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OFFICE OF 

CHEMICAL SAFETY AND

POLLUTION PREVENTION

U. S. ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460 

PC Code: 101701

DP Barcode: D414467

MEMORANDUM 

April 21, 2015 

SUBJECT: Propyzamide (Pronamide): Tier II Drinking Water Exposure Assessment in 

support of the Proposed Use of Propyzamide on Leaf Lettuce 

TO: Wilhelmena Livingston, Chemical Review Manager 

Kevin Costello, Acting Branch Chief 

Risk Management and Implementation Branch IV 

Pesticide Re-evaluation Division (7508P) 

 

Ideliz Negrón-Encarnación, Ph.D., Chemist 

Danette Drew, Senior Chemist 

Stephen Dapson, Ph.D., Toxicologist 

Mike Metzger, Branch Chief 

Risk Assessment Branch V and VII 

Health Effects Division (7509P)

CC: Keri Grinstead, Risk Manager 

Tawanda Maignan, Emergency Response Team Leader 

Minor Use and Emergency Response Branch 

Registration Division (7505P) 

Mindy Ondish, Risk Manager 

Kathryn Montague, Product Manager 

Daniel Kenny, Branch Chief 

Herbicide Branch 

Registration Division (7505P)

FROM: Karen Milians, Ph.D., Chemist 

Environmental Risk Branch IV 

 Environmental Fate and Effects Division (7507P)

REVIEWED 

BY:

 Jim Carleton, Ph.D., Senior Scientist 

 Environmental Risk Branch IV 

 Environmental Fate and Effects Division (7507P) 
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APPROVED 

BY: Jean Holmes, DVM, MPH, Branch Chief 

Environmental Risk Branch IV 

 Environmental Fate and Effects Division (7507P) 

The Environmental Fate and Effects Division (EFED) has completed a review of a proposed new 

use of propyzamide (Kerb® 3.3 SC, EPA Reg. No. 62719-578, 35.6 % active ingredient) on leaf 

lettuce. The proposed single application rate ranges from 0.5 to 2.0 lbs a.i./acre. Because leaf lettuce 

may be cropped twice per year, this use represents a maximum annual application rate of 4.0 lbs 

a.i./acre. 

In the previous drinking water assessment (DWA), estimated concentrations (EDWCs) of 

propyzamide in surface water and in ground water were generated based upon maximum use 

patterns of propyzamide (USEPA, 2007). That assessment used a total toxic residues (TTR) 

approach to estimate exposure to the residues of concern, i.e. propyzamide and all of its degradates 

that contain the 3,5-dichlorobenzoyl moiety (USEPA, 2002; 2007). In the current assessment, 

available monitoring data on propyzamide are reviewed, and up-to-date models used to estimate 

residues in surface and ground water-based drinking water. Like the previous assessment, this one 

uses a TTR approach in estimating exposures to propyzamide residues of concern (USEPA, 2002; 

2007). Various procedural and informational changes have been incorporated into this assessment, 

resulting in EDWCs that differ from those generated previously. These changes include a new batch 

equilibrium study (OCSPP 835.1230), input parameter guidance (USEPA, 2009), use of the PRZMGW model to generate ground water EDWCs (USEPA, 2012a), new percent cropped area (PCA) 

adjustment factors (USEPA, 2012b) and new off-site spray drift guidance (USEPA 2013). 

Current propyzamide labels fail to state maximum application rates for certain crops in annual terms. 

Application rates for these crops are instead given on a per season (e.g., for turf, leaf lettuce) or per 

crop basis (e.g., head lettuce, endive, escarole, and radicchio greens), or else are not given in terms 

of any particular time frame (e.g., alfalfa seed). For these crops, conservative assumptions were 

employed to estimate plausible maximum annual application rates. 

 
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1. EXECUTIVE SUMMARY

The Environmental Fate and Effects Division (EFED) has reviewed a request for a new use of 

propyzamide (also referred as pronamide) on leaf lettuce. The maximum proposed single application 

rate for leaf lettuce is 2.0 lbs a.i./acre, however neither a maximum number of applications annually, 

nor a maximum annual rate are specified on the proposed label. For assessment purposes, EFED 

assumed two leaf lettuce growing seasons may occur per year, resulting in a maximum annual rate 

of 4.0 lbs a.i./acre. In this assessment the artichoke use was also modeled because this use allows 

the maximum application rate (for any crop) of 8 lbs a.i./acre (i.e., 4 lbs a.i./acre x 2 assumed 

applications/yr). Table 1 show the estimated drinking water concentrations in surface water and 

ground water (including values using Sci-Grow and PRZM-GW for ground water. The 

recommended estimated drinking water concentrations (EDWCs) for the Health Effects Division’s 

(HED) dietary assessment is 102 ppb for the acute dietary assessment and 47.0 ppb for the chronic 

and cancer dietary assessments. 

Table 1. Tier II Total Residue of Concern EDWCs in Surface Water and Ground Water from 

Propyzamide Uses on New Uses (Maximum EDWCs in Bold).

