UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D

. C

., 20460

OFFICE OF

CHEMICAL SAFETY AND

POLLUTION PREVENTION



### PC Code: 1 20051

DP Barcode: 422167



## MEMORANDUM August 14, 2014

SUB JECT:

TO:

FROM:

REVIEWED

BY: 

### Dimethenamid-P: ADDENDUM: Drinking Water Exposure Assessment for

Existing Orname ntal and Green Onion Uses and the Proposed Cotton Use

Elissa Reaves, Branch Chief

, RAB4

Bonnie Cropp-Ko hlligian

, Environmenta l Scientist

Health Effects Division (7509P)

Danie l Kenny, Branch Chief

Kable Davis, Produc t Manager 25

Erik Kraft

, 

### Risk Manager Reviewer

1 

### Registration Division (7505P)

Melanie Biscoe, Physical Scientist

Environmenta l Risk Branch 3

Envi r onmental Fate and Effects Division

Rosanna Louie-Juzwiak, RAPL

EnvironmentalRiskBranch3

Environmental Fate and E ffects Division

THROUGH: Dana Spatz

, Branch Chie

Environmental Risk Branch 3

Environmental Fate and Effects Division (7507P)



### Executive Summary

This drinking water assessme nt (DWA) was conducted as an addendum to the April29, 2014

DW A (DP 415506) initially developed in r esponse to BASF's request to register dimethenamidp (the common name of the s -i somer of dimethenamid, or s-dimethenamid) for use on cotton.

Pa ge 

### 1 of 

### 19

### Page 2 of 19 This DWA updates the April 29, 2014 DWA by providing Estimated Drinking Water

Concentrations (EDWCs) for two residues of concern, dimethenamid oxanilic acid (oxalamide)

and dimethenamid ethanesulfonic acid (sulfonate ), in addition to dimethenamid-P. The April

assessment only considered parent dimethenamid-P . EDWCs are calculated for dimethenamid-P

and its residues of concern us ing the Residue Summation Appro ach outlined in EFED’s Draft

Guidance for Modeling Pesticide Total Toxic Residues (TTR) v.01 from January 3, 2013.

The maximum EDWCs calculated in this assessm ent result from the modeled ornamental uses,

and are shown in Table 1 . In surface water, the highest estim ated peak (acute) concentration of

dimethenamid-P and its re sidues of concern is 73 μ g/L, the highest estimat ed 1-in-10 year annual

average concentration is 27 μ g/L, and the highest estimated 30-year annual average

concentration is 16 μ g/L. In groundwater, the estimated peak concentration is 153 μ g/L, and

the estimated post-breakthrough average concentration is 140 μ g/L. EFED recommends

using the maximum groundwater EDWC value s for the human health dietary risk

assessment.

Table 1. Maximum estimated drinking water concentrations (EDWCs) for dimethenamid-P,

oxalamide, and sulfonate resulting from dimethenamid-P use on ornamentals.

Drinking Water

Source (model) Model Scenario &

Application Method Acute Chronic Cancer

μ g/L

Surface Water

(PRZM

‐ EXAMS) New Jersey Nursery

(Ornamentals)

Ground Application Peak

1

‐ in

‐ 10 Year Chronic

1

‐ in

‐ 10 Year 30

‐ year Annual

Average

73 27 16

Groundwater

(PRZM

‐ GW 30

‐

year simulation) Wisconsin Corn

(Ornamentals) Peak Post

‐ Breakthrough Average

153 140

### Page 3 of 19 Environmental Fate and Transport Characterization

The active ingredient dimethenamid-P, or s-dimeth enamid, is the herbicidally active isomer of

the racemic mixture of the r- and s-dimethenamid isomers. Additional discussion of the physical,

chemical, and fate properties of dimethenamid -P may be found in the April 29, 2014 DWA, and

are summarized in Table 2

.

In laboratory studies, the proposed residues of concern oxalamide and sulfonate were formed

through aerobic soil metabolism at up to 14.8% and 9% of the applied parent compound,

respectively. The physical, chemical, and fate properties of oxalamide and sulfonate are

summarized in Table 3

.

Table 2. Physical, Chemical, and Environm ental Fate Properties of Dimethenamid-P.

Property Dimethenamid

‐ P Source/Comments

Chemical

Name

Formula

Smiles Code

CAS Number

Structure s

‐ dimethenamid (2

‐ chloro

‐ N

‐ (1

‐ methyl

‐ 2

‐ methoxy)ethyl)

‐ N

‐ (2,4

‐ dimethy

‐ thien

‐ 3

‐ yl)

acetamide

C

12 H

18 ClNO

2 S

163515

‐ 14

‐ 8

s1c(c([N@]([C@@H](C) COC)C(=O)CCl)c(c1)C)C

Molecular Weight 275.8 g/mole Product Chemistry

Solubility in water (25 o C) 1,449 mg/L MRID 44332214

s

‐ isomer

Vapor pressure (25 o C) 1.88 x 10

‐ 5 torr MRID 44332215

s

‐ isomer

Henry’s Law Constant 8.52 x 10

‐ 8 atm

‐ m 3 /mole DP Barcode: D285445

r/s isomer mixture

pKa (25 o C) No dissociation between pH 1 and pH 11 MRID 41596510

r/s isomer mixture

Octanol

‐ Water Partition

Coefficient (K

ow at 25 o C) 141 ± 6 MRID 41596511

r/s isomer mixture S H

N

C H

3

O

H

3 C O C

l H

3 C

C H

3

### Page 4 of 19 Property Dimethenamid

‐ P Source/Comments

Hydrolysis

(pH 5, 7, and 9 at 25 o C) Stable MRID 44332258

s

‐ isomer

Aqueous Photolysis

Half

‐ life (pH 7) 50 days MRID 44332259

s

‐ isomer

Dark corrected; 12 hour

light/12 hour dark

cycle.

