2

The maximum EDWCs for surface water and groundwater are listed in Table 1. The 

PRZM/EXAMS model predicted that total coumaphos residue concentrations (coumaphos + 

coumaphoxon) in surface water are not likely to exceed 0.10 μg coumaphos equivalent/L for the

maximum peak concentration (acute) and 0.03 μg coumaphos equivalent/L for the average 

concentration (chronic). For groundwater, no breakthrough of coumaphos into shallow 

groundwater was observed using 100-year PRZM-GW simulations. However, breakthroughs 

were observed for coumaphoxon, but predicted EDWCs were several orders of magnitude lower 

than the predicted values of SCIGROW model. SCIGROW modeling results for groundwater are 

listed in Table 1. SCIGROW predicted total coumaphos residue concentration in groundwater is 

not likely to exceed 1.91E-03 μg coumaphos equivalent/L for the maximum peak concentration 

(acute) and the average concentration (chronic).

Table 1. Maximum EDWCs for Drinking Water Sources for Coumaphos and 

Coumaphoxon 

Source of Drinking 

Water

Estimated Drinking Water concentration (μg/L)

Acute Chronic Average

chronic

Coumaphos

Surface Water1 0.10 0.05 0.03

Groundwater2 1.91 x 10-03 1.91 x 10-03 1.91 x 10-03

Coumaphoxon

Surface Water 0.002 0 0

Groundwater,2 5.06 x 10-06 5.06 x 10-06 5.06 x 10-06

Coumaphos Equivalents (Coumaphos+Coumaphoxon)

Surface Water 0.102 0.05 0.03

Groundwater 1.91 x 10-03 1.91 x 10-03 1.91 x 10-03

1 EDWCs based on PRZM/EXAMS model

2 EDWCs derived from SCIGROW 

Introduction

Coumaphos (O-[3-chloro-4-methyl-2-oxo-2H-1-benzopyran-7-yl] O,O-diethyl phosphorothioate) 

is an organophosphate insecticide/acaricide. Coumaphos can be applied by dip vat, aerosol can, 

dustbag, hand-held duster, hand-held sprayer, backrubber oiler, mechanical duster, shaker can, 

and squeeze applicator. Based on the above understanding of the uses and methods of application 

on animals, there is a potential for indirect exposure to coumaphos in the environment via 

dislodging of applied chemical from animal hides. Coumaphos is also registered for the control 

of insects, mites, and ticks on livestock and swine bedding, and for the control of varroa mites 

and small hive beetles in bee hives. However, the indoor use of coumaphos (e.g., to treat swine 

bedding) and the placement of coumaphos-treated strips in bee hives would not be considered in 

the drinking water assessment because they do not provide complete routes of exposure to 

surface waters or groundwater.

In an earlier assessment, the Environmental Fate and Effects Division (EFED) assumed that the 

disposal of bioremediated coumaphos dip vat solution on non-agricultural land would be a major 

exposure route to drinking water sources for human consumption. Since dried sludge generated 

in evaporation ponds containing bioremediated dip vat solution is discarded in a landfill by 
3

USDA APHIS (US EPA, 2008), EFED concludes that exposure via application of bioremediated 

spent dip vat solutions to land is not an exposure pathway for drinking water sources. Therefore, 

the application of bioremediated spent dip vat solutions to land is not included in modeling of

EDWCs in surface water and groundwater. 

However, during a rain event, a certain fraction of coumaphos wash-off from treated cattle can 

come contact into with and be adsorbed onto manure as well as transported as runoff from 

Concentrated Animal Feeding Operations (CAFOs) and pasture/rangeland. In registrantsubmitted wash-off studies, fresh cow hides were treated with either Co-Ral® 11.6% 

emulsifiable liquid (MRID 42512601) or Co-Ral® 25% wettable powder (MRID 42512602) and 

then dried for 0.5, 3, or 24 hours. The wash-off fraction was measured after hides had been 

soaked in water for 0.5, 1, 2, or 4 hours. Results of these studies indicate that wash-off fraction 

is inversely related to drying time and dependent upon the formulation (Table 2) but not affected 

by soaking time (data not shown). Although not the most conservative, wash-off fractions for 

the 24-hour drying time were used in this assessment because they represent a reasonable time 

frame after application for a treated cow to be caught in a rainstorm. 

Table 2. Percent Wash-Off for Different Formulations of Coumaphos at Different Drying 

Times (MRIDs 42512601 and 42512602)

Formulation 

(%)

Drying Time 

(hrs)

Wash-Off 

Fraction

Comment

Emulsifiable 

powder/concentrate 

(11.6)

0.5 0.116 Represents formulation associated with maximum 

application rates for the U.S. with the exception of Texas 

(back rubbers and spray)

3 0.046

24 0.027

Wettable 

powder/flowable

concentrate (25)

0.5 0.38 Represents formulation associated with maximum 

3 0.21 application rates for Texas (dip vat and spray)

24 0.02

Bolded values were used in EDWCs assessment

To accurately characterize the potential environmental exposure pathways, selecting the 

appropriate livestock management system and various exposure pathway scenarios is necessary. 

Several scenarios were considered to estimate the application rate for coumaphos and potential 

exposure to coumaphos and coumaphoxon for surface water and groundwater. Application rates 

for manure applied to land and runoff from rangeland are based on spray (Texas) or back rubber 

(rest of the U.S.) application on cattle. Table 3 provides application rates for various scenarios.

Detailed descriptions and example calculations of application rates for coumaphos are also 

provided in Appendix A. 

It is assumed that there are no surface water and groundwater intakes directly adjacent to 

CAFOs; therefore, runoff from CAFOs is not considered for the drinking water assessment.

Since the estimated application rate of 0.0004 lbs a.i./A for runoff from rangeland is 

approximately 38 times lower than the application rate for coumaphos-containing manure, the 

EDWCs are based on a single application of the maximum coumaphos-containing manure for 

land application. In general, the recommended application rate of manure is based on the nutrient 

(i.e., nitrogen, phosphorus and potassium) requirements for crops. For this assessment, the 

application rate for manure applied to pasture and rangeland is based on a 250 lb total 
4

nitrogen/acre/year requirement for growing warm season perennial grass in Texas (Stichles and 

McFarland1).

