OFFICE OF 

CHEMICAL SAFETY AND 

POLLUTION PREVENTION

 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

PC Code : 059101 

DP Barcode: 424487 

December 23, 2014 

MEMORANDUM 

SUBJECT: Chlorpyrifos: Updated Drinking Water Assessment for Registration Review 

TO: Joel Wolf, Chemical Review Manager 

 Tom Myers, Team Leader 

 Kevin Costello, Branch Chief 

 Risk Management and Implementation Branch 2 

 Pesticide Re-Evaluation Division (7508P) 

THROUGH: Dana Spatz, Chief 

 Environmental Risk Branch 3 

Environmental Fate and Effects Division (7507P) 

FROM: Rochelle F. H. Bohaty, Ph.D., Chemist 

 Environmental Risk Branch 3 

 Environmental Fate and Effects Division (7507P) 

PEER REVIEW: James Hetrick, Ph.D., Senior Science Advisor 

 Environmental Risk Branch 3 

 Environmental Fate and Effects Division (7507P) 

This document provides an update to the registration review drinking water assessment (DWA) for 

chlorpyrifos. A preliminary DWA was completed in 20111

 and posted to the docket for public comment. 

Since this assessment was completed and in response to public comment, several additional analyses were 

completed focusing on: 1) clarifying labeled uses, 2) evaluating volatility and spray drift, 3) revising 

aquatic modeling input values, 4) comparing aquatic modeling and monitoring data, 5) summarizing the 

effects of drinking water treatment, and 6) updating model simulations using current exposure tools. The 

first five topics are discussed in the Additional Analyses section of this assessment or are attached 

(APPENDIX 1: Registered Use Clarification; APPENDIX 2: Spray Drift Considerations; APPENDIX 

3: Volatility Considerations) to this assessment. The new model runs are presented in the Updated 

Modeling Simulation section of this document. The additional analyses did not change the exposure 

assessment conclusions previously reported in the preliminary DWA. 

 

 

1

 Bohaty, R. Revised Chlorpyrifos Preliminary Registration Review Drinking Water Assessment, June 20, 2011, PC 

Code: 059101; DP Barcode: 368388, 389480 
2 

ABSTRACT 

A national screening level drinking water assessment was completed for the registration review of 

chlorpyrifos, with focus on the agricultural uses. The primary drinking water residue of concern is 

chlorpyrifos-oxon, the predominant chlorpyrifos transformation product formed during drinking water 

treatment (e.g., chlorination). To illustrate a range of estimated drinking water concentrations (EDWC), 

two maximum label rate application scenarios were selected to represent high and low end exposures, i.e., 

tart cherries at 5 applications totaling 14.5 pounds per acre per year, and bulb onions at a single 

application of 1 pound per acre per year, respectively. The application of chlorpyrifos to tart cherries 

resulted in concentrations that exceeded the drinking water level of comparison (DWLOC); whereas, 

chlorpyrifos applications to bulb onions result in concentrations below the DWLOC. Concentrations in 

groundwater are not expected to exceed the DWLOC. 

To investigate whether other chlorpyrifos application scenarios may result in concentrations that exceed 

the DWLOC, a screen of all available surface water modeling scenarios was completed considering three 

different application dates and a single application at several different application rates that ranged from 

one to six pounds. This analysis showed that even with only one application, several chlorpyrifos uses 

may exceed the DWLOC at rates lower than maximum labeled rates (both single as well as yearly), 

including an application rate of one pound per acre per year. The analysis also showed that the DWLOC 

exceedances are not expected to be uniformly distributed across the country. 

Further analysis was conducted to look at the spatial distribution of EDWCs at a regional level, as well as 

by using a drinking water intake watershed approach. This exercise demonstrated that chlorpyrifos 

applications will result in variable drinking water exposures that are highly localized and that the highest 

exposures generally occur in small hydrologic regions where there is a high percent cropped area on 

which chlorpyrifos use could occur. 

Finally, EDWCs were compared to monitoring data. This analysis showed that when modeling scenarios 

are parameterized to reflect reported use and EDWCs are adjusted to reflect percent cropped area, the 

EDWCs are within an order of magnitude of the measured concentrations reported in the monitoring data. 

Therefore, although there are uncertainties associated with the model input parameters for which 

conservative assumptions were made (e.g., one aerobic aquatic metabolism half-life value multiplied by 

the uncertainty factor of three, stable hydrolysis, 100% of the cropped watershed is treated on the same 

day, and use of the Index Reservoir as the receiving waterbody), these assumptions do not appear to lead 

to an overly conservative estimate of exposure. In addition, evaluation of the monitoring data further 

illustrates that exposures are highly localized. Additional work can be done to examine EDWCs on a 

regional and/or watershed scale to pinpoint community drinking water systems where exposure to 

chlorpyrifos-oxon as a result of chlorpyrifos applications may pose an exposure concern. 

RESULTS SUMMARY 

EDWCs are provided for chlorpyrifos and chlorpyrifos-oxon. Chlorpyrifos EDWCs were multiplied by 

0.9541 (molecular weight correction factor) and 100% (maximum conversion during water purification) 

to generate chlorpyrifos-oxon EDWCs. Essentially, the concentration of chlorpyrifos and chlorpyrifosoxon are the same. A 100% conversion factor for the oxidation of chlorpyrifos to chlorpyrifos-oxon was 

used as an approximation based on empirical bench scale laboratory data that indicate chlorpyrifos rapidly 

oxidizes to form chlorpyrifos-oxon almost quantitatively during typical water treatment (chlorination).2

 

2

 Duirk, S. E.; Collette, T. W.; Degradation of Chlorpyrifos in Aqueous Chlorine Solutions: Pathways, Kinetics, and 

Modeling. Environ. Sci. Technol., 2006, 40(2), 546-550. 
3 

There are limited data available on the removal efficiency of chlorpyrifos prior to oxidation or the 

removal efficiency of chlorpyrifos-oxon during the drinking water treatment process. Based on empirical 

data showing that more than 75 percent of community water systems use chlorination to disinfect 

drinking water in the United States3

, the assumption of exposure to chlorpyrifos-oxon equivalent to 100% 

conversion of chlorpyrifos is not considered overly conservative. It is possible that some drinking water 

treatment procedures, such as granular activated carbon filtration and water softening (increased rate of 

chlorpyrifos-oxon hydrolysis at pH > 9) could reduce the amount of chlorpyrifos-oxon in finished 

drinking water; however, these treatment methods are not typical practices across the country for surface 

water. 

While there is the potential to have both chlorpyrifos and chlorpyrifos-oxon present in finished drinking 

water, limited (or no) information is available to readily quantify how much of each form remains 

following treatment. In the absence of available information, all the chlorpyrifos that enters a drinking 

water treatment facility is assumed to be converted to chlorpyrifos-oxon during treatment. 

Although chlorpyrifos-oxon has a hydrolysis half-life of 5 days, the drinking water treatment simulation 

half-life for chlorpyrifos-oxon is approximately 12 days.4,5,6 Therefore, once chlorpyrifos-oxon forms 

during treatment, little transformation is expected to occur before consumption (during drinking water 

distribution). There is a wide range of treatment processes and sequences of treatment processes 

employed at community water systems across the country and there are limited data available on a 

community water system specific basis to assess the removal or transformation of chlorpyrifos during 

treatment. These processes are not specifically designed to remove pesticides and pesticide transformation 

products including chlorpyrifos and chlorpyrifos-oxon. In general, drinking water treatment processes, 

with the exception of activated carbon,7

 have been shown to have little impact on removal of pesticide 

residues. Additional discussion of drinking water treatment can be found in the Drinking Water 

Treatment section of this DWA or in the preliminary DWA. 

National Screen 

The 2011 preliminary DWA, as well as the additional analyses completed as part of this assessment, 

indicate that exposure to chlorpyrifos-oxon in drinking water derived from surface water may pose an 

exposure concern. Since a large number of chlorpyrifos uses were identified in the preliminary DWA as 

triggering a concern, a bounding estimate of exposure was completed using a screening level national 

assessment approach. This was done to determine which currently registered uses could result in exposure 

to chlorpyrifos-oxon in drinking water that exceed the DWLOC. 

Use of chlorpyrifos on tart cherries is expected to result in the highest EDWC. EDWCs for chlorpyrifos 

and chlorpyrifos-oxon8

 are reported below for Tier I groundwater and Tier II surface water model 

 

3

 Community Water System Survey 2006; U.S. Environmental Protection Agency, Washington, DC 20460 May 

2009 (survey data) 4

 Tunink, A. Chlorpyrifos-oxon: Determination of hydrolysis as a function of pH, 2010 (MRID 48355201; 

acceptable) 

5

 Wu, J.; Laird, D. A. Abiotic Transformation of Chlorpyrifos to Chlorpyrifos Oxon in Chlorinated Water. Environ. 

Toxcol.Chem., 2003, 22(2), 261-264. 6

 Tierney, D. P.; Christensen, B. R.; Culpepper, V. C. Chlorine Degradation of Six Organophosphate Insecticides 

and Four Oxons in Drinking Water Matrix. Submitted by Syngenta Crop Protection, Inc. 2001. 7 Progress Report on Estimating Pesticide Concentrations in Drinking Water and Assessing Water Treatment 

Effects on Pesticide Removal and Transformation: A Consultation. FIFRA Scientific Advisory Panel Meeting, 

September 29, 2000; SAP Report No. 2001-02 February 12, 2011. 8

 Chlorpyrifos EDWCs were multiplied by 0.9541 (molecular weight correction factor) and 100% (maximum 

conversion during water purification) to generate chlorpyrifos-oxon EDWCs. Additional details on the potential 
4 

simulations. Because chlorpyrifos is used on a number of agricultural crops, as well as turf, a drinking 

water intake percent cropped area (PCA) adjustment factor of 1 was used.9,10 While the model input 

values11 have been updated since the preliminary assessment, the results presented in Table 1 are similar 

to those previously reported. 

Table 1. Estimated Drinking Water Concentrations Resulting from the Use of Chlorpyrifos 

Residue 

Surface Water Groundwater 

1-in-10 Year 

Peak 

Concentration 

μg/L 

21-day Average 

Concentration 

μg/L 

1-in-10 Year 

Annual Average 

Concentration 

μg/L 

30 Year Annual 

Average

Concentration 

μg/L 

SCI-GROW Tier 

I Concentration 

μg/La 

Michigan Tart Cherries 

Chlorpyrifos 129 83.8 39.2 29.7 0.16 

Chlorpyrifosoxon 

123 80.0 37.4 28.3 0.15 

Georgia Bulb Onion 

Chlorpyrifos 6.2 3.1 1.2 0.8 0.01 

Chlorpyrifosoxon 

5.9 3.0 1.1 0.8 0.01 

a. SCI-GROW resulted in higher EDWCs than PRZM-GW simulations. 

In order to better define the extent to which other chlorpyrifos use scenarios may result in an exposure 

concern, the Health Effects Division developed a 21-day average DWLOC of 3.9 μg/L for chlorpyrifosoxon12 that could be compared to model output values. Uncertainties in this approach include potential 

temporal aspects of relative concentrations from day to day on AChE inhibition, geospatial distribution of 

exposure as a result of variability in use, environmental factors, and drinking water treatment processes. 

Previous risk assessments13 suggest that typical upper bound application rates for chlorpyrifos are similar 

to the maximum single application rates for a wide range of crops; however, often the number of typical 

applications per year is lower than the maximum number of applications currently permitted on product 

labels (i.e., summarized in Master Use Summary Document). Considering this information, a screening 

 

impacts on drinking water treatment on chlorpyrifos and chlorpyrifos-oxon see the Additional Analyses section on 

Drinking Water Treatment. 

9

 U.S. Environmental Protection Agency Brady, D. Guidance on Development and Use of Community Water 

System Drinking Water Intake Percent Cropped Area Adjustment Factors for Use in Drinking Water Exposure 

Assessments: 2014 Updated, September 12, 2014. 

10 U.S. Environmental Protection Agency, Bohaty, R., Carleton, J., Crk, T., Echeverria, M., Ruhman, M., Thawley, 

M., Thurman, N., Villanueva, P., White, K., Development of Community Water System Drinking Water Intake 

Percent Cropped Area Adjustment Factors for Use in Drinking Water Exposure Assessments: 2014 Update, 

September 9, 2014. 

11 Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides, 

Version 2.1, October 22, 2009. 