Soil Photolysis

Half

‐ life 89 days MRID 44332260

s

‐ isomer

Dark corrected; 12 hour

light/12 hour dark

cycle.

Aerobic Soil Metabolism Half

‐ life 26 days (s

‐ isomer) at 25 o C

27 days (r/s mixture) at 25 o C

38 days (r/s mixture) at 25 o C

mean = 30 days

Maximum formed: 109.6 % applied

radioactivity MRIDs 44332261

s

‐ isomer and r/s isomer

mixture

(23 o C, temperature

‐ adjusted)

MRID 41596532 (25 o C)

r/s isomer mixture

Anaerobic Soil Metabolism Half

‐ life 54 days MRID 41706801

r/s isomer mixture

Anaerobic Aquatic Metabolism

Half

‐ life 36 days MRID 42367210

r/s isomer mixture

Soil Partition Coefficient K d 1.2, 1.4, 2.0, 2.1, 2.1, 2.5, 2.5, 3.0, 6.6, and 13.5

mL/g

mean = 3.59 mL/g MRID 44332263

s

‐ isomer on 5 American

soils and 5 foreign soils.

Soil Partition Coefficient K

oc 90, 101, 105, 123, 129, 212, 247, 393, 396, and

474 mL/g

oc

mean = 227 mL/g

oc MRID 44332263

s

‐ isomer on 5 American

soils and 5 foreign soils.

Terrestrial Field Dissipation 8 days (Missouri)

8 days (North Carolina)

4 days (Indiana)

43 days (Minnesota) MRID 42266202

MRID 42266203

MRID 42266204

MRID 42266205

r/s isomer mixture

Studies acceptable but

not representative of

worst

‐ case conditions.

### Page 5 of 19 Table 3. Physical, Chemical, and Environmenta l Fate Properties of Oxalamide and Sulfonate

Residues.

Property Dimethenamid Oxalamide Dimethenamid Sulfonate Source/

Comments

Chemical

Name

Registrant ID

Formula

Smiles Code

Structure (1RSaRS)

‐ N

‐ (2,4

‐ dimethyl

‐ 3

‐ thienyl)

‐ N

‐ (2methoxy

‐ 1

‐ methylethyl)

‐ oxamic acid

M23

C12 H17 N1 O4 S1

c1(csc(c1N(C(=O)(C(=O)(O)))C(C)

COC)C)C (1RSaRS)

‐ N

‐ (2,4

‐ dimethyl

‐ 3

‐ thienyl)

‐ N

‐ (2methoxy

‐ 1

‐ methylethyl)

‐ 2sulfonyl

‐

acetamide

M27

C12 H19 N1 O5 S2

c1 (C)c ( N(C(=O)CS(=O)(=O)O)C(C)