Drinking Water Source 

(Model, Use, Modeled rate) Scenario 

EDWCs 

Acute (μg/L) Chronic (μg/L) Cancer (μg/L) 

Surface Water (SWCC, 

Artichokes, 

4 lb a.i./A x 2 applic.; total of 8 

lb/A/yr) 

CA row crop 

RLF (aerial 

application) 

61.4 33.4 26.0 

Surface Water (SWCC, Leaf 

Lettuce, 2 lb a.i./A x 2 applic.; 

total of 4 lb/A/yr) 

CA lettuce 

(aerial 

application) 

102 47.0 33.6 

Ground Water (PRZM-GW, 

Artichokes, 

4 lb a.i./A x 2 applic.; total of 4 

lb/A/yr) 

WI sands 21 18.6 18.6 

Ground Water (SCI-GROW, 

Artichokes, 

4 lb a.i./A x 2 applic.; total of 8 

lb/A/yr) 

N/A 0.802 0.802 0.802 

Ground Water (SCI-GROW, 

Leaf Lettuce, 2 lb a.i./A x 2 

applic.; total of 4 lb/A/yr) 

N/A 0.401 0.401 0.401 

N/A= Not Applicable 

Values in bold show the EDWCs recommended for HED’s acute (102 ppb) and chronic (47.0 ppb) and cancer (33.6 

ppb) dietary risk assessment as they are considered protective of all the registered uses of pronamide.

The standard all-agricultural PCA of 1.0 was used for all other uses because they are not limited to 

specific regions of the U.S. Surface water EDWCs were calculated using the Surface Water 

Concentration Calculator (SWCC). Ground water EDWCs were calculated using both SCI-GROW 

and PRZM-GW. 

 
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Monitoring data on propyzamide have revealed concentrations in the environment consistent with 

the peak (3.7-10.3 μg/L) and annual mean (0.53-4.45 μg/L). Monitoring data are not available on 

any degradates of propyzamide. Therefore, concentration estimates for total toxic residues cannot be 

directly compared against available monitoring data. 

Propyzamide is an organochlorine herbicide (pre-emergence and early postemergence control of 

winter annual and perennial grasses and chickweed) that is typically applied aerial or ground, and 

wetted in, during the fall or winter months. The major routes of degradation of parent appear to be 

aerobic microbial degradation in soil (44.6 d) and photolysis in water (217 d). Four major degradates 

of propyzamide have been identified (RH-24644, RH-24655, RH-24580 and RH-26059, with a 

maximum applied radioactivity of 31.9%, 27.3%, 32.2%, and 15.0%, respectively). The Health 

Effects Division (HED) found all degradates of propyzamide that contain the 3,5-dichlorobenzoyl 

moiety to be of risk concern, assuming that their toxicity is similar to that of propyzamide parent 

(USEPA, 2002; 2007). A total toxic residues (TTR) approach was therefore used to generate 

EDWCs that reflect residues, in drinking water, of the parent compound plus all such degradates of 

concern. 

Propyzamide has relatively low vapor pressure (8.5 x 10-5 torr; 25°C) and is soluble in water up to 

15 mg/L (25°C). The compound is stable to hydrolysis, relatively resistant to soil photolysis (t1/2 = 

249 d), and moderately susceptible to aquatic photolysis (t1/2 = 42 d). Propyzamide degrades 

relatively readily in aerobic soil environments (t1/2 = 20-44.6 d), but is more persistent in anaerobic 

environments (t1/2 = 127-450 d) and aquatic environments (aerobic aquatic and anaerobic aquatic 

half-lives of 119 d and 450 d, respectively). Sorption to soils is a function of organic carbon. Soil 

sorption also correlates with cation exchange capacity. Nonetheless the compound is mobile in soil 

[KF range = 3.15 (1/n=1.22) – 10.1 (1/n=1.00)], and thus presents a potential groundwater concern 

in some areas, e.g., those with sandy soils and high water tables. Propyzamide has been detected in 

both surface water and groundwater. 

EDWCs based on total toxic residues for propyzamide likely exceed actual concentrations in most 

drinking water supplies due to the screening (conservative) nature of the exposure models, use 

national PCA (1.0), and limited acceptable environmental fate data. In accordance with EFED’s 

Input Parameter Guidance, degradation half-lives employed in the models are 90 percent upper 

confidence limits on mean values.

2. USE CHARACTERIZATION 

Propyzamide is a systemic, organochlorine herbicide. There are two active registrations (EPA Reg. 

No. 62719-578 and 62719-397), allowing use on alfalfa, apples, globe artichokes (CA), birdsfoot 

trefoil, blackberry/boysenberry/rasberries (IH, OR, WA), blueberries, cherries, clover, crown vetch, 

endive, escarole, grapes, fallow land, head lettuce, nectarines, peaches, pears, plums, prune, 

radicchio greens, raspberries, rhubarb, sainfoin, winter peas, woody ornamentals, nursery stock of 

ornamentals, and Christmas trees. 

Propyzamide is formulated as a wettable powder in water soluble pouches and can be applied preplant, pre-emergence, and post-emergence by ground or aerial spray equipment, depending on the 

use. Wetting in of applications is recommended with rainfall or irrigation. The maximum annual 

application rate for propyzamide uses is 8 pounds of active ingredient per acre (lbs a.i./A) on 
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artichokes. The use on artichokes which are only grown in California, can involve up to two 

applications per season for a maximum annual application rate of 8 lbs a.i./A (aerial and/or ground 

application). 

The uses on lettuce (leaf and head) and artichokes are the maximum use patterns affecting surface 

water and ground water exposure (Table 2). 

Table 2 displays the maximum use patterns of the current labels (EPA Reg. No. 62719-578). 

Table 2. Maximum Use Patterns for Current Propyzamide Uses.