12 The average 21-day concentration of chlorpyrifos-oxon necessary to cause 10% AChE inhibition was determined 

by HED to be 217 ppb. This value was divided by the safety factors (50x; 4.3 ppb) and then the contribution from 

food (0.4 ppb) was subtracted out to give to derive a DWLOC (3.9 ppb). 13 Dawson, J., Bohaty, R., Mallampalli, N. Evaluation of the Potential Risks from Spray Drift and the Impact of 

Potential Risk Reduction Measures, June 20, 2012 PC 059101 DP 399483 and 399485. 
5 

analysis (see the DWA for details) was completed to determine which chlorpyrifos uses do not exceed the 

DWLOC, based on a single application of chlorpyrifos per year at 1 and 4 pounds of chlorpyrifos per 

acre. The results for 1 and 4 pounds per acre are reported here as a representation of the range of potential 

chlorpyrifos application rates, bearing in mind that chlorpyrifos can be applied at lower and higher single 

rates (e.g., an application rate of 6 pounds per acre on citrus). This analysis showed that over a 30 year 

period, the current maximum application rate scenarios, as well as maximum single application rates for a 

wide range of chlorpyrifos use scenarios, may result in multiple 21-day average concentrations that 

exceed the DWLOC (Figure 1). 

Figure 1. National Screen: Exceedance Count/Percent (one application per year) 

Regional Screen 

Although there are several exceedances of the DWLOC on a national basis, the incidence of high 

exposures is expected to be highly localized. While it is currently extremely challenging to assess 

exposure on a local scale due to the unavailability of data and wide range of characteristics [i.e., 

environmental such as soil, weather, etc. or otherwise (e.g., drinking water treatment process)] that affect 

the vulnerability of a given community drinking system to chlorpyrifos-oxon contamination, a method 

was developed to examine the potential geospatial concentration differences for two Hydrological Unit 

Code (HUC) 2 Regions – HUC 2 Region 17: Pacific Northwest and HUC 2 Region 3: South AtlanticGulf, in order to identify use patterns that may result in EDWCs that exceed the DWLOC on a regional 

basis.14 This analysis considered all potential chlorpyrifos use sites within the HUC 2 regions based on 

the National Agricultural Statistics Service cropland data layers and survey data. Due to the uncertainty 

associated with some urban uses (e.g., wide area/general outdoor treatment) that are represented by the 

impervious scenarios, modeled results from the impervious scenarios are not included in this analysis. 

Additional clarification from the registrants is needed in order to determine if these uses pose an exposure 

concern. 

For HUC 2 Region 17, four chlorpyrifos scenarios were identified as a potential concern based on 

maximum single application rates of 1 and 4 pounds per acre. However, for HUC 2 Region 3, several 

chlorpyrifos use scenarios were identified that could exceed the DWLOC. 

 

14 http://water.usgs.gov/GIS/huc.html 
6 

Watershed Screen 

The uses that exceeded the DWLOC from the regional screening exercise for HUC 2 Region 3 were 

further explored for one example by utilizing the drinking water intake (DWI) watershed database. This 

example shows an overlap of potential chlorpyrifos use sites that may result in an exceedance of the 

DWLOC with watersheds that supply source water for community drinking water systems. In addition, 

this analysis shows that exposure is not uniform within a HUC 2 Region and that some watersheds are 

more vulnerable than others. Watershed vulnerability is expected to be greatest for smaller watersheds 

with high percent cropped areas. Smaller community water systems are generally more vulnerable due to 

short distribution times and the reliance of chlorination to treat source surface water as well as limited 

access to other treatment methods such as granular activated carbon. 

Monitoring Data Analysis 

Water monitoring data from the USGS National Water-Quality Assessment Program (NAWQA), 

USEPA/USGS Pilot Reservoir Monitoring Program, USDA Pesticide Data Program (PDP), and 

California Department of Pesticide Regulation (CDPR) were evaluated in the preliminary DWA with 

reference to an acute exposure to chlorpyrifos and its degradation product chlorpyrifos-oxon. The 

monitoring data showed chlorpyrifos detections at low concentrations, generally not exceeding 0.5 μg/L. 

For example, USGS NAWQA, which contains an extensive monitoring dataset for chlorpyrifos and 

chlorpyrifos oxon, reports a peak chlorpyrifos detection of 0.57 μg/L in surface water with a detection 

frequency of approximately 15%. CDPR has detected chlorpyrifos concentrations greater than 1 μg/L in 

surface water on several occasions, with an observed peak chlorpyrifos concentration of 3.96 μg/L. 

Sampling frequencies in these monitoring programs were sporadic and generally range from once per year 

to twice per month. 

Since the preliminary assessment, water monitoring data from Washington State Department of Ecology 

and Agriculture (WSDE/WSDA) Cooperative Surface Water Monitoring Program15,16, Dow 

AgroSciences (MRID 44711601), and Oregon Department of Environmental Quality were evaluated and 

are presented as part of this update. The previously referenced data have also been re-examined to 

consider short-term exposure (i.e., 21-day average concentrations) considering the importance of the 

single day exposure and the temporal relationship of exposure. A summary of all surface water 

monitoring data examined to date for chlorpyrifos are presented in Table 2. Some of the monitoring 

programs analyzed for chlorpyrifos-oxon; however, the number of detections, as well as the 

concentrations, was generally much lower. Since the majority of the conversion of chlorpyrifos to 

chlorpyrifos-oxon is assumed to occur during drinking water treatment, and not in the environment, the 

monitoring data presented in Table 2 are limited to chlorpyrifos. 

 

 

15 Sargeant, D, Dugger, D. Newell, E., Anderson, P, Cowles, J. Surface Water Monitoring Program for Pesticides in 

Salmonid-Bearing Streams 2006-2008 Triennial Report, February 2010 (Washington State Department of Ecology 

and Washington State Department of Agriculture) 

https://fortress.wa.gov/ecy/publications/summarypages/1003008.html; 

http://agr.wa.gov/PestFert/natresources/docs/swm/2008_swm_report.pdf 

16 Sargeant, D., Newell, E., Anderson, P., Cook, A. Surface Water Monitoring Program for Pesticides in SalmonidBearing Streams 2009-2011 Triennial Report, February 2013 (Washington State Department of Ecology and 

Washington State Department of Agriculture) http://agr.wa.gov/FP/Pubs/docs/377-SWM2009-11Report.pdf 
7 

Table 2. Surface Water Monitoring Data Summary for Chlorpyrifos 

Monitoring Data Scale

Years of 

Sampling 

(number of 

samples)

Detection 

Frequency

(%)

Maximum 

Concentration

(μg/L)

USGS NAWQA National 1991-2012 

(30,542) 15 0.57 

California Department of Pesticide 

Regulation State 1991-2012 

(13,121)

20 3.96 

Washington State Department of 

Ecology and Agriculture Cooperative 

Surface Water Monitoring Program 

State 2003-2013 

(4,091) 8.4 0.4 

USDA Pesticide Data Program National 

2004-2009 

(raw water; 

1,178) 

2001-2009 

(finished 

water; 2,918) 

0 na 

USGS-EPA Pilot Drinking Water 

Reservoir National 1999-2000 (323) 5.3 0.034 

Oregon Department of Environmental 

Quality

Watershed 

(Clackamas) 

2005-2011 

(363) 13 2.4 

MRID 44711601

Watershed 

(Orestimba 

Creek) 

1996-1997 

(1,089) 61 2.22 

In general, the monitoring data include sampling sites that represent a wide range of aquatic environments 

including small and large water bodies, rivers, reservoirs, and urban and agricultural locations, but are 

limited for some areas of the United States where chlorpyrifos use occurs. Also, the sampling sites, as 

well as the number of samples, vary by year. In addition, the vulnerability of the sampling site to 

chlorpyrifos contamination varies substantially due to use, soil characteristics, weather and agronomic 

practices. None of the monitoring programs examined to date were specifically designed to target 

chlorpyrifos use (except the Registrant Monitoring Program MRID 44711601); therefore, peak 

concentrations (and likely 21-day average concentrations) of chlorpyrifos and chlorpyrifos-oxon likely 

went undetected in these programs. See the Revised Chlorpyrifos Preliminary Registration Review 

Drinking Water Assessment dated June 30, 2011 for further details on the monitoring programs discussed 

here. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2008-0850-0026 

In general, sampling frequency needs to be approximately equal to the duration of exposure concern.17

The chlorpyrifos monitoring data evaluated thus far also show that as sample frequency increases, so does 

 

17 U.S. Environmental Protection Agency. Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) Scientific 

Advisory Panel: Problem Formulation for the Reassessment of Ecological Risks from the Use of Atrazine, June 12-

14, 2012, Docket Number: EPA-HQ-OPP-2012-0230. 
8 

the detection frequency. This is evident in the registrant-submitted monitoring data, as well as 

examination of individual sampling sites within the various datasets. 

Therefore, while there are many individual samples collected and analyzed for chlorpyrifos (or 

chlorpyrifos-oxon) across the United States, it would not be appropriate to combine these data sources to 

generate exposure estimates or to use these datasets to represent exposure on a national or even regional 

basis. Thus, comparing the monitoring data results to the DWLOC would not be a reasonable approach 

for the reasons given above, including limited sample frequency, limited use information, and sampling 

site variability, on a national or even a regional basis. Model estimated concentrations should be 

considered suitable upper bound concentrations for chlorpyrifos and chlorpyrifos-oxon. 

Additionally, model simulations were completed to represent two different water monitoring datasets - 

Washington State Department of Ecology and Agriculture (WSDE/WSDA) Cooperative Surface Water 

Monitoring Program and Dow AgroSciences (MRID 44711601) Orestimba Creek. For both of these 

water monitoring programs, enough information was available, including chlorpyrifos use information as 

well as the PCA, to parameterize the model. In these simulations, the modeled EDWCs were within an 

order of magnitude of the measured concentrations. This suggests that the modeling results are not overly 

conservative and supports the use of the model to estimate chlorpyrifos-oxon concentrations in drinking 

water. 

Additional modeling can be done to pinpoint regions or watersheds where EDWCs may exceed the 

DWLOC. This would include completing the regional assessment presented here for all HUC 2 Regions 

and crop uses, as well as considering multiple applications per year. Nevertheless, based on the current 

analysis, concentrations of chlorpyrifos-oxon in drinking water are expected to be highly localized 

primarily in small watersheds with high PCA. 

Synopsis 

In summary, examination of chlorpyrifos agricultural use across the country indicates that there are a 

number of uses that may result in potential exposure to chlorpyrifos-oxon in finished drinking water at 

levels that exceed the DWLOC. The EDWCs for tart cherries and bulb onion reported here are expected 

to provide a reasonable bounding estimation of exposure based on maximum rates included in the Master 

Use Summary Document. This analysis showed that the maximum use scenario for tart cherries exceeds 

the DWLOC, while it does not for bulb onions. 

The rate used for the bulb onion simulation was 1 pound chlorpyrifos per acre; therefore a screen of all 

Surface Water Concentration Calculator modeling scenarios was done using a single application of 

chlorpyrifos. This analysis showed that exceedances are expected even for one application of chlorpyrifos 

applied at 1 pound per acre per year. 

While there are uncertainties associated with the model input parameters for which conservative 

assumptions were made (e.g., one aerobic aquatic metabolism half-life value multiplied by the uncertainty 

factor of 3, stable hydrolysis, 100% of the cropped watershed is treated on the same day, and use of the 

Index Reservoir as the receiving waterbody), these assumptions do not appear to lead to an overly 

conservative estimate of exposure based on a comparison of model estimates with measured 

concentrations. Comparison of model estimated concentrations with measured concentrations suggests 

that model estimates are consistent with measured concentrations when actual application rates and 

representative SWCC scenarios are considered and a PCA adjustment factor is applied to the model 

estimates. This modeling/monitoring comparison suggests that when growers use maximum application 

rates, or even rates much lower than maximum, chlorpyrifos-oxon concentrations in drinking water could 

pose an exposure concern for a wide range of chlorpyrifos uses. However, these exposures are not 
9 

expected to be uniformly distributed across the country. Additional analyses are needed in order to 

pinpoint the exact community water systems where concentrations may be of concern. 

BACKGROUND 

The 2001 Interim Reregistration Eligibility Decision (IRED) considered exposure to chlorpyrifos in 

drinking water18,19 and recommended the quantitative use of monitoring data to estimate chlorpyrifos 

exposure. At the time of the IRED, chlorpyrifos concentrations in groundwater (greater than 2000 μg/L) 

from termiticide uses were the primary focus of drinking water exposure. The model estimated 

concentrations were orders of magnitude lower than the measured concentrations. Subsequent to the 

IRED, the termiticide use was canceled. 

The preliminary drinking water assessment conducted in 20111

 recommended the use of surface water 

EDWCs for chlorpyrifos-oxon derived from modeling, and concluded that a range of chlorpyrifos uses 

could lead to high levels (peak concentrations greater than 100 μg/L) of chlorpyrifos in surface water that 

could potentially be used by community water systems to supply drinking water. Once chlorpyrifos 

reaches a drinking water treatment facility, it readily converts to chlorpyrifos-oxon upon disinfection 

(primarily oxidative treatment methods such as chlorination). Therefore, chlorpyrifos and chlorpyrifosoxon were considered residues of concern in the preliminary assessment to account for the variation of 

drinking water treatment methods. 