COC)c(C)sc1

Molecular Weight 271.33 g/mole 321.41 g/mole EpiSuite v. 4.1

Solubility in water

(25 o C) 4126 mg/L 1.098 mg/L EpiSuite v. 4.1

EpiSuite v. 4.1

Vapor pressure

(25 o C) 9.41E

‐ 008 mm Hg 9.89E

‐ 012 mm Hg EpiSuite v. 4.1

Henry’s Law

Constant 8.142 x 10

‐ 12 atm

‐ m3/mole 3.809 x 10

‐ 12 atm

‐ m3/mole EpiSuite v. 4.1

Octanol

‐ Water

Partition

Coefficient (K

ow at

25 o C) 0.75 1.02 EpiSuite v. 4.1

Hydrolysis

(pH 5, 7, and 9 at

25 o C) No data No data

Aqueous

Photolysis

Half

‐ life (pH 7) No data No data

Soil Photolysis

Half

‐ life No data No data S H N O O

O H

C H

3

O

C H

3 H

3 C

C H

3 C H

3

N O

S O

O

H

O C

H

3 O H

3 C H

3 C S H

### Page 6 of 19 Property Dimethenamid Oxalamide Dimethenamid Sulfonate Source/

Comments

Aerobic Soil

Metabolism Half

‐

life 24

‐ 41 days at 20 °C 2

mean 30 days

median 26 days

n = 3

Maximum formed: 14.8 %

applied radioactivity 3 40

‐ 140 days at 20 °C 2

mean 80 days

median 60 days

n = 3

Maximum formed: 9 % applied

radioactivity 3 2 EFSA Scientific

Report (2005) 53, 1

‐

73, Conclusion on

the peer review of

dimethenamid

3 MRIDs 44332261,

41596532, and

44083202

Anaerobic Soil

Metabolism Half

‐

life Stable Stable Conservative

Assumption

supported by

EpiSuite v. 4.1

Anaerobic

Aquatic

Metabolism Half

‐

life Stable Stable Conservative

Assumption

supported by

EpiSuite v. 4.1

Soil Partition

Coefficient K d 0.05

‐ 0.35 mL/g 0.0

‐ 0.43 mL/g EFSA Scientific

Report (2005) 53, 1

‐

73, Conclusion on

the peer review of

dimethenamid

Soil Partition

Coefficient K

oc 1.612 mL/g

oc 1

3.5

‐ 17 mL/g

oc 2

mean 7.7

median 6.0

n = 6 22.47 mL/g

oc 1

0.0

‐ 14 mL/g

oc 2

mean 6.7

median 6.9

n = 6 1 EpiSuite v. 4.1

2 EFSA 2Scientific

Report (2005) 53, 1

‐

73, Conclusion on

the peer review of

dimethenamid

Terrestrial Field

Dissipation DT 50 ’s

(Bare Soil) Germany: 45 and 18 days

France: 42 days

Italy: 98, 53 and 159 days Germany: 76 and 22 days

France: 25 and 42 days

Italy: 24, 74 and 137 days EFSA Scientific

Report (2005) 53, 1

‐

73, Conclusion on

the peer review of

dimethenamid; 1 st

order multi

‐

compartment

model used to

calculate half

‐ lives.



### Drinking Water Modeling

Models and Scenarios Used

For this addendum, The EDWCs for dimethenamid -P were generated using the SWCC model

(Surface Water Concentration Calculator version 1.106). EFED’s standard scenarios were used

and are listed in Table 

### 7 . The metadata for each scenario id entifies the growing season for the

### Page 7 of 19 crop of concern in that scenari o. The EDWCs were calculated based on the crop emergence date

identified in the scenario metadata and listed in Table 

### 8 . The only exception is the Georgia

Onion scenario, for which the application date is the same as the date used in a DWA conducted

for green onion in 2007 (D324972, D326977, D327936) . This was done for comparison

purposes. The Percent Cropped Area (PCA) factor of 1 was applied to all uses, per EFED PCA

guidance. Guidance for using PCAs and a thorou gh discussion of this method and comparisons

of monitoring and modeling results for selected pesticide/crop/site combinations is located at

http://www.epa.gov/oppefed1/models /water/pca_adjustment_dwa.html

.

Groundwater EDWCs for dimethenamid-P, resulting from its use on ornamentals, were derived

with PRZM-GW (Pesticide Root Zone M odel for Groundwater, version 1.07).

Detailed descriptions, documentation, and links for running the SWCC and PRZM-GW models

may found at http://www.epa.gov/oppefe d1/models/water/index.htm

.

Modeling Input Parameters

The application rate inputs used to model dimethenamid-P and its oxalamide, and sulfonate

degradates in surface water and groundwater were developed using the residue summation

approach outlined in EFED’s Draft Guidance for Modeling Pesticide Total Toxic Residues

(TTR) v.01 from January 3, 2013. Using this me thod, the dimethenamid-P application rates

were normalized according to the percentage of residue observed in th e aerobic soil metabolism

studies and the molecular weight ratio of the metabolite and parent compounds. Tables 4, 5, and

6 illustrate how model application rates are calculated from each dimethenamid-P use rate

considered in this addendum.

The model input parameters for SWCC and PRZM-GW are summarized in Table 7 and 8

, respectively

. Model input values were prepared following EFED input parameter guidance 1



### . Note that these tables include corrected half-life inputs for meta bolic degradation, as compared

to the April 29, 2014 DWA.

Subsequent to modeling EDWCs for each chemical and scenario combination, for each scenario

the daily time series outputs for each chemical we re summed to create daily time series. 1-in-10

year peak and annual averages, 30-year annual averages, peak, and pos t-breakthrough averages

were subsequently derived from each scenario-s pecific time series of the total residues.

1 Parameters selected for PRZM-EXAMS per Guidance for Selecting Input Parameters in Modeling the

Environmental Fate and Transport of Pesticides; Version 2.1, October 22, 2009 and Guidance on Modeling Offsite

Deposition of Pesticides via Spray Drift for Ecological and Drinking Water Assessments; October 20, 2013.

Parameters selected for PRZM-GW per PRZM-GW Input Parameter Guidance; Version 1.0, October 15, 2012.

### Page 8 of 19 Table 4. Residue Summation to Determine App lication Rate Inputs for Ornamental Uses

(1.5 lb ai/acre)

Chemical Species % Maximum in Aerobic Soil Studies Application

Rate

(kg/ha) Molecular

Weight Molecular

Ratio Model

Application

Rate

(kg/ha) Observed* MRID Normalized

Dimethenamid-P 109.6% 41596532 82.2% 1.38 275.80 1 1.38

Oxalamide 14.8% 41596532 11.1% 0.19 271.33 0.98 0.18

Sulfonate 9.0% 44083202 6.7% 0.11 321.41 1.17 0.13

Total 133.4% n/a 100.0%

* Observed maximum values for parent 1 and metabolite 1 in all acceptable aerobic soil studies



### Table 5. Residue Summation to Determine A pplication Rate Inputs for Green Onion Use

and second application of Proposed Cotton Use (0.98 lb ai/acre)

Chemical Species % Maximum in Aerobic Soil Studies Application

Rate

(kg/ha) Molecular

Weight Molecular

Ratio Model

Application

Rate

(kg/ha) Observed* MRID Normalized

Dimethenamid-P 109.6% 41596532 82.2% 0.90 275.80 1 0.90

Oxalamide 14.8% 41596532 11.1% 0.12 271.33 0.98 0.12

Sulfonate 9.0% 44083202 6.7% 0.07 321.41 1.17 0.09

Total 133.4% n/a 100.0%

* Observed maximum values for parent 1 and metabolite 1 in all acceptable aerobic soil studies



