### 1 OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION 

### UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

December 4 , 2014

PC Code: 122019

MEMORANDUM DP Barcode: 4 23552

SUBJECT : Propoxycarbazone

- sodium : Drinking Water Exposure Assessment for

Registration Review

FROM : James Lin, Environmental Engineer

ERB2 /EFED (7507P)

REVIEWED BY: Greg Orrick, Environmental Scientist

ERB2 /EFED (7507P)

THROUGH : Brian Anderson , Chief

ERB2 /EFED (7507P)

TO : Marianne Mannix

, Chemical Risk Manager

RMIB3 / PRD (750 8 P)

This assessment provides estimated drinking water concentrations (EDWC) of propoxycarbazone in surface water and in ground water in support of human health risk

assessment for registration review

. Screening EDWCs ( Table 1 ) o f propoxycarbazone were generated with the Surface Water Concentration Calculator ( SWCC ) and with the Pesticide Root Zone Model for Ground Water ( PRZM

- GW ) . Modeled application rates represent the maximum

use pattern s of proposed end

- use labels and current registered labels . Remaining model input

parameters were chosen according to current guidance ( USEPA , 2009 ) 1 

### . EDWCs reflect

exposure to propoxycarbazone residues of concern in drinking water , which include the parent compound and propoxycarbazone

- carboxylic acid

. If the screening EDWC s listed in this memo result in dietary risk exceedances, contact James Lin (703

- 30 8

- 9591 ) of Environmental Risk

Branch II (7507P) to request a refined drinking water exposure assessment.

1 USEPA. 2009. Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides. Version 2.1. U.S. Environmental Protection Agency, Office of Pesticide Programs , Environmental Fate and Effects Division, Oct. 22, 2009. http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm

### 2

Table 1. Maximum Screening Drinking Water Exposure Estimates for Propoxycarbazone

Residues of Concern *

Source (Model) Use (Maximum Rate) Peak Exposure (μg/L) Annual Mean

Exposure (μg/L)

Surface water ( SWCC ) 2 @ 0.02625 lb a.i./acre 4.1 6 1.0 7

Ground water (PRZM

- GW ) 1 @ 0.0525 lb a.i./acre 3 .47 2.8

* Maximum values in bold.



### The Environmental Fate and Effects Division (EFED) has produced two drinking water

assessments for propoxycarbazone :

1. D P 28 4671

– Tier 1 Drinking Water Assessment for Propoxycarbazone

- sodium (Olympus  ) ( November 2003 )

2. D P 348511

- Drinking Water Assessment and Ecological Risk Summary for Tier 1 Drinking Water Assessment for Propoxycarbazone

- sodium (Olympus  ) use on Rangeland ( August 2008 )

Due to recent updated modeling approaches, EFED is required to use new tools : the Surface Water Concentration Calculator (SWCC) 2 

### for surface water and the Pesticide Root Zone Model for Ground Water (PRZM

- GW) 3 

### for ground water.

USE INFORMATION

Propoxycarbazone

- sodium ( which dissociates in the presence of moisture to form propoxycarbazone) is a sulfonyl

- amino

- carbonyl

- triazolinone herbicide ( a type of ALS inhibitor similar to the sulfonylureas) used for the selective post

- emergence control of grasses and broad

leaved plants in wheat, triticale, rangeland , pastures, and agricultural fallow/conservation

reserve

. The only commercial available formulation is water dispersible granules (dry flowable). It can be applied by either aerial or ground spray equipment. Table 2 lists the maximum use patterns for the labeled use sites. The table is a summary of the “EFED Table 1 Report”, which is a part of the Biological and Economic Analysis Division’s (BEAD) La bel Use Report Package

for registration review (August 2014)

.

2 USEPA, 2014. Implementation of the Surface Water Concentration Calculator for use in the Environmental Fate and Effects Division (EFED)

3 USEPA. 2012. Guidance for Using PRZM

- GW in Drinking Water Exposure Assessments. U.S. Environmental Protection Agency , Office of Pesticide Programs, Environmental Fate and Effects Division, Oct. 15, 2012.

