### Page 2 of 19 lower-than-maximum application ra tes based on reported usage data for six of the ten current uses assessed in 2010. The remaining four curren t 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 Eff ects Division (HED) (email communication with Mohsen Sahafeyan, May 26, 2010). Reported use patt erns were based on usage data collected by the Biological and Economic Analysis Divisi on (BEAD) from a variety of sources (USEPA, 2010). Ground water exposure estimates and charac terization of monitori ng data that were reported in the 2009 assessment were not impact ed by comments submitted by DuPont and were not updated in this memorandum.

Surface water exposure estimates from the curre ntly labeled maximum use patterns using current models and adjusted with national a nd regional percent cropped area (PCA) values are
listed below in Table 1 . Updated values are included. Ti er 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 us es 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 e xposure; results from this characterization are tabulated in parentheses. Tier II modeling was conducted to estim ate 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; provis ional 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 aer obic 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 th e 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 patt erns 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 delimite d 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 la bel directions used for modeling are changed to eliminate potential risk exceedances, other use patterns not modeled in this assessment may still re sult in risk exceedances. For example, both use patterns for eggplant modeled in the 2010 DWA, one for nemat odes 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 Oxam yl 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 wa s 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 DW A 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 prohib its use in California; grown in Hawai’i and Puerto Rico).
Other assessed uses were mode led with the Tier II PE model because PRZM scenarios or reasonable surrogate PRZM scenarios were availa ble. 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 Parameter s 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 exp licit 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 (K OC ) (L/kg OC ) 35 Mean of five K OC 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 dr inking 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 La w Constant was input rather than a vapor pressure. The use of the Henry’s Law Constant is consistent with gui dance and does not alter exposure estimates. The new aerobic aquatic meta bolism 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 a nnual 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 insubstantia l 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 m 3 /mol) 3.9 x 10 -13 Product chemistry data Calculated from MRID 42526101,
40499702
Solubility in Water (mg/L) 2.8 x 10 5 Product chemistry data MRID 40499702
Organic Carbon Partition Coefficient (K OC ) (L/kg OC ) 35 Mean of five K OC 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 m 3 /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 assess ments. Updates to the model input parameters in this assessment relative to previous assessm ents include: 1) the removal of the South Texas vegetable scenario for modeling use on carrots (due to the poor drai nage of the heavy clay soil of the scenario), 2) an initial application date of August 9 th 

### rather than September 7 th 

### 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 25 th 

### rather than April 1 st 

### for modeling use on eggplant with the Florida pe pper scenario (also to be co nsistent 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, th is 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 pa ttern for the Florida cabbage scenario used to assess use on celery and 2) the nematode-control use pattern with two initi al applications of 2.0 lbs a.i./A followed by two applica tions 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

PA vegetable NMC May 7 Carrot

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

STX grapefruit NMC Citrus (bearing fruit)

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 ST D Apr. 15 2.0 1 N/A 4 G 2 0.99/0.064

CA tomato STD Apr. 1 Tomato

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 11 th 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, fo llowed 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 th e 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 a ll 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 represen ted 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 revi sited recently due to a r eevaluation of toxicity data upon which the FQPA factor is based. A lthough 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 (e mail communication with Mohsen Sahafeyan, May 26, 2010). Therefore, the cu t-off point of 80 μg/L was retained as an approximate level of concern.

As with past drinking water exposure asse ssments, this assessment update applies regional PCA refinements for uses within the co ntiguous 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 th at account for the highest extent of HUC-8 watershed in the HUC-2 regions on whic h agricultural crops are grown (Effland et al. , 1999). Figure 1 displays the 18 regions (or HUC-2 watershe d 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 Hawa i’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 pr evious drinking water exposure assessments.