### Table 6. Residue Summation to Determine Applic ation Rate Inputs for first application of

Proposed Cotton Use (0.47 lb ai/acre)

Chemical Species % Maximum in Aerobic Soil Studies Application

Rate

(kg/ha) Molecular

Weight Molecular

Ratio Model

Application

Rate

(kg/ha) Observed* MRID Normalized

Dimethenamid-P 109.6% 41596532 82.2% 0.44 275.80 1 0.44

Oxalamide 14.8% 41596532 11.1% 0.06 271.33 0.98 0.06

Sulfonate 9.0% 44083202 6.7% 0.04 321.41 1.17 0.04

Total 133.4% n/a 100.0%

* Observed maximum values for parent 1 and metabolite 1 in all acceptable aerobic soil studies

### Page 9 of 19 Table 7. Dimethenamid-P, Oxalamide, and Sulfonate Inputs Used to Mo del Surface Water EDWCs

for Ornamentals, Spring Onion, and Propo sed Cotton Uses using the SWCC (v. 1.106).

Model

Input

Parameter Input Value and Unit

Source/Comments

Ornamentals Green

Onion Proposed

Cotton Use

PRZM

‐

EXAMS

Scenarios CA Nursery

FL Nursery

MI Nursery

NJ Nursery

OR Nursery

TN Nursery GA Onion MS Cotton

NC Cotton

CA Cotton

with

Irrigation Label for Reg. No. 7969

‐ 156, Outlook ®

Herbicide and the associated proposed

supplemental label for Cotton, and

label for Reg. No. 7969

‐ 239, Tower ®

Herbicide. All PRZM

‐ EXAMS scenarios

used are standard scenarios. The

second versions of the nursery

scenarios are used.

Maximum

Single

Application

Rate Parent: 1.38 kg ai/ha

Oxalamide: 0.18 kg ai/ha

Sulfonate 0.13 kg ai/ha Parent:

0.90 kg

ai/ha

Oxalamide:

0.12 kg

ai/ha

Sulfonate:

0.09 kg

ai/ha First

Application

Parent: 0.44

kg ai/ha

Oxalamide:

0.06 kg ai/ha

Sulfonate:

0.04 kg ai/ha

Second

Application

Parent: 0.90

kg ai/ha

Oxalamide:

0.12 kg ai /ha

Sulfonate:

0.0 9 kg ai /ha Label for Reg. No. 7969

‐ 156, Outlook ®

Herbicide and the associated proposed

supplemental label for Cotton, label

for Reg. No. 7969

‐ 239, Tower ®

Herbicide, and EFED Draft Residue

Summation Guidance, 2013

Ornamental rate: 1.68 kg ai/ha

Green Onion rate: 1.10 kg ai/ha

Proposed Cotton rates: 0.53 kg ai/ha

pre

‐ plant/pre

‐ emergence, 1.10 kg

ai/ha post

‐ emergence

Maximum

Number of

Applications 2 1 1 pre

‐ , 1 post

‐ Label for Reg. No. 7969

‐ 156, Outlook ®

Herbicide and the associated proposed

supplemental label for Cotton, and

label for Reg. No. 7969

‐ 239, Tower ®

Herbicide.

Method of

Application Ground Ground Aerial Label for Reg. No. 7969

‐ 156, Outlook ®

Herbicide and the associated proposed

supplemental label for Cotton, and

label for Reg. No. 7969

‐ 239, Tower ®

Herbicide. Ground and chemigation

applications may also be used for

Cotton, but were not assessed as

ground applications are expected to

result in lower EDWCs (i.e., decisions

based on aerial estimates are

protective of exposure expected from

ground and chemigation applications).

### Page 10 of 19 Model

Input

Parameter Input Value and Unit

Source/Comments

Ornamentals Green

Onion Proposed

Cotton Use

Application

Efficiency 0.99 0.99 0.95 December 2013 EFED Spray Drift

Guidance

Spray Drift

Fraction 0.066 0.066 0.135 December 2013 EFED Spray Drift

Guidance

Type of

Application Foliar Label for Reg. No. 7969

‐ 156, Outlook ®

Herbicide and the associated proposed

supplemental label for Cotton, and

label for Reg. No. 7969

‐ 239, Tower ®

Herbicide.

Initial Date

of

Application CA: 1

‐ Apr

FL: 1

‐ Feb

MI: 1

‐ Feb

NJ: 1

‐ Feb

OR: 1

‐ Feb

TN: 15

‐ Apr 15

‐ Jun MS: 1

‐ May

NC: 1

‐ Jun

CA: 1

‐ May Nursery and Cotton application dates

begin at crop the crop maturity dates

listed in scenario metadata. GA Onion

application date chose n for

comparison with prior ED WC

estimates.

Minimum

Interval

between

Applications 42 days n/a 14 days Label for Reg. No. 7969

‐ 156, Outlook ®

Herbicide and the associated proposed

supplemental label for Cotton, and

label for Reg. No. 7969

‐ 239, Tower ®

Herbicide.

Soil

Partition

Coefficient

K

oc Parent: 227 mL/g

oc (mean)

Oxalamide: 7.7 mL/g

oc (mean)

Sulfonate: 6.7 mL/g

oc (mean) Parent: MRID 44332263; mean of K

oc ’s

for 5 US soils and 5 foreign soils.

Degradates: Mean K

oc ’s reported in

EFSA Scientific Report (2005) 53, 1

‐ 73,

Conclusion on the peer review of

dimethenamid.