3. Estimated Coumaphos Application Rates for Various Scenarios

Sources of a.i.

from Application Scenario

Wash-Off 

Fraction

Maximum Single 

Application Rate 

(lb/A)

Number of 

Applications/

Year

Maximum 

Annual 

Application Rate

(lb/A)

Texas: Spray Application (42% flowable concentrate)

CAFO manure applied to landa No incorporation of manure into soil 

0.02 0.015 1

b 0.015

Incorporation of manure into soil within a day 

0.02 0.009 1

b 0.009

Rest of U.S.: Back Rubber Application (11.6% emulsifiable concentration)

CAFO manure applied to landa No incorporation of manure into soil

0.027 0.0092 1

b 0.0092

Incorporation of manure into soil within a day

0.027 0.0051 1

b 0.0051

AU = animal unit

a Application rate of coumaphos depends on nutrient management and application method of manure. 

b Application rate can be split based on total nitrogen (TN) requirement during the growing season.

Residues of Concern

The residues of concern (ROC) for human health risk assessment and for tolerance expression 

are coumaphos and its oxygen analog coumaphoxon (US EPA, 2007). A maximum conversion 

efficiency of coumaphos to coumaphoxon of 10.2% was derived from available data on 

photodegradation in water. 

Input Parameters and Modeling Approach

A limited environmental fate database for coumaphos indicates that it is persistent (DT50 of >1 

year in aerobic soil) and slightly mobile to hardly mobile (Koc=1874 to 10297 L/kg) in soil

according to the FAO classification of mobility in soil (FAO, 2000). The major pathway of 

coumaphos degradation appears to be photodegradation in water (DT50 of 33 hours). A major 

degradate, oxygen analog coumaphoxon, was detected in an aqueous photodegradation study at a 

maximum of 10.2% of applied chemical. Limited environmental fate data are available for 

coumaphoxon, which suggests that it is not persistent in the terrestrial environment (DT50 of 0.49 

to 2.27 days), but it is mobile (Koc=198.4 L/kg) in soil according to FAO classification of 

mobility in soil (FAO, 2000). Since the environmental fate data suggest that the fate behaviors of 

coumaphos and coumaphoxon differ in the environment, EDWCs were estimated independently 

for these chemicals. 

The EDWCs of coumaphos and coumaphoxon were generated using Tier II PRZM/EXAMS 

model for surface water and Tier I SCIGROW (Screening Concentration in Groundwater

Program) for groundwater. Pesticide Root Zone Model-Ground Water model (PRZM-GW) was 

also used for groundwater based on a recent EFED guidance document (US EPA, 2012a). 

 

1 http://agrilifeextension.tamu.edu/
5

Surface Water 

The EDWCs were generated using EFED’s standard suite of models. Pesticide Root Zone Model 

(PRZM v3.12.2, May 12, 2005) and Exposure Analysis Modeling System (EXAMS v2.98.04.06, 

Apr. 25, 2005). PRZM and EXAMS are simulation models coupled with the input shell 

PRZM/EXAMS (PE v5.0, Nov. 15, 2006) to generate EDWCs of coumaphos and its major 

degradate, coumaphoxon, that may occur in surface water used as drinking water. The PRZM 

model simulates pesticide movement and transformation from crop application through soil 

residue processes. The EXAMS model simulates pesticide loading via runoff and erosion 

assuming a standard watershed of 172.8 ha that drains into an adjacent standard drinking water 

index reservoir with surface area of 5.26 ha and an average depth of 2.74 m. A more detailed 

description of the index reservoir watershed can be found in Jones et al., 1998. Standard percent 

cropped areas (PCA) were used for proposed uses as estimates of the extent of watershed on 

which crops are grown. The national default for non-agricultural use (PCA of 1.0) was applied in 

this assessment according to the current PCA guidance (US EPA 2012b).

Groundwater

Screening Concentration in Groundwater (SCIGROW v2.3, Jul. 29, 2003) is a regression model 

used as a screening tool to estimate pesticide concentrations found in groundwater used as 

drinking water. The SCIGROW model and user’s manual may also be downloaded from the 

EPA Water Models web-page (http://www.epa.gov/oppefed1/models/water/#scigrow). Percent 

Crop Areas (PCAs) are not used with the SCIGROW model.

In addition, Tier 1 groundwater EDWCs for coumaphos and coumaphoxon, resulting from use as 

land farming, were also derived using the PRZM-GW model (Pesticide Root Zone Model for 

Groundwater, version 1.07, August 31, 2012), with the GW-GUI (Graphical User Interface, 

version 1.07, August 31, 2012). PRZM-GW is a one-dimensional, finite-difference model that 

estimates the concentrations of pesticides in groundwater. It accounts for pesticide fate in the 

crop root zone by simulating pesticide transport and degradation through the soil profile after a 

pesticide is applied to an agricultural field. PRZM-GW permits the assessment of multiple years 

of pesticide application (up to 100 years) on a single site. Six standard scenarios, each 

representing a different region known to be vulnerable to groundwater contaminations, are 

available for use with PRZM-GW for risk assessment purposes. In PRZM-GW simulations, each 

of these standard scenarios was used. PRZM-GW output values represent pesticide 

concentrations in a vulnerable groundwater supply that is located directly beneath a rural 

agricultural field following many years of pesticide application. Descriptions of all executable 

versions of current models used in drinking water exposure can be obtained from the URL link:

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

Input Parameters

A summary of the model input parameter values used in PRZM/EXAMS, SCIGROW, and 

PRZM-GW Models are in Table 4, Table 5, and Table 6, respectively. Input parameters were 

selected in accordance with EFED’s “Guidance for Selecting Input Parameters in Modeling the 

Environmental Fate and Transport of Pesticides,” Version 2.1 (USEPA, 2009). Sample model 
6

output files are located in Appendix C. PRZM/EXAMS time series for coumaphos and 

coumaphoxon for the highest surface water EDWCs (i.e., BSS Turf scenario) are also attached in 

Appendix C.

Table 4. PRZM/EXAMS Input Parameters for Coumaphos and Coumaphoxon

Parameter Value Data Source Comments

Coumaphos

Maximum Application 

Rate (lb a.i./A)

[kg a.i./ha]

0.015 [0.017]

Estimated

Appendix A and Table 2

Maximum application rate 

applied to TX 

0.0092 [0.01]

See Appendix A and Table 2

Maximum application rate 

applied to rest of U.S. 

Number of 

Applications 1

Assumed, however, application 

rate can be split based on total 

nitrogen requirement during the 

growing season.