### Page 9 of 19 Figure 1. The Eighteen HUC-2 Watershed Basi ns 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 19Table 6. Scenario assigned to each combination of use and major basin (HUC-2 region).MajorBasin #BasinNameRegionalPCACarrotCeleryCitrusCottonCucumberDry bulbonionEggplantNon-bearingfruitPepperPotatoTomatoEast of Eastern Divide1NewEngland14PA vegetableNMC– – –NJ melonSTD– PA tomato STDPA appleSTDPA vegetableNMCME potatoSTDPA tomato STD2MidAtlantic46PA vegetableNMCFL cabbageSTD–NC cottonSTDNJ melonSTD– PA tomato STDPA appleSTDPA vegetableNMCME potatoSTDPA tomato STD3SouthAtlantic38FL carrotSTDFL cabbageSTDFL citrusSTDMS cottonSTDFL cucumberSTD– FL pepper STDFL citrusSTDFL pepper STDFL potatoNMCFL tomato STDMid-Continent (Mississippi River Basin)4 Great Lakes 77PA vegetableNMCFL cabbageSTD– –MI melonSTDPA vegetableNMCPA tomato STDMI cherrySTDPA vegetableNMCME potatoSTDPA tomato STD5 Ohio 82PA vegetableNMCFL cabbageSTD– –MO melonSTD– PA tomato STDPA appleSTDPA vegetableNMCME potatoSTDPA tomato STD6 Tennessee 38PA vegetableNMC– –MS cottonSTDMO melonSTD– FL pepper STDNC appleSTDPA vegetableNMC– PA tomato STD7UpperMississippi85PA vegetableNMC– – –MI melonSTD– PA tomato STDMI cherrySTDPA vegetableNMCME potatoSTDPA tomato STD8LowerMississippi85FL carrotSTD–STX grape-fruit NMCMS cottonSTDMO melonSTD–STX vegetableNMCGA peachSTDSTX vegetableNMCFL potatoNMCSTX vegetableNMC9 Souris 83PA vegetableNMC– – – – – PA tomato STD –PA vegetableNMCME potatoSTD–10 Missouri 87PA vegetableNMC– – –MO melonSTD– PA tomato STDMI cherrySTDPA vegetableNMCME potatoSTD–11 Arkansas 80FL carrotSTDFL cabbageSTD–TX cottonOPMO melonSTDWA onionNMCSTX vegetableNMCOrchard BSSSTX vegetableNMCFL potatoNMC–12 Texas Gulf 67FL carrotSTDFL cabbageSTDSTX grape-fruit NMCSTX cottonNMCSTX melonNMCGA onionSTDSTX vegetableNMCOrchard BSSSTX vegetableNMCFL potatoNMCSTX vegetableNMC13 Rio Grande 28FL carrotSTDFL cabbageSTD–TX cottonOP–CA onionSTDSTX vegetableNMCCA citrusSTDSTX vegetableNMCWA potatoNMC–West of Western Divide14UpperColorado7CA row cropRLFCA row cropRLF– – – –CA tomato STDOR appleSTDCA row cropRLFWA potatoNMCCA tomato STD15LowerColorado11CA row cropRLFCA row cropRLFCA citrusSTDCA cottonSTD–CA onionSTDCA tomato STDCA citrusSTDCA row cropRLFCA potatoRLF–16 Great Basin 28CA row cropRLFCA row cropRLF– – – –CA tomato STDOR appleSTDCA row cropRLFWA potatoNMC–17PacificNorthwest63CA row cropRLF– – –CA melonRLFWA onionNMCCA tomato STDOR appleSTDCA row cropRLFWA potatoNMCCA tomato STD18 California 56 –CA row cropRLFCA citrusSTDCA cottonSTDCA melonRLFCA onionSTDCA tomato STD CA fruit STDCA row cropRLFCA potatoRLFCA tomato STD

### Page 11 of 19 2. Exposure Modeling Results

2.1. Tier I Results

Tier I modeling results of the 2010 DWA di d not change in this assessment update because model input parameters were not upda ted. Screening acute and chronic exposure estimates in surface water drinking wate r sources from FIRST are listed in Table 7 . Use on pineapple resulted in the highest es timated 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. Unrela ted 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 me teorological 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 scenar ios because the PE model is sensitive to precipitation. Therefore, the metfile for H ilo, Hawai’i (w21504) was used to model use on ginger root grown in Hawai’i, si nce it is near where most ginge r root is grown on the Hawaiian Islands (USDA, 2010e). The metfile for San Jua n, Puerto Rico was used for yams grown in Puerto Rico because it is the only metfile avai lable for the Territory. And lastly, because pineapple is grown in both Puerto Rico and Hawa i’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 wa s not changed in this assessment update.

