U. S. ENVIRONMENTAL PROTECTION AGENCY 

Washington, D.C. 20460 

OFFICE OF 

CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

Date: September 11, 2014 

PC Code: 103901 

DP Barcode: DP 422778 

MEMORANDUM 

SUBJECT: 

TO: 

FROM: 

THRU: 

Drinking Water Assessment in support of the Registration Review Preliminary 

Risk Assessment and Clarification on the Degradates of Concern for the Sodium 

Salt ofBentazon 

Carolyn Schroeder, Chemical Review Manager 

Kathryn Montague, Risk Manager 

Risk Management and Implementation Branch IV 

Pesticide Re-evaluation Division (7508P) 

Stephen P. Wente, Ph.D., Biologist 

Environmental Risk Branch I 

__sr~ 

Environmental Fate and Effects Division (7;~4P) }q. ~ 

Sujatha Sankula, Ph.D., Branch Chief .~-L~._,___ =:<""' 

Environmental Risk Branch I 

Environmental Fate and Effects Division (7504P) 

This memo addresses two subjects: the sodium salt of bentazon (hereafter referred to as 

bentazon) drinking water assessment (DWA) and the clarification on the degradates of concern 

for bentazon. 

Drinking Water Assessment for Bentazon 

The environmental Fate and Effects Division (EFED) has developed a conservative (tier 1) 

DWA for bentazon uses in support of the Bentazon Registration Review. Typically EFED would 

prepare a more refined (higher tier) DWA for bentazon because previous Agency assessments 

have identified ground and surface water as an important source of bentazon exposure to humans 

(USEPA 1994). However, there are two reasons that suggest a lower tier assessment is 

appropriate. First, the Health Effects Division has recently revised the chronic drinking water 

endpoint to a higher (less toxic) value, which will reduce the need for a higher tier DWA:. 

Second, many of the bentazon labels are missing important application information (number of 

1 
2 

applications on an annual basis, annual application rate, and re-application intervals) necessary 

for the higher tier DWA (the Agency is currently working with registrants to remedy these label 

omissions). Rather than delay the time-line for the registration review of bentazon, EFED is 

providing a conservative assessment which HED believes will not result in chronic risk concerns 

(George Kramer email, 8/28/2014) based on the revised chronic endpoint. If this conservative 

assessment does for unforeseen reasons result in risk issues, a more refined (higher tier) DWA 

for surface water and groundwater sources will be produced once the label issues are rectified. 

Bentazon has a rice use for which label information is sufficient. EFED has a Tier 1 Rice Model1

which produces highly conservative estimates because it does not consider degradation in the 

rice paddy. Additionally, the rice model EDWCs will not be adjusted by the percent crop 

adjustment (PCA) factors. EFED believes these estimated drinking water concentrations 

(EDWCs) would be much higher than any of the other bentazon uses2

. Based on two applications 

of 1.1 lbs ai/acre for a total application of 2.2 lbs ai/acre/year and a Kd of 0.898 (MRID 

40470501), the tier 1 Rice Model produces a surface water EDWC of 2112 μg/L for both 

acute and chronic risk concerns. Therefore EFED believes all of the other uses of bentazon 

would produce EDWCs lower than this conservative value for both surface and groundwater. 

USGS NAWQA monitoring data has maximum bentazon concentrations in surface water of 8.6 

μg/L and 11.46 in groundwater. This monitoring is not targeted to bentazon applications in 

neither time nor location. This contrasts with a registrant-submitted aquatic field dissipation 

study (MRID 43431901) of applications to rice paddies, which measured a peak concentration of 

3157 μg/L. However, this application was to only a 1.38 in. depth of paddy water (the Tier 1 

Rice Model assumes a 3.94 in. depth). (Note that unlike the Tier 1 Rice Model, the measured 

concentration in rice paddy water dropped to 912 μg/L after 1 day and to 500 μg/L after 7 days.) 

Clarification on the Degradates of Concern for Bentazon 

In preparation for the registration review of bentazon, a meeting was held on August 14, 2014 

between the Health Effects and Environmental Fate and Effects Divisions to better identify 

bentazon degradates of concern to be included in the registration review drinking water 

assessment. The meeting was organized by Ed Scollon of EFED. Other EFED attendees included 

Sujatha Sankula, Meghan Radtke, and Steve Wente. HED attendees included Charles Smith, 

Anwar Dunbar, George Kramer, and Ray Kent. The meeting identified O-amino-N-isopropyl 

benzamide (AIBA), O-nitro-N-isopropyl benzamide, O-nitroso-N-isopropylbenzamide, 

photoproduct 10 from MRID 00040785, and 8-Cl-bentazon as degradates of concern (see 

Appendix A for structures). 