UPDATED MODELING SIMULATIONS 

Revision of Metabolism Model Input Values 

In December 2011, EFED along with Canada’s Pest Management Regulatory Agency (PMRA) completed 

the NAFTA degradation kinetics project. As part of this project, guidance20 was developed describing a 

general approach for calculating and selecting representative half-life values from soil and aquatic 

transformation studies for risk assessment and exposure modeling. In 2013, EFED published a standard 

operating procedure (SOP)21 for following the NAFTA kinetics guidance. Updated kinetic analyses were 

completed for chlorpyrifos following the recently updated SOP22 using the PestDF Tool (version 0.8.13) 

along with R (version 3.1.0). The kinetic analyses are provided in APPENDIX 4: Kinetic analysis and 

the results are summarized in Table 3. Table 3 also provides the previously reported half-life values for 

comparison. 

 

 

18 U.S. Environmental Protection Agency, Finalization of Interim Reregistration Eligibility Decisions (IREDs) and 

Interim Tolerance Reassessment and Risk Management Decisions (TREDs) for the Organophosphate Pesticides, and 

Completion of the Tolerance Reassessment and Reregistration Eligibility Process for the Organophosphate 

Pesticides, September 28, 2001 

19 Barrett, M, Nelson, H, Rabert, W., Spatz, D. Reregistration Eligibility Science Chapter for Chlorpyrifos Fate and 

Environmental Risk Assessment Chapter, June 2000 

20 Guidance for Evaluating and Calculating Degradation Kinetics in Environmental Media, Health Canada, U.S. 

Environmental Protection Agency, December 21, 2011. 

21 Bohaty, R., Eckel, W., Shamim, M., Spatz, D., White, K., Young, D. Standard Operating Procedure for Using the 

NAFTA Guidance to Calculate Representative Half-life Values and Characterizing Pesticide Degradation, 

November 20, 2013. 

22 Bohaty, R., Eckel, W., Shamim, M., Spatz, D., White, K., Young, D. Standard Operating Procedure for Using the 

NAFTA Guidance to Calculate Representative Half-life Values and Characterizing Pesticide Degradation, 

December 1, 2014 (Draft). 
10 

Table 3. Environmental Fate and Transport Characteristics of Chlorpyrifos

Parameter 

Test System 

Name or 

Characteristics 

Previously 

Report Half-life 

Values 

NAFTA 

Representative 

Half-life Values 

(fitting model) 

Study ID Study Status 

Laboratory Data 

Aerobic Soil 

Metabolism 

Half-life 

(t1/2)

Commerce 11 days 19 days (IORE) 

Acc. 241547 

MRID 

00025619) 

Acceptable 

Barnes 22 days 36.7 days (IORE) 

Miami 24 days 31.1 days (IORE) 

Catlin 34 days 33.4 days (SFO) 

Norfolk 102 days 156 days (DFOP) 

Stockton Clay 107 days 297 days (IORE) 

German 141 days 193 (IORE) 

Sandy loam 180 days 185 days (DFOP) MRID 42144911 Acceptable 

Aerobic 

Aquatic 

Metabolism 

Half-life 

(t1/2)

Water, pH 8.1 

Sediment, pH 

7.7 

25  ̊C

30.5 days 30.4 days (SFO) MRID 44083401 Supplemental

Anaerobic 

Soil 

Metabolism 

half-life 

(t1/2)

Commerce 15 days 78 (IORE) 

MRID 00025619 Acceptable Stockton 58 days 

171 days (SFO) 

Values represent 

only anaerobic 

phase 

Anaerobic 

Aquatic 

Metabolism 

half-life 

(t1/2) 

Commerce 

pH 7.4 39 days 50.2 days (IORE) 

MRID 00025619 Supplemental Stockton

pH 5.9 

51 days 125 days 

(SFO) 

Model Simulations 

Groundwater 

Tier I groundwater EDWCs for chlorpyrifos and chlorpyrifos-oxon were calculated using SCI-GROW 

(Screening Concentration in Groundwater, version 2.3, August 8, 2003) and PRZM-Groundwater 

(PRZM-GW version 1.0, December 11, 2012), using the GW-GUI (Graphical User Interface, version 1.0, 

December 11, 2012).23 For Tier I groundwater assessments, the results from the model (either SCIGROW or PRZM-GW) that provides the highest EDWCs is recommended for incorporation into the 

human health assessment, along with surface water EDWCs in order to provide an upper bound 

estimation of the potential impact of chlorpyrifos use on drinking water supplies. Model input values for 

SCI-GROW and PRZM-GW are provided in Table 4 and Table 5, respectively, and reflect current input 

parameter guidance.11 Table 6 and Table 7 highlight the use scenarios simulated for Michigan tart 

cherries and Georgia onions (i.e., bulb onion production), respectively. 

Based on the surface water EDWCs reported in the preliminary drinking water assessment (see Figure 2) 

and the application rates included in the Chlorpyrifos Master Use Summary Document, chlorpyrifos 

applications to tart cherries is expected to provide upper bound EDWCs, while chlorpyrifos applications 

to bulb onion is expected to provide a lower bound value. These use scenarios were confirmed by the 

 

23 http://www.epa.gov/oppefed1/models/water/
11 

Biological and Economic Analysis Division (BEAD) as reasonably representative based on the maximum 

label rates for tart cherries and bulb onions prior to model simulations.24 

Table 4. SCI-GROW Input Parameters

Parameter (units) Input 

Value Data Source Comments 

Application Rate 

(lb a.i./A)

See Table 6

and Table 7

Master Use Summary 

Document 

Maximum yearly application rate is for tart 

cherries and bulb onion (see ATTACHMENT 

1: Master Use Summary Document). 

Number of 

Applications

See Table 6

and Table 7

Master Use Summary 

Document 

For tart cherries the five different applications 

were combined into one. (see ATTACHMENT 

1: Master Use Summary Document) 

Soil Metabolism Halflife (days) 96 MRID 00025619 

Half-life values of 19, 36.7, 31.1, 33.4, 156, 297, 

193, and 185 days were obtained from empirical 

data following the NAFTA kinetics guidance. 

The median half-life value of 96 days was used 

in SCI-GROW modeling. 

Koc (mL/goc) 5860 Acc. 260794 

Soil binding for chlorpyrifos is correlated with 

organic carbon content (i.e., the coefficient of 

variation for Koc values is less than that for Kd

values). The median Koc value (Koc values = 

7300, 5860 and 4960 mL/g) was used for 

modeling. 

Table 5. PRZM-GW Input Parameters

Parameter (units) Input 

Value Data Source Comments 

Application Rate (kg 

a.i./ha) 

See Table 6 Master Use 

Summary Document 

Maximum yearly application rate for chlorpyrifos is for 

tart cherries and bulb onions (see ATTACHMENT 1: 

Master Use Summary Document). 

Number of 

Applications 

Application Date 

Annual Application 

Retreatment 

Application Method 

Hydrolysis Half-life 

(days) 81 MRIDs 00155577 and 

40840901 

Since aerobic aquatic metabolism is not considered as part 

of groundwater modeling, a maximum hydrolysis value of 

72 and 81 days was used in model simulations. 

Aerobic Soil 

Metabolism Half-life 

(days)

170.6 Acc. # 241547 and 

MRID 42144911 

Half-life values of 19, 36.7, 31.1, 33.4, 156, 297, 193, and 

185 days were obtained from empirical data following the 

NAFTA kinetics guidance. The 90th percentile confidence 

bound on the mean chlorpyrifos half-life value is 118.9 + 

[(1.415 x 103.3)/√8)] = 170.6 days. 

Koc (mL/goc) 6040 Acc. # 260794

Soil binding for chlorpyrifos is correlated with organic 

carbon content (i.e., the coefficient of variation for Koc

values is less than that for Kd values). The mean Koc value 

(Koc values = 7300, 5860 and 4960 mL/g) was used for 

modeling. 

 

 

24 Email from Clayton, Myers, RE: Chlorpyrifos Use March 26, 2014 
12 

Table 6. Michigan Tart Cherry Chlorpyrifos Application Scenario 

Application 

Number 

Application 

Timing; Type Date Method 

Application 

Rate (lb 

a.i./A) 

Formulation Comments 

1 Dormant/delayed 

Dormant; broadcast 4/1 Aircraft 2.0 liquid

150 ft. buffer for 

aerial 

applications 

2 Foliar; broadcast 5/15 Orchard blast 4.0 liquid

50 ft. buffer for 

orchard blast 

applications 

3 Foliar; broadcast 5/25 Orchard blast 4.0 liquid

50 ft. buffer for 

orchard blast 

applications 

4 Foliar; broadcast 6/4 Orchard blast 2.0 liquid

50 ft. buffer for 

orchard blast 

applications 

5 Foliar; Post harvest 

trunk drench 8/1 

Ground 

(hand-held or 

backpack) 

2.5 liquid

25 ft. buffer for 

ground boom 

applications 

Table 7. Georgia Onion Chlorpyrifos Application Scenario 

Application 

Number 

Application 

Timing; Type Date Method 

Application 

Rate (lb 

a.i./A) 

Formulation Comments 

1 preplant; soil 12/4 Ground 1.0 liquid

25 ft. buffer for 

ground boom 

applications 

Figure 2. Summary of 1-in-10 Year Peak Chlorpyrifos-oxon EDWCs Previously Reported in the 

Preliminary Drinking Water Assessment for Registered Uses of Chlorpyrifos-oxon Derived From 

Surface Water 

The tart cherries use has the highest annual application rate (14.5 pounds per acre per year with a 

maximum single application rate of 4.0 pounds per acre) of all the chlorpyrifos uses highlighted in the 

Master Use Summary Document. Tart cherries was also identified in the preliminary DWA as an 

application scenario with a high end exposure based on surface water simulations, even though it does not 

represent the highest single application rate scenario for chlorpyrifos. The highest single application rate 
13 

for chlorpyrifos is for citrus at 6.0 pounds per acre (10.5 pounds per acre per year). This annual rate 

reduction is not expected to substantially change the exposure estimates and; therefore, are not expected 

to alter the risk assessment conclusions. Bulb onion production in Georgia was identified as a lower 

bound scenario, as the maximum single and yearly application rate is 1 pound per acre. Although 

chlorpyrifos is not expected to pose a significant groundwater exposure (Koc > 1000 mL/goc), the tart 

cherries and bulb onion application scenarios were also considered for groundwater modeling. 

Tier I groundwater EDWCs for chlorpyrifos and chlorpyrifos-oxon are provided in Table 8 and Table 9, 

respectively. EDWCs are not expected to be greater than 0.16 μg/L for chlorpyrifos and 0.15 μg/L for 

chlorpyrifos-oxon (based on SCI-GROW). These EDWCs are expected to be an upper bound value and 

may not actually reflect groundwater concentrations across the country, but rather reflect the potential 

exposure in vulnerable groundwater supplies. The reported groundwater EDWCs for chlorpyrifos-oxon 

are representative of drinking water supplies that utilize oxidative treatment methods such as chlorination. 

In general, drinking water taken from private wells is not treated; however, community drinking water 

supplied by wells may be treated with chlorine in order to protect drinking water during distribution. 

Table 8. Estimated Drinking Water Concentrations of Chlorpyrifos in Groundwater 

Crop/Scenario 

SCI-GROW PRZM-GW 

μg/L 

Highest 

Daily Value 

μg/L

Post 

Breakthrough 

Average 

μg/L 

Average 

Simulation 

Breakthrough 

Time 

days 

Tart Cherries 

Florida Citrus 

0.16 

 0.06 

Incomplete with 100 year simulation 

Florida Potato 5.0E-11 

Wisconsin Corn 9.4E-05 

Georgia Peanuts 3.6E-08 

North Carolina Cotton 2.9E-06 

Delmarva Sweet Corn 0.0001 

Bulb Onion 

Florida Citrus 

0.01 

0.0043 

Incomplete with 100 year simulation 

Florida Potato 3.9E-12 

Wisconsin Corn 6.0E-06 

Georgia Peanuts 2.6E-09 

North Carolina Cotton 2.3E-07 

Delmarva Sweet Corn 9.2E-06 

 
14 

Table 9. Estimated Drinking Water Concentrations of Chlorpyrifos-oxon in Treated Groundwater 

Crop/Scenario

SCIGROW PRZM-GW 

ug/L

Highest Daily 

Value 

μg/L 

Post Breakthrough 

Average 

μg/L 

Average Simulation 

Breakthrough Time

days 

Tart Cherries 

Florida Citrus 

0.15

0.06 

Incomplete with 100 year simulation 

Florida Potato 4.8E-11 

Wisconsin Corn 9.0E-05 

Georgia Peanuts 3.4E-08 

North Carolina Cotton 2.8E-06 

Delmarva Sweet Corn 0.0001 

Bulb Onion 

Florida Citrus 

0.01

0.0041 

Incomplete with 100 year simulation 

Florida Potato 3.7E-12 

Wisconsin Corn 5.7E-06 

Georgia Peanuts 2.5E-09 

North Carolina Cotton 2.23E-07 

Delmarva Sweet Corn 8.8E-06 

EDWCs for chlorpyrifos-oxon were derived from EDWCs calculated for chlorpyrifos because chlorpyrifos is 

expected to transform to chlorpyrifos-oxon during drinking water treatment. Chlorpyrifos EDWCs were multiplied 

by 0.9541 (molecular weight correction factor) and 100% (maximum conversion during water purification) to 

generate chlorpyrifos-oxon EDWCs. 