Henry’s Law

Constant Parent: 8.52 x 10

‐ 8 atm

‐ m 3 /mole

Oxalamide: 8.142E

‐ 012 atm

‐ m3/mole

Sulfonate: 3.809E

‐ 012 atm

‐ m3/mole Parent: DP Barcode D285445.

Measured on the r/s isomer mixture.

Degradates: EpiSuite v. 4.1

Hydrolysis Stable Parent: MRID 44332258. Stable at pH

5, 7, and 9.

Degradates: No data available;

assumed to be stable.

Aerobic Soil

Metabolism

Half

‐ life

(25 o C) Parent: 38 days

Oxalamide: 29 days

Sulfonate: 99 days Parent: MRIDs 44332261 and

41596532. Upper 90th percentile of

three half

‐ lives (two with r/s isomer

mixture as the test substance). Two of

the three half

‐ lives were temperature

‐ adjusted.

### Page 11 of 19 Model

Input

Parameter Input Value and Unit

Source/Comments

Ornamentals Green

Onion Proposed

Cotton Use

Degradates: Highest aerobic soil

metabolism half

‐ life reported in EFSA

Scientific Report (2005) 53, 1

‐ 73,

Conclusion on the peer review of

dimethenamid, (adjusted for

temperature.)

Aerobic

Aquatic

Metabolism

Half

‐ life

(25 o C) Parent: 76 days

Oxalamide: stable

Sulfonate: stable Parent: No data available; used 2 X

aerobic soil metabolism half

‐ life input

according to EFED Input Parameter

Guidance.

Degradates: No data available;

assumed to be stable.

Anaerobic

Aquatic

Metabolism

Half

‐ life

(25 o C) Parent: 108 days

Oxalamide: stable

Sulfonate: stable Parent: MRID 42367210. 3 x single

reported half

‐ life value measured on

the r/s isomer mixture.

Degradates: No data available;

assumption that it is stable is

consistent with estimate from EpiSuite

v. 4.1

Aqueous

Photolysis

Half

‐ life

(40 o

Latitude) Parent: 50 days

Oxalamide: stable

Sulfonate: stable Parent: MRID 44332259. Dark

corrected; 12 hour light/12 hour dark

cycle.

Degradates: No data available;

assumed to be stable.

Vapor

pressure Parent: 1.88 x 10

‐ 5 torr

Oxalamide: 9.41E

‐ 008 torr

Sulfonate: 9.89E

‐ 012 torr Parent: MRID 44332215

Degradates: EpiSuite v. 4.1

Solubility in

water

(25 o C) Parent: 1,449 mg/L

Oxalamide: 4126 mg/L

Sulfonate: 1.098 mg/L Parent: MRID 44332214

Degradates: EpiSuite v. 4.1

Molecular

Weight Parent: 275.8 g/mole

Oxalamide: 271.33 g/mole

Sulfonate: 321.41 g/mole Product Chemistry & EpiSuite v. 4.1

### Page 12 of 19 Table 8. Dimethenamid-P, Oxalamide, and Sulfo nate Inputs Used to Model Groundwater EDWCs

for Ornamental Uses using PRZM-GW (v. 1.07).

Model Input

Parameter Dimethenamid

‐ P Oxalamide Sulfonate

Source/Comments

PRZM

‐ GW Input Value and Unit

Maximum

Application Rate 1.38 kg ai/ha 0.18 kg ai/ha 0.13 kg ai/ha Label for Reg. No. 7969

‐ 239, Tower ®

Herbicide, and EFED Residue

Summation Method Draft Guidance,

2013

Method of

Application Foliar Label for Reg. No. 7969

‐ 239, Tower ®

Herbicide

Date of Initial

Application 0 days post

‐ emergence Emergence dates are specified in

each PRZM

‐ GW scenario.

Maximum #

Applications 2 Label for Reg. No. 7969

‐ 239, Tower ®

Herbicide

Minimum

Interval

between

Applications 42 days Label for Reg. No. 7969

‐ 239, Tower ®

Herbicide

Soil Partition

Coefficient K

oc 227 mL/g

oc (mean) 7.7 mL/g

oc (mean) 6.7 mL/g

oc (mean) Parent: MRID 44332263; mean of

K

oc ’s for 5 US soils and 5 foreign

soils.

Degradates: Mean K

oc ’s reported,

from EFSA Scientific Report (2005)

53, 1

‐ 73

Hydrolysis Half

‐

Life Stable Parent: MRID 44332258

Oxalamide and Sulfonate: assumed

to be stable to hydrolysis.

Aerobic Soil

Metabolism

Half

‐ Life (25°C) 38 days

(90th percent

upper bound on

mean using

temperature

‐ adjusted half

‐ lives) 29 days

(Highest half

‐

life reported

by EFSA,

adjusted for

temperature) 99 days

(Highest half

‐

life reported by

EFSA, adjusted

for

temperature) Parent: MRIDs 44332261 and

41596532.

Oxalamide and Sulfonate: EFSA

Scientific Re port (200 5) 53

, 1

‐ 73,

Conclusion on the peer review of

dimethenamid

### Page 13 of 19 Modeling Results

Surface Water

Table 9 reports the EDWCs calculated for each SWCC ( i.e. , surface water) scenario.

For ornamentals, the maximum 1-in-10 year peak EDWCs in surface water range from 29 to 73

μg/L, the 1-in-10 year annual average EDWCs in surface water range from 9 to 27 μg/L, and the

30-year average EDWCs range from 6 to 16 μg/L. The New Jersey Nursery scenario results in

the maximum surface water EDWCs for ornamentals.