Use 

Pattern

Single 

App. Rate 

(lbs a.i./A)

Number of 

Apps per 

Year.1

Annual 

App. Rate 

(lbs a.i./A)

Minimum 

Retreatment 

Interval 

(days)

Application 

Method Comments 

Artichoke 4 2 8 Not specified Aerial/ground In CA only 

Leaf 

Lettuce 

2 2 4 183 d Aerial/ground Assuming two 

crops/year 

1

Assumed 

3. ENVIRONMENTAL FATE AND TRANSPORT CHARACTERIZATION 

The environmental fate and transport-related properties of propyzamide are shown in Table 3. 

Parent propyzamide is slightly to moderately mobile (FAO 2000), and moderately labile to 

degradation under aerobic conditions in soil, and via photolysis in water. Half-lives for total toxic 

residues generally range from months to years, in part because all identified degradates except 

carbon dioxide are considered to be of risk concern due to the 3,5-dichlorobenzoyl moiety (USEPA, 

2007). 

Table 3. General Chemical Properties and Environmental Fate Parameters of 

Propyzamide. 

Chemical/Fate Value Source 

Chemical name 3,5-dichloro-N-(1,1-

dimethylprop-2-ynyl)benzamide USEPA, 1994 

Molecular mass 256.13 g/mol USEPA, 1994 

Vapor pressure (25C) 8.5 x 10-5 torr USEPA, 1994 

Solubility (25C) 15 mg/L USEPA, 1994 

Octanol-water partition 

coefficient (KOW) 1000-2000 MRID 46413408 

Freundlich soil-water 

distribution coefficient (KF); 

Freundlich organic carbon 

partitioning coefficient (KFOC) in 

L/ kgOC

700 

1026 

1150 

1317 

1586 

2283 

2287 

5383 

MRID 49126805 

Hydrolysis half-life at pH 4.7, 

7.4 and 8.8 (20C) No significant degradation MRID 00107980 
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Table 3. General Chemical Properties and Environmental Fate Parameters of 

Propyzamide. 

Chemical/Fate Value Source 

Aqueous photolysis half-life; 

Total toxic residues half-life 41.7 d; 217 d MRID 40420301, MRID 40320601 

Soil photolysis half-life; 

Total toxic residues 

249 d; No significant 

degradation MRID 41913504 

Aerobic soil metabolism halflife; 

Total toxic residues half-life 

(soil texture) 

20.1 d; 64.9 d (sandy loam) 

21.5 d; 96.6 d (silty clay loam) 

44.6 d; 166 d (loamy sand) 

MRID 46413407 

Anaerobic soil metabolism halflife; 

Total toxic residues half-life 

(soil texture) 

450 d; No significant 

degradation (sandy loam) MRID 41913505 

Aerobic aqueous metabolism 

half-life; 

Total toxic residues half-life 

(sediment texture) 

69.0 d; 899 d (silt loam) 

119 d; 782 d (sand) MRID 46427901 

Anaerobic aqueous metabolism 

half-life; 

Total toxic residues half-life 

(soil texture) 

127 d; 402 d (loamy sand) MRID 46413408 

Terrestrial field dissipation halflife 

(soil texture) 

18-24 d (sandy loam) 

34-53 d (loam) MRID 44078601 

Propyzamide is a soluble chemical (15 mg/L in water at 25C; USEPA, 1994) that is not expected 

to volatilize significantly due to the compound’s relatively low vapor pressure of 8.5 x 10-5 torr 

(25C; USEPA, 1994). Propyzamide is slightly to moderately mobile, with Freundlich soil-water 

partitioning coefficients (KF) that ranged from 18.3 (1/n=0.96) to 47.2 (1/n=0.96). Additionally, 

organic carbon partitioning coefficients (KFOC) ranged from 700 to 5383 L/kgOC. These values range 

in classification from moderately mobile to slightly mobile (FAO 2000). Mobility is partially 

explained by affinity to organic matter, as the coefficient of variation (CV) across six soils for KFOC

(40%) is less than that for KF (47%). The compound may also have greater mobility in sandy, claypoor soils, as KF values for propyzamide correlate with cation exchange capacity (R2

 = 0.9214). In 

general, compounds with KF values less than five are sufficiently mobile to present a potential 

ground water concern, especially in areas with soils that are sandy and where water tables are close 

to the surface. 

Propyzamide is stable to hydrolysis at pH 5, 7, and 9, relatively persistent with respect to photolysis 

on soil (t1⁄2 = 249 d), but moderately susceptible to degradation by aquatic photolysis (t1⁄2 = 41.7 d). 

Two major photodegradates were identified: RH-26059 and RH-24580. 

Parent propyzamide is slightly persistent (Goring scale, 1975) in aerobic soils (t1⁄2 = 20.1-44.6 d) and 

moderately persistent in aerobic aquatic systems (t1⁄2 = 69.0-119 d). Propyzamide is also moderately 

persistent in anaerobic aquatic systems (t1⁄2 = 127 d), and persistent in anaerobic soils (t1⁄2 = 450 d). 
Page 7 of 17 

Major degradates of propyzamide (>10% of the applied radioactivity) include RH-24644, RH24580, RH-26059, and carbon dioxide. Six minor degradates have also been identified: RH-24655, 

RH-20839, RH-26521, RH-25891, RH-26702, 3,5-dichlorobenzamide. A batch equilibrium study 

on RH-24644 and RH-24580 indicates that RH-24644 has similar to lower mobility compared to 

propyzamide (KF range = 2.34 (1/n=0.98) to 55.1 (1/n=0.86); KFOC range = 993-3910 L/kgOC), 

whereas RH-24580 is unambiguously more mobile than propyzamide (KF range = 0.283 (1/n=0.83) 

to 2.36 (1/n=0.87); KFOC range = 96.3-210 L/kgOC. 