Depth of Incorporation 

(inches) 0 and 8 http://ohioline.osu.edu/agffact/0208.html

Common practices for 

application of manure

Method of Application Ground application Applied as manure

Spray Drift 0

Applied with manure spreader Application Efficiency 1.0 Assumed

Scenario and 

Application Date

(day-month)

PA Turf, 15-10

FL Turf, 15-10

BSS Turf, 15-10

Based on PRZM/EXAMS 

Scenarios

Assumed manure applied during 

dormant season

Molecular Mass 

(g/mol) 362.5 US EPA 2007 ---

Vapor Pressure (Torr) 1.0 x 10-07 US EPA 2007 ---

Henry’s Law Constant 

(atm m3/mol) 2.62 x 10-07 Estimated ==

Solubility in Water 

(mg/L) 20 US EPA 2007 ---

Hydrolysis t1/2 at pH 

7.0 (days) 0 Not Available Considered stable to hydrolysis @ pH 7.0

Aquatic Photolysis t1/2

(days) 1.38 MRID 42764101MRID 43103901

Coumaphoxon is a major 

degradate (10.2%)

Aerobic Soil 

Metabolism t1/2 (days)

0 MRID 40518701 Considered stable

Aerobic Aquatic 

Metabolism t1/2 (days)

0 ---

Input parameter guidance 

(USEPA, 2009)

Soil Partitioning 

Coefficient 

(Koc; ml/go)

5904 MRID 45721401 Represents average KFoc from 4 

soils 

Wetted in? No --- Assumed

Percent Crop Area

(Decimal) 1.0 US EPA 2012b Recommended PCA for nonagricultural uses

Coumaphoxon

Maximum Application

Rate (lb a.i./A)

[kg a.i./ha]

0.0015 [0.0017] Estimated1---

Number of 

Applications 1 Assumed Based on application rate of coumaphos 

Depth of Incorporation 

(inches) 0 Assumed ---
7

Table 4. PRZM/EXAMS Input Parameters for Coumaphos and Coumaphoxon

Parameter Value Data Source Comments

Method of Application Not applicable ---

Degradation product of 

coumaphos

Scenario and 

Application Date

(day-month)

BSS Turf, 15-10 Based on PRZM/EXAMS 

Scenarios

Assumed manure applied during 

dormant season

Molecular Mass 

(g/mol) 346.7 EPISUITE Estimated value

Vapor Pressure (Torr) 7.68 x 10-08 EPISUITE Estimated value

Henry’s Law Constant 

(atm m3/mol) 1.10 x 10-09 EPISUITE Estimated value

Solubility in Water 

(mg/L) 31.6 EPISUITE 4.1 Estimated value

Hydrolysis t1/2 at pH 

7.0 (days) 0 Not available Assumed stable

Aquatic Photolysis t1/2

(days) 0 Not available Assumed stable

Aerobic Soil 

Metabolism DT50

(days)

4.1 MRID 48705501

90th percentile upper confidence 

bound on the mean half-life of 

coumaphoxon

Aerobic Aquatic 

Metabolism t1/2 (days)

8.2

2

---

2X of Aerobic Soil Metabolism 

DT50 (days)

Soil Partitioning 

Coefficient 

(Koc; ml/goc)

198.4 EPISUITE 4.1 Estimated value

Percent Crop Area 

(Decimal) 1.0 US EPA 2012c Recommended PCA for nonagricultural uses

1 Coumaphos application rate (0.015 lb a.i/A) x [(0.102, the maximum conversion rate from aquatic photolytic 

degradation of coumaphos to coumaphoxon in laboratory studies) x (0.96, the molecular weight ratio of 

coumaphos to coumaphoxon)]

2 In the absence of a aerobic aquatic metabolism study, 2X of aerobic soil metabolism DT50 value was multiplied 

by 2 according to “Guidance for selecting input parameters in modeling for environmental fate and transport of 

pesticides.” Version 2.1 October 22, 2009.

Table 5. SCI-GROW (v2.3) Input Parameter Values for Coumaphos and Coumaphoxon

Parameter Value Data Source Comments

Coumaphos

Maximum Application 

Rate (lbs a.i./acre)

[kg a.i./ha]

0.015 [0.017] Table 2

---

Number of 

Applications 1 Table 4 ---

KFoc (mL/g) 1870 MRID 45721401

Since there is a threefold difference in 

observed values, the lowest non-sand 

KFOC value used. 

Aerobic Soil 

Metabolism DT50

(days)

0 MRID 45118631 Stable

Coumaphoxon

Maximum Application 0.0015 (0.0017) Table 4 ---
8

Table 5. SCI-GROW (v2.3) Input Parameter Values for Coumaphos and Coumaphoxon

Parameter Value Data Source Comments

Rate lb a.i./A 

(kg a.i./ha)

Number of 

Applications 1 Table 4 ---

Koc (mL/g) 198.4 EPISUITE 4.1 Estimated value

Aerobic soil 

metabolism (DT50) d

4.1 MRID 48705501 90th percentile upper confidence bound 

on the mean half-life of coumaphoxon

Table 6. PRZM-GW (v1.7) Input Parameter Values for Coumaphos and Coumaphoxon

Parameters Value Data Source Comments

Coumaphos

Application Method Ground Table 4 ---

Application Rate 

(lbs. a.i./acre) 

[kg a.i./ha]

0.015 [0.017] Table 2 ---

Application 

Frequency 1 Table 4 ---

Hydrolysis (DT50) 

(days) Stable --- No study

Aerobic soil 

metabolism (DT50) 

(days)

10951 MRID 45118631 Stable. Assumed 3X of duration of 

study

Koc 5904 L/Kg MRID 46808411 Average KFoc

2

Coumaphoxon

Application Method Ground Table 4 ---

Application Rate 

(lbs. a.i./acre) [kg/ha] 0.0015 [0.0017] Table 2 ---

Application 

Frequency 1 Table 4 ---

Hydrolysis (DT50) 

(days) 0 Not available Assumed stable2

Aerobic soil 

metabolism (DT50) 

(days)

4.12 MRID 48705501 90th percentile upper confidence bound 

on the mean half-life of coumaphoxon

Koc 198.4 EPISUITE 4.1 Estimated value

1 Model requires a numerical value for DT50 was estimated using the NAFTA degradation kinetics procedure and 

did not have a recommendation for modeling (Figure 1, Appendix B). In addition, the estimated Single First Order 

(SFO) DT50 of 2761 days is well beyond the duration of study. Therefore, 3x of duration (i.e., 3 x 365 day) of 

aerobic soil metabolism study was used in the modeling

2 EFED input parameter guidance 

http://www.epa.gov/oppefed1/models/water/przm_gw/wqtt_przm_gw_input_guidance.htm

Results

Drinking water estimated coumaphos concentrations in surface water and groundwater are 

summarized in Tables 6 and 7. Sample output from model runs are provided in Appendix C.
9

PRZM/EXAMS model concentrations (μg/L) represent untreated surface water concentrations. 