Surrogate PRZM scenarios were selected fo r this provisional modeling refinement based on crop similarity and without regard to locati on 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 wa s used to model use on pineapples. These surrogate scenarios were select ed for modeling rather than ot her 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 us e patterns were modeled for us e on ginger root in order to evaluate exposure from different application me thods 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) app lications of 1.0 lb a.i./A, 30-days apart. Updates with respect to the previous assessment include changes in th e initial application dates for yams and ginger root. The initial applicat ion date for yams was pushe d forward from January 1 st 

### to February 15 th 

### in order to occur approximately two months after planting, as dire cted by the label, consistent with the PRZM scenario. The initial application date for post-emergent foliar applications to ginger root was changed from January 15 th 

### to April 4 th 

### in order to better approximate the application timing that may occur in the spring. The initial applicati on date for pre-plant incorporated applications was not changed to the spring becaus e it should not occur after the crop emergence date in the PRZM scenario, which is January 1 st



### .

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 4 A Ginger root FL potato NMC Hilo, HI Apr. 4 1.0 8 30 2 1 0.99/0.064

Honolulu, HI

Kahului, HI Pineapple FL cabbage STD

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, in corporated (CAM 4) to a 5-cm minimum depth.



### Exposure estimates from this provisional refinement are li sted for char acterization in
Table 9 . The results indicate that the Tier I exposure estimates were conservative, but not unreasonable. With respect to Ti er I values, this provisional re finement approach reduces peak EDWCs from 218 μg/L to 108 μg/L for use on ya ms, 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. Update s with respect to the previous assessment include a decrease in the pe ak 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 ca used 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 FL cabbage STD/ Kahului 167 7.3 3.0 Pineapple (8.0 lbs a.i./A/year) 100%
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 re servoirs down-gradient from these uses, these EDWCs may underestimate th e 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 al so 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 su rface 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 con tiguous United States we re adjusted by the default national PCA (87%) where exposure fr om that use was initially below 80 μg/L. Exposure estimates for the remainder of uses with in 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 e ggplant 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 valu es, reported estimates in Table 10 for carrots and cotton have changed with respect to those of the pr evious assessments. The PRZM scenario and regional PCA listed for cotton ha ve changed from Mississippi cotton and 85% to Texas cotton and 80% because the updated exposure estimates fo r 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. Oxam yl use on bananas/plantains, carrots, celery, cotton, cucumbers, dry bulb onions , eggplant, non-bearing fruit, pe ppers, potatoes, and tomatoes resulted in 1-in-10-year peak expos ure estimates greater than 80 μg/L.

Table 10. Tier II Estimated Drinking Water Con centrations (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 Con centrations (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 tobacc o 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 ma ximum 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. Th erefore, exposure estimates in acidic water bodies are expected to be higher than those modeled in this assessm ent. 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 es timated 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 (Maj or Basin 1) or any PCA region west of the Continental Divide. Update s to input parameters resu lted in updated EDWCs in Table 12 with respect to those in pr evious assessments, including values for carrots in PCA regions 8, 11, 12, and 13; for cotton in PCA region 8; a nd for eggplant in PCA regions 3 and 6.Page 15 of 19Table 12. Regional PCA-refined1-in-10-year Peak EDWCs for Oxamyl Uses InitiallyExceeding 80 μg/L (values greater than 80 μg/L in bold).MajorBasin #Basin NameRegionalPCACarrotCeleryCitrusCottonCucumberDry bulbonionEggplantNon-bearingfruitPepperPotatoTomatoEast of Eastern Divide1 New England 14 13 – – – 7 – 22 14 9.9 10 342 Mid Atlantic 46 44 77 – 72 23 – 73 47 33 331123 South Atlantic 38 71 64 70 55105–124 12467109 177Mid-Continent (Mississippi River Basin)4 Great Lakes 77 74129– – 29 5212238 54 551885 Ohio 82 79138– – 68 –130 8458 592006 Tennessee 38 37 – – 55 32 –12441 27 –937 Upper Mississippi 8582– – – 32 –13442 60 612088 Lower Mississippi 85161– 539471 –23726256 243 1209 Souris 8380– – – – –131– 59 59 –10 Missouri 8784– – – 73 –13843 61 62 –11 Arkansas 80152 134–9667 15223 121 241 229–12 Texas Gulf 67127 1124194 147 90 187 101 202 191 9513 Rio Grande 28 53 47 – 34 – 4.3 78 9.08432 –West of Western Divide14 Upper Colorado 7 7.2 5.5 – – – –4.5 2.6 3.9 7.9 3.215 Lower Colorado 11 11 8.6 3.4 5.1 – 1.7 7.1 3.5 6.1 2.7 –16 Great Basin 28 29 22 – – – –18 10 15 32 –17 Pacific Northwest 63 65 – – – 7.7 12 41 23 35 71 2818 California 56 – 44 17 26 6.8 8.7 36 28 31 14 25