The two major degradates observed in metabolism studies were RH-24580 at up to 32.2% of the 

applied, and RH-24644 at up to 31.9% of the applied. Carbon dioxide was also formed, at up to 

50.4% of the applied. Both RH-24580 and RH-24644 appear to degrade no more quickly than the 

parent based on biotic studies. 

The 2002 TRED and the HED memorandum (USEPA, 2007) state that for human dietary risk 

assessment, propyzamide and its metabolites containing the 3,5-dichlorobenzoyl moiety are the 

residues of concern (USEPA, 2002). Because all identified organic degradates of propyzamide 

contain the 3,5-dichlorobenzoyl moiety, and toxicity data for these degradates are unavailable, HED 

assumes that they have toxicity equivalent to that of parent propyzamide, and are thus residues of 

concern (USEPA, 2007). A total toxic residues approach was therefore used in the current 

assessment to evaluate potential exposures to people via drinking water. 

4. DRINKING WATER MODELING 

EDWCs were generated for this assessment using EFED’s standard suite of models. The last DWA 

for propyzamide was conducted in 2007. Since then, new input parameter guidance has been 

developed, Drinking Water Intake watershed PCAs have been developed, and new surface water 

modeling (SWCC) and ground water modeling (PRZM-GW) tools have become available. This 

DWA reflects these changes in the form of new EDWCs. Model input parameters listed in Tables 

4 and 5 were generated based upon the fate properties discussed in the previous section. 

Models

Exposure estimates were revised with the recently released Surface Water Concentration Calculator 

(SWCC). SWCC estimate pesticide concentrations in water bodies that result from pesticide 

applications to land. The SWCC uses PRZM version 5.0+ (PRZM5) and the Variable Volume 

Water Body Model (VVWM). 

Groundwater EDWCs for propyzamide based upon the chemical’s labeled uses were derived using 

PRZM-GW (Pesticide Root Zone Model for Groundwater, version 1.0, August 31, 2012). PRZMGW is a one-dimensional leaching model that estimates potential concentrations of pesticides in 

groundwater. The model accounts for pesticide sorption and decay during vertical transport through 

the crop root zone and deeper soil profile, to a shallow water table aquifer. In keeping with standard 

practice, PRZM-GW was used to simulate 30 or more years of repeated propyzamide applications 

in six standard scenarios that represent especially leaching-vulnerable areas: the Delmarva 

Peninsula, coastal GA, coastal NC, WI “corn”, FL “potato” and FL “citrus”. Input parameters 

employed in the model are listed in Table 6. The model generated the greatest single-day maximum 

concentration and the average breakthrough for the WI sands scenario (Table 9). 
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Tier 1 groundwater EDWCs for propyzamide were also developed using the Screening 

Concentration In GROund Water (SCI-GROW v2.3, Jul. 29, 2003) model. SCI-GROW is a 

regression model used as a screening tool to estimate pesticide concentrations in leaching-vulnerable 

groundwater. SCI-GROW was developed by fitting a linear model to monitored groundwater 

concentrations, with the Relative Index of Leaching Potential (RILP) as the independent variable. 

Groundwater concentrations were taken from 90-day average high concentrations from Prospective 

Ground Water monitoring studies. The RILP is a function of a pesticide’s aerobic soil metabolism 

and soil-water partition coefficient. The output of SCI-GROW represents pesticide residue 

concentrations that might occur in shallow, unconfined aquifers underlying sandy soils, following a 

single year’s application. Such locations are representative of groundwater that is likely to be 

maximally vulnerable to pesticide contamination. SWCC, PRZM-GW and SCI-GROW were run to 

estimate screening-level concentrations of total toxic residues of propyzamide in potential drinking 

water sources. 

Input Parameters

Input parameters used in the SWCC modeling appear in Table 4 and Table 5. In addition, Table 6

and 7 present the input parameters for the groundwater models (PRZM-GW and SCI-GROW, 

respectively). Explanations of various model input parameters are discussed below. 

Table 4. SWCC Application-Specific Input Parameters for Propyzamide 

Uses PRZM Scenario Max App rate in 

lbs a.i./A (kg 

a.i./ha)

# 

Apps/ye

ar 

Interval 

(days)

% Drift/ Efficiency Date of 1st of 

application 

Artichoke1 CA row crop 

RLF 8 (8.96) 2 120 0.135/0.95 Feb 1 

Leaf Lettuce CA Lettuce 2 (2.24) 2 183 0.135/0.95 Feb 1 

1. There is not a standard scenario available for the artichoke group. The CA row crop RLF scenario was used because this 

scenario was felt to provide the closest representation of agricultural practices for artichokes from among available 

EFED-approved scenarios. 

Table 5. SWCC Input Parameters for Propyzamide (TTR approach). Source Data are in Table 3. 

