Use records suggest that what use has occurred has not 

been in the same regions where the major methomyl use occurred on sweet com and vegetables. 

Consideration of drinking water exposure in the co~J.text of methomyl usage data 

Given the usage data described above, we undertook a "what-if' assessment along the lines of 

that performed for the oxamyl drinking water assessment, exploring which use/region 

combinations might pose the greatest risk of drinking water contamination. In this risk 

management exercise we looked at modeling runs that best approximated the areas of major use 

of methomyl, and applied combined PCA factors for crops on which methomyl has been used, 

most often those for vegetables and com (to account for sweet com). In the cases for which a 

nearby scenario was not available, we took the results of the national standard scenario and 

applied the appropriate PCAs for the major use region being evaluated. This exercise does not 

by itself change the risk assessment nor the status of the methomyl "risk cup." It does, however, 

clarify which uses most require mitigation for protection of drinking water, and where. 

Table 2 indicates which uses failed both with the national representative standard scenario and 

regional default PCAs, and under the "what-if' scenarios using more representative scenarios 

and smaller PCA factors. In short, the main drinking water concerns which require resolution are 

the use of methomyl on sweet com in Florida and Georgia, the use on vegetables (especially 

lettuce and brassicas) in California, and the use on onions in New York. The region-specific 

PCAs include EPA's recently released regional PCA adjustment factors 6 for vegetables along 

with regional PCAs for other crops for which there was reported methomyl use between 2007 

and 2011. 

Table 2 

PCARegion 

Crop States Scenario Specific 

Sweet Corn FL, GA FL sweet corn OP 0.16, 0.30 

Lettuce (and spinach) CA CA lettuce STD >0.29 

Peppers CA FL pepper STD >0.29 

6 Available at http://www.epa. gov/oppefed 1/models/water/pca adjustment dwa.html# 3 regional group. 

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Sweet corn in Florida and Georgia 

Methomyl's major uses in Florida appear to be on vegetables and sweet com, with no reported 

use on wheat, soybeans, citrus, or field com. A Florida sweet com scenario was run with the 

default regional PCA of 0.41, which resulted in residues that caused the human health aggregate 

assessment to fail. In looking at the regional vegetable PCA, the maximum is 0.07 and the 

maximum for com is 0.09. If one were to conservatively combine these two maximum PCA 

factors, recognizing that the com value may in part represent land cropped to field com, the 

resulting drinking water concentration is near to that which would result in an acceptable dietary 

risk. 

The major use of methomyl in Georgia is on sweet com, with lesser amounts used on vegetables 

and cotton. According to 2007 Census of Agriculture maps, major cotton, vegetable and sweet 

com growing areas coincide in the southwestern portion of the state. When considered with the 

additional reported use on watermelons and cantaloupe, the default regional PCA could be as 

high as 0.30, but in any case would be higher than that needed to result in acceptable dietary risk. 

Methomyl usage data for sweet com suggest that actual usage is significantly less than modeled 

by both the Agency and DuPont. Modeled concentrations for sweet com were derived using an 

application rate of 0.45lb/A applied 14 times with a 1-day application interval. Usage data 

indicate that the average application rate in Florida and Georgia was 0.3 lb/ A, with an average of 

about 9 applications a year. It appears that there is room to reduce the rate, number of 

applications and perhaps application interval to reduce the potential for risk to drinking water. 

Vegetables in California 

Lettuce: Lettuce would fail using the California lettuce scenario and the regional vegetable PCA 

of 0.29 alone, which does not account for reported use on sweet com, cotton and citrus crops. 

The lettuce scenario was also used to represent use on spinach, which therefore also would fail in 

this "what-if' exercise. 

Methomyl usage data for lettuce suggest that actual usage is significantly less than simulated by 

both the Agency and DuPont. Modeled concentrations for lettuce were derived using an 

application rate of 0.9lb/A applied 6 times a year with a 2-day application interval. Usage data 

indicate that the average application rate in California was 0.8lb/A, with an average of about 2 

applications a year. It appears that there is room to reduce the number of applications and 

perhaps the interval to reduce the potential for risk to drinking water. 