### 3

Table 2 . Maximum Use Patterns for Current Registered Use Sites of Propoxycarbazone

sodium (PC 122019)

Use Site Single Max.

Rate (lbs/Acre) Max. Rate per

Crop Cycle Max. Rate per

Year (lbs/Acre) Application Methods

Agricultural

Fallow /

Conservation

Reserve 0.0525 NS 0.0525 Broadcast

- Aerial

Broadcast

– Ground Spot Treatment

- Ground

Pastures 0.0525 NS 0.0525 Broadcast

- Aerial

Broadcast

– Ground Spot Treatment

- Ground

Rangeland 0.0525 NS 0.0525 Broadcast

- Aerial

Broadcast

– Ground Spot Treatment

- Ground

Triticale 0.0148 0.0148
0.0395 Broadcast

- Aerial

Broadcast

– Ground 0.0395 NS

Wheat 0.026 3 0.0525

0.0525 Broadcast

- Aerial

Broadcast

– Ground 0.0394 0.0525

0.0175 0.0175 Spray

- Aerial Spray

– Ground



### FATE AND TRANSPORT CHARACTERIZATION

Transport and Mobility

Propoxycarbazone has a high water solub ility (4 2,0 00 mg/L in pH 7 water) and a low vapor pressure ( 7. 1 x 10

- 11 

### torr at 20 o 

### C). The calculated Henry's Law Constant of 9.35 x 10

- 1 6



### atm

- m 3 

### /mol) indicates that propoxycarbazone is not expected to be volatile under field

conditions and from water. The high water solubility and low soil partitioning coefficients (K d 

### = 0.22 to 1. 0 7) indicate that it is very mobile in soil. Due to its low K OW 

### value of 0.028

, bioaccumulation is not likely to occur.

Degradation

Propoxycarbazone degradation in the environment appears to be variable. The compound hydrolyzes at relatively slow rates , t he half

- lives at pH 7 are 49 5 and 4 33 days, with an average of 464 days. In pH 7 buffered wate r, the photolysis half

- li ves of propoxycarbazone are 93.5 and

37 days , with an average of 65 days. For p hotodegradation on soil, the half

- lives are 70 and 38 days, with an average of 54 d ays. Several aerobic soil metabolism studies show a range of half

life values: 8.7, 16, 21, 4 7 , 77, 83, 103, and 2 24 day s

. A erobic aquatic metabolism study half

lives are 107, 110, 193, and 210 day s . The anaerobic aquatic metabolism study has the longe st
half

- life of 1155 day s

.

### 4

Table 3 summaries the product chemistry and environmental fate properties of propoxycarbazone

.

Table 3

. Product Chemistry and Environmental Fate Properties of Propoxycarbazone

Parameter Value Source

Selected Physical/Chemical Parameters

Molecular mass (molecular formula) 420 g/mol (C 15 H 17 N 4 O 7 S Na ) (Calculated)

Vapor pressure (2 0 °C) 7.1 x 10

- 7 torr Product Chemistry Aqueous solubility (20  C , pH 7 ) 42000 mg/L

Henry’s Law Constant (2 0 °C) 9.35 x10

- 16 atm

- m 3 /mol (Calculated)

Log o ctanol

- to

- water partition coefficient ( log

K OW ) (20  C , pH 7 ) - 1.55 Product Chemistry

Dissociation constant (pKa) 2.1

Persistence in Water

Hydrolysis half

- life (2 0  C) pH 4: 110 day, pH 7 : 495 d ay, pH 9: 408 day MRID 45012733

MRID 45012740

pH 4: 154 day, pH 7 : 433 d ay, pH 9: 385 day MRID 45012724

MRID 45012725

Aqueous photolysis half

- life (2 0  C) (pH 7) 93.5 day 37 day MRID 45012703

MRID 45012702

Persistence in Soil

Photodegradation half

- life on soil 70 day 38 day MRID 45012729

MRID 45012728

Aerobic soil metabolism half

- life (2 0 °C) 77 day MRID 45012720

MRID 45012736

103 day MRID 45012723

21day, 16 day, 83 day MRID 45012721

MRID 45012735

8.7 day, 46.5 day, 223.6 day MRID 45012722

MRID 45012736

Aerobic aquatic metabolism half

- life (20 o C) 1 10 day , 107 day, 193 day, 210 day MRID 4512704

Anaerobic aquatic metabolism half

- life (20 °C) 1155 days MRID 45012708

MRID 45012707

Mobility

Freundlich Adsorption coefficient (K d )