Input Parameter Value Justification Source 

Molecular Mass 

(g/mol) 

256.13 Product chemistry data USEPA, 1994 

Vapor Pressure at 25°C 

(torr) 

8.5 x 10-5 Study value USEPA, 1994 

Solubility in Water at 

25o

C (mg/L) 

15.0 Product chemistry data USEPA, 1994 

Organic Carbon 

Partition Coefficient 

(KOC) (L/kgOC) 

1966 Represents the mean 

KFOC for propyzamide 

parent as an estimate of 

the partition coefficient 

for the total residues. 

MRID 40211103 
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Table 5. SWCC Input Parameters for Propyzamide (TTR approach). Source Data are in Table 3. 

Input Parameter Value Justification Source 

Aerobic Soil 

Metabolism Half-life 

(days) 

165 Represents the 90 

percent upper 

confidence limit on the 

mean (two soils) total 

residue half-life. 

MRID 46413407 

Aerobic Aquatic 

Metabolism Half-life 

(days) 

1020 Represents the 90 

percent upper 

confidence limit on the 

mean total residue halflife. 

MRID 46427901 

Anaerobic Aquatic 

Metabolism Half-life 

(days) 

1210 Represents 3 times the 

single available total 

residue half-life. 

MRID 46413408 

Hydrolysis Half-lives at 

pH 5, 7 and 9 (days) 

Stable No measureable 

degradation in study. 

MRID 00107980 

Aqueous Photolysis 

Half-life (days) 

217 Represents the single 

environmental 

phototransformation 

total residue half-life. 

MRID 40420301 

Currently approved SWCC scenarios were used for the drinking (surface) water modeling. The 

California Row Crop regional scenario was used to model use on artichokes, because this scenario 

was parameterized to represent row crop vegetables and propyzamide may only be applied to 

artichokes in California. The California lettuce scenario was used to model application to leaf 

lettuce, as this scenario was designed to be nationally protective for use on lettuce (IPM, 2013). 

Application methods, rates and time of application were obtained/derived from proposed labels for 

leaf lettuce uses (EPA Reg. No. 62719-578). The second seasonal application to lettuce represents 

application to a second crop planted 183 days after the first; all applications were modeled as aerial. 

Chemical property input values were chosen in accordance with current EFED input parameter 

guidance (USEPA, 2009 and USEPA, 2013). Based on analysis of total toxic residues, the upper 90% 

confidence limit on the mean half-life was selected as the model input value for aerobic soil and 

aerobic aquatic metabolism pathways (165 d and 1,020 d TTR half-lives respectively). For the 

anaerobic aquatic metabolism pathway (used to represent decay within the benthic zone of the 

receiving water body), the single available half-life was multiplied by 3 (producing a value of 1,210 

d) to account for uncertainty associated with limited data. 

Standard percent cropped area (PCA) adjustment factor was used for these uses. These constitute 

conservative estimates of the crop acreage portions of watersheds in which specific crops or crop 

combinations are grown (USEPA, 2012b). The national all-agriculture PCA of 1.0 was employed 

to adjust results for all uses, because these uses are not as confined to specific regions of the country. 

Input parameters used in PRZM-GW and SCI-GROW appear in Table 6 and Table 7, respectively. 

Data sources and justification accompany values for each parameter. 
Page 10 of 17 

Table 6. PRZM-GW Input Parameters

Parameter (units) Input Value Data Source 

Application Rate (lbs a.i./A) 4 Label 

Number of Applications/yr 2 Label 

Application Dates 

(month/day) Feb 1 and Aug 1 IPM center 

Hydrolysis Half-life (days) Stable (0) MRID 00107980 

Soil Metabolism Half-life (days) 165 (upper 90 percent 

confidence limit on the mean) MRID 46413407 

Koc (mL/goc) 1966 (average) MRID 40211103 

Table 7. SCI-GROW Input Parameters for Propyzamide. 

Input Parameter Value Comment Source

Application Rate (lbs 

a.i./A) 

Artichoke: 4 (4.48) 

Leaf Lettuce: 2 (2.24) Label directions Proposed and 

current labels 

Applications per Year 

2 applic. for Artichoke and 

Lettuce and the rest just one 

application 

Label directions Proposed and 

current labels 

Organic Carbon Partition 

Coefficient (KOC) (L/kgOC) 1451 Represents the median of eight values MRID 40211103 

Aerobic Soil Metabolism 

Half-life (days) 109 Represents the mean of three values for total toxic residues MRID 46413407 

Modeling Results

The proposed use pattern and the maximum application rate were modeled for surface water and 

groundwater exposure estimates, as described above. Tables 8 list EDWCs for the highest use 

patterns of propyzamide, which are also reported in Tables 1. The maximum use patterns that 

yielded the maximum surface water and groundwater EDWCs for use in drinking water exposure 

estimation were lettuce and artichokes, respectively. Model input/output data for these estimates 

are attached in Appendix A and B. 

Table 8. Tier II Total Residue of Concern EDWCs in Surface Water and Ground Water from 

Propyzamide Uses on New Uses (Maximum EDWCs in Bold).

