UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

OFFICE OF 

CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

PC Code: 120051 

DP Barcode: 422167 

MEMORANDUM August 14, 2014 

SUBJECT: 

TO: 

FROM: 

REVIEWED 

BY: 

Dimethenamid-P: ADDENDUM: Drinking Water Exposure Assessment for 

Existing Ornamental and Green Onion Uses and the Proposed Cotton Use 

Elissa Reaves, Branch Chief, RAB4 

Bonnie Cropp-Kohlligian, Environmental Scientist 

Health Effects Division (7509P) 

Daniel Kenny, Branch Chief 

Kable Davis, Product Manager 25 

Erik Kraft, Risk Manager Reviewer 

1 

Registration Division (7505P) 

Melanie Biscoe, Physical Scientist 

Environmental Risk Branch 3 

Environmental Fate and Effects Division 

Rosanna Louie-Juzwiak, RAPL 

EnvironmentalRiskBranch3 

Environmental Fate and Effects Division 

THROUGH: Dana Spatz, Branch Chie 

Environmental Risk Branch 3 

Environmental Fate and Effects Division (7507P) 

Executive Summary 

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

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

Page 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 using the Residue Summation Approach 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 assessment result from the modeled ornamental uses, 

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

dimethenamid-P and its residues of concern is 73 μg/L, the highest estimated 1-in-10 year annual 

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

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

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

using the maximum groundwater EDWC values 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

μg/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-dimethenamid, 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 Environmental 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

C12H18ClNO2

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  (25oC) 1,449 mg/L MRID 44332214

s‐isomer

Vapor pressure (25oC) 1.88 x 10‐5 torr

MRID 44332215

s‐isomer

Henry’s Law Constant 8.52 x 10‐8 atm‐m3/mole DP Barcode: D285445

r/s isomer mixture

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

r/s isomer mixture

Octanol‐Water Partition  

Coefficient (Kow at 25o

C) 141 ± 6 MRID 41596511r/s isomer mixture

SH

N

CH3

O

H3C

O

Cl

H3C

CH3
Page 4 of 19

Property Dimethenamid‐P Source/Comments

Hydrolysis  

(pH 5, 7, and 9 at 25o

C) Stable MRID 44332258s‐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 25o

C

27 days (r/s mixture) at 25o

C

38 days (r/s mixture) at 25o

C

mean = 30 days

Maximum formed: 109.6 % applied

radioactivity

MRIDs 44332261

s‐isomer and r/s isomer

mixture

(23o

C, temperature‐

adjusted)

MRID 41596532 (25o

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 42367210r/s isomer mixture

Soil Partition Coefficient  Kd

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  Koc

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

474 mL/goc

mean = 227 mL/goc

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 Environmental 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  

(25o

C) 4126 mg/L 1.098 mg/L EpiSuite v. 4.1EpiSuite v. 4.1

Vapor pressure

(25o

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 (Kow at

25o

C)

0.75 1.02 EpiSuite v. 4.1

Hydrolysis  

(pH 5, 7, and 9 at

25o

C)

No data No data   

Aqueous

Photolysis  

Half‐life (pH 7)

No data No data   

Soil Photolysis  

Half‐life No data No data   

SH

N

O

O

OH

CH3

O

CH3

H3C

CH3

CH3

N

O

S

O

O

HO

CH3

O H3C

H3C

SH
Page 6 of 19

Property Dimethenamid Oxalamide Dimethenamid Sulfonate Source/

Comments

Aerobic Soil

Metabolism Half‐

life  

24 ‐ 41 days at 20 °C2

mean 30 days

median 26 days

n = 3

Maximum formed: 14.8 %

applied radioactivity3

40 ‐ 140 days at 20 °C2

mean 80 days

median 60 days

n = 3

Maximum formed: 9 % applied

radioactivity3

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  Kd

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  Koc

1.612 mL/goc1

3.5 ‐ 17 mL/goc2

mean 7.7

median 6.0

n = 6

22.47 mL/goc1

0.0 ‐ 14 mL/goc2

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 DT50’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; 1st

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 identifies the growing season for the 
Page 7 of 19

crop of concern in that scenario. 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 thorough 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 Model 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/oppefed1/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 method, the dimethenamid-P application rates 

were normalized according to the percentage of residue observed in the 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 guidance1

. 