(Koc) (20 o C) 0.2504, 0.4968, 0.2239, 0.2134,

1.0747 L/kg 10.1, 18.7, 26, 57.7, 66.7 MRID 45012634

Terrestrial Field Dissipation

Field Dissipation half

- life 22.4 day 16.8 day 44.4 day MRID 45012716

MRID 45012719

MRID 45012715

### 5

Parameter Value Source

Fish Bioconcentration

Not required

- Kow (0.028) is less than 1,000



### Environmental Degradates

The most prominent degradate of propoxycarbazone is propoxycarbazone

- carboxylic acid (MKH 7018 or MKH 8394), which results from the loss of a methyl ester group, but has the intact sulfonylurea bridge. This degradate was quite stable in aerobic and anaerobic aqueous

metabol ism studies, forming 50% or more of the applied test compound at the end of 100

- day or

365

- day experiments. However, this was a minor degradate in soil. This degradate may persist

and accumulat e in ponds, lakes, and reservoirs.

There are two sets of degradates that result from the cleaving of the sulfonylurea bridge. These include the triazolinones, and the sulfonamide/saccharins. The former set include s N

methylpropoxytriazolinone amide and N

- methylpropoxytriazolinone (MKH 7017), which was a major d egradate in all soil metabolism studies. The latter set include s propoxycarbazone

sulfonamide methyl ester (STJ 4934), sulfonamide acid (MKH 7283), saccharin (MKH 7284)

and 4

- hydroxysaccharin. All of these were major metabolites in soil or aquatic metabo lism experiments. With the exception of 4

- hydroxysaccharin, all are of equal or greater mobility than the parent compound

. The a vailable chemical names and structures are listed in Table 4

.

Residues of Concern

The modeled residues of concern include t he parent compound plus propoxycarbazone

carboxylic acid (MKH 8394), which has the intact sulfonylurea bridge (Report of the

Metabolism Assessment Review Committee

– MARC, DP 299170, April 2004)

. The other degradates are assumed less toxic than the parent compound and are not of concern because the sulfonylurea bridge is cleaved

.

### 6

Table 4

. Propoxycarbazone

- sodium and Its Environmental Transformation Products

Code Name/ Synonym Chemical Name Chemical Structure Study Type MRID Maximum %AR (day) Final %AR

(study length)

PARENT 

### Propoxycarbazone

MKH 6561 Methyl 2

- (4,5

- dihydro

- 4

- methyl

- 5

- oxo

3

- propoxy

- 1H

- 1,2,4

- triazol

- 1

- yl) carboxamidosulfonylbenzoate, sodium

salt

CAS Reg. No.

181274

- 15

- 7 (sodium salt);

145026

- 81

- 9 (acid)

Formula: C 15 H 18 N 4 O 7 S Na MW: 420 g/mol (sodium salt) 398 g/mol (acid, MKH 5554)

TRANSFORMATION PRODUCTS



### Saccharin

MKH 7284 1,2

- Benzisothiazol

- 3(2H)

- one,1,1

- dioxide

Formula: C 7 H 5 NO 3 S MW: 183 g/mol Hydrolysis 45012733

45012740 1.19% (30 d)

@ pH 4 3.26% (30 d) @ pH 7 3.78% (30d) @ pH 9 1.19% (30 d)

@ pH 4 3.26% (30 d) @ pH 7 3.78% (30d) @ pH 9 Soil photolysis 45012729 4.7% (18 d) 4.7% (18 d) Aqueous p hotolysis 45012702 22.26% (19 d) 22.265 (19 d)

Aerobic soil 45012720

45012736 1.4% (88 d) 1.4% (361 d)

45012722

45012736 26.6% (14 d) 15.65 (180 d)