Drinking Water 

Source (Model, Use, 

Modeled rate) 

Scenario 

EDWCs 

Acute (μg/L) Chronic (μg/L) Cancer 

(μg/L) 

Surface Water (SWCC, 

Artichokes, 

4 lb a.i./A x 2 applic.; total 

of 8 lb/A/yr) 

CA row crop RLF 

(aerial application) 

61.4 33.4 26.0 

Surface Water (SWCC, 

Leaf Lettuce, 2 lb a.i./A x 

CA lettuce (aerial 

application) 102 47.0 33.6 
Page 11 of 17 

2 applic.; total of 4 

lb/A/yr) 

Ground Water (PRZMGW, Artichokes, 

4 lb a.i./A x 2 applic.; total 

of 4 lb/A/yr) 

WI sands 21 18.6 18.6 

Ground Water (SCIGROW, Artichokes, 

4 lb a.i./A x 2 applic.; total 

of 8 lb/A/yr) 

N/A 0.802 0.802 0.802 

Ground Water (SCIGROW, Leaf Lettuce, 2 lb 

a.i./A x 2 applic.; total of 4 

lb/A/yr) 

N/A 0.401 0.401 0.401 

N/A= Not Applicable 

Values in bold show the EDWCs recommended for HED’s acute (102 ppb) and chronic (47.0 ppb) and cancer (33.6 

ppb) dietary risk assessment as they are considered protective of all the registered uses of pronamide.

Surface water EDWCs based on total toxic residues and maximum annual application rates were 

highest for leaf lettuce (102, 47.0 and 33.6 ppb, for peak concentration and chronic values, 

respectively). 

The groundwater EDWCs listed in Table 8 are smaller than those reported in the most recent DWA 

(USEPA 2007), mainly because of a new batch equilibrium data that demonstrated a more immobile 

compound compared to the previous study submitted. Using PRZM-GW, the acute groundwater 

EDWC (21.0 ppb) do not exceeds the acute surface water EDWC (102 ppb) for artichokes at the 

maximum annual application rate (8 lbs a.i./A). This groundwater EDWC is associated with the WI 

sands scenario. The potential for groundwater contamination is expected to be greatest in areas 

where soils are relatively permeable and the water table is relatively close to the surface. 

 

5. MONITORING DATA 

A cursory review of both groundwater and surface water monitoring data on propyzamide was 

conducted as part of the 2002 TRED (USEPA, 2002a). The current assessment contains additional 

review of currently available monitoring data. The USGS NAWQA national database contains 

monitoring data of pesticides through 2005 (USGS, 2006). In surface water, propyzamide (only 

parent) was detected above the level of quantitation in 2.2% of samples (459 of 20,720 samples). 

The maximum measured surface water concentration was 1.12 μg/L in Shelby County, Tennessee 

in January, 2003. In groundwater, propyzamide was detected above the level of quantitation in 

0.05% of samples (5 of 9624 samples). The maximum concentration measured in groundwater was 

0.820 μg/L in Benton County, Arkansas in April, 1994. 

The USGS NASQAN national database contains monitoring data of pesticides by regional basin 

from 1996 to 2000 (USGS, 2006a). The maximum concentration of propyzamide detected in this 

program was 0.125 μg/L in the Colorado Basin in June, 1997. Concentrations of propyzamide were 

detected above the reporting limit in the Columbia, Colorado, Rio Grande, and Mississippi River 

basins; however, detections only occurred in the Northwest and Southwest. 
Page 12 of 17 

The California Department of Pesticide Regulation (DPR) Surface Water Database contains 

monitoring data of pesticides in California from 1990 to 2005 (CDPR, 2006). Propyzamide was 

detected in 8% of 1678 samples collected in the state, with the majority of detections occurring in 

water bodies within the Sacramento Valley. The maximum concentration of propyzamide reported 

in this database was 0.25 μg/L, detected in Yolo County in February, 1994. 

Propyzamide was detected in one Oklahoma reservoir out of twelve which were monitored in the 

Pilot Reservoir Monitoring Program due to their particular vulnerability to pesticide contamination 

(USEPA, 2002a). The compound was detected at up to 0.044 ppb in 83% of 41 raw water samples 

and up to 0.012 ppb in 42% of 19 finished water samples. 

Propyzamide was not detected in 432 ground water wells from 1984 to 1990, according to the EPA 

Pesticides in Ground Water Database (USEPA, 1992). Propyzamide is not a regulated chemical 

under the Safe Water Drinking Act (SWDA) or related statutes. Therefore, it is not listed in the EPA 

Safe Drinking Water Information System (SDWIS/FED) database (USEPA, 2007a) nor is it found 

in the EPA Unregulated Contaminants Monitoring Rules (UCMR) chemical monitoring database 

(USEPA, 2006b). 

The available monitoring data show peaks of 3.7-10.3 μg/L and annual mean of 0.53-4.45 μg/L 

parent propyzamide EDWCs generated in support of the 2002 TRED (USEPA, 2002a). Recently, 

an article published by Smalling, K.L. et al. 2013 mentioned that propyzamide was detected in water 

samples analyzed (at Santa Maria estuary in California, N=19), however, no pesticide 

concentrations were provided (Smalling, 2013). Monitoring data are not available on the degradates 

of propyzamide. Therefore, exposure estimates of total toxic residues cannot be directly compared 

against monitoring data. 

Recently, water and sediment (both bed and suspended) were collected from January 2008 through 

October 2009 from 12 sites in 3 of the largest watersheds along California’s Central Coast (Pajaro, 

Salinas, and Santa Maria Rivers) and analyzed for a suite of pesticides by the U.S. Geological 

Survey in cooperation with the California State Water Resources Control Board. Propyzamide was 

detected in more than 50% of the samples in the Salinas and Pajaro Rivers and greater than 95% in 

Santa Maria River. The maximum concentrations of propyzamide ranged from 30.4 to 14,000 

ng/L (14 ppb) during summer dry season and 47.8 to 1,390 ng/L (1.3 ppb) in storm events in 

Pajaro and Santa Maria Estuaries, respectively (USGS, 2011). 