For green onion, the 1-in-10 year acute EDWC in surface water is 57 μg/L, the 1-in-10 year

annual EDWC in surface water is 10 μg/L, a nd the 30-year average EDWC is 6 μg/L.

For the proposed cotton use, the maximum 1-in-10 year acute EDWCs in surface water range

from 9 to 61 μg/L, the 1-in-10 year annual EDWC s in surface water rang e from 3 to 14 μg/L,

and the 30-year overall average EDWCs range from 3 to 8 μg/L. The Mississippi Cotton and

North Carolina Cotton scenarios result in the maximum 1-in-10 year acute EDWC while the

North Carolina Cotton scenario results in th e maximum 1-in-10 year chronic and 30-year

average EDWCs.

Table 9. Tier II Total Dimethenamid-P Resi dues (Parent, Oxalamide, and Sulfonate)

Surface Water EDWCs for Ornamental, Green Onion, and Proposed Cotton Uses.

Use Use

Assumptions Application

Rates (lb

a.i./acre) and

Reapplication

Intervals PRZM

‐

EXAMS

Scenario First

Application

Date 1

‐ in

‐ 10 year EDWC 30

‐ Year

Average

Peak Annual Overall

day

‐ month μg/L

Existing Uses

Ornamentals Ground Spray Maximum

Single: 1.5

Maximum

Annual: 3.0

Minimum Re

‐ Application

Interval: 42

days CA

Nursery 1

‐ Apr 31 23 15

FL Nursery 1

‐ Feb 44 10 6

MI

Nursery 1

‐ Feb 29 12 10

NJ

Nursery 1

‐ Feb 73 27 16

OR

Nursery 1

‐ Feb 30 14 9

TN

Nursery 15

‐ Apr 48 13 8

Green Onion Ground Spray Maximum

Single &

Annual: 0.98 GA Onion 15

‐ Jun 57 10 6

Proposed Ornamental Uses

### Page 14 of 19 Cotton Aerial* Maximum

Single: 0.98

Maximum

Annual: 1.45

Minimum Re

‐ Application

Interval: 14

days CA Cotton

(irr) 1

‐ May 9 3 3

MS

Cotton 1

‐ May 61 12 6

NC Cotton 1

‐ Jun 61 14 8

*Ground spray use on cotton was not assessed.



### Ground Water

Table 10 reports the Tier I groundwater EDWCs calcu lated using PRZM-GW; the peak EDWCs

in this 30-year simulation range from 36 to 153 μg/L, while the post-breakthrough average

EDWCs range from 31 to 140 μg/L. The Wisconsin Corn scenario results in the maximum

EDWCs for the ornamental use, as well as the maximum EDWCs for all the uses considered in

this assessment.

Table 10. Tier I Groundwater EDWCs for Ornamental Uses of Dimethenamid-P and its Residues -

30-Year Simulation.

PRZM

‐ GW Scenario Peak

(μg/L) Time to Breakthrough (days) Post

‐ Breakthrough

Average*

(μg/L)

DMV Corn 77 Parent: 3747

Oxalamide: 1166

Sulfonate: 1155 66

FL Citrus 130 Parent: 3000

Oxalamide: 793

Sulfonate: 783 106

FL Potato 46 Parent: 5525

Oxalamide: 706

Sulfonate: 684 34

GA Peanuts 36 Parent: 4976

Oxalamide: 1340

Sulfonate: 1324 31

NC Cotton 63 Parent: 4053

Oxalamide: 2024

Sulfonate: 2015 51

WI Corn 153 Parent: 5411

Oxalamide: 2475

Sulfonate: 2461 140

*Calculated using longest time to breakthrough of the three chemicals modeled.

### Page 15 of 19 Data and Modeling Uncertainties

 Aerobic aquatic metabolism data have not been submitted for dimethenamid-P. This lack

of data introduces uncertainty into the dr inking water concentration estimates. To

account for this uncertainty, the half-life us ed in modeling assumes that the aerobic

aquatic metabolism half-life is twice as long as the aerobic soil metabolism half-life (per

EFED Input Parameter Guidance).

 In the anaerobic aquatic metabolism study, only a single half-lif e value could be

estimated from the data provided. Use of a single anaerobic aquatic metabolism half-life

(as opposed to multiple half-lives) introdu ces uncertainty into the drinking water

concentration estimates. To account for this uncertainty, the half- life used in modeling

assumes that the anaerobic aquatic metabolis m is three times as long as the half-life

derived from the study data (per EFED Input Parameter Guidance).

 Data on the oxalamide and sulfonate degradates have not been submitted by the

registrant, as oxalamide and sulfonate have not previously been considered as part of the

residues of concern. Registrant-submitted da ta are not available for the degradates;

therefore, model inputs were based on data from EpiSuite v. 4.1 and the 2005 European

Food Safety Authority (EFSA) Scientific Re port on dimethenamid. Because the EFSA

report did not include raw data from the study or information on individu al laboratory test

systems in the aerobic soil metabolism and adsorption/desorption studies referenced,

EPA could not verify the accuracy of the half-lives and K

oc 

### s reported for oxalamide and

sulfonate. Additionally, it is assumed that Eu ropean soils were used to develop aerobic

soil metabolism half-lives and adsorption coefficients, which may or may not be

representative of US soils. This intr oduces some uncertainty into the EDWCs.