### MKH 6561 sulfonamide methyl

ester

STJ 4934 2

- carbomethoxybenzene

- sulfonamide

Formula: C 8 H 9 NO 4 S MW: 215 g/mol Hydrolysis 45012733

45012740 16.61% ( 30 d ) 16.61 % ( 30 d )

Aqueous photolysis 45012702 5.8% (7 d) 4.165 (19 d) Soil photolysis 45012729 9.7% (11 d) 8.7% (18 d)

Aerobic soil 45012720

4501273 6 4.1% (13 d) < 0.5% (163 d)

45012722

45012736 20.9% (6 d) 4.6% (180 d)

Aerobic Aqua t ic 45012704 11.3% (100 d) 11.3% (100 d)

### 7

N

- methyl propoxy

triazolinone

MKH 7017 3H

- 1,2,4

- Triazol

- 3

- one, 2,4

- dihydro

- 4

- methyl

- 5

- propoxy

Formula: C 6 H 11 N 3 O 2 MW: 157 g/mol Hydrolysis 45012724

45012725 13.92% (33 d)

@ pH 4 4.15% (33 d) @ pH 7 4.72% (33 d) @ pH 9 13.92% (33 d)

@ pH 4 4.15% (33 d) @ pH 7 4.72% (33 d) @ pH 9 Aqueous photolysis 45012703 13.6% (19 d) 13.6 % (19 d) Soil photolysis 4501272 8 8.57% (18 d) 8.57% (18 d)

Aerobic soil 45012723 28.7% (365 d) 28.7% (365 d)

45012721

45012735 32% (28 d)

43.9% (29 d)

55.2% (182 d) 14% (182 d)

19.9% (182 d) 55.2% (182 d) Anaerobic Aquatic 45012708 20.5% (196 d) 15.1% (365 d) Aerobic Aquatic 45012704 34.4% (100 d) 34.4% (100 d) 

### 4

- Hydroxy

Saccharin 1,2

- Benzisothiazol

- 3(2H)

- one,4

- hydroxy

- ,1,1

- dioxide

Formula: C 7 H 5 NO 4 S

MW: 199 g/mol Aerobic soil 45012720

45012736 13.8% (361 d) 13.8% (161 d)

45012722

45012736 21.9% (180 d) 21.9% (180 d)



### MKH 6151 Carboxylic Acid

MKH 8394 Benzoic acid, 2

- ( (( 4,5

- dihydro

- 4

- methyl

- 5

- oxo

- 3

- propoxy

- 1H

- 1,2,4

- triazol

- 1

- yl) carbonyl)amino)sulfonyl

Formula: C 14 H 16 N 4 O 7 S MW: 384 g/mol Aerobic soil 45012720

45012736 1.2% (88 d) 0.5% (361 d)

45012722

45012736 3.7% (180 d) 3.7% (180 d)

Anaerobic Aquatic 45012708 87.8% (90 d) 76.1% (365 d)

45012707 84.9% (120 d) 68.8% (365 d) Aerobic Aquatic 45012704 71.6% (62 d) 48.3% (100 d)


### MKH 6151

Sulfonamide Acid

MKH 7283 Benzoic acid, 2

- (aminosulfonyl)

Formula: C 7 H 7 NO 4 S MW: 201 g/mol Aerobic soil 45012722

45012736 5.0% (14 d) ND (180 d)

Anaerobic Aquatic 45012707 24.6% (365 d) 24.6% (365 d)

Aerobic Aquatic 45012704 19.4% (100 d) 19.4% (100 d)



### N

- Methyl propoxy

triazolinones amide 3H

- 1,2,4

- Triazol

- 3

- one

- 2

- carboxamide

- 2,4

- dihydro

- 4

- methyl

- 5

- propoxy

Formula: C 7 H 12 N 4 O 3 MW: 200 g/mol Aerobic soil 45012723 16.1% (313 d) 16% (365 d)

45012721

45012735 8% (93 d) 7.1% (182 d)

### 8

Drinking Water Exposure A ssessment

Drinking water exposure to the residues of concern is estimated using available chemical properties and environmental fate data.