Drinking Water Treatment

Some data on the effects of drinking water treatment on propyzamide concentrations are available 

from the Pilot Reservoir Monitoring Program (USEPA, 2002a). The compound was detected twice 

as often in raw water samples as in finished water samples. However, monitored treatment data carry 

some inherent uncertainty due to variability in treatment facility design. Collecting analogous 

samples of water before and after treatment for purposes of comparison is challenging due, among 

other things, to dilution and transit time effects. 

Flocculation and sedimentation might be expected to be effective at removing some propyzamide 

residue concentrations due to the chemical’s weak affinity for organic carbon. Activated carbon 
Page 13 of 17 

filtration might similarly decrease propyzamide residue concentrations, although this technique is 

not employed in most water treatment operations. Changes in pH are not expected to affect 

propyzamide, as the compound is stable to hydrolysis. Data regarding the effects of specific drinking 

water treatment practices on propyzamide residues of risk concern have not been provided to the 

Agency, and have not been found in the published literature. 

6. CONCLUSION 

The EDWCs reported here are based on artichoke (CA) and leaf lettuce uses. Tables 1 and 2 reflect 

the most conservative (highest) EDWCs for surface and groundwater, which are recommended for 

use in HED’s dietary assessment. The leaf lettuce use generated the highest surface water and 

groundwater EDWCs. The total toxic residues of propyzamide include propyzamide parent and all 

degradates with the 3,5-dichlorobenzoyl moiety, which are assumed to have toxicity similar to that 

of propyzamide parent. 

The recommended estimated drinking water concentrations (EDWCs) for the Health Effects 

Division’s (HED) dietary assessment is 102 ppb for the acute dietary assessment and 47.0 ppb for 

the chronic and cancer dietary assessments.

 
Page 14 of 17 

LITERATURE CITATIONS

CDPR. 2006. Surface Water Database. California Department of Pesticide Regulation, Surface 

Water Protection Program. Online at: http://www.cdpr.ca.gov/docs/sw/surfdata.htm 

Jones, R. D., S. Abel, W. R. Effland, R. Matzner, R. Parker. 1998. An Index Reservoir for Use in 

Assessing Drinking Water Exposure. Proposed Methods for Basin-scale Estimation of 

Pesticide Concentrations in Flowing Water and Reservoirs for Tolerance Reassessment. 

Presentation to FIFRA Science Advisory Panel, June 29-30, 1998. Online at: 

http://www.epa.gov/scipoly/sap/1998/index.htm 

IPM, 2013. NSF Center for Integrated Pest Management (host). U.S. Department of Agricultre 

Pest Management Centers. Last updated: September 16, 2013. Online at: 

http://www.ipmcenters.org/cropprofiles/CP_form.cfm 

USEPA. 1992. Pesticides in Ground Water Database: A Compilation of Monitoring Studies: 1971-

1991: National Summary. U.S. Environmental Protection Agency. Washington, DC. 

USEPA. 2002. Report of FQPA Tolerance Reassessment Progress and Interim Risk Management 

Decision: Pronamide. U.S. Environmental Protection Agency, Office of Prevention, 

Pesticides, and Toxic Substances, Mar. 8, 2002. 

USEPA. 2002a. Tier II Drinking Water Assessment to Support TRED for Pronamide 

(Propyzamide). U.S. Environmental Protection Agency, Office of Pesticide Programs, 

Environmental Fate and Effects Division, Memorandum, Jun. 5, 2002. 

USEPA. 2002. SCIGROW: Users Manual. Online at: 

http://www.epa.gov/oppefed1/models/water/#scigrow

USEPA. 2005. PRZM 5: Users Manual. Online at: 

http://www.epa.gov/oppefed1/models/water/#przm 

USEPA. 2005. EXAMS 2.98.04.06: Users Manual. Online at: 

http://www.epa.gov/oppefed1/models/water/#exams 

USEPA. 2006. Water models PE Version 5: User Manual. Online at: 

http://www.epa.gov/oppefed1/models/water/pe5_user_manual.htm 

USEPA. 2009. Guidance for Selecting Input Parameters in Modeling the Environmental Fate 

 and Transport of Pesticides. U.S. Environmental Protection Agency, Office of chemical 

 Safety and Pollution Prevention, Office of Pesticide Programs, Environmental Fate and 

 Effects Division, Oct. 22, 2009. Online at: 

http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm

USEPA. 2006a. Water Models. U.S. Environmental Protection Agency, Pesticides: Science and 

Policy. Last updated: July 9, 2013. Online at: 

http://www.epa.gov/oppefed1/models/water/ 
Page 15 of 17 

USEPA. 2006b. Unregulated Contaminant Monitoring Rules (UCMR). U.S. Environmental 

Protection Agency, Unregulated Contaminant Monitoring Program. Last updated: Nov. 

24, 2006. Online at: http://www.epa.gov/safewater/data/ucmrgetdata.html 

USEPA. 2007. Clock-Rust, M. Residues of Concern for Pronamide (Propyzamide) for Drinking 

Water. DP Barcode: 328077. HED Memorandum to EFED. 

USEPA. 2007a. Safe Drinking Water Information System/Federal Version (SDWIS/FED). U.S. 