Monitoring Data

Surface- and groundwater data from one stat e and three nationwide pesticide monitoring

programs were reviewed to pr ovide additional context concer ning the potential presence of

dimethenamid-P in drinking water resources. These water monitoring programs do not target

sample collection to peak use loca tions or application times for pa rticular pesticides, nor do they

target sample collection to high precipitation events ( i.e.

, high-runoff events). Additionally, the

sampling frequency in these monitoring pr ograms was not designed to capture peak

concentrations. Therefore, the monitoring data reported by these program s may not represent the

highest concentrations in drinki ng water source water, and are cons idered qualitative information

for the purposes of this drinking water assessment.

USGS-EPA Pilot Reservoir Monitoring Program

- Dimethenamid-P data were not analyzed as

part of this program.

USGS National Water-Quality Assessment (NAWQA) Program Data

– NAWQA program data

are available at http://infotrek.er.usgs.gov/nawqa_queries/index.jsp . Although USGS NAWQA

surface water and groundwater data specific to the s- isomer of dimethenamid were not available,

USGS NAWQA has conducted mon itoring for dimethenamid and dimethenamid degradates.

### Page 16 of 19 Table 11, 12, and Table 2 

### 3 summarize the findings for surface water, treated water supplies and

groundwater, respectively. Surface water monito ring data indicate that dimethenamid

concentrations occur up to 7 μg/L, which is within one to two orders of magnitude of the peak

EDWCs modeled for dimethenamid-P in this ad dendum. Dimethenamid degradates in surface

water and groundwater are measured at levels le ss than 0.5 μg/L. Groundwater monitoring data

indicate that dimethenamid occurs at levels lo wer than the limit of quant ification (0.02 μg/L).

Dimethenamid was present in trea ted drinking water up to 0.12 μg/L.

Table 11. USGS-NAWQA Surface Water Monitori ng Data for Dimethenamid, Oxalamide, and

Sulfonate.

Compound CAS Number* NAWQA

Parameter

Code(s) n n at

or

above

the

LOQ Detection

Frequency Concentration

Range

(μg/L) County, State,

and Timing of

Maximum

Measured

Concentration

Dimethenamid

Oxanilic Acid none

identified 62482,

68581 1387 83 6% < 0.02

‐ 0.46 Kent, MD

Spring 2004

Dimethenamid

Sulfonic Acid 205939

‐ 58

‐ 8 61951,

68582 1387 212 15% < 0.079

‐ 0.36 Hancock, IN

and Kent,

MD

Spring 2003

Dimethenamid 87674

‐ 68

‐ 8 61588,

68580 623 88 14% < 0.02

‐ 7 Dodge, NE

Spring 2004

*CAS Number as reported by USGS NAWQA



### Table 12. USGS-NAWQA Treated Water Supply Moni toring Data for Dimethenamid, Oxalamide,

and Sulfonate.

Compound CAS Number* NAWQA

Parameter

Code(s) n n at

or

above

the

LOQ Detection

Frequency Concentration

Range

(μg/L) County, State,

and Timing of

Maximum

Measured

Concentration

Dimethenamid

Oxanilic Acid none

identified 62482,

68581 44 0 0% < 0.02 n/a

Dimethenamid

Sulfonic Acid 205939

‐ 58

‐ 8 61951,

68582 44 0 0% < 0.02 n/a

Dimethenamid 87674

‐ 68

‐ 8 61588,

68580 44 1 2% < 0.02

‐ 0.12 Hamilton, IN

Spring 2005

*CAS Number as reported by USGS NAWQA



### Table 23. USGS-NAWQA Groundwater Monitoring Data for Dimethenamid, Oxalamide, and

Sulfonate.

Compound CAS Number* NAWQA

Parameter

Code(s) n n at

or

above

the

LOQ Detection

Frequency Concentration

Range

(μg/L) County, State,

and Timing of

Maximum

Measured

Concentration

Dimethenamid

Oxanilic Acid none

identified 62482,

68581 1131 3 <1% <0.02

‐ 0.15 Jasper, IN

Spring 2012

Dimethenamid

Sulfonic Acid 205939

‐ 58

‐ 8 61951,

68582 1132 19 2% <0.02

‐ 0.31 Jasper, IN

Spring 2012

### Page 17 of 19 Compound CAS Number* NAWQA

Parameter

Code(s) n n at

or

above

the

LOQ Detection

Frequency Concentration

Range

(μg/L) County, State,

and Timing of

Maximum

Measured

Concentration

Dimethenamid 87674

‐ 68

‐ 8 61588,

68580 835 0 0% <0.02 or <0.5 n/a

*CAS Number as reported by USGS NAWQA



### California Surface Water Monitoring Program Data

- The California surface water monitoring

program represents pesticide occurrence data fo r surface waters in the Sacramento Valley, San

Joaquin Valley, and other locations in the state. California Surface Water Monitoring Program

data are available at http://www.cdpr.ca.gov/docs/emon/surfwtr/surfdata.htm . The California

surface water and ground water monitoring data did not include any data for the s-isomer or

other isomers or degradates of dimethenamid.

Pesticide Data Program (PDP) Data - The PDP drinking water mon itoring project provides nontargeted pesticide occurrence data in raw, fini shed (treated/tap), and gr ound water in the United

States. PDP data are available at http://www.ams.usda.gov/AMSv1.0/pdp

. Table 14, 15, and 16 summarize the findings for untreated drinking water, treated drinking

water, and groundwater, respectively, from 2008 to 2012. Older PDP monitoring data for

dimethenamid and dimethenamid/dimethenamid-P from 1992 to 2007 may be accessed on the

PDP website.