Drinking Water from Surface Water Source s

The Surface Water Concentration Calculator (SWCC v 1.10 6 ) wa s used to calculate EDWCs

from surface water sources

. Based on the use site table, the modeling effort is focusing on two maximum annual rate scenarios: (1) a single application rate of 0.0525 lb ai/ac for agricultural fallow/conservation reserve, pastures, and rangeland, an d (2) a fall application of 0.02625 lb ai/ac, followed by a spring application of 0.02625 lb ai/ac for wheat.

There are two rangeland modeling scenarios in the SWCC database

. They are for California rangeland hay and Texas Barton Springs r ange

. For t he wheat use site , two applicable s cenario s are for North Dakota and Texas. Table 5 presents some background information of these modeling

scenarios. Table 6 lists the chemical modeling input parameters. Table 7 lists the application

related information and assumptions. Since propoxycarbazone is used to control post

- emergence grass weeds , the application date s w ere assume d during the heavy weed growing time

.

Table 5

. Modeling Scenarios Used for Surface Water Concentration Calculator Modeling Scenario Met. File (.dvf) Emergency

Date Maturation

Date Harvest

Date California Rangeland Hay 23232 Nov. 1 April 1 May 1 Texas Barron Spring Range 13958 March 1 June 15 Nov. 15

North Dakota Wheat 14914 Oct. 16 April 30 June 17

Texas Wheat 13958 May 16 July 25 August 5

Table 6

. Chemical Model Inputs for Propoxycarbazone R esidues of C oncern

Parameter Value Source

Molecular Weight (g/mol) 420 C 15 H 17 N 4 O 7 S Na

Water Solubility (mg/L) 42000 Product Chemistry

Vapor Pressure (torr) 7.1 x 10

- 7

Hydrolysis half

- life (day) @pH

7 4 95

, 43 3 ( use the higher value : 4 95 ) MRID 45012733

, 45012740

MRID 45012724

, 45012725

Aqueous photolysis half

- life (day) 37 and 93.5 ( use the higher value 93. 5) MRID 45012703

MRID 45012702

Aerobic soil metabolism half

life (day) 107 (upper 90 th percentile on eight

values of 77, 103, 21, 16, 83, 8.7, 46.5,

and 22 4 ) MRID 45012720

, 45012736

MRID 45012723

, 45012721

MRID 45012735

, 45012722

MRID 45012736

Aerobic aquatic metabolism

half

- life (day) 199 (upper 90 th percentile on four values

of 110, 107, 193, and 210 ) MRID 4512704

### 9

Parameter Value Source

Anaerobic aquatic metabolism

half

- life (day) 1155 (the single available value was not multiplied by 3 because it is large ) MRID 45012708

MRID 45012707

Adsorption coefficients (K d ) 0.4518 (Mean of five values: 0.2504

, 0.4968, 0.2239, 0.2134 and 1.0747 ) MRID 45012634



### Table 7

. Application Information Related to Propoxycarbazone Use on Modeling Scenarios

Model Input Variable Input Value Comments

Application Date (s) December 1 for California Rangeland Hay April 1 for Texas Barron Spring Range April 1 and November 16 for North Dakota

Wheat

June 16 and October 1 for Texas Wheat Post

- emergenc e (aft er

emergenc e date)

Maximum Application Rate (maximum) and Number of Application 1 @ 0. 0 525 lb a.i./acre Range land use

2 @ 0.02625 lb a.i./acre Wheat use

Application method, App. Efficiency / Spray Drift Ground, 0.99 / 0.066 USEPA, 2013 4

Aerial, 0.95/0.135



### Standard percent cropped areas (PCA) are used as conservative default estimates of the extent of watershed on which agricultural crops of unknown specific PCA are grown

. 5 

### Considering

the many use site s of propoxycarbazone , the PCA value of 1 was used to represent the national

default PCA for al l agricultural land

. The S WCC results are tabulated in Table 8

.

3 USEPA. 2013. Guidance on Modeling Offsite Deposition of Pesticides via Spray Drift for Ecological and Drinking

Water Assessments. U.S. Environmental Protection Agency , Office of Pesticide Programs, Environmental Fate and Effects Division. Internal memorandum. Dec. 20, 2013.

