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: 423552

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 (7508P)

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) of 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 patterns 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 EDWCs listed in this memo 

result in dietary risk exceedances, contact James Lin (703-308-9591) 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 4.16 1.07

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. DP 284671 – Tier 1 Drinking Water Assessment for Propoxycarbazone-sodium 

(Olympus) (November 2003)

2. DP 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)2for surface water and the Pesticide Root Zone 

Model for Ground Water (PRZM-GW)3for 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 broadleaved 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) Label 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 Propoxycarbazonesodium (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

0.0263 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 solubility (42,000 mg/L in pH 7 water) and a low 

vapor pressure (7.1 x 10-11 torr at 20oC). The calculated Henry's Law Constant of 9.35 x 10-16

atm-m3/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 (Kd = 

0.22 to 1.07) indicate that it is very mobile in soil. Due to its low KOW 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, the half-lives at pH 7 are 495 and 433 days, with an average 

of 464 days. In pH 7 buffered water, the photolysis half-lives of propoxycarbazone are 93.5 and 

37 days, with an average of 65 days. For photodegradation on soil, the half-lives are 70 and 38 

days, with an average of 54 days. Several aerobic soil metabolism studies show a range of halflife values: 8.7, 16, 21, 47, 77, 83, 103, and 224 days. Aerobic aquatic metabolism study halflives are 107, 110, 193, and 210 days. The anaerobic aquatic metabolism study has the longest 

half-life of 1155 days. 
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 (C15H17N4O7SNa ) (Calculated)

Vapor pressure (20 °C) 7.1x 10-7torr Product 

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

Henry’s Law Constant (20°C) 9.35x10-16 atm-m3/mol (Calculated)

Log octanol-to-water partition coefficient (log 

KOW) (20C, pH 7)

-1.55 Product 

Chemistry

Dissociation constant (pKa) 2.1

Persistence in Water

Hydrolysis half-life (20C) pH 4: 110 day, pH 7: 495 day,

pH 9: 408 day

MRID 45012733

MRID 45012740

pH 4: 154 day, pH 7: 433 day,

pH 9: 385 day

MRID 45012724

MRID 45012725

Aqueous photolysis half-life (20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 (20°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 oC) 110 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 (Kd)

 

(Koc) (20 oC)

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 

metabolism 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 accumulate 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 includes Nmethylpropoxytriazolinone amide and N-methylpropoxytriazolinone (MKH 7017), which was a 

major degradate in all soil metabolism studies. The latter set includes propoxycarbazonesulfonamide methyl ester (STJ 4934), sulfonamide acid (MKH 7283), saccharin (MKH 7284) 

and 4-hydroxysaccharin. All of these were major metabolites in soil or aquatic metabolism 

experiments. With the exception of 4-hydroxysaccharin, all are of equal or greater mobility than 

the parent compound. The available chemical names and structures are listed in Table 4. 

Residues of Concern

The modeled residues of concern include the parent compound plus propoxycarbazonecarboxylic 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-oxo3-propoxy-1H-1,2,4-triazol-1-yl)

carboxamidosulfonylbenzoate, sodium 

salt

CAS Reg. No. 

181274-15-7 (sodium salt);

145026-81-9 (acid)

Formula: C15H18N4O7S 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: C7H5NO3S

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 photolysis 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: C8H9NO4S

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

45012736

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

45012722

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

Aerobic Aquatic 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

H11N

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 45012728 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

5NO4

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: C14H16N

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

7NO4

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

H12N

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 Assessment

Drinking water exposure to the residues of concern is estimated using available chemical 

properties and environmental fate data. 

Drinking Water from Surface Water Sources

The Surface Water Concentration Calculator (SWCC v1.106) was 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, and (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 range. For the wheat use site, two applicable scenarios 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 dates were assumed 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 Residues of Concern

Parameter Value Source

Molecular Weight (g/mol) 420 C15H17N4O7SNa

Water Solubility (mg/L) 42000 Product Chemistry

Vapor Pressure (torr) 7.1 x 10-7

Hydrolysis half-life (day) @pH 

7

495, 433 (use the higher value: 495) 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 halflife (day) 107 (upper 90th percentile on eight

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

and 224)

MRID 45012720, 45012736

MRID 45012723, 45012721

MRID 45012735, 45012722

MRID 45012736

Aerobic aquatic metabolism 

half-life (day)

199 (upper 90th 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 (Kd) 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-emergence (after 

emergence date)

Maximum Application Rate 

(maximum) and Number of 

Application

1 @ 0.0525 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 sites of propoxycarbazone, the PCA value of 1 was used to represent the national 

default PCA for all agricultural land. The SWCC 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 Exposure 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 1.19 0.410 0.280

Ground 1.07 0.353 0.218

TX Barron Spring 

Range

Aerial 1.57 0.424 0.210

Ground 1.46 0.390 0.175

ND Wheat

Aerial 0.942 0.420 0.272

Ground 0.843 0.362 0.208

TX Wheat

Aerial 4.07 1.06 0.491

Ground 4.16 1.07 0.480

The modeling results of the Texas Wheat scenario with ground applications provided the 

higher EDWCs of 4.16 μg/L and 1.07 μg/L to represent the 1-in-10-year peak and mean exposure 

values, respectively.

Drinking Water from Ground Water Sources

PRZM-GW (v1.07) 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 (Kd) are taken from Table 6 and application related inputs are taken from 

Table 7. Only the inputs used for the Texas Barton Springs Range surface water scenario with 

ground applications were modeled, since they provided 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 highest EDWCs as shown in Table 9. The EDWCs of 

3.47 μg/L and 2.8 μg/L represent the acute and chronic exposure values, 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 30 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 NAWQA surface and ground 

water database (http://cida.usgs.gov/nawqa_queries_public/), the USEPA STORET Data 

Warehouse (http://www.epa.gov/storet/), and the USDA 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 water concentrations are on the 

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

water concentration (4.16 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 (DP 348511): surface water acute, 4.59 μg/L; surface water chronic, 1.79

μg/L; ground water acute and chronic, 0.36 μg/L.