The SCIGROW and PRZM-GW concentrations represent groundwater concentrations that might 

be expected in shallow unconfined aquifers under sandy soils. All scenarios run in PRZM-GW 

required the use of an extended weather file, which allows the user to run the simulation for up to 

100 years in order to observe breakthrough into shallow groundwater. No breakthrough of 

coumaphos in shallow groundwater was observed using 100-year PRZM-GW simulations. 

However, breakthroughs were observed for coumaphoxon for four scenarios (Table 7).

The simulated concentrations provided in this assessment are conservative estimates of 

concentrations in drinking water. If dietary risks require refinement, higher-tiered, crop-specific 

and location-specific models and modeling scenarios can be used.

Table 6. Maximum EDWCs Based on Manure Containing Coumaphos and its Degradate 

Coumaphoxon application

Drinking Water Source Crop Scenario

1-in-10 year 

acute

(μg/L)

1-in-10 year 

chronic

(μg/L)

30- year annual 

average

(μg/L)

Coumaphos

Non-incorporated Manure

Surface Water1 BSS Turf 0.10 0.05 0.03

FL Turf 0.05 0.03 0.02

PA Turf 0.08 0.05 0.03

Incorporated Manure2 

BSS Turf 0.01 0 0

Groundwater Generic Scenario3 1.91 x 10-03 1.91 x 10-03 1.91 x 10-03

Coumaphoxon

Surface Water BSS Turf 0.002 0 0

Groundwater GenericScenario3 5.04 x 10-06 5.04 x 10-06 5.04 x 10-06

1 EDWCs generated using PRZM/EXAMS model 

2 EDWCs were generated for the highest non-incorporated scenario (BSS turf) for surface water

3 EDWCs generated using SCIGROW model and can be considered for both acute and chronic values

Table 7. PRZM-GW EDWCs Based on Manure Containing Coumaphos and its 

Degradate Coumaphoxon 

Application Rate 

and Frequency Scenario1

Highest

Daily

Value (μg/L)

Post 

Breakthrough 

Average (μg/L)

Average Simulation 

Breakthrough Time 

(days)

0.015 lbs a.i./A x 1

application

Coumaphos

FL Citrus 0.1852 Not Reported Incomplete

FL Potato 3.22 x 10-062 Not Reported Incomplete

GA peanut 2.74 x 10-062 Not Reported Incomplete

NC Cotton 0.0382 Not Reported Incomplete

Delmarva sweet corn 0.0032 Not Reported Incomplete

WI corn 4.98 x 10-042 Not Reported Incomplete

Coumaphoxon

0.0015 lbs a.i./A x 1

application

FL Citrus 5.02 x 10-12 4.78 x 10-12 30012

FL potato 0

2

0

2

Incomplete

GA peanut 9.14 x 10-182 Not Reported Incomplete

NC cotton 2.65 x 10-17 2.61 x 10-17 29441

Delmarva sweet corn 2.02 x 10-16 1.77 x 10-16 24107
10

Table 7. PRZM-GW EDWCs Based on Manure Containing Coumaphos and its 

Degradate Coumaphoxon 

Application Rate 

and Frequency Scenario1

Highest

Daily

Value (μg/L)

Post 

Breakthrough 

Average (μg/L)

Average Simulation 

Breakthrough Time 

(days)

WI corn 2.49 x 10-142 Not Reported Incomplete

1 These scenarios are regional vulnerable sites for groundwater evaluation. 

2 Since there is no breakthrough with 100-yr PZRM-GW simulation, the reported values are not reliable. 

Monitoring Data

There were no national-scale or state monitoring data available for this assessment. 

Drinking Water Treatment

There is no available information on the drinking water treatment effects on coumaphos and 

coumaphoxon.

Uncertainties

The main uncertainty associated with this drinking water assessment is the lack of acceptable 

environmental fate data for coumaphos and its degradate coumaphoxon. Limited data are 

available for coumaphos and its degradate, coumaphoxon. Supplemental photodegradation in 

water data (MRID 42764101 and 42764102) indicate that the maximum coumaphoxon 

concentration at any sampling time was 10.2% of coumaphos application rate. This conversion 

rate was used to estimate a coumaphoxon application rate. 

 

In addition, there is an additional uncertainty related to the estimated DT50 value, which is 

approximately 7X higher than the duration of the aerobic soil metabolism study and 15 to 23X 

higher than the reported field dissipation half-lives. Groundwater concentrations were based on 

3X of the duration of the aerobic soil metabolism study. 

In this drinking water assessment, EFED attempted to locate the best available data/models for 

estimating coumaphos and its degradate, coumaphoxon, residues in drinking water sources, 

CAFO manure applied to land, and potential runoff from rangeland. EFED used wash-off 

fractions for the 24-hour drying time in this assessment because they represent a reasonable time 

frame after application for a treated cow to be caught in a rainstorm. Potential exposure could be 

higher or lower depending on CAFO operations such as: indoor versus outdoor facilities, 

number of cattle treated/day, and other variables associated with manure management for crop 

production as well as weather conditions. Uncertainty associated with each of these individual 

components could potentially dictate higher or lower EDWCs. 
11

References

ASAE. 2005. Manure Production and Characteristics. ASAE Standard D384.1 FEB 03.American 

Society of Agricultural Engineers. St. Joseph, MI 

FAO 2000. Appendix 2. Parameters of pesticides that influence processes in the soil. In FAO 

Information Division Editorial Group (Ed.), Pesticide Disposal Series 8. Assessing Soil 

Contamination. A reference Manual, Rome: Food and Agricultural Organization of the 

United Nations. Available at http://www.fao.org/DOCREP/003/X2570E/X2570E06.htm 

(Accessed April 10, 2013).

USDA. 2008. Agricultural Waste Management Field Handbook, Part 651. Natural Resources 

Conservation Services, U.S. Department of Agriculture, Washington, D.C.

US EPA, 2013a. Drinking Water Assessment for Registration Review of Coumaphos. 

Environmental Fate and Effects Division, Office of Chemical Safety and Pollution 

Prevention. U. S. Environmental Protection Agency.(DP 409560)

US EPA, 2013b. Revised Drinking Water Assessment for Registration Review of Coumaphos. 