Surface Water 

Tier II surface water EDWCs for chlorpyrifos and chlorpyrifos-oxon were calculated using the Surface 

Water Concentration Calculator (SWCC) version 1.106. The SWCC uses PRZM version 5.0+ (PRZM5) 

and the Variable Volume Water Body Model (VVWM). PRZM is used to simulate pesticide transport as a 

result of runoff and erosion from an agricultural field. VVWM estimates environmental fate and transport 

of pesticides in surface water. The input parameters used in SWCC simulations are presented in Table 

10. 

National Screen 

Tart cherries and onions were modeled as upper and lower bound exposure scenarios for surface water for 

reasons described above in the groundwater section of this assessment. Tier II EDWCs for surface water 

are presented in Table 11 for chlorpyrifos in untreated surface water and chlorpyrifos-oxon following 

oxidative drinking water treatment. Tier II modeling results were corrected using the DWI PCA 

adjustment factor.9,10 Since chlorpyrifos is registered for use on turf (including sod farms, golf courses, 

road medians and industrial areas) a PCA of 1 (considers 100% of the watershed can and is treated) was 

applied to surface water modeling results for this national screening analysis. EDWCs for chlorpyrifosoxon were derived from EDWCs for chlorpyrifos by multiplying chlorpyrifos EDWCs by 0.9541 

(molecular weight adjustment factor) and 100% (maximum conversion of chlorpyrifos to chlorpyrifosoxon during water treatment). 

Although the model simulations suggest relatively high concentrations of chlorpyrifos in the receiving 

waterbody, only a small amount (≤ 1.2%) applied to the field reaches the water body for the two scenarios 

examined. This is consistent with a runoff study conducted by the registrant (MRID 00144906) that 
15 

suggests that the amount of chlorpyrifos transported from a treated field (corn watersheds in Illinois) to 

proximal water bodies is generally less than one percent of the applied material.25 Depending on the 

scenario used in the modeling simulations, the transport of chlorpyrifos from the field to the receiving 

water body is either primarily through runoff or erosion (Table 11) and the total mass transported from 

the field may be higher than 1.2% for other SWCC scenarios. 

While model simulations consider the required aquatic spray drift buffers, these buffers may also reduce 

the transport of chlorpyrifos via runoff and erosion of chlorpyrifos from the field to the water body. Spray 

drift buffers provide distance between the field and the neighboring water body; however, it is unclear to 

what extent they may act like a filter strip. EFED does not currently have an exposure tool to assess the 

impact of vegetative filter strips (VFS) on reducing runoff and erosion; however, the development and 

maintenance of VFS is highly variable. Large runoff or erosion events are trigged by larger storm events, 

which are likely to overcome the buffer or VFS with sheet or channelized flow providing a direct conduit 

to the nearby water body. A U.S. Geological Survey (USGS) report suggests that sheet flow is expected at 

distances up to 100 feet.26 Moreover, a review article on the reduction of herbicide concentrations from 

fields with VFS was not able to document a decline in herbicide concentrations in receiving water bodies 

as a result of VFS, and that data specifically on a watershed scale is lacking.27 In addition, this review 

concluded that retention of sediment as a function of the VSF width was nonlinear, with most of the 

retention occurring within the first few meters. 

Once in the water body, chlorpyrifos dissipation is scenario specific; however, the primary mechanisms of 

chlorpyrifos dissipation are volatilization, metabolism and washout. Based on laboratory studies 

chlorpyrifos is expected to partition to sediment; however, this does not mean a complete reduction in 

chlorpyrifos in the water column is expected. 

 

 

25 McCall, P. J., Oliver, G. R., McKeller, R. L. Modeling the runoff potential and behavior of chlorpyrifos in a 

terrestrial aquatic watershed (DowElanco unpublished report GH-C 1964) 1984 26 U. S. Department of Agriculture, National Resources Conservation Service, Small Watershed Hydrology WinTR55 User Guide, January 2009. 

27 Krutz, L. J., Senseman, S. A., Zablotowicz, R. M., Matocha, M. A., Reducing Herbicide Runoff from Agricultural 

Fields with Vegetative Filter Strips: A Review, Weed Science, 2005, 53, 353-367. 
16 

Table 10. SWCC Input Parameters 

Parameter (units) Input Value Data Source Comments 

Molecular Weight 

(g/mol) 350.57 product chemistry 

Water Solubility 

(mg/L) 20 °C 1.4 MRID 41829006 

The water solubility of chlorpyrifos is reported to be 

between 0.5-2.0 mg/L for temperatures between 20-25 °C. 

Based on data submitted to EPA, 1.4 mg/L was used in 

modeling. 

Vapor Pressure (torr) 

25 °C 1.87x10-5 torr 

product 

chemistry 

BC 2062713 

Henry’s Law Constant 6.2 x 10-6 atm - 

m3

/mol calculated 

Application Rate (kg 

a.i./ha) 

See Table 6

Master Use 

Summary 

Document

Maximum yearly application rate for use on tart cherries 

(see ATTACHMENT 1: Master Use Summary 

Document). Tart cherries was also previously determined 

to be a high exposure scenario (see Figure 1)

Number of 

Applications 

Application Date 

Spray Drift

3.9% (aerial)a 

0.9% (airblast)b 

0.8% (ground)c 

AgDRIFT 

modeling 

based on label 

restrictions 

Labels contain aquatic buffer distances of 25, 50 and 150 

ft. for ground, airblast and aerial applications. 

Application Efficiency 

0.99 (ground; 

air-blast)) 

0.95 (aerial) 

Default Values 

Crop Application 

Method See Table 6

Master Use 

Summary 

Incorporation Depth Document 

Hydrolysis Half-life 

(days) 0 

MRIDs 

00155577 

(Acc. # 

260794) and 

40840901 

Since the aerobic aquatic metabolism half-life value was 

not corrected for hydrolysis, it is possible that hydrolysis 

would be double-counted in the model simulation. 

Therefore, hydrolysis was set to 0 (stable) here as it is 

already accounted for in the aerobic aquatic metabolism 

study and input parameter. 

Aqueous Photolysis 

(days) 29.6 MRID 41747206 

Aerobic Soil 

Metabolism Half-life 

(days)

170.6 

(109) 

Acc. # 241547 

and MRID 

42144911 

Half-life values of 19, 36.7, 31.1, 33.4, 156, 297, 193, and 

185 days were obtained from empirical data following the 

NAFTA kinetics guidance. The 90th percentile confidence 

bound on the mean chlorpyrifos half-life value is 118.9 + 

[(1.415 x 103.3)/√8)] = 170.6 days.

Aerobic Aquatic 

Metabolism Half-life 

(days)

91.2 

(91.5) 

MRID 

44083401 

Only one half-life value is available, so this value (30.4 

days) was multiplied by 3 to get 91.5 days. The 30.4 day 

half-life value was not corrected for hydrolysis as 

hydrolysis data conducted under the same experimental 

conditions were not provided. In addition, the aerobic 

aquatic metabolism study was conducted under slightly 

basic conditions (pH 7.7). Chlorpyrifos hydrolysis is pH 

dependent and faster under basic conditions. 

Anaerobic Aquatic 

Metabolism Half-life 

(days)

203 

(63) 

MRID 

00025619 

The 90th percentile confidence bound on the mean 

chlorpyrifos half-life value determined following the 

NAFTA kinetics guidance is 87.6 + [(3.078 x 52.9)/√2)] = 

202.7 days. 
17 

Koc (mL/goc) 6040 Acc. # 260794 

Soil binding for chlorpyrifos is correlated with organic 

carbon content (i.e., the coefficient of variation for Koc

values is less than that for Kd values). The mean Koc value 

(Koc values = 7300, 5860 and 4960 mL/g) was used for 

modeling. 

Percent Cropped Area 1.0 PCA 

guidanced 

a. Aerial: 150 ft. distance to water body from edge of field based on labeled buffer; ASAE fine to medium (dv0.5 = 255 

μm; labels specify 255-340 μm); Index Reservoir - downwind water body width 82 m (fraction applied 0.0331); 

Streams – 4 m (fraction applied 0.0552); Adjusted Spray drift fraction 0.0331 (spray drift fraction for the Index 

Reservoir) + [0.0552 (spray drift fraction for all Stream) x 0.114 (Surface areas of all streams/surface area of 

reservoir)] = 0.039 

b. Air-blast: 50 ft. distance to water body from edge of field based on labeled buffer; droplet size not specified; sparse 

(young, dormant); Index Reservoir - downwind water body width 82 m (fraction applied 0.0056); Streams – 4 m 

(fraction applied 0.0265); Adjusted Spray drift fraction 0.0056 (spray drift fraction for the Index Reservoir) + [0.0265 

(spray drift fraction for all Stream) x 0.114 (Surface areas of all streams/surface area of reservoir)] = 0.0086 

c. Ground: 25 ft. distance to water body from edge of field based on labeled buffer; ASAE Fine to medium/course [dv0.5 

= 341 μm; labels specify 255-340 μm which is larger than ASAE very fine to fine (dv0.5 = 175 μm); highboom; 90th

percentile; Index Reservoir - downwind water body width 82 m (fraction applied 0.0061); Streams – 4 m (fraction 

applied 0.0164); Adjusted Spray drift fraction 0.0061 (spray drift fraction for the Index Reservoir) + [0.0164 (spray 

drift fraction for all Stream) x 0.114 (Surface areas of all streams/surface area of reservoir)] = 0.0079 

d. See Footnotes 9 and 10. 

Scenario: MICherriesSTD; GAOnion_WirringSTD (Weather: W14850, W03822, respectively) 

EFED file room barcode (BC)

Table 11. Estimated Drinking Water Concentrations of Chlorpyrifos in Untreated Surface Water 

(Model Output Values; PCA 1.0; all ag + turf) 

Absolute 

Peak

1-in-10 Year Concentration (ppb) 

Relative 

Transport

Field to 

Watera Peak 21-day 

Average 

Annual 

Average 

30 Year 

Annual 

Average 

Michigan Tart Cherries 

172

(164)b

129

(123) 

83.8 

(80.0)

39.2 

(37.4)

29.7 

(28.3) 

Runoff 18% 

Erosion 77%

Drift 5% 

1.2% 

Georgia Bulb Onion 

8.5 

(8.1)

6.2

(5.9) 

3.1 

(3.0) 

1.2 

(1.1) 

0.8 

(0.8) 

Runoff 78% 

Erosion 18%

Drift 3% 

<1%

a. The relative amount of the material applied to the field that is transported off field and into the water 

body (i.e., index reservoir). 

b. Bracketed concentrations are for chlorpyrifos-oxon in treated drinking water 

EFED recommends the use of the EDWCs presented in Table 11 in the human health risk assessment 

conducted for chlorpyrifos (and chlorpyrifos-oxon), as these values are expected to provide bounds on the 

exposure as a result of the currently registered uses as described in the Master Use Summary 

Document. It should be noted that there are still a few uses, specifically urban uses (e.g., wide area 

treatment of miscellaneous pests) that need to be clarified in order to determine the potential exposure as 

a result of these uses. 

 
18 

To screen the potential exposure resulting from the large number of other currently registered uses of 

chlorpyrifos, a batch run simulation was completed for one chlorpyrifos application per year for all 

current SWCC standard scenarios (n=124). A ground application was simulated for three different 

application dates; 30 days preemergence (-30dpe), 7 days postemergence (7dpe) and 30 days 

postemergence (30dpe). 

While spray drift is expected to be higher for aerial applications, the application efficiency is higher for 

ground applications, and when both parameters are considered, the resulting EDWCs are generally 

similar. Therefore, if an exposure concern is triggered for a ground application, it is expected that there 

would also be exposure concern for other application types including aerial and airblast applications. 

EDWCs are highly sensitive to the application date, which is variable from year to year; therefore, 

examination of multiple application dates was done to better understand the potential variability in 

EDWCs as a result of application date. In addition, the three selected application dates generally represent 

the various types [i.e., timing of application permitted (e.g., pre-plant, at plant, foliar, and dormant)] of 

applications currently allowed for a number of the registered uses of chlorpyrifos. 

Figure 3 presents the range of the highest 21-day average chlorpyrifos-oxon concentrations for each of 

the application dates assessed for all scenarios compared to the DWLOC for chlorpyrifos-oxon resulting 

from chlorpyrifos applications at 1 pound per acre. The national default DWI PCA of 1 for all agricultural 

and turf was used in this analysis. Absent from this analysis are the impervious scenarios (i.e., 

CAImperviousRLF), due to the uncertainty associated with the registered uses that are represented by 

these scenarios. As mentioned above, clarification from the registrants is needed in order to determine if 

these uses pose an exposure concern. 