 

1 http://www.epa.gov/oppefed1/models/water/index.htm#rice

2

 Other applications include foliar applications: alfalfa, clover grown for seed, beans, beans, dried-type, beans, 

succulent, beans, succulent (lima), peas, dried-type, and peas, succulent, corn (silage), corn (unspecified), corn, 

field, corn, pop, and corn, sweet, flax, nonagricultural rights-of-way/fencerows/hedgerows, and nonagricultural 

uncultivated areas/soils, nursery stock, ornamental and/or shade trees, ornamental herbaceous plants, ornamental 

lawns and turf, ornamental nonflowering plants, and ornamental woody shrubs and vines, ornamentals (unspecified), 

paved areas (private roads/sidewalks), peanuts (unspecified), peppermint and spearmint, residential lawns, sorghum 

and sorghum (silage), soybeans (unspecified), and soybeans, edible (edamame); as well as at planting/pre-plant 

applications: almond, apple, apricot, avocado, blackberry, blueberry, cherry, crabapple, date, fig, grapefruit, grapes, 

lemon, lime, macadamia nut (bushnut), nectarine, olive, orange, peach, pear, pecan, pistachio, plum, pomegranate, 

prune, raspberry (black, red), tangelo, tangerines, and walnut (English/black) 
3 

Note that the bentazon degradates of concern do not affect the Tier 1 Rice Model EDWCs 

because of the conservative assumption in this tier 1 model that the pesticide parent does not 

degrade. If for unseen reasons these Tier 1 Rice Model EDWCs need to be further refined, the 

degradates of concern will be considered in any higher tier modeling. 

References 

USEPA. 1994. Reregistration Eligibility Decision (RED): Bentazon (EPA 738-R-94-029). U.S. 

Environmental Protection Agency, Office of Prevention, Pesticides and Toxic Substances. 

September 1994. 198 pp. 

USEPA. 2007. Tier I Rice Model v1.0 for Estimating Pesticide Concentrations in Rice Paddies. 

Environmental Fate and Effects Division, Office of Pesticide Programs, United States 

Environmental Protection Agency.
4

Appendix A: Bentazon Sodium Salt and Its Environmental Transformation Pro

Appendix Table A-1. Bentazon Sodium Salt and Its Environmental Transformation Products. A

Chemical Name, Solubility, and KOC Chemical Structure Study Type MRID 

L

Ma

%A

PARENT

Bentazon (BAS 351H) IUPAC: 3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide CAS: 3-(1-methylethyl)-1H-2,1,3-benzothiadiazin-4(3H)-

one 2,2-dioxide CAS No.: 25057-89-0 Formula: C10H12N2O3S 

MW: 240.3 g/molSMILES: O=C1N(C(C)C)S(=O)(=O)Nc2ccccc12 Mobility 

Water solubility: 500 mg/L (measured); 268.13 mg/L (EPI 

Suite estimate) 

Kd: 0.176 L/kg (measured); Koc: 10 L/kg (MCI method) 

Aqueous Photolysis 00040785

Soil Photolysis 00040785 Aqueous Photolysis 00161294Aqueous Photolysis 4364201 Aerobic Soil Metab. 40470502Aerobic Soil Metab. 00040209 

MAJOR (>10%) TRANSFORMATION PRODUCTS 

O-amino-N-isopropyl benzamide (AIBA) – drinking 

water degradate of concern 

CAS: 2-amino-N-isopropylbenzamide 

CAS No.: 30391-89-0 Formula: C10H14N2O 

MW: 178.24 g/molSMILES: O=C(NC(C)C)c1ccccc1N Mobility 

Water solubility: 33,247 mg/L (EPI Suite estimate) Koc: 27.83 L/kg (MCI method) 

Aqueous Photolysis 00040785 2

O-nitro-N-isopropyl benzamide (7) ) – drinking water Aqueous Photolysis 00040785 2

N

NH

SO2

O

CH3

CH3

NH

NH2

O

CH3

CH3
5

Chemical Name, Solubility, and KOC Chemical Structure Study Type MRID 

L

Ma

%A

degradate of concern 

Formula: C10H12N2O3

MW: 208.22 g/molSMILES: O=C(NC(C)C)c1ccccc1[N+](=O)[O-] Mobility 

Water solubility: 1327 mg/L (EPI Suite estimate) Koc: 89.72 L/kg (MCI method)

Aerobic Soil Metab. 00040209 0.6

O-nitroso-N-isopropylbenzamide (8) ) – drinking water degradate of concern Formula: C10H12N2O2

MW: 192.22 g/molSMILES: O=C(NC(C)C)c1ccccc1N=O Mobility 

Water solubility: 660.3 mg/L (EPI Suite estimate) Koc: 53.09 L/kg (MCI method)

Soil Photolysis 00040785 2

Photoproduct 10 (MRID 00040785) ) – drinking water degradate of concern Formula: C17H20N4O2

MW: 312.37 g/molKoc: 66.37 L/kg (MCI method) Upper Structure 

SMILES: C(=O)(NN(C(=O)(c1ccccc1N))C(C)C)c1ccccc1N Mobility 

Water solubility 9790 mg/L (EPI Suite estimate) 

Or: Lower Structure

SMILES: C(N)(=O)c1c(NN(C(=O)c2c(N)cccc2)C(C)C)cccc1 Mobility 

Water solubility 6617.4 mg/L (EPI Suite estimate)