5 USEPA. 2014. Development of Community Water System Drinking Water Intake. Percent Cropped Area Adjustment Factor for use in Drinking Water Exp osure Assessments: 2014 Update

### 10

Table 8

. Propoxycarbazone Total Residue of Concern EDWCs from Surface Water Sources

PRZM Scenario Type of

Application 1

- in

- 10

- year

Peak Exposure ( μg/L ) 1

- in

- 10

- year

Annual Mean Exposure ( μg/L ) 30

- year Mean

Exposure ( μg/L )

CA Rangeland Hay Aerial 1.1 9 0. 410 0.2 80

Ground 1.0 7 0.3 53 0.2 18

TX Barron Spring Range Aerial 1.57 0.4 24 0.2 10

Ground 1.46 0.3 90 0.17 5

ND Wheat Aerial 0.9 42 0. 420 0.2 72

Ground 0.8 43 0.3 62 0. 208

TX Wheat Aerial 4.0 7 1.0 6 0.49 1

Ground 4.1 6 1.0 7 0.4 80



### The modeling results of the Texas Wheat scenario with ground applications provided the higher EDWCs of 4.1 6 μg/L and 1.0 7 μg/L to represent the 1

- in

- 10

- year peak and mean exposure values, respectively.

D rinking Water from Ground Water Source s

PRZM

- GW (v 1.07 ) is used to calculate EDWCs from ground water sources. The chemical specific input parameters including hydrolysis half

- life, aerobic soil metabolism half

- life, and adsorption coefficient (K d 

### ) are taken f rom Table 6 and application related inputs are taken from

Table 7

. Only the inputs used for the Texas Bar t on Spring s Range surface water s cenario with ground applications were modeled, since they provide d more conservative surface water results.

All six available ground water scenarios were modeled as surrogates for range land scenarios, with

the Florida citrus scenario producing the h ighest EDWCs as shown in Table 9

. The EDWCs of

3 .47 μg/L and 2. 8 μg/L represent the acute and chronic exposure va lue s , respectively.

Table 9

. PRZM

- GW Output of EDWCs for Propoxycarbazone Total Residue of Concerns

Modeled

Scenario Max. Daily Conc.

(μg/L) Mean Breakthrough

Time (years) Post

- breakthrough

Mean (μg/L)

DMV corn 2.18 12.706 1.93

FL citrus 3

. 47 7.254 2.8

FL potato 1.8 6.020 1.31

GA peanut 0.591 11.059 0.517

NC cotton 0.631 19.258 

### 0.538

WI corn 1.67 26.872 

### 1.48

### 11

Figure 1. PRZM

- GW EDWCs over 3 0 years for the Florida citrus scenario

Monitoring Data

Propoxycarbazone is not an analyte in the following water monitoring programs: the California Department of Pesticide Regulation ( CDPR) surface water database ( http://www.cdpr.ca.gov/docs/emon/surfwtr/surfcont.htm , the USGS NAWQ A surface and ground water database ( http://cida.usgs.gov/nawqa_queries_public/ ), the USEPA STORET Data Warehouse ( http://www.epa.gov/storet/ ), and the US DA Pesticide Data Program drinking water monitoring analyses ( http://www.ams.usda.gov/AMSv1.0/ams.fetchTemplateData.do?template=TemplateG&navID=&ri ghtNav1=&topNav=&leftNav=ScienceandLaboratories&page=PDPDownloadData/Reports&result Type=&acct=pestcddataprg )

.

Conclusion

The overall estimated drinking water concentrations from surface water sources and ground water sources are summarized in Table 1

. The surface wa ter concentrations are o n the

same order of magnit ude as the ground water concentrations. For acute exposure, the surface

water concentration ( 4.1 6 μg/L ) is higher than that for ground water , whereas for chronic exposure, the ground water value ( 2. 8 μg/L ) is higher

. These results are similar to previous drinking water assessment results , with an increase in ground water estimates relative to previous estimates (D P 348511) : surface water acute, 4.59 μg/L ; surface water chronic, 1.79 μg/L ; ground water acu te and chronic, 0. 36 μg/L

.