Figure 3. National Screen: Estimated Chlorpyrifos-oxon Concentration by Scenario (one 

application per year) 

Figure 4 presents the total number of exceedance periods (i.e., 21-days) over the entire model simulation 

(approximately 30 years, but is scenario dependent) for the application date that results in the highest 

number of exceedances calculated for 1 and 4 pound(s) per acre for each standard SWCC scenario. Also 

shown are the number of exceedances that correspond to the 99.9th, 99th, and 90th percentiles, i.e., 10, 100, 

and 1000 exceedances, respectively. The exceedance count was calculated using an Excel macro to 

screen the daily concentration time series files generated by the SWCC. For this analysis, the 21-day 

DWLOC28 for chlorpyrifos-oxon was adjusted by the molecular weight adjustment factor to calculate the 

corresponding chlorpyrifos concentration for use in the Excel macro, since the time series data generated 

 

28 3.9 ppb oxon / 0.9541 oxon molecular weight adjustment factor = 4.1 ppb chlorpyrifos 

0

5

10

15

20

25

30

TXsorghumOP

STXvegetableN...

PAtomatoSTD

PAAppleSTD

KSsorghumSTD

PRcoffeeSTD

MSsoybeanSTD

FLpeppersSTD

CAWheatRLF

FLcucumberSTD

NCpeanutSTD

STXcottonNMC

CARangelandh...

CAColeCropRLF

CAWineGrapes...

NCcornWOP

NDWheatSTD

FLtomatoSTD

ORBerriesOP

NJnurserySTD

CAAvocadoRLF

NDcornOP

WAbeansNMC

CAsugarbeet_...

CAonion_Wirri...

ORFilbertsSTD

ORAppleSTD

CAcotton_Wirri...

IDNpotato_Wir...

TurfBSS

CAresidentialRLF

Concentration (μg/L)

Scenario

DWLOC National Screen 1 lb a.i./A 

Range of Highest 21-day Average

Concentration

DWLOC
19 

by the SWCC are for chlorpyrifos and does not consider the transformation of chlorpyrifos to 

chlorpyrifos-oxon as a result of drinking water treatment. An uncertainty with using the 21-day average 

concentration as the DWLOC is the temporal relationship of chlorpyrifos and corresponding chlorpyrifosoxon concentrations from day to day. For example, a one day exposure concentration may result in an 

average 21-day concentration that exceeds the 21-day DWLOC while a more constant exposure over 21 

days may also result in an average 21-day concentration that exceeds the 21-day DWLOC. Alternatively a 

one day exposure concentration may not trigger a risk concern using this approach, as the average 21-day 

concentration may be below the DWLOC. 

Figure 4. National Screen: Exceedance Count/Percent (one application per year) 

Not all the SWCC scenarios represent use sites where 4 pounds of chlorpyrifos can be applied; therefore, 

the results presented in Figure 4 are only for those SWCC scenarios that reasonably represent use sites 

where chlorpyrifos can be applied at a single application rate up to 4 pounds per acre. For the graphs, the 

left y-axis corresponds to the number of 21-day time periods where the average concentration exceeds the 

DWLOC. There are approximately 10,000 21-day time periods per 30 year simulation. The labels on the 

right y-axis represents the DWLOC exceedance percentile based on the total number of 21-day time 

periods.29 

Considering maximum single application rates and the representation of the scenarios, at least one 21-day 

average concentration was determined to be greater than the DWLOC for all use sites/crops except for 

 

29 Exceedance Count/~10000; the actual number of days included in each simulation was considered 

1

10

100

1000

10000

Highest Exceedance (count)

Scenario

DWLOC National Screen 4 lb a.i./A 

Exceedance Count 90th percentile

99.9th percentile

99th percentile
20 

pumpkin (Table 12). A summary of the results for all the scenarios and all application rates [1, 2 (2.3 for 

citrus scenarios), 3, 4, and 6 pounds] is provided in ATTACHMENT 2. Table 13 provides a snapshot of 

the scenarios that result in a 21-day average concentration that exceeds the DWLOC, and examples of the 

represented uses. This is not intended to be a comprehensive list, but rather to associate the simulated 

scenario to chlorpyrifos use scenarios. 

Using this approach, the number of 21-day exceedance periods associated with a single event cannot 

easily be parsed out, nor can the number of 21-day exceedance periods associated with individual events. 

Note that the application date that results in the highest 21-day average concentration does not always 

correspond to the application date that results in the highest number of 21-day averaging periods that 

exceed the DWLOC. In addition, examination of the EDWC exceedances across the modeled scenarios 

highlight that exposure concentrations of chlorpyrifos and chlorpyrifos-oxon are not expected to be 

uniform across the country. 

Table 12. National Screening Results Using DWLOC Approach – Scenario Representation and 

Labeled Rate Comparison for Uses that Do Not Exceed the DWLOC 

Use Site/Crop 

(representative 

scenario) 

Highesta 21-day 

Average 

Concentration ppb 

(application date) 

Maximum Single 

Application Rate Comments 

Pumpkin

(FLCucumbersSTD)

3.3 (-30dpe) – at 0.3 lb 

a.i./A 

0.3 (aerial and ground 

liquid) 

This is a preplant seed 

treatment and assumes 

100% of the applied 

material washes off the 

seed coat in the field and 

is available for transport. 

a. Referenced EDWCs reflect highest 21-day average concentration calculated for each of the three 

application dates simulated. 

 
21 

Table 13. National Screening Results Using DWLOC Approach – Scenario Representation and 

Labeled Rate Comparison for Example Uses that Exceed the DWLOC 

Scenario 

Highest 21-day Average 

Concentration ppb 

(application date) 

21-day Exceedance 

Count Represented Use Site 

Examples 

(maximum single application 

rate) 

Highesta 

(application 

dateb)

Percentc 

1 lb a.i./A

MScornSTD 16.5 (-30dpe) at 1.0 lb a.i./A 2273 21 Corn [2 lb a.i./A (aerial and 

ground)] 

Soybean [1 lb a.i./A (aerial); 2.2 

(ground)] 

TXcornOP 13.9 (30dpe) at 1.0 lb a.i./A 1418 13 

ILcornSTD 14.6 (30dpe) at 1.0 lb a.i./A 1697 

(-30pde) 16 

MScotton 19.8 (-30dpe) at 1.0 lb 

a.i./Ag 1697 16 Cotton [1 lb a.i./A (foliar aerial 

and ground); seed treatment 

permitted at 2.2 lb a.i./A] NCcotton 14.4 (7dpe) at 1.0 lb a.i./A 2768 (-30pde) 25 

TXcotton 15.1 (30dpe) at 1.0 lb a.i./A 868 8 

NYgrape 15.7 (-30dpe) at 1.0 lb a.i./A 2918 

(30pde) 27 Grape [2.25 lab a.i./A (ground)] 

TXsorghumOP 25.8 (30dpe) at 1.0 lb a.i./A 1328 

(-30pde) 12 Wheat [1 lb a.i./A (aerial and ground)] 

Sunflower [2 lb a.i./A (aerial and 

ground)] 

Other Grains: 

Sorghum [3.3 lb a.i./A 

(granular)d] 

Alfalfa [1 lb a.i./A (aerial and 

ground)] 

TXwheatOP 21.0 (-30dpeh

) at 1.0 lb 

a.i./A 705 6

PAVegetableNMC 21.1 (30dpe) at 1.0 lb a.i./A 1972 

(7dpe) 18 Vegetables and Ground Fruit: 

Strawberry [2 lb a.i./A (aerial 

and ground)] 

Radish [3 lb a.i./A (ground)f] 

Pepper [1 lb a.i./A (ground)] 

Onion [1 lb a.i./A (ground)] 

CAlettuce 12.8 (-30dpe) at 1.0 lb a.i./A 840 8

MEpotato 10.7 (-30dpe) at 1.0 lb a.i./A 1857 17 Other Row Crops: 

Tobacco [2 lb a.i./A (aerial and 

ground)] 

Sugarbeets [2 lb a.i./A 

(granular)d] 

Peanuts [4 lb a.i./A (granular)e] 

Sweet Potato [2 lb a.i./A (aerial 

and ground)] 

NCsweetpotatoSTD 13.5 (30dpe) at 1.0 lb a.i./A 1006 9

2 lb a.i./A

MIcherriesSTD 19.6 (30dpe) at 2.0 lb a.i./A 4574 42 Orchards and Vineyards (Tree 

fruit and Nuts): 

Fruit and Nuts [4 lb a.i./A 

(ground)] 

Pecans [2 lb a.i./A (air); 4.3 

(ground)] 

Apple [2 lb a.i./A (air and 

ground)] 

Peach [2 lb a.i./A (air); 3 

(ground)] 

GApecansSTD 20.7 (-30dpe) at 2.0 lb a.i./A 1353 

(30dpe) 12 

PAapples 

29.1 (30dpe) at 2.0 lb a.i./A 

1212 11 

 
22 

NCPeanutSTD 21.0 (30dpe) at 2.0 lb 

a.i./A 

2282

(-30dpe) 21 

Peanut 

2.0 lb a.i./A (aerial and ground) 

4 lb a.i./A (granular ground)

FLCitrusSTD 10.1 (30dpe) at 2.0 lb 

a.i./A 684 6 

Citrus 

6.0 lb a.i./A [ground including 

airblast] 

2.3 lb a.i./A (aerial) 

a. The highest number of 21-day time periods where the average concentration exceeds the DWLOC of the 

three use scenarios considered (i.e., application date -30dpe, 7dpe, or 30dpe). 

b. If different than the application date reported for the highest 21-day average concentration. 

c. The highest percent of 21-day time periods where the average concentration exceeds the DWLOC. There 

are approximately 10,000 21-day time periods per 30 year simulation; however, it should be noted that not 

all scenarios contain exactly 30 years of weather data. 

d. [1.0 (air and ground)] 

e. [2.0 (air and ground)] 

f. Incorporated or in furrow otherwise [1.0 (air and ground)] 

g. A preplant seed treatment is permitted at 2.2 lb a.i./A and assumes 100% of the applied material washes off 

the seed coat in the field and is available for transport. 

h. The application date that resulted in the highest 21-day average concentration does not represent the 

registered use; however, the other applications dates also result in exceedances (21-day average EDWCs 

range from 7.1- 8.2 for the two application dates) 

Typical use rates were also examined for Michigan tart cherries to characterize what the actual exposure 

may be as a result of current use practices. For this analysis, two applications at 2 pounds per acre were 

assumed since the upper bound typical rate for cherries is 2 pounds per acre (99.6th centile) with an 

average number of applications of 1.1 per year.30 The use scenario modeled is provided in Table 14 while 

the results are presented in Table 15. A national DWI PCA of 1 was considered for this analysis. The 

regional maximum PCA for HUC 2 Region 4: Great Lakes, where tart cherries are predominately grown, 

is also 1. If only the orchards and vineyards crop group is considered, the maximum DWI PCA in HUC 2 

Region 4 is 0.05. This suggests the relative contribution (ignoring the application rate and corresponding 

EDWC) of chlorpyrifos transported to an aquatic body as a result of an application to tart cherries is 

expected to be lower than the contribution from other use sites within the watershed. If the only 

chlorpyrifos use permitted within this region was orchards and vineyards, the resulting EDWCs would not 

be expected to exceed the DWLOCs. 

Additional analyses are needed in order to determine if other uses within HUC 2 Region 4 would result in 

an exposure concern. Considering only the maximum DWI PCAs calculated for individual crop groups 

within the HUC 2 Region 4, corn (PCA = 0.35), soybean (PCA = 0.20), and turf (PCA = 0.85) are likely 

to present the highest exposure concerns. 

Table 14. Typical Michigan Tart Cherry Chlorpyrifos Application Scenario

Application 

Number 

Application Timing; 

Type Date Method Application Rate (lb a.i./A) Formulation Comments

1 Dormant/delayed 

Dormant; broadcast 4/30 Orchard blast 2.0 liquid

50 ft. buffer for 

orchard blast 

applications 

2 Foliar; broadcast 6/1 Orchard 

blast 2.0 liquid

50 ft. buffer for 

orchard blast 

applications 

 

30 Becker, J., Stebbins, K., Typical Use Data for Chlorpyrifos, June 24, 2011. 
23 

Table 15. Estimated Drinking Water Concentrations of Chlorpyrifos in Untreated Surface Water 

(Model Output Values; PCA 1.0; all ag + turf) for Typical Use on Tart Cherries 

Absolute 

Peak

1-in-10 Year Concentration (ppb) 

Relative 

Transport

Field to 

Watera Peak 21-day 

Average 

Annual 

Average 

30 Year 

Annual 

Average 

Michigan Tart Cherries 

55.2

(52.7)

b

40.0 

(38.2) 

25.8 

(24.6)

10.6 

(10.1)

7.9 

(7.5) 

Runoff 18% 

Erosion 80%

Drift 2% 

1.2% 

a. The relative amount of the material applied to the field that is transported off field and into the water 

body (i.e., index reservoir). 

b. Bracketed concentrations are for chlorpyrifos-oxon in treated drinking water 

In summary, this analysis shows that the current maximum single application rates for a wide range of 

chlorpyrifos use scenarios may result in a 21-day average concentration that exceed the DWLOC. Again, 

this DWLOC approach does not consider the temporal aspects of the exposure concentrations on AChE 

inhibition or the geospatial distribution of exposure, but provides a means to easily identify use patterns 

that should not result in EDWCs that exceed the DWLOC. 