Environmental Protection Agency. Last updated: September 19, 2013. Online at: 

http://www.epa.gov/safewater/data/getdata.html 

USGS. 2006. National Water-Quality Assessment (NAWQA) Program. U.S. Geological Service. 

Last updated: Oct. 19, 2006. Online at: 

http://infotrek.er.usgs.gov/traverse/f?p=136:1:1779537078393353::NO::: 

USGS. 2006a. Kelly, V., R. Hooper, B. Aulenbach, and M. Janet. Concentrations and Annual 

Fluxes for Selected Water-Quality Constituents from the USGS National Stream Quality 

Accounting Network (NASQAN), 1996-2000. U.S. Geological Survey. Last updated: 

Nov. 20, 2006. Online at: http://pubs.usgs.gov/wri/wri014255/results/detect.htm 

USGS. 2011. Smalling, K.L. and Orlando, J.L.; Ocurrence of Pesticides in Surface Water and 

Sediment from Three Central California Coastal Watersheds, 2008-2009. 

USEPA. 2012a. Guidance for Selecting Input Parameters for Modeling Pesticide Concentrations 

 in Groundwater Using the Pesticide Root Zone Model. Office of chemical Safety and 

 Pollution Prevention, Office of Pesticide Programs, Environmental Fate and Effects 

 Division, and Health Canada Pesticide Management Regulatory Agency, Oct.15, 2012. 

USEPA. 2012b. Development and Use of Percent Cropped Area Adjustment Factors in Drinking 

 Water Exposure Assessments. U.S. Environmental Protection Agency, Office of chemical 

 Safety and Pollution Prevention, Office of Pesticide Programs, Environmental Fate and 

 Effects Division, September 9, 2010. Online at: 

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

USEPA. 2013. Guidance for Modeling Offsite Deposition of Pesticides via Spray Drift for 

Ecological and Drinking Water Assessments. Office of chemical Safety and Pollution Prevention, 

Office of Pesticide Programs, Environmental Fate and Effects Division, Dec. 20, 2013. 

Smalling, K.L.; Kuivila, K. M.; Orlando, J.L.; Phillips, B.M.; Anderson, B.M.; Siegler, K.; Hunt, 

J.W.; Hamilton, M. Environmental fate of fungicides and other current-use pesticides in a central 

California. Marine Pollution Bulletin 73 (2013) 144–153. 

FAO, 2000. Food and Agriculture Organization of the United Nations. Pesticide Disposal Series 8. 

Assessing Soil Contamination: A Reference Manual. Appendix 2. Parameters of pesticides that 

influence processes in the soil. Editorial Group, FAO Information Division: Rome, 2000. 

http://www.fao.org/docrep/003/X2570E/X2570E00.htm. 
Page 16 of 17 

Appendix A. SWCC Input/Output Data for Drinking Water Exposure Assessment. 

 Summary of Water Modeling of Pronamide and the USEPA 

Standard Reservoir 

Estimated Environmental Concentrations for Pronamide are presented in Table 1 for the USEPA 

standard reservoir with the CAlettuceSTD field scenario. A graphical presentation of the year-toyear peaks is presented in Figure 1. These values were generated with the Surface Water 

Concentration Calculator (SWCC Version 1.106). Critical input values for the model are 

summarized in Tables 2 and 3.

This model estimates that about 1.8% of Pronamide applied to the field eventually reaches the 

water body. The main mechanism of transport from the field to the water body is by runoff ( 70% 

of the total transport), followed by spray drift (22.2%) and erosion (7.8%). 

In the water body, pesticide dissipates with an effective water column half-life of 91.7 days. (This 

value does not include dissipation by transport to the benthic region; it includes only processes 

that result in removal of pesticide from the complete system.) The main source of dissipation in 

the water column is volatilization (effective average half-life = 157.7 days) followed by washout 

(245.1 days), metabolism (2259.2 days), and photolysis (27914 days). 

In the benthic region, pesticide dissipation is negligible (2680.1 days). The main source of 

dissipation in the benthic region is metabolism (effective average half-life = 2680.1 days). The 

vast majority of the pesticide in the benthic region (99.53%) is sorbed to sediment rather than in 

the pore water. 

Table 1. Estimated Environmental Concentrations (ppb) for Pronamide. 

Peak (1-in-10 yr) 102. 

4-day Avg (1-in-10 yr) 97.0 

21-day Avg (1-in-10 yr) 82.5 

60-day Avg (1-in-10 yr) 69.1 

365-day Avg (1-in-10 yr) 47.0 

Entire Simulation Mean 33.6 

Table 2. Summary of Model Inputs for Pronamide. 

Scenario CAlettuceSTD 

Cropped Area Fraction 1 

Koc (ml/g) 1966.5 

Water Half-Life (days) @ 25 °C 1020 

Benthic Half-Life (days) @ 25 °C 1210 

Photolysis Half-Life (days) @ 40 

°Lat 

217 
Page 17 of 17 

Hydrolysis Half-Life (days) 0 

Soil Half-Life (days) @ 25 °C 165 

Foliar Half-Life (days) 0 

Molecular Wt 256.13 

Vapor Pressure (torr) 8.5e-5 

Solubility (mg/l) 15 

Table 3. Application Schedule for Pronamide. 

Date (Mon/Day) Type Amount (kg/ha) Eff. Drift 

2/1 Foliar 2.24 0.95 0.135 

8/1 Foliar 2.24 0.95 0.135 

Figure 1. Yearly Peak Concentrations