8 
both the Agency and DuPont. Modeled concentrations were derived using an application rate for 

peppers of 0.9lb/A applied 5 times a year with a 5-day application interval. Usage data indicate 

that the average application rate for peppers in California was 0.7lb/A, with an average of about 

2 applications a year. It appears that there is room to reduce the rate, number of applications and 

perhaps application interval to reduce the potential for risk to drinking water. 

Cabbage: A California standard scenario was available for cabbage, and it resulted in higher 

peak concentrations than the scenario chosen as representative of the rest of the country. DEEM 

calculated exposure of 102% of the aPad for a lower-bound PCA of0.13. California cabbage 

would therefore still fail with a regional vegetable PCA of 0.29, and more so if one considered 

use of sweet com, cotton and citrus crops in the PCA. 

Methomyl usage data for cabbage suggest that actual usage is significantly less than modeled by 

both the Agency and DuPont. Modeled concentrations were derived using an application rate for 

cabbage of 0.9lb/A applied 8 times a year with a 2-day application interval. Usage data indicate 

that the average application rate in California for cabbage was 0.7lb/A, with an average of about 

2 applications a year. It appears that there is room to reduce the rate, number of applications and 

perhaps application interval to reduce the potential for risk to drinking water. 

Celery: Use on celery was simulated using the same standard scenario as for cabbage, but with a 

different application interval. DEEM calculated exposure of 97% of the aPad for a lower-bound 

PCA of 0.13, and exceedance of the aPad from water alone using a PCA of 0.35. Given the 

regional PCA of 0.29 for vegetables, and the use of methomyl on sweet com, cotton and citrus in 

the same region of California, one cannot dismiss risk from celery in this "what-if' exercise. 

Methomyl usage data for celery suggest that actual usage is significantly less than modeled by 

both the Agency and DuPont. Modeled concentrations were derived using an application rate for 

celery of 0.9lb/A applied 8 times a year with a 5-day application interval. Usage data indicate 

that the average application rate for celery in California was 0.7lb/A, with an average of about 2 

applications a year. It appears that there is room to reduce the rate, number of applications and 

perhaps application interval to reduce the potential for risk to drinking water. 

Onions in New York 

Usage data indicate that the second most important state for methomyl use on onions is New 

York. Onions and sweet com seem to be grown in the same area, much of it in the Great Lakes 

region, and methomyl use on apples was reported for New York, as well. Drinking water 

concentrations derived using the representative standard scenario caused the dietary assessment 

9 
As described above, a risk management exercise considering PCA factors without the inclusion 

of major row crops was only possible because our usage data indicate that methomyl is not used 

much on these crops. The average percent crop treated for wheat, soybeans and corn all were 

calculated to be 0.0 for the most recent 5-year period reviewed, suggesting that there is little 

benefit associated with these methomyl registrations. However, these crops do contribute greatly 

to the national and regional default PCAs used for the human health dietary risk assessment. We 

suggest that DuPont consider removing these registered uses from methomyl.labels to provide 

room in the "risk cup" for the existing high-use crops, and perhaps then-methyl carbamate 

cumulative assessment. 

Conclusion 

The Agency's dietary risk assessment included drinking water exposure estimates that used the 

most refined regional PCA factors that are permissible by the recommendations provided 

through SAP peer review. This results in a number of methomyl uses which cause the human 

health dietary assessment to indicate potential risk of concern. This stands in contrast to the 

assessment provided by DuPont, which explored crop-by-crop and region-by-region PCA factors 

that are not consistent with SAP recommendations. 

The Agency looked at its drinking water simulations in the context of recent methomyl usage 

data as a risk management exercise. Identification of where methomyl was used most, and on 

which crops, allowed us to perform a "what-if' evaluation consistent with that done for oxamyl. 

Through this we identified which crop-location combinations would still result in estimated 

dietary risk due to drinking water exposure. 

The usage data used in this exercise also suggests that the application rate, retreatment intervals, 

and number of applications for these crops could be reduced below that modeled in order to 

reduce drinking water exposure. In addition, the usage data indicate that methomyl has very little 

use on several major row crops. Removal of these crops from the methomyllabel would go a 

long way in reducing the estimated drinking water concentrations in the nationwide risk 

assessment, and could open space in the risk cup for methomyl and the n-methyl carbamate 

cumulative assessment. 