Regional Screen 

To examine the potential geospatial concentration differences, a regionally-specific analysis was 

completed for two Hydrological Unit Code (HUC) 2 Regions – HUC 2 Region 3: South Atlantic-Gulf and 

HUC 2 Region 17: Pacific Northwest. These two HUC 2 regions were selected to represent the range of 

SWCC standard scenarios that fall within the HUC 2 regions, the different chlorpyrifos use scenarios 

expected to occur within the HUC 2 region, as well as to provide a reasonable representation of the 

bounds of potential exposure on a regional basis. The same model simulations that were used in the 

national screen were used in this analysis; however, regional DWI PCAs, as well as the molecular weight 

adjustment factor, were used to adjust the EDWCs to estimate the potential exposure to chlorpyrifos-oxon 

in drinking water. The maximum regional DWI PCAs for all agriculture plus turf are 0.74 and 0.65 for the 

Pacific Northwest and the South Atlantic-Gulf HUC 2 Regions, respectively. 

The total number of exceedance periods (i.e., 21-days) over the entire model simulation (approximately 

30 years) for the application date that results in the highest number of exceedances calculated for 1 and 4 

pound(s) per acre for each standard SWCC scenario that falls within the HUC 2 Region are presented. 

The exceedance count was calculated using the Excel macro mentioned above; however, the 21-day 

DWLOC for chlorpyrifos-oxon was adjusted by the molecular weight adjustment factor as well as the 

maximum regional DWI PCA to calculate the corresponding chlorpyrifos concentration, since the time 

series data generated by the SWCC are for chlorpyrifos. The corresponding chlorpyrifos concentrations 

are 5.5 μg/L31 and 6.3 μg/L32 for the Pacific Northwest and the South Atlantic-Gulf HUC 2 Regions, 

respectively. The results of this analysis are presented in Figure 5 for HUC 2 Region 17: Pacific 

Northwest for a single application of chlorpyrifos at 1 and 4 pounds per acre. The results for HUC 2 

Region 3: South Atlantic-Gulf are provided in Figure 6 for a single application at 1 and 4 pounds per 

acre. Only the results from the scenarios that reasonably represent current chlorpyrifos uses within the 

respective regions are presented in these figures. 

 

31 3.9 ppb chlorpyrifos-oxon / 0.9541 / 0.74 = 5.5 ppb chlorpyrifos 

32 3.9 ppb chlorpyrifos-oxon / 0.9541 / 0.65 = 6.3 ppb chlorpyrifos 
24 

Figure 5. Regional Screening Results Using DWLOC Approach for HUC 2 Region 17: Pacific 

Northwest

Figure 6. Regional Screening Results Using DWLOC Approach for HUC 2 Region 3: South 

Atlantic-Gulf 

For HUC 2 Region 17: Pacific Northwest, exceedances are only observed for two scenarios 

(ORSWCornOP and ORBerriesOP) at a single application rate of 1 pound per acre. When a single 

application rate of 4 pounds per acre is considered, several scenarios (ORFilbertSTD, ORGrassSeedSTD, 

ORAppleSTD, ORXmasTree) result in 21-day average concentrations that exceed the DWLOC. The tree 

1

10

100

1000

10000

ORFilbertsSTD ORGrassSeedSTD ORAppleSTD ORXmasTree WAOrchardsNMC

Highest Exceedance (count)

Scenario

Adjusted DWLOC HUC2 Region 17 Screen 4 lb a.i./A 

Exceedance Count

99.9th percentile

99th percentile

90th percentile

1

10

100

1000

10000

Highest Exceedance (count)

Scenario

Adjusted DWLOC HUC2 Region 3 Screen 1 lb a.i./A 

Exceedance Count

99.9th percentile

90th percentile

99th percentile
25 

fruit and nut fruit scenarios may represent a 4 pounds per acre application rate for chlorpyrifos applied to 

fruit and nuts trees [for non-bearing (not to bear fruit within 1 year)] in nurseries including: almonds, 

citrus, filbert, apple, cherry, nectarine, peach, pear, plum, and prune]. Additional clarification is needed 

on this use to confirm that this scenario represents the registered use. The grass seed scenario is 

representative of the potential use sites for ornamental lawns and turf and sod farms. However, the 

maximum single application rate is 3.76 pounds per acre. The concentrations will be slightly lower than 

those calculated for a 4 pound application, reducing the number of likely exceedances. 

In contrast to the results presented for the Pacific Northwest, a larger number of scenarios (primarily 

representing corn, cotton, soybean, and vegetable and ground fruit, and fruit and nut tree use sites) were 

determined to result in 21-day average concentrations that exceed the DWLOC when only a single 

application rate at 1 pound per acre is considered. More exceedances are expected for higher application 

rates; however, not all of the SWCC scenarios considered in the 1 pound analysis would be representative 

of use sites where higher chlorpyrifos applications are permitted. 

This analysis underscores the regional exposure variations that likely exist across the United States. For 

those scenarios where exceedances are already expected, more exceedances would be expected for 

multiple applications. However, for those use scenarios where a single application does not result in 

exceedances, additional analyses are needed to explore the potential of multiple applications per year, as 

this screen only considered one application per year. Similar to the national analysis, this regional 

approach does not parse out the number of 21-day exceedance periods associated with a single event, or 

the number of 21-day exceedance periods associated with individual events within a given year. 

Furthermore, the temporal variability in concentrations is an uncertainty. 

This regional analysis does not confirm overlap of potential chlorpyrifos use sites with vulnerable 

watersheds. To investigate this further, potential use sites (i.e., corn33) were overlaid with the drinking 

water intake delineated watersheds (Figure 7). The watersheds with a maximum yearly 21-day average 

concentration that exceeds the DWLOC are shaded in Figure 7. The cropland overlay used is for corn and 

does not take into account other chlorpyrifos uses that occur within the HUC 2 Region. However, the 

average pounds of chlorpyrifos applied per 1,000 acres of farmland by state was used to highlight the 

chlorpyrifos expected use intensity within the region. These data should not be used as a means to 

calculate an application rate for chlorpyrifos per acre as the data are provided in terms of acres of total 

farmland and not acres of farmland treated with chlorpyrifos. It should be noted that use information on a 

smaller scale (e.g., crop reporting district, county or watershed) may be available; however, the sample 

size for small geographical areas are generally low. 

There are a number of known DWIs that do not have delineated watersheds. For some of these DWIs, 

surrogate PCAs have been assigned from the HUC 12 region PCAs34 that encompass the intake, while 

other known intakes35 do not have a surrogate PCA at this time. None of these intakes or surrogate HUC 

12s are presented in Figure 7. Additional analysis could be done, overlaying the intake locations that do 

not have PCAs with potential chlorpyrifos use sites. 

 

33 Cropland Data Layer for corn aggregated for the years 2010 through 2013 

34 634 surrogate HUC 12 PCA were developed for the United States 

35 761 “new” intakes and 359 canals or aqueducts
26 

Figure 7. Region 3: South Atlantic-Gulf: Corn Cropland Overlay with Drinking Water Intake 

Watersheds Where the 21-day Average Concentrations are expected to Exceed the DWLOC 

Figure 8 provides the ranking distribution of the highest 21-day average EDWCs for the three application 

dates assessed for HUC 2 Region 3 for corn. This distribution does not include DWIs that have been 

assigned a surrogate HUC 12 PCA, or those intakes where a PCA has not been developed. The y-axis of 
27 

this graph represents the highest 21-day average concentration, while the x-axis represents the relative 

rank of the 21-day average concentration for each of the DWI watersheds (i.e., DWI PCA corrected 

EDWCs) from the highest to the lowest. This distribution suggests that depending on the application date, 

there is generally more than one (n=13) community drinking water system that could be using source 

surface water for supplying drinking water where a 21-day average concentration of chlorpyrifos or the 

corresponding chlorpyrifos-oxon is estimated to be higher than the DWLOC. 

For additional characterization, the exceedance count for the DWIs where the 21-day average 

concentration is expected to exceed the DWLOC at least once was determined. These results are 

presented in Figure 9. 

Figure 8. Regional Distribution of the Maximum Yearly Corn 21-day EDWC for DWI Watershed 

in Region 3: South Atlantic-Gulf 

Figure 9. Regional Screening Results Using DWLOC Approach for Vulnerable Drinking Water 

Intakes Falling Within HUC 2 Region 3: South Atlantic-Gulf; 

While the field size and the index reservoir (the receiving water body) used in the SWCC simulations 

may provide reasonable upper bound EDWCs on a national scale, the watershed sizes and the receiving 

0

2

4

6

8

Chlorpyrifos-oxon 

Concentration (

μg/L)

Rank

HUC 2 Region 3 - South Atlantic-Gulf DWI 

PCA Adjusted Corn EDWCs 

DWLOC

DWI PCA

Corrected

EDWCs

1

10

100

1000

10000

2527672-4 1825516-4 3959677-4 2504980-4 2645548-1 3041357-3 2878941-1 5568697-1 3959676-4 3493772-4 3959073-1 1768880-1 5148864-4

Highest Exceedance (count)

Basin-Identification

Adjusted DWLOC HUC2 Region 3 Screen 1 lb a.i./A 

Exceedance Count

99.9th percentile

90th percentile

99th percentile
28 

water bodies represented by the DWI dataset vary substantially from very large to very small (Figure 10). 

The index reservoir represents a vulnerable drinking water scenario in the Midwest (i.e., Shipman City 

Lake in Shipman, Illinois) and although the index reservoir serves as a screening tool, it represents the 

drainage area/normal capacity of a drinking water reservoir in other parts of the United States.36 In 

addition, as the water body size changes, the relative watershed size is also expected to change. Therefore, 

the mass coming from the treated watershed relative to the waterbody volume may stay relatively the 

same for vulnerable scenarios. Nevertheless, the assumption that the entire watershed is treated with 

chlorpyrifos on the same day at the same rate is likely conservative for larger watersheds (27,887 square 

mile; 95th centile). However, as the watershed size decreases it is more likely that an entire watershed 

could be treated with chlorpyrifos on the same day, especially when considering some of the small 

watersheds (1 square mile; 10th centile). The index reservoir is approximately 0.67 square miles. 

Figure 10. Drinking Water Intake Watershed Size Distribution 

Based on the regional analysis for HUC 2 Region 3, up to 3% of the watersheds may have chlorpyrifos 

concentrations high enough that upon drinking water treatment, the concentration of chlorpyrifos-oxon 

will exceed the DWLOC resulting from chlorpyrifos application made to corn at 1 pound per acre. In 

addition, this analysis shows there is overlap with the potential use sites (corn) and known chlorpyrifos 

use with watersheds that supply source surface water for community drinking water systems. This 

analysis also demonstrates that even within a HUC 2 region, there is a wide range of estimated 

concentrations that are expected to be highly localized (e.g., watershed/community drinking water 

system); however, the community water systems where chlorpyrifos and chlorpyrifos-oxon exposure is 

expected to be higher than the DWLOC can be identified with reasonable certainty. 

Additional analysis is needed in order to appropriately characterize the expected exposure for other 

chlorpyrifos uses within HUC 2 Region 3, as well as the intakes that do not have delineated watersheds or 

surrogate HUC 12 PCAs. Examination of the other HUC 2 Regions could be completed. 

 

36 U.S. Environmental Protection Agency. Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) Scientific 

Advisory Panel: Proposed Methods for Basin-scale Estimation of Pesticide Concentrations in Flowing Water and 

Reservoirs for Tolerance Reassessment; Linear Low Dose Extrapolation for Cancer Risk Decisions; DDVP Risk 

Issues; FQPA 10 Safety Factor Status Report; and Chlorothalonil: Mechanism for the Formation of Renal and 

Forestomach Tumors, July 29-30, 1998. 

0.00

0.25

0.50

0.75

1.00

0.001 0.100 10.000 1,000.000 100,000.000

Rel. Frequency

Watershed Area (sq. mi.)
29 

ADDITIONAL ANALYSES 

Modeling and Monitoring Data Comparison 

As part of the preliminary DWA, several sources of surface water and groundwater monitoring data were 

examined. Sources included: USGS National Water-Quality Assessment Program (NAWQA), 

USEPA/USGS Pilot Reservoir Monitoring Program, USDA Pesticide Data Program (PDP), California 

Department of Pesticide Regulation (CDPR), and National Center for Water Quality Research (NCWQR) 

at Heidelberg College.37,38 In summary, the monitoring data showed that detections of chlorpyrifos are 

much more likely to occur in surface water than groundwater, and concentrations in surface water are 

generally higher than groundwater. 