Environmental Fate and Effects Division, Office of Chemical Safety and Pollution 

Prevention. U. S. Environmental Protection Agency.(DP 409560)

US EPA. 2012a. Memorandum: Approval of PRZM-GW for use of Drinking Water Exposure 

Assessment. Environmental Fate and Effects Division, Office of Chemical Safety and 

Pollution Prevention. U. S. Environmental Protection Agency.

US EPA. 2012b. Memorandum: NAFTA Guidance for Evaluating and Calculating Degradation 

Kinetics in Environmental Media. Environmental Fate and Effects Division, Office of 

Chemical Safety and Pollution Prevention. U. S. Environmental Protection Agency.

US EPA. 2012c. Development and Use of Percent Cropped Area and Percent Turf Area 

Adjustment Factors in Drinking Water Exposure Assessments: 2012 Update 

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

US EPA, 2009. Guidance for Selecting Input Parameters in Modeling the Environmental Fate 

and Transport of Pesticides, Version II. U. S. Environmental Protection Agency. 

Washington, D.C. http://www.epa.gov/oppefed1/models/water/

US EPA. 2007. Coumaphos: Human Health Risk Assessment for Proposed Use on Honey and 

Honeycomb. PC Code: 036501; Petition Number: 2E6504; DP Number: D315769.

US EPA. 2008. Memorandum: EFED Response to Comments for Coumaphos Registration 

Review Regarding Data Needed to Refine Ecological Risk Assessment Environmental 

Fate and Effects Division, Office of Chemical Safety and Pollution Prevention. U. S. 

Environmental Protection Agency (DP Barcode D347373).
12

US EPA, 2000. Reregistration Eligibility Decision Addendum and FQPA Tolerance 

Reassessment Progress Report: Coumaphos. Office of Prevention, Pesticides, and Toxic 

Substances. United States Environmental Protection Agency. EPA 738-R-00-010.

US EPA. 1998. Coumaphos-EFED Reply to Registrant’s Rebuttal. Office of Prevention, 

Pesticides and Toxic Substances, DP Barcodes D230394 and D239676

US EPA. 1994. Coumaphos (36501) Reregistration Case No. 0018. Product and Residue 

Chemistry Chapters for the Coumaphos Reregistration Eligibility Decision (RED) 

Document. DP Barcode D207352.
13

Appendix A

The maximum single application rate (i.e., 0.027 lb a.i./animal for dip vat2) and the maximum annual application rate (i.e., 0.063 lb 

a.i./animal for spray3) for cattle are for the end-use product Co-Ral® Flowable Insecticide (EPA Reg. no. 11556-98). Use of this 

product is restricted to employees of the USDA-APHIS who are enrolled in the USDA-APHIS cholinesterase monitoring program. The 

USDA’s Cattle Fever Tick Eradication Program (CFTEP) uses this product solely in Texas. As a result, these maximum application 

rates were used to assess exposures in drinking water sources in Texas only. The next highest maximum single application rate (i.e., 

0.01 lb a.i./A for dust or spray4) and maximum annual application rate for cattle (i.e., 0.05 lb a.i./animal for back rubbers5) were used 

to assess exposures in drinking water sources in the rest of the United States.

Table A-1. Application Information for Registered Uses of Coumaphos: Cattlea,b,c

Use Application 

Method/

Equipment

Form. 

(% a.i.)

Maximum Single

Application Rate

Annual 

Number of

Applications

Minimum

Application 

Interval 

(Days)

Maximum 

Annual 

Application 

Rated

(lb a.i./animal)

Comments

(lb a.i./

animal)

(lb a.i./

gal)

Beef/range/ 

feeder cattle; 

dairy cattle

Back rubbers EC (11.6) 0.00829 

(avg.; est.) 0.0762 3.5 (avg.) NS or AS 0.029 --

Back rubbers EC (6.2) 0.00829 

(avg.; est.) 0.0385 6 or NS 10 or NS 0.050

Represents maximum annual application 

rate for the U.S. with the exception of 

Texas

Dip vat FC (42) 0.027 

(est.) 0.0255e 2 10 0.054

EPA Reg No. 11556-98; use restricted to 

employees of the USDA-APHIS

Represents maximum annual application 

rate for Texas

Dust Dust (1) 0.01 3 (avg.) NS 0.03

Represents maximum single application 

rate for the U.S. with the exception of 

Texas

Dust Dust (1) 0.0013 3 (avg.) 10 or 14 0.0039 --

Dust Dust (1) 0.000625 3 (avg.) 1 0.0019 --

 

2 2 applications @ 0.027 lb a.i./animal = 0.054 lb a.i./animal/yr for dip vat

3 3 applications @ 0.021 lb a.i./animal = 0.063 lb a.i./animal/yr for spray

4 3 applications @ 0.01 lb a.i./animal = 0.03 lb a.i./animal/yr for spray or dust

5 6 applications @ 0.00829 lb a.i./animal = 0.05 lb a.i./animal/yr for back rubbers
14

Table A-1. Application Information for Registered Uses of Coumaphos: Cattlea,b,c

Use Application 

Method/

Equipment

Form. 

(% a.i.)

Maximum Single

Application Rate

Annual 

Number of

Applications

Minimum

Application 

Interval 

(Days)

Maximum 

Annual 

Application 

Rated

(lb a.i./animal)

Comments

(lb a.i./

animal)

(lb a.i./

gal)

Spray FC (42) 0.021 

(est.) 0.021 3 (avg.) 10 0.063

EPA Reg No. 11556-98; use restricted to 

employees of the USDA-APHIS

Represents maximum single application 

rate for Texas

Spray EC (6.2) 0.01 

(est.) 0.01 3 (avg.) 10 0.03

Represents maximum single application 

rate for the U.S. with the exception of 

Texas

Spray EC (11.6) 0.00978 

(est.) 0.00978 3 (avg.) AS 0.029 --

Ear Tag IM (20) 0.00625 3 (avg.) NS 0.019 --

AS = as needed; avg. = average; est. = estimated (by BEAD); NS = not specified; EM = emulsifiable concentrate; FC = flowable concentrate; Form. = 

formulation; IM = impregnated material; Max. = Maximum; Min. = Minimum; NA = not applicable; RTU = ready to use 

a

label data report (Label Use Information System report; LUIS) dated September 13, 2007

b

application information for maximum single and annual rates in BOLD

c

estimated/average values provided by BEAD

d not specified on label; calculated based on maximum single application rate and maximum annual number of applications

e 0.306% suspension
15

In registrant-submitted wash-off studies, fresh cow hides were treated with either Co-Ral® 

11.6% emulsifiable liquid (MRID 42512601) or Co-Ral® 25% wettable powder (MRID 

42512602) and then dried for 0.5, 3, or 24 hours. The wash-off fraction was measured after 

hides had been soaked in water for 0.5, 1, 1, or 4 hours. Results of these studies indicate that 

wash-off fraction is inversely related to drying time and dependent upon the formulation (Table 

A-2) but not affected by soaking time (data not shown). Although not the most conservative, 

wash-off fractions for the 24-hour drying time were used in this assessment because they 

represent a reasonable time frame after application for a treated cow to be caught in a rainstorm. 