Concentrations of dimethenamid/dimethenamid- P in untreated drinking water were observed up

to 0.5 μg/L. Concentrations of dimethenamid/dim ethenamid-P in treated drinking water were an

order of magnitude lower than concen trations in the untreated water.

Dimethenamid alone reached only 0.02 μg/L in untre ated drinking water. The concentrations of

dimethenamid in treated versus untreat ed drinking water are comparable ( i.e., within the same

orders of magnitude). Dimethenamid/dimethenamid-P reached 0.004 μg/L in groundwater, and

dimethenamid was not detected in groundwater.

The frequency with which dimethenamid and dimethenamid/dimethenamid-P are detected is

upwards of 30% in untreated drinking water, wh ich is very high. Dete ction frequencies in

treated drinking water are sligh tly lower, but still reach 20%. The data indicate that

dimethenamid and dimethenamid/dimethenami d-P are rarely detected in groundwater.

Dimethenamid oxanilic acid was detected in untr eated drinking water, treated drinking water,

and groundwater at maximum concentrations of 0.061, 0.030, 0.0323 μg/L, respectively. It was

detected most frequently in untreated drinking water, where it reached a detection frequency of

42%. Its highest detection frequencies in treat ed drinking water and gr oundwater were 15% and

2%, respectively.

Dimethenamid ethanesulfonic acid was not regularl y detected or measured in surface drinking

water sources, but was detected at a maximum concentration of 0.193 μg/L in groundwater. Its

frequency of detection in groundwater reached 9%.

### Page 18 of 19 Table 14. PDP Untreated Drinking Water Monito ring Data for Dimethenamid, Oxalamide, and

Sulfonate (peak concentrations and LOD rang es reported in ng/L, or parts per trillion).

Compound 2012 2011 2010 2009 2008

Peak

(ng/L) Freq. Peak

(ng/L) Freq. Peak

(ng/L) Freq. Peak

(ng/L) Freq. Peak

(ng/L) Freq.

Dimethenamid/Dimethenamid

P 220 30%

Not Measured 140 13% 510 23% 26 21%

LOD Range (ng/L) 0.91

‐ 10 2.5 2.5 2.5

Dimethenamid

Not Measured 20 29% 33 30% 4.2 15% 5.5 4%

LOD Range (ng/L) 0.60 0.60 0.60 0.60

Dimethenamid Ethanesulfonic

Acid ND 0%

Not Measured Not Measured Not Measured Not Measured

LOD Range (ng/L) 2.0

Dimethenamid Oxanilic Acid 57 27% 31 31% 61 36% 47 42%

LOD Range (ng/L) 0.63

‐ 3.0 0.63 0.63 0.63



### Table 15. PDP Treated Water Supply Monitoring Data for Dimethenamid, Oxalamide, and

Sulfonate (peak concentrations and LOD rang es reported in ng, or parts per trillion).

Compound 2012 2011 2010 2009 2008

Peak

(ng/L) Freq. Peak

(ng/L) Freq. Peak

(ng/L) Freq. Peak

(ng/L) Freq. Peak

(ng/L) Freq.

Dimethenamid/Dimethenamid P 38 20%

Not Measured 47 5% 17 7% 12 8%

LOD Range (ng/L) 0.91

‐ 10 2.5 2.5 2.5

Dimethenamid

Not Measured 12 14% 5.3 5% 1 3% 18 4%

LOD Range (ng/L) 0.60 0.60 0.60 0.60

Dimethenamid Ethanesulfonic

Acid ND 0%

Not Measured Not Measured Not Measured Not Measured

LOD Range (ng/L) 2.0

Dimethenamid Oxanilic Acid 4.8 13% 8.8 15% 21 12% 30 13%

LOD Range (ng/L) 0.63

‐ 3.0 0.63 0.63 0.63



### Table 16. PDP Groundwater Monitoring Data for Dimethenamid, Oxalamide, and Sulfonate (peak

concentrations and LOD ranges reporte d in ng, or parts per trillion).

Compound 2012 2011 2010 2009 2008

Peak

(ng/L) Freq. Peak

(ng/L) Freq. Peak

(ng/L) Freq. Peak

(ng/L) Freq. Peak

(ng/L) Freq.

Dimethenamid/Dimethenamid P ND 0% 4.2 1%

Not Measured Not Measured Not Measured

LOD Range (ng/L) 0.91

‐ 10 0.91

‐ 2.5

Dimethenamid Not Measured ND 0% ND 0% ND 0% ND 0%

### Page 19 of 19 Compound 2012 2011 2010 2009 2008

Peak

(ng/L) Freq. Peak

(ng/L) Freq. Peak

(ng/L) Freq. Peak

(ng/L) Freq. Peak

(ng/L) Freq.

LOD Range (ng/L) 10.0 0.60

‐ 10 10.0 10.0

Dimethenamid Ethanesulfonic

Acid 10.7 7% 24.2 9% ND 0% 80.3 2% 193 1%

LOD Range (ng/L) 3.0

‐ 10.7 2.0 2.0 2.0 2.0

Dimethenamid Oxanilic Acid 32.3 1% 20.2 2% ND 0% 15.4 <1% 13 1%

LOD Range (ng/L) 5.0

‐ 32.3 0.63

‐ 3.0 3.0 3.0 3.0