We conclude from our analysis of the available surface water monitoring data that it likely underestimates 

chlorpyrifos and chlorpyrifos-oxon concentrations in drinking water, and thus it is not recommended for 

quantitative risk assessment purposes. These water monitoring sampling programs did not specifically 

target chlorpyrifos use and likely do not represent high chlorpyrifos use areas. In addition, sample timing 

may not have corresponded with applications or runoff events; therefore, detections cannot be directly 

associated with a particular use pattern or site. In addition, monitoring locations, sampling frequencies, 

and sampling timing were not designed to capture peak concentrations. Model generated times series data 

along with anticipated use (i.e., sporadic) suggest that monitoring programs need to sample frequently in 

order to capture peak concentrations of chlorpyrifos in surface water. Even in the case of a pesticide such 

as atrazine, which has a more consistent use pattern, the sample frequency should be daily, otherwise a 

bias factor is recommend to be applied to ensure peak concentrations are captured.39

Since the finalization of the preliminary DWA, three additional water monitoring datasets were evaluated. 

The Washington State Department of Ecology and Agriculture (WSDE/WSDA) Cooperative Surface 

Water Monitoring Program published two reports on multi-year aquatic monitoring studies conducted in 

Washington.15,16 Dow AgroSciences submitted data (MRID 44711601) for a surface water monitoring 

study conducted on a tributary of the San Joaquin River in California. A summary of these studies is 

provided below. 

California (Registrant Monitoring Program MRID 44711601) 

Sampling was conducted at three locations on the lower reach of Orestimba Creek for one year (May 1, 

1996 to April 30, 1997). Daily time-proportional composite samples40 were collected, along with weekly 

samples. The report included chlorpyrifos use information for fields that drained into the creek or had the 

potential to contribute spray drift41. All chlorpyrifos applications were made to alfalfa and walnut by 

aerial equipment and were made during the irrigation season. The total mass of chlorpyrifos applied to all 

the fields that were identified to have the potential to impact the creek was 2.2 lb a.i./A (1308 kg). 

 

37 Note, at the time of the preliminary DWA was completed the NCWQR data had not been thoroughly reviewed by 

EPA and since this time the authors have indicated that proper quality assurance and quality control standards may 

not have been met. 38 A discussion of each of the individual datasets is provided in the preliminary assessment. 

39 U.S. Environmental Protection Agency. Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) Scientific 

Advisory Panel Meeting: Problem Formulation for the Reassessment of Ecological Risks from the Use of Atrazine, 

June 12-14, 2012, Docket Number: EPA-HQ-OPP-2012-0230 40 Hourly samples were collected and composited over a 24-hour period; relatively large fluctuations in stream flow 

were anticipated during unattended operation of the auto samplers 

41 Fields within 305 m buffer on either side of the mid-stream line 
30 

Applications occurred throughout the study period (or the day prior to study initiation) with, at most, 

three fields treated in the study area on the same day. The report suggests that typical chlorpyrifos use 

occurred during the study period, with the exception of dormant season applications to tree crops, which 

were limited due to the rainy weather during the study. 

The measured concentrations at the three sample locations are provided in Figure 91. The highest 

measured concentration was 2.2 μg/L and was associated with a chlorpyrifos application to alfalfa 

followed by flood irrigation. 

In several cases, the weekly grab samples were observed to have higher concentrations of chlorpyrifos. 

This suggests that the composite sampling methodology used in the study for daily samples resulted in the 

dilution of peak daily concentrations. Thirteen chlorpyrifos peak concentrations could be associated with 

specific events. The report authors suggest that nine of the events were related to spray drift (peak 

concentrations occurring within a three day window of application,) and were not linked to an irrigation 

event. The other four events were linked to irrigation tail water. Flood irrigation was reportedly used in 

the treated fields. Most of the peak concentrations were observed following chlorpyrifos applications to 

walnuts. The report noted that many of the walnut orchards are planted adjacent to the creek with an 

outside row located on the creek bank. This practice was done to maximize drainage from the orchard 

floor directly into the stream channel. It is unclear if any buffer zones were in place during application, 

but the observed concentrations suggest that the spray drift occurred during application even in the 

absence of adverse wind conditions. 

Figure 91. Orestimba Creek Water Monitoring Data (May 1, 1996 to April 30, 1997) 

Not all monitored concentrations were observed shortly after the application event. There is one example 

where the peak measured concentration (0.32 μg/L) associated with an application event occurred 56 days 

after application. The detection was associated with an irrigation event. This suggests that chlorpyrifos 

residues available for transport may persist on the field for several days (approximately two months) after 

application. No detections of chlorpyrifos were observed during the rainy season. 

Representative model simulations were completed for comparative purposes and are presented in 
31 

Table 16. The scenarios used in this analysis are provided in 

Table 16, while chemical specific model input values are provided in Table 10. The estimated peak 

concentrations are higher than the measured concentrations; however, the estimated concentrations are 

within an order of magnitude of the measured concentrations. 

The estimated concentrations are expected to be highly conservative for a few reasons. A PCA adjustment 

factor was not applied and it is known that the entire watershed was not treated on the same day or 

planted with crops that chlorpyrifos may be applied. The report noted that approximately 80 percent of 

the watershed was forest. If the remaining watershed was assumed to be treated (PCA = 0.20) the peak 

estimated concentrations are in reasonable agreement with the measured concentrations. Also, the 

amount of chlorpyrifos applied to the entire area of influence was only 2.2 lb a.i./A spread out over the 

course of the study. The model simulations assumed all the chlorpyrifos applied over the course of the 

study (one year) was applied as a single application event. Lastly, the model simulation also considered a 

worst case spray drift scenario. It is unclear if any drift reduction technologies (spray drift buffer, large 

droplet sizes, etc.) were utilized; however, spray drift reduction strategies (i.e., buffers) were not added to 

the chlorpyrifos labels until the Interim Registration Eligibility Decision in February 2002. 

Table 16. Surface Water Concentration Calculator Simulation Results Comparison with 

Orestimba Creek Surface Water Monitoring Data 

Represented 

Location

Represented 

Crop Use 

Estimated Drinking Water Concentration μg/L 

(PCA adjusted concentration)

Maximum 

Detected 

Chlorpyrifos 

Concentration 

(associated use) 

1-in-10 Year 

Peak 

1-in-10 Year 

Annual 

Average 

30 Year 

Average

1 Walnut 13.4 

(2.68) 

2.35 

(0.47) 

1.73 

(0.35) 

1.32 μg/L 

(walnut, spray 

drift) 

June 11, 1997 

(day 357) 

2 

Alfalfa 5.66-12.9

(1.13-2.58) 

0.69-1.56 

(0.14-0.31) 

0.61-1.39

(0.12-0.28) 

0.92 μg/L 

(alfalfa, flood 

irrigation)

May 6, 1997 

(day 325) 

3 

1.22 μg/L 

(alfalfa, flood 

irrigation)

May 13, 1997 

(day 331) 

a. CA Almond, 1/2.2 lb a.i./A(assumes total annual application of chlorpyrifos was made to the single field on 

one day), June 10, aerial application [0.95; 0.135 (spray drift assuming no buffer zones or droplet size 

restrictions) 

b. CA Alfalfa, 1/2.2 lb a.i./A (assumes total annual application of chlorpyrifos was made to the single field on 

one day) or 1/1.0 lb a.i./A (maximum currently registered application rate), May 6, aerial application [0.95; 

0.135 (spray drift assuming no buffer zones or droplet size restrictions) 

This analysis suggests that the model estimated concentrations of chlorpyrifos compare well with 

monitoring data when the model is parameterized to reflect the actual use and the PCA. Therefore, it is 

expected that the model estimated chlorpyrifos concentrations provide a reasonable upper bound of 

concentrations that may occur in the environment based on the modeled use and PCA applied. In addition, 

this dataset indicates sporadic detections and rapidly fluctuating concentrations of chlorpyrifos, further 
32 

supporting the use of model EDWCs for deriving a reasonable upper bound estimation of chlorpyrifos 

exposure in drinking water. 

The time series data were further investigated to identify bias factors. The approach employed was the 

same as that developed for atrazine.39 The results are presented in the Table 17. Bias factors were 

developed for each of the three sampling sites included in the study. 

Based on this bias factor analysis, if monitoring data were available, for example, with a sample 

frequency of 21 days, a bias factor of 6.0 would be needed to adjust the measured concentration to obtain 

an upper bound estimate of the 21-day average exposure concentration. For the same sample frequency, a 

bias factor of 32 is needed to adjusted measured concentrations to capture an upper bound average daily 

concentration. 

Table 17. Bias Factor Values Developed based on Orestimba Creek Surface Water Monitoring 

Data

Annual Rolling Average 

Maxima 

Sampling Frequency 

7-day 14-day 21-day 

 Average Bias Factor (range of bias factors)a 

Daily 4.35 (3.05 – 5.99) 12.0 (5.73 – 14.2) 14.3 (4.36 – 31.7) 

21-day 2.08 (1.35 – 2.99) 3.34 (1.96 – 5.12) 3.06 (1.43 – 5.98) 

a. Bias factors calculated based on the three different sampling sties included in the monitoring study. 

Washington State 

Sampling focused on salmon-bearing streams in five different basins within Washington. Primarily 

weekly sampling was conducted during the pesticide use season; however, some daily sampling was also 

conducted. While the study did not specifically target chlorpyrifos use, nor did the report provide 

pesticide use information, some pesticide use survey data was obtained from WSDA. In addition, the 

report included information on the PCA for each of the basins included in the report. 

The highest chlorpyrifos detections occurred within the Lower Yakima Agricultural Watershed (Table 

18). The highest concentration (0.27 μg/L) was detected in Spring Creek in 2007. Within the Lower 

Yakima Agricultural Watershed, use of chlorpyrifos includes: wine grapes (early dormant spray), tree 

fruits (early dormant spray), and mint (late season). Chlorpyrifos detection frequencies ranged from 3 to 

68% for weekly sampling. Daily samples were collected (mid-May-June) for one year at one location. 

When daily and weekly sampling frequencies of detection were compared, daily sampling detection 

frequency was more than 25% higher. 

 
33 

Table 18. WSDA Monitoring Summary for Chlorpyrifos (2006-2011) 

Location Spring Creek Sulphur Creek 

Wasteway Marion Drain 

Maximum Detected 

Chlorpyrifos 

Concentration 

0.27 μg/L 0.28 μg/L 0.12 μg/L 

Sample Yeara 2007 2009 2006 and 2007 

Watershed Size (acres) 27,373 103,010 80,491 

PCAb 50 42 66 

Primary Crops (PCA)c

Apples (4); Concord 

Grape (6); CRP (12%); 

Wine Grape (7); Hopsd (3); 

Wheat (12) 

Apples (5); Corn (8); 

Concord Grape (7); Wine 

Grape (4); Wheat (3) 

Apples (9); Corn (12); 

Concord Grape (3); Hops 

(13); Mint (6); Wheat (8) 

a. The exact sampling date is not provided in the report. 

b. Percent cropped area provided for each basin in the report; includes grass, hay, and CRP (Conservation 

Reserve Program) 

c. Survey data from report 

d. Not a registered chlorpyrifos use 

Combined with the chlorpyrifos use information (type/timing of application), maximum label rates, and 

PCA, model simulations were completed for comparative purposes. The use scenarios used in model 

simulations for this analysis are provided in Table 19, while chemical specific model input values are 

provided in Table 10. Note that a range of application dates was examined and the date that provided the 

highest concentration is reported. The results of this analysis are shown in Table 19. In addition, the 

maximum detected concentrations were adjusted based on the maximum bias factor (2.99 based on a peak 

concentration and a sampling interval of 7 days) developed (presented in Table 17) for Orestimba Creek 

Surface Water Monitoring Data and are reported in Table 19. 