Structure is Approximate: 

Or: 

Soil Photolysis 00040785 1

Aqueous Photolysis 00040785 1

NH

NO2

O

CH3

CH3

NH

NOO

CH3

CH3

C

O

NH

N C

H3C CH3

O

NH2 H2N

NH

N C

H3C CH3

O

O H2N

H2N
6

Chemical Name, Solubility, and KOC Chemical Structure Study Type MRID 

L

Ma

%A

Photoproduct 12 (MRID 00040785) Formula: C21H23N3O6S2

MW: 477.55 g/molSMILES: C1(=O)c2c(c(N3c4c(C(=O)N(C(C)C)S3(=O)=O)cccc4)ccc2)NS(=O)(=O)C1C(C)C Mobility 

Water solubility: 1.37 mg/L (EPI Suite estimate) Koc: 59.61 L/kg (MCI method)

Soil Photolysis 9

Photoproduct 13 (MRID 00040785) Formula: C21H23N3O6S2

MW: 477.55 g/molSMILES: C1(=O)c2c(ccc(N3c4c(C(=O)N(C(C)C)S3(=O)=O)cccc4)c2)NS(=O)(=O)C1C(C)C Mobility 

Water solubility: 1.37 mg/L (EPI Suite estimate) Koc: 58.42 L/kg (MCI method)

Aqueous Photolysis 

00040785

1

Soil Photolysis 8

N

N

SO2

O

CH3

CH3

N

HN

SO2

O

CH3

CH3

N

N

SO2

O

CH3

CH3

HN N

SO2

O

CH3

CH3
7

Chemical Name, Solubility, and KOC Chemical Structure Study Type MRID 

L

Ma

%A

Photoproduct B (MRID 4364201) IUPAC: 3-isopropyl-2,2-dioxo-5-oxo-cyclopentano[d]IH2,1,3-thiadiazln-4(3H)-one β-carbonic acid

Formula: C10H10N2O6S 

MW: 286.26g/mol

SMILES: C(=O)(O)C1C(=O)C2C(=O)N(C(C)C)S(=O)(=O)NC=2C=1 Mobility 

Water solubility: 286,510 mg/L (EPI Suite estimate) Koc: 10 L/kg (MCI method)

Aqueous Photolysis 4364201 21 

Unextracted residues 

(not applicable) 

Aerobic Soil Metab. 00010209 73.Aerobic Soil Metab. 40470502

60.

80.62.

Carbon dioxide Formula: CO2

MW: 44.1 g/molSMILES: O=C=O 

Aerobic Soil Metab. 40470502

24.12.23.

MINOR (<10%) TRANSFORMATION PRODUCTS

N-methylbentazon ) – drinking water degradate of 

concern 

Formula: C11H14N2O3S 

MW: 254.31 g/molSMILES: O=C1N(C(C)C)S(=O)(=O)N(C)c2ccccc12 Mobility 

Water solubility: 135.43 mg/L (EPI Suite estimate) Koc: 10 L/kg (MCI method)

Aerobic Soil Metab. 40470502

3.8 2.3 1.8 

N

NH

SO2

O

CH3

CH3

O

O

HO

O C O

N

N

SO2

O

CH3

CH3

CH3
8

Chemical Name, Solubility, and KOC Chemical Structure Study Type MRID 

L

Ma

%A

8-Cl-bentazon Formula: C10H11ClN2O3S 

MW: 274.72 g/molSMILES: O=C1N(C(C)C)S(=O)(=O)Nc2c(Cl)cccc12 Mobility 

Water solubility: 62.32 mg/L (EPI Suite estimate) Koc: 11.23 L/kg (MCI method)

Aerobic Soil Metab. 40470502

3.8 2.3 1.8 

Photoproduct 11 (MRID 00040785) Formula: C21H23N3O4S 

MW: 413.49 g/molSMILES: C1(=O)c2c(ccc(N3c4c(C(=O)N3C(C)C)cccc4)c2)NS(=O)(=O)C1C(C)C Mobility 

Water solubility: 133.99 mg/L (EPI Suite estimate) Koc: 260.6 L/kg (MCI method) Soil Photolysis 00040785 5Photoproduct C (MRIDs 00161294, 4364201) IUPAC: 1-{N-(1-methylethyl)}-2-sulfoamino benzamide

Formula: C10H14N2O3S 

MW: 242.29 g/molSMILES: C(=O)(c1c(NS(=O)=O)cccc1)NC(C)C Mobility 

Water solubility: 49452 mg/L (EPI Suite estimate) Koc: 10 L/kg (MCI method)

Aqueous Photolysis 00161294

pH 5: 

pH 7

pH 9

Aqueous Photolysis 4364201 6.

A nd means “not detected”. AR means “applied radioactivity”. MW means “molecular weight”. LOQ means “limit of quantitation”. Bolded values a>10%AR. 

N

NH

SO2

O

CH3

CH3

Cl

N

HN N

SO2

O

CH3

CH3

N

O

CH3

CH3

NH

NHO

CH3

CH3

SO3H