Note that these tables include corrected half-life inputs for metabolic 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 were summed to create daily time series. 1-in-10 

year peak and annual averages, 30-year annual averages, peak, and post-breakthrough averages 

were subsequently derived from each scenario-specific 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 Application 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 Application 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 Application 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 Model Surface Water EDWCs 

for Ornamentals, Spring Onion, and Proposed 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:

0.09 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 DriftGuidance

Spray Drift

Fraction 0.066 0.066 0.135 December 2013 EFED Spray DriftGuidance

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 chosen for

comparison with prior EDWC

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  

Koc

Parent: 227 mL/goc (mean)

Oxalamide: 7.7 mL/goc (mean)

Sulfonate: 6.7 mL/goc (mean)

Parent: MRID 44332263; mean of Koc’s

for 5 US soils and 5 foreign soils.

Degradates: Mean Koc’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‐m3

/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

(25o

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

(25o

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

(25o

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

(40o

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  

(25o

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 Sulfonate 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 ineach 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 Koc

227 mL/goc  

(mean)

7.7 mL/goc

(mean)

6.7 mL/goc

(mean)

Parent: MRID 44332263; mean of

Koc’s for 5 US soils and 5 foreign

soils.

Degradates: Mean Koc’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 Report (2005) 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, and 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 EDWCs in surface water range 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 the maximum 1-in-10 year chronic and 30-year 

average EDWCs. 

Table 9. Tier II Total Dimethenamid-P Residues (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 calculated 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 drinking water concentration estimates. To 

account for this uncertainty, the half-life used 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-life value could be 

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

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

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

assumes that the anaerobic aquatic metabolism 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 data 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 Report on dimethenamid. Because the EFSA 

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

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

EPA could not verify the accuracy of the half-lives and Kocs reported for oxalamide and 

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

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

representative of US soils. This introduces some uncertainty into the EDWCs. 

Monitoring Data 

Surface- and groundwater data from one state and three nationwide pesticide monitoring 

programs were reviewed to provide additional context concerning the potential presence of 

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

sample collection to peak use locations or application times for particular pesticides, nor do they 

target sample collection to high precipitation events (i.e., high-runoff events). Additionally, the 

sampling frequency in these monitoring programs was not designed to capture peak 

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

highest concentrations in drinking water source water, and are considered 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 monitoring for dimethenamid and dimethenamid degradates. 
Page 16 of 19

Table 11, 12, and Table 23 summarize the findings for surface water, treated water supplies and 

groundwater, respectively. Surface water monitoring 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 addendum. Dimethenamid degradates in surface 

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

indicate that dimethenamid occurs at levels lower than the limit of quantification (0.02 μg/L). 

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

Table 11. USGS-NAWQA Surface Water 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 1387 83 6% < 0.02 ‐ 0.46 Kent, MDSpring 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, NESpring 2004

*CAS Number as reported by USGS NAWQA

Table 12. USGS-NAWQA Treated Water Supply 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 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, INSpring 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, INSpring 2012

Dimethenamid

Sulfonic Acid 205939‐58‐8   61951,68582 1132 19 2% <0.02 ‐ 0.31 Jasper, INSpring 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 for 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 monitoring project provides nontargeted pesticide occurrence data in raw, finished (treated/tap), and ground 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/dimethenamid-P in treated drinking water were an 

order of magnitude lower than concentrations in the untreated water. 

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

dimethenamid in treated versus untreated 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, which is very high. Detection frequencies in 

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

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

Dimethenamid oxanilic acid was detected in untreated 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 treated drinking water and groundwater were 15% and 

2%, respectively. 

Dimethenamid ethanesulfonic acid was not regularly 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 Monitoring Data for Dimethenamid, Oxalamide, and 

Sulfonate (peak concentrations and LOD ranges 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 ranges 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 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 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