### Page 16 of 19 Exposure Characterization for Reported Rates

In order to characterize reductions in expos ure 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 an d eggplant and direct communication with USDA personnel for the tropical uses bananas/plan tains, 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/E XAMS to estimate their resulting exposure and to explore whether the exposure would remain at le vels 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 incr ease in the re-application interval for use on carrots from 5 to 14 days in order to conform to label directions, a nd 3) an initial application date of August 9 th 

### rather than September 7 th 

### for modeling use on cotton w ith the Mississippi cotton scenario. Reported use patterns were not mode led 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 Descri bing “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

STX cotton NMC Jul. 20 Cotton

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

PA tomato STD Jul. 15 Eggplant

STX vegetable NMC Jan. 15 0.38 5 7 2 1 0.99/0.064

### Page 17 of 19 Table 13. PRZM Input Parameters Descri bing “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

PA apple STD Apr. 16 Non-bearing fruit

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

FL tomato STD Mar. 24 Tomato

PA tomato STD Aug. 15 1.5 3 5 2 1 0.99/0.064



### The regional PCA-adjusted 1-in-10-year p eak 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 pattern s (cells with highl ighted values in Table 12 ). Updates with respect to these values in previous assessm ents include reduced values for carrots in PCA regions 8, 11, 12, and 13 and for cotton in PCA re gion 8 and new values for celery and eggplant in the relevant PCA regions.

The 1-in-10-year peak exposure estimate fo r 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 (μ g /L) from Reported Use Patterns b y Use and b y Re g ional PCA Specific to each Ma j or 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 applica tion patterns reduce exposure estimates for most uses below target values. At the reporte d application patterns mode led for uses on carrots, celery, cotton, cucumbers, dry bulb onions, eggpl ant, and non-bearing fruit, estimated drinking

### Page 18 of 19 water exposure from any major basin does not ex ceed 80 μg/L (celery and eggplant analyses are new). However, use on tomatoes at reported ap plication rates results in EDWCs that exceed 80 μg/L in six watershed regions. Reported app lication 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 tr opical crops for which Tier I exposure was estimated and provisionally char acterized with Tier II models in the 2010 DWA. Reported use patterns are less than the maximum use patterns fo r each crop except for the pre-plant application to ginger root (at 4.0 lbs a.i./A), for which re ported usage was at the maximum rate. Because FIRST cannot model different appl ication rates throughout the seas on, 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 applicatio ns of 4.0 lbs a.i./A e ach, 60 days apart, and incorporated to a 5-cm depth. Because PE cannot model different application methods throughout the season, only the pre-plant applic ation (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, a nd Input Parameters for Characterizati on 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 4 A 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 dr inking 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 modeli ng are provided in parentheses for characterization. Exposure resulting from reported rates has not been esti mated prior to this DWA update. The results indicate that reported ap plication 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) 10 0% (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. Kenne dy. 1999. Proposed Methods for Determining Watershed-derived Percent Crop Areas and Considerations for Applying Crop Area Adjustments to Surface Water Screening Mode ls. Presentation to the FIFRA Science Advisory Panel, May 27, 1999. Online at: http://www.epa.gov/scip oly/sap/1999/index.htm

USEPA. 2009. Stebbins, K. State-Level Pest icide Usage Data Packag e in Support of EPA’s Drinking Water Risk Analysis for Existi ng and Pending Oxamyl Uses. DP Barcode 359723. U.S. Environmental Protection Agenc y, Office of Prevention, Pesticides and Toxic Substances, Biological and Economic Analysis Divi sion. Memorandum to the
Environmental Fate and Eff ects Division, Special Review and Reregistration Division, and Registration Division. Feb. 3, 2009.

USEPA. 2010. Stebbins, K. and C. Chen. Pest icide Usage Data in Support of EPA’s Drinking Water Exposure Assessment for Oxamyl. DP barcode 377411. U.S. Environmental Protection Agency, Office of Chemical Sa fety and Pollution Prevention, Office of Pesticide Programs. Memorandum from the Biological and Economic Analysis Division
to the Environmental Fate and Effects Divi sion and Pesticide Re-e valuation Division. May 19, 2010.