Table A-2. Percent Wash-Off for Different Formulations of Coumaphos at Different 

Drying Times (MRIDs 42512601 and 42512602)

Formulation (%) Drying Time (hrs) Wash-Off Fractiona

Emulsifiable powder/concentrate 

(11.6)

0.5 0.116

3 0.046

24 0.027

Wettable powder/flowable 

concentrate (42)

0.5 0.38

3 0.21

24 0.20

a Bolded values were used in the aquatic exposure assessment

To accurately characterize the potential environmental exposure pathways, selecting the 

appropriate livestock management system and various exposure pathway scenarios is necessary. 

Two scenarios were considered to estimate the application rate of coumaphos for drinking water 

assessment. The following scenarios and example calculations of application rates are based on 

spray application on cattle. Table A-3 provides application rates for various scenarios.

Table A-3. Estimated Coumaphos Application Rates for Various Scenarios

Sources of a.i.

from Application Scenario

Wash-Off 

Fraction

Maximum Single 

Application Rate 

(lb/A)

Number of 

Applications/

Year

Maximum 

Annual 

Application Rate

(lb/A)

Texas: Spray Application (42% flowable concentrate)

CAFO manure applied to landa No incorporation of manure into soil 

0.02 0.015 1

b 0.015

Incorporation of manure into soil within a day 

0.02 0.009 1

b 0.009

Runoff from range land 0.02 0.00013 3 0.0004

Rest of U.S.: Back Rubber Application (11.6% emulsifiable concentration)

CAFO manure applied to landa No incorporation of manure into soil

0.027 0.0092 1

b 0.0092

Incorporation of manure into soil within a day

0.027 0.0051 1

b 0.0051

Runoff from range land 0.027 0.0001 3 0.0003

AU = animal unit

a Application rate of coumaphos depends on nutrient management and application method of manure. 

b Application rate can be split based on total nitrogen (TN) requirement during the growing season.
16

Example Calculation: Manure from CAFOs (Concentrated Animal Feeding Operation)

Manure is a valuable soil amendment/organic fertilizer for any farming operation and has been 

used for centuries to supply needed nutrients for crop growth. Manure not only supplies many 

beneficial nutrients for crop production, but could also be a potential source for pesticides that 

are embedded into manure from wash-off from treated livestock. Application rate of coumaphos 

was estimated based on dry weight of manure application for crop production. The following 

steps were used to calculate the application rate of coumaphos. 

Example Calculations: Manure from CAFOs (Concentrated Animal Feeding Operation

Step 1: Total dry weight of manure (DM)/AU(animal unit) /year 

DM = 8.5 lb solid in manure [ASAE, 2003] /AU x 365 days = 3103 lb dry manure/AU/year

or 1.55 tons/AU/year

Step 2: Active ingredient in manure (AM) lb a.i./AU 

AM = (A x F x S x W x PA) lb a.i./AU/year

Where:

A = application rate: 0.021 lb/AU for spray application (Table A-1)

F = frequency of application: 3/AU/year (Table A-1)

S = # of stocking/year: 4 (Based on 90-120 days stocking period for cattle in feedlot6)

W = wash-off fraction: 0.02 (Texas; coumaphos formulations restricted to APHIS) or 

0.027 (for non-restricted coumaphos formulations; rest of the U.S.) (MRIDs 42512601 

and 42512602)

PA = potential fraction of coumaphos washed off of cattle during a rain event that can 

come into contact with and adsorb to manure: 0.36 (assumed based on EPISUITE 

estimate for adsorption into sludge) 

Sample calculation is based on Co-Ral® Flowable Insecticide: 

AM = (0.021 x 3 x 4 x 0.02 x 0.36) = 0.0018 a.i. lb/AU

Step 3: Active ingredient in manure (lb a.i./ton)

(0.0018 lb a.i./1.55 ton manure) = 0.0012 lbs a.i./ton dry manure

Step 4: Total nitrogen production (TN) per animal (lbs TN/AU/year)

TN = (N x L x V x D) lbs TN/AU/year

Where: 

N = nitrogen content in manure per AU (TN lb/AU) (ASABE, 2003)

 

6 http://www.epa.gov/agriculture/ag101/beefproducts.html
17

L = average fraction of N retained during storage and handling: 0.5 (Table 11.5, USDA, 

2008). The range of N retention varies from 40 to 60 for arid region and 55 to 70 in 

humid region. 

V= Fraction of N loss due to volatilization: 0.1 (based on next day incorporation into soil 

after application in warm wet soil condition) to 0.5 (based on no incorporation for 

seven days into soil) (Table 11.6, USDA, 2006). The range of volatility loss varies 

from 50 percent in warn dry soil to 10 percent in cool wet soil. In addition, volatility 

loss may also depend on method of manure application (i.e. 5% and 25% 

volatilization loss from injection and sprinkling methods respectively. Since there is 

an inverse relationship between volatilization loss and application rate of manure, 

the highest and lowest volatilization rate was considered to calculate application rate 

of coumaphos. 

D = 365 of days /year

Sample calculation:

TN = (0.34 x 0.5 x 0.5 x 365) = 31 lbs TN in manure/AU/year [For no incorporation for 

seven days under warm dry soil scenario]

Step 5: Total N in manure (lb/ton manure)

(31 lbs TN/1.55 ton manure) = 20 lbs TN/ton manure/AU

Step 6: Application rate of manure (ton/acre)

In general, the application rate of manure is based on TN recommendation for crop types. For 

example, 250 lb TN/acre per year requires for growing warm season perennial grass in Texas7.

Sample calculation: 

(250 lbs TN/acre) x (1 ton Manure /20 lbs TN)

12.5 tons manure/acre require for growing perennial grass in Texas

Step 7: Application rate of active ingredient (lb/acre)

(0.0012 lbs a.i/ton) x (12.5 tons manure/acre) = 0.015 lbs a.i./acre

Therefore, the application rate of 0.015 lbs a.i/A is based on 2% coumaphos wash-off from 

treated cattle. 