10 
The main concern for possible methomyl in drinking water in Florida is associated with use on 

vegetables. Although it can be used on orchard crops, usage data available to the Agency does 

not indicate use in Florida. 

In its response to the Agency's request, DuPont provided information on the co-occurrence of 

other potential methomyl crops in areas of Florida where vegetables are grown. These maps 

indicate that sweet com is grown more in Georgia and up the southeastern seaboard than in 

Florida. USDA Agricultural Census maps from 2007 indicate that vegetables and sweet com are 

both grown in Palm Beach County (most likely the Everglades Agricultural Area. However, as 

indicated by the Palm Beach County Water Utilities Department's 2012 report, "Palm Beach 

County Water Utilities Department's drinking water is drawn from wells extending 

approximately 150 feet underground." 

Furthermore, the City of West Palm Beach, in their 2012 report, indicated that "the City of West 

Palm Beach gets its water from rainfall captured and stored in a part of the Everglades 

Ecosystem known as the Grassy Waters Preserve. This system feeds and sustains Lake Mangonia 

and Clear Lake. In past years the City has, at times, been able to supplement its water supply 

from Lake Okeechobee." It states further th~t "in 2012 the Florida Department of Environmental 

Protection performed a Source Water Assessment on our system. These assessments were 

conducted to provide information on any potential sources of contamination in the vicinity of our 

wells and source water intake. A search of the data sources indicated no potential sources of 

contamination within the assessment area for our system." 

The DuPont response also provided information on potential co-occurrence of vegetables with 

alfalfa and pasture grass. This memo did not indicate co-occurrence with alfalfa, which is 

consistent with usage data available to the Agency. There is co-occurrence of pastureland in 

watersheds in which vegetables are grown, but the predominant pasture grass grown in Florida is 

bahia grass, and methomyl is only labeled for use on bermudagrass. 

The Agency believes that, to the extent that surface water is used as a drinking water source in 

Florida, that potential drinking water exposure to methomyl is best characterized by the use on 

vegetables. The proposed reduction in the maximum label rates for methomyl use on vegetables 

is sufficient to mitigate concerns for drinking water in Florida for methomyl itself. The potential 

cumulative exposure to methomyl and other n-methyl carbamates is currently being reassessed. 

California 

When the Agency first identified use on vegetables in California and Florida as the most likely 

causes of significant drinking water exposure to methomyl, it was based on available methomyl 

11 
orchards includes use on grapes, for which methomyl is no longer registered, and 2) the 

assessment for the various orchard crops passed the dietary screen. In addition, available data 

indicate that a small amount of methomyl is used on orchard crops in California, and only on a 

small percentage of the crops grown. Use on cotton also is much less significant than on 

vegetables, with a very small percentage of the crop in California treated. 

The Agency acknowledged that the corrected PCA for vegetables improved the picture for 

drinking water exposure to methomyl in California, but requested additional information on 

potential co-occurrence with areas in which alfalfa is grown, even though the assessment for 

alfalfa itself passed the dietary screen. DuPont provided information on the co-occurrence of 

alfalfa and vegetables in California watersheds, which indicated that the percent cropped to 

alfalfa in the great majority of watersheds in California was below 5%, with a maximum .of 

9.6%. The highest PCAs for alfalfa do not correspond with the maximum PCAs for vegetables. 

Furthermore, while there is a significant amount of methomyl used on alfalfa in California, the 

percent of the crop treated is only around 10%. 

Therefore, while DuPont indicated that the dietary assessment for vegetables would pass if one 

applies the vegetable PCA of 0.10 to the drinking water exposure values for vegetables, the PCA 

should perhaps be adjusted slightly higher for use on alfalfa. However, it is important to 

acknowledge that the screening drinking water exposure values were derived using the highest 

application rates, maximum number of applications and shortest retreatment intervals allowed on 

the labels. Usage data for California indicate that less methomyl is applied in practice, and the 

percent of each crop treated is significantly less than the 100% assumed in the screen. The 

proposed reduction in the maximum label rates for methomyl use on vegetables is sufficient to 

mitigate concerns for drinking water in California for methomyl itself. The potential cumulative 

exposure to methomyl and other n-methyl carbamates is currently being reassessed. 

12