Example Calculation: Cattle Grazing in Rangeland

Runoff of washed-off coumaphos from treated cattle could be a major contributor from treated 

cattle grazing on rangeland. Application rate was estimated from runoff contribution based on 

wash-off of coumaphos and animals stocking rate per acre. 

 

7 Stichles and McFarland, http://agrilifeextension.tamu.edu/
18

Application Rate (AR) of active Ingredient (lbs/Acre)

AR = (A x F x C x W) 

Where:

A = application rate: 0.021 lb/AU (spray application)

F = frequency of application: 3 (spray application)

C = # of AU in pasture/land: 0.3 was based on 800 lbs cattle (Pratt and Rasmaussan, 

2001). There is an inverse relationship between weight of cattle and number of AU 

in pasture/land. Numbers of AU on pasture land also depends on the size of cattle 

and forage production.

W = wash-off fraction: 0.02 (Texas) or 0.027 (rest of the U.S.) (MRIDs 42512601 and 

42512602)

Sample calculation:

AR = (0.021 x 3 x 0.3 x 0.02) = 0.0004 lbs/A 
19

Appendix B

Figure 1. Aerobic Soil Degradation Kinetics (MRID 48705501) 
20

Appendix C-Model Outputs

Surface Water 

Sample PRZM/EXAMS Output

stored as TX_M02_D.out

Chemical: Coumaphos

PRZM environment: TurfBSS.txt, modified Wedday, 31 July 2013 at 14:00:27

EXAMS environment: ir298.exv,modified Tueday, 26 August 2008 at 06:14:08

Metfile: w13958.dvf, modified Tueday, 26 August 2008 at 06:14:44

Water segment concentrations (ppb)

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly

1961 0.01 0.01 0.00 0.00 0.00 0.00

1962 0.02 0.02 0.01 0.01 0.01 0.00

1963 0.02 0.02 0.02 0.01 0.01 0.01

1964 0.07 0.06 0.05 0.04 0.03 0.02

1965 0.06 0.06 0.05 0.04 0.04 0.03

1966 0.05 0.04 0.04 0.04 0.03 0.03

1967 0.06 0.06 0.05 0.04 0.04 0.03

1968 0.05 0.05 0.04 0.04 0.04 0.04

1969 0.04 0.04 0.04 0.04 0.03 0.03

1970 0.06 0.06 0.05 0.04 0.04 0.03

1971 0.03 0.03 0.03 0.03 0.03 0.03

1972 0.05 0.04 0.04 0.03 0.03 0.03

1973 0.06 0.06 0.05 0.04 0.04 0.03

1974 0.11 0.10 0.08 0.05 0.04 0.03

1975 0.08 0.07 0.06 0.05 0.05 0.05

1976 0.07 0.07 0.06 0.05 0.05 0.04

1977 0.05 0.05 0.05 0.04 0.04 0.04

1978 0.08 0.08 0.06 0.05 0.04 0.04

1979 0.10 0.10 0.08 0.06 0.06 0.05

1980 0.06 0.06 0.06 0.05 0.05 0.05

1981 0.15 0.14 0.11 0.08 0.08 0.06

1982 0.08 0.08 0.07 0.06 0.06 0.06

1983 0.05 0.05 0.05 0.05 0.05 0.05

1984 0.05 0.05 0.04 0.04 0.04 0.04

1985 0.05 0.05 0.04 0.04 0.04 0.04

1986 0.06 0.05 0.05 0.04 0.04 0.04

1987 0.06 0.06 0.05 0.05 0.04 0.04

1988 0.04 0.04 0.04 0.04 0.04 0.03

1989 0.04 0.03 0.03 0.03 0.03 0.03

1990 0.06 0.05 0.04 0.04 0.03 0.03
21

Sorted results

Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly

0.03 0.15 0.14 0.11 0.08 0.08 0.06

0.06 0.11 0.10 0.08 0.06 0.06 0.06

0.10 0.10 0.10 0.08 0.06 0.06 0.05

0.13 0.08 0.08 0.07 0.05 0.05 0.05

0.16 0.08 0.08 0.06 0.05 0.05 0.05

0.19 0.08 0.07 0.06 0.05 0.05 0.05

0.23 0.07 0.07 0.06 0.05 0.05 0.04

0.26 0.07 0.06 0.06 0.05 0.04 0.04

0.29 0.06 0.06 0.05 0.05 0.04 0.04

0.32 0.06 0.06 0.05 0.05 0.04 0.04

0.35 0.06 0.06 0.05 0.04 0.04 0.04

0.39 0.06 0.06 0.05 0.04 0.04 0.04

0.42 0.06 0.06 0.05 0.04 0.04 0.04

0.45 0.06 0.06 0.05 0.04 0.04 0.04

0.48 0.06 0.05 0.05 0.04 0.04 0.03

0.52 0.06 0.05 0.05 0.04 0.04 0.03

0.55 0.05 0.05 0.05 0.04 0.04 0.03

0.58 0.05 0.05 0.04 0.04 0.04 0.03

0.61 0.05 0.05 0.04 0.04 0.04 0.03

0.65 0.05 0.05 0.04 0.04 0.04 0.03

0.68 0.05 0.05 0.04 0.04 0.03 0.03

0.71 0.05 0.04 0.04 0.04 0.03 0.03

0.74 0.05 0.04 0.04 0.04 0.03 0.03

0.77 0.04 0.04 0.04 0.04 0.03 0.03

0.81 0.04 0.04 0.04 0.03 0.03 0.03

0.84 0.04 0.03 0.03 0.03 0.03 0.03

0.87 0.03 0.03 0.03 0.03 0.03 0.02

0.90 0.02 0.02 0.02 0.01 0.01 0.01

0.94 0.02 0.02 0.01 0.01 0.01 0.00

0.97 0.01 0.01 0.00 0.00 0.00 0.00

0.1 0.10 0.09 0.08 0.06 0.06 0.05

Average 

of yearly 

averages:

0.03

Inputs generated by pe5.pl - Novemeber 2006

Data used for this run:

Output File: TX_M02_D

Metfile: w13958.dvf
22

PRZM 

scenario:

TurfBSS.txt

EXAMS 

environm

ent file:

ir298.exv

Chemical 

Name:

Coumaphos

Descripti

on

Variable 

Name

Value Units Comments

Molecula

r weight

mwt 362.5 g/mol

Henry's 

Law 

Const.

henry 2.62E-09 atm-m^3/mol

Vapor 

Pressure

vapr 1.00E-07 torr

Solubility sol 20 mg/L

Kd Kd mg/L

Koc Koc 5904 mg/L

Photolysi

s half-life

kdp 1.38 days Half-life

Aerobic 

Aquatic 

Metabolis

m

kbacw 0 days Halfife

Anaerobi

c Aquatic 

Metabolis

m

kbacs 0 days Halfife

Aerobic 

Soil 

Metabolis

m

asm 0 days Halfife

Hydrolysi

s:

pH 7 0 days Half-life

Method: CAM 1 integer See PRZM manual

Incorpora

tion 

Depth:

DEPI cm

Applicati

on Rate:

TAPP 0.017 kg/ha

Applicati

on 

Efficienc

y:

APPEFF 1 fraction

Spray 

Drift

DRFT 0 fraction of application rate applied to pond

Applicati

on Date

Date 15-10 dd/mm or dd/mmm or dd-mm or dd-mmm

Record 

17:

FILTRA

IPSCND 1

UPTKF
23

PRZM/EXAMS Time Series 

 

TX_M02_DW_Parent

_TS.csv

TX_M02_DW_Oxon_

TS.csv

 

Ground water

Sample SCIGROW Outputs

SCIGROW VERSION 2.3

ENVIRONMENTAL FATE AND EFFECTS DIVISION

OFFICE OF PESTICIDE PROGRAMS

U.S. ENVIRONMENTAL PROTECTION AGENCY

SCREENING MODEL

FOR AQUATIC PESTICIDE EXPOSURE

SciGrow version 2.3

chemical:Coumaphos

time is 5/22/2014 10:25: 9

------------------------------------------------------------------------

Application Number of Total Use Koc Soil Aerobic

rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

------------------------------------------------------------------------

0.015 1.0 0.015 1.87E+03 1095.0

------------------------------------------------------------------------

groundwater screening cond (ppb) = 1.91E-03

************************************************************************

SciGrow version 2.3

chemical:Coumaphoxon

time is 5/22/2014 10:27:30

------------------------------------------------------------------------

Application Number of Total Use Koc Soil Aerobic

rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

------------------------------------------------------------------------

0.002 1.0 0.002 1.98E+02 4.1

------------------------------------------------------------------------

groundwater screening cond (ppb) = 5.04E-06

************************************************************************
24

Sample PRZM-GW Outputs

Groundwater Analysis for Coumaphos and the Florida Citrus - FL Central Ridge, Polk 

County - (Tampa) Met File (12842.Dvf) - Astatula Sand, Hrgb A Scenario

Estimated groundwater concentrations and breakthrough times for Coumaphos are presented in 

Table 1 for the Florida Citrus - FL Central Ridge, Polk County - (Tampa) Met File (12842.dvf) -

Astatula sand, hrgb A groundwater scenario. A graphical presentation of the daily concentrations 

in the aquifer is presented in Figure 1. These values were generated with the PRZM-GW 

(Version 1.07). Critical input values for the model are summarized in Tables 2 and 3.

Table 1. Groundwater Results for Coumaphos and the Florida Citrus - FL Central Ridge, 

Polk County - (Tampa) Met File (12842.dvf) - Astatula sand, hrgb A Scenario.

Peak Concentration (ppb) 0.185

Post-Breakthrough Mean 

Concentration (ppb)

Incomplete

Entire Simulation Mean 

Concentration (ppb)

 0.0476

Average Breakthrough 

Time (days)

Incomplete

Throughputs 0.6034609

Table 2. Chemical Properties for Groundwater Modeling of Coumaphos.

Koc (ml/g) 5905

Surface Soil Half Life (days) 1095

Hydrolysis Half Life (days) 0

Diffusion Coefficint Air (cm2/day) 0.0

Henry's Constant 0.0

Enthalpy (kcal/mol) 0.0

Table 3. Pesticide application scheme used for Coumaphos. This application scheme was 

applied every year of the simulation.

Application Date

(Month/Day)

Application Method Application Rate

(kg/ha)

10/15 Ground application with mass 

distribution increasing 

proportionally with depth to 4 cm

0.017
25

Figure 1. Aquifer Breakthrough Curve for Coumaphos and the Florida Citrus - FL Central 

Ridge, Polk County - (Tampa) Met File (12842.Dvf) - Astatula Sand, Hrgb A Scenario

Groundwater Analysis for Coumaphoxon and the Florida Citrus - FL Central Ridge, Polk 

County - (Tampa) Met File (12842.Dvf) - Astatula Sand, Hrgb A Scenario

Estimated groundwater concentrations and breakthrough times for Coumaphos are presented in 

Table 1 for the Florida Citrus - FL Central Ridge, Polk County - (Tampa) Met File (12842.dvf) -

Astatula sand, hrgb A groundwater scenario. A graphical presentation of the daily concentrations 

in the aquifer is presented in Figure 1. These values were generated with the PRZM-GW 

(Version 1.07). Critical input values for the model are summarized in Tables 2 and 3.

Table 1. Groundwater Results for Coumaphos and the Florida Citrus - FL Central Ridge, 

Polk County - (Tampa) Met File (12842.dvf) - Astatula sand, hrgb A Scenario.

Peak Concentration (ppb) 5.02E-12

Post-Breakthrough Mean 

Concentration (ppb)

4.78E-12

Entire Simulation Mean 

Concentration (ppb)

2.49E-12

Average Breakthrough 

Time (days)

30012.66

Throughputs 1.204892

Table 2. Chemical Properties for Groundwater Modeling of Coumaphos.

Koc (ml/g) 2922

Surface Soil Half Life (days) 4.1
26

Hydrolysis Half Life (days) 0

Diffusion Coefficint Air (cm2/day) 0.0

Henry's Constant 0.0

Enthalpy (kcal/mol) 0.0

Table 3. Pesticide application scheme used for Coumaphos. This application scheme was 

applied every year of the simulation.

Application Days 

Relative to 

Emergence Date 

(01/01)

Application Method Application Rate

(kg/ha)

0 Ground application with mass 

distribution increasing 

proportionally with depth to 4 cm

0.0017

Figure 1. Aquifer Breakthrough Curve for Coumaphos and the Florida Citrus - FL Central 

Ridge, Polk County - (Tampa) Met File (12842.Dvf) - Astatula Sand, Hrgb A Scenario