 
34 

Table 19. Surface Water Concentration Calculation Simulation Comparison with Washington State 

Department of Ecology and Agriculture Cooperative Surface Water Monitoring Program 

Represented 

Location 

Represented 

Crop Use 

Model Output 

PCA Corrected for 

Total Cropland 

(PCA Corrected for Specific Cropa) 

Maximum 

Detected 

Chlorpyrifos 

Concentration 

(bias factor 

adjusted value) 

Absolute 

Peak 

1-in-10 

Year 

Peak 

1-in-10 

Year 

Annual 

Average 

30 Year 

Average

Spring Creek 

Applesb 

4.0 

2.0 

(0.16) 

2.6 

1.3 

(0.10) 

0.35 

0.18 

(0.01) 

0.23 

0.12 

(0.01) 0.27 μg/L

(0.81) 

Grapec,d 

4.3 

2.2 

(0.56)

1.7 

0.85 

(0.22)

0.25 

0.13 

(0.03)

0.15 

0.08 

(0.02)

Sulphur 

Creek 

Wasteway 

Applesb 

4.0 

1.7 

(0.20)

2.6 

1.1 

(0.13)

0.35 

0.15 

(0.02)

0.23 

0.10 

(0.01) 0.28 μg/L

(0.84) 

Grapec,d

4.3 

1.8 

(0.47)

1.7 

0.71 

(0.19)

0.25 

0.11 

(0.03)

0.15 

0.06 

(0.02)

Marion Drain 

Applesb 

4.0 

2.6 

(0.36)

2.6 

1.7 

(0.23)

0.35 

0.23 

(0.03)

0.23 

0.15 

(0.02)

0.12 μg/L

(0.36) Grape 

4.3 

2.8 

0.13

1.7 

1.1 

0.05

0.25 

0.17 

0.01

0.15 

0.01 

<0.01

Mint 

6.1 

4.0 

(0.37)

3.0 

2.0 

(0.18)

0.36 

0.24 

(0.02)

0.22 

0.15 

(0.01)

a. PCA adjusted EDWCs reflect EDWCs if only the crop specified is treated within the watershed 

b. ORApple, w24243 (Yakima), 1/2.0 lb a.i./a, dormant 1/14 (dates examined: 1/1-3/31 based on 

emergence date in scenario), ground application 

c. CAGrape, w24243 (Yakima), 2/2.0 lb a.i./a, 7-day application retreatment, dormant 1/13 (dates 

examined: 1/1-1/23 based on emergence date in scenario), ground application 

d. Individual and combined PCA for concord and wine grapes. 

e. ORMint, w24243 (Yakima), 1/2.0 lb a.i./a, 8/17 (8/1-9/31), ground application 

Current national spray drift restrictions were considered as part of this analysis. 

The estimated peak concentrations including bias factor adjusted concentrations are generally higher but 

never greater than an order of magnitude higher than the maximum observed concentrations when a total 

cropland PCA is applied to the output values. The estimated concentrations may be higher than the 

measured values because 1) the sampling program missed the peak concentration, 2) the monitored 

locations were less vulnerable than the standard “scenarios” used in the model simulations, and/or 3) the 

application rate and dates were different between the monitoring program and model simulations. Another 

consideration is the site to site extrapolation of bias factors. At this time, the relative differences between 

the vulnerability of the sampling sites along Orestimba Creek and those sites included in this dataset are 

unknown. Therefore, the appropriateness of applying the bias factors calculated for the Orestimba Creek 

data across the board to a dataset like NAWQA, where the site vulnerability varies substantially, is 

uncertain. 
35 

When individual crop PCAs are considered, the estimated peak concentrations in some cases 

underestimate the measured maximum concentrations. This may be the result of multiple chlorpyrifos 

applications (i.e., multi-crop) contributing to the measured concentration. 

This analysis demonstrates that the model estimated concentrations reasonably compare to measured 

concentrations. This suggests that if the maximum labeled rates were applied, as simulated using the 

SWCC, the model EDWCs provide a reasonable upper bound on the potential exposure and are not overly 

conservative. 

USGS National Water-Quality Assessment Program (NAWQA) 

The NAWQA data were re-examined and the bias factor needed to result in a 21-day exceedance was 

calculated for each sampling site. Based on this analysis, the lowest bias factor calculated for a maximum 

21-day average concentration to exceed the DWLOC was 8.2. The highest calculated bias factor for a 21-

day average concentration based on a 21-day sampling interval was 6 based on the Orestimba Creek 

Surface Water Monitoring data. This would suggest that none of the sites exceeded the DWLOC. 

However, using a crude approximation of the sampling frequency (365 divided by the number of samples 

taken in a year), these sites had samples taken less frequently than every 21 days. Thus, a larger bias 

factor is likely needed to account for the limited sampling at these sites in order to estimate an upper 

bound 21-day average concentration. Therefore, it is likely that only of a few sampling sites included in 

the NAWQA dataset may have actually had a 21-day average concentration that exceeded the DWLOC. 

This suggests actual use of chlorpyrifos differs from the maximum rates included in the Master Use 

Summary Document. This is consistent with the typical rate analysis completed by BEAD.30,42 

The conclusion of the Model Simulations section of this document (i.e., chlorpyrifos and the 

corresponding chlorpyrifos-oxon concentrations vary substantially across the United States, and the 

exceedances of the DWLOC are highly localized) is underscored by this analysis. In addition, the relative 

differences between the vulnerability of the sampling sites along Orestimba Creek and those sites 

included in the NAWQA dataset are unknown. Therefore, the appropriateness of applying the bias factors 

calculated for the Orestimba Creek data across the board to a dataset like NAWQA, where the site 

vulnerability varies substantially, is uncertain. 

Drinking Water Treatment 

The preliminary DWA concluded that there are a number of different drinking water treatment processes 

that may impact the amount of chlorpyrifos and chlorpyrifos-oxon in drinking water and that the variation 

and combinations of processes used by the different treatment plant across the country make it difficult to 

estimate the exact amount of chlorpyrifos or chlorpyrifos-oxon that may be in drinking water on a 

national basis. In absence of evaluating each individual community drinking water treatment facility 

separately, the preliminary DWA recommended that all of the chlorpyrifos that enters a drinking water 

treatment facility be assumed to remain after treatment, as well as to assume that all the chlorpyrifos 

entering the facility was converted to chlorpyrifos-oxon during treatment. This was recommended to 

provide a bounding estimate of the potential exposure. It is likely that this approach overestimates the 

potential of exposure to chlorpyrifos and chlorpyrifos-oxon in drinking water distributed by some 

community drinking water systems, because processes like filtering with activated carbon, sedimentation, 

or water softening are not considered. Recent publications that examined the effectiveness of the use of 

activated carbon have shown that the source of activated carbon has a significant impact on the removal 

 

42 Stebbins, K., Additional Typical Use Data for Chlorpyrifos, January 11, 2012
36 

efficiency of various organic compounds. Table 20 includes additional information on the breakdown of 

drinking water treatment processes used across the United States and supports the recommendations of 

the preliminary DWA, as well as empirical data on the percent removal of chlorpyrifos under such 

conditions.43 

All facilities distributing drinking water derived from surface water are required to filter and disinfect.44

The majority of treatment plants use chlorine as a disinfectant; however, less than 18% rely solely on 

chlorine. Generally, smaller community water systems rely on chlorination as their primary drinking 

water treatment method. Larger systems are more likely to use alternative disinfectant process to chlorine, 

such as chloramines when compared to smaller treatment plants. On average, 15% of treatment plants are 

not using chlorine. Water softening and chlorination are the most effective ways to reduce chlorpyrifos 

concentrations in surface source drinking water. However, use of chlorination results in the formation of 

chlorpyrifos-oxon. 

To date, studies looking at the removal efficiency of chlorpyrifos across a range of treatment process have 

not looked at the formation of the chlorpyrifos-oxon. Moreover, no data are currently available on the 

percent chlorpyrifos-oxon reduction under typical drinking water treatment conditions. Water softening is 

expected to reduce the concentration of chlorpyrifos and chlorpyrifos-oxon due to rapid hydrolysis. While 

the USGS-EPA Pilot Reservoir Monitoring Program monitored raw and finished water, the correlation 

between sampling was not adequate, as finished water sampling generally occurred before raw water 

sampling. The removal of chlorpyrifos or chlorpyrifos-oxon from other processes such as sedimentation 

and flocculation is also unknown. However, in general, these processes have not been shown to be 

effective treatment processes for removing pesticides. 

One study45 examined the impact of pesticide removal on a combination of potential drinking water 

treatment methods; however, this study did not assess the formation or dissipation of chlorpyrifos-oxon. 

The results of this study are consistent with other available data (Table 20) that examined the reduction of 

chlorpyrifos under individual treatment processes. EFED is not aware of data for individual treatment 

plants on the impact of pesticide removal specifically for chlorpyrifos and chlorpyrifos-oxon. EFED is 

also unaware of any monitoring data for chlorpyrifos or chlorpyrifos-oxon at the point of consumption 

(i.e., consumer tap water). 

 

43 Chamberlain, E. Shi, H., Wang, T., Ma, Y., Fulmer, A., Adams. C. J Agric. Food Chem. 2012, 60, 354-363. 44 (54 FR 27486, June 29, 1989) (EPA, 1989b) 40 CFR Parts 141 and 142 Drinking Water; National Primary 

Drinking Water Regulations; Filtration, Disinfection; Turbitity, Giardia lamblia, Viruses, Legionella, and 

Heterotrophic Bacteria; Final Rule 

45 Ormand, M. P., Miguel, N., Claver, A., Matesanz, J. M., Ovelleiro, J. L. Chemosphere, 2008, 71, 97-106. 
Table 20. Screening Analysis of Chlorpyrifos Degradation Under Typical Drinking Water Treatment Processes (surface water) 

Treatment Methoda

FC MCA ClO2 MnO4- UV 

H

O2 2 O3 Softening 

pH 

6.6 

pH 

8.6 

pH 

6.6 

pH 

8.6 

pH 

6.6 

pH 

8.6 

pH 

6.6 

pH 

8.6 

pH 

6.6 

pH 

8.6 

pH 

6.6 

pH 

8.6 

pH 

6.6 

pH 

8.6 pH 12 

Percent Reductionb 90.3 85.7 8.7 9.2 34.3 27.5 15.3 5.2 14.5 1.9 7.6 3.1 60.9 30.3 100.0 

System Population 

Category Percentage of Plants Performing Each Treatment Practice for Surface Waterc 

100 or less 98.4 0 0 1.6 3.1 - - 0 0 

101-500 79 1.2 0 9.2 1.7 - - 1.4 2.5 

501-3,300 97.4 2.2 0 7.8 2.2 - - 1.5 3.4 

3,301-10,000 80.8 13.7 11 24.7 1.4 - - 1.4 19.2 

10,001-50,000 80.5 14.8 8.7 32.9 1.3 - - 1.2 16.9 

50,001-100,000 75.1 17.1 18.5 26.8 2.6 - - 11.8 5.2 

100,001-500,000 78.9 32.4 14 26.3 4.7 - - 15.8 11.8 

Over-500,000 78.0 35.6 2.5 21.2 1.7 - - 14.4 21.2 

a. Experimental time was representative of typical drinking water treatment condition b. See footnote 43 c. U.S. EPA Office of Water 2006 Community Water System Survey, May 2009 (survey data) 

Chlorine (FC); Chlorine dioxide (ClO2); Chloramines (MCA); Lime/soda ash softener (assumed to be similar to hydrolysis at pH 12); Ultraviolet light 

(UV); Ozone (O3); Potassium permanganate (MnO4-)
APPENDIX 1: Registered Use Clarification 

In the preliminary DWA, several uncertainties relating to the registered uses of chlorpyrifos were 

identified, including: 

1) Application restrictions provided on many chlorpyrifos labels are on a per season or crop cycle 

basis. For some crops there can be multiple seasons per year; however, the number of potential 

crops grown on the same field either as a result of multiple crops or crop rotations that may be 

treated with chlorpyrifos is not defined. 

2) Some labels did not provide maximum single or annual application rates for chlorpyrifos or 

application retreatment intervals. This was common for trunk spray or basal drenches, which 

were reported as dilution factors. 

3) Some labels restrict the amount of a specific chlorpyrifos formulation (i.e., products), but do not 

restrict total active ingredient (a.i.) that may be applied. Therefore, the use of multiple 

chlorpyrifos-containing formulations is possible. 

In order to seek clarification of chlorpyrifos usage, the Agency compiled a Master Use Summary 

Document (ATTACHMENT 1) reflective of the use profile of all active product labels (as of January 

2012). All currently registered labels were reevaluated to define the labeled uses. Currently, many of the 

product labels do not state a maximum number of applications allowed per year or crop season. Through 

discussions with the registrants, EFED believes that the detailed information on maximum application 

rates and use patterns given in the Master Use Summary Document will be implemented on all 

chlorpyrifos labels. The chlorpyrifos drinking water assessment is based on the information shown in the 

Master Use Summary Document. If for any reason the final chlorpyrifos labels contain higher 

application rates, higher numbers of applications, and/or shorter minimum retreatment intervals, the 

actual exposure to chlorpyrifos and chlorpyrifos-oxon may be greater than presented in this assessment. 

Highlights of this effort are provided below. 

1. For chlorpyrifos soil treatments to grape east of the continental divide, the single application rate 

was provided as a dilution factor. Based on a high density vineyard planting of nearly 3000 vines 

per acre [vines spaced 4 feet by 4 feet approximately 2756 vines (11-15ft2

 (3.75-4.4 ft) can be 

planted (e.g., 62719-301)] chlorpyrifos could be applied at an application rate of 33 lbs a.i./acre. 

While the calculated single application rate is correct, based on the dilution factor provided on 

chlorpyrifos labels and the potential vine density, the registrants indicated that this high 

application rate was not an intended use. As a result, the registrants agreed to update the labels to 

reflect a maximum single application rate of 2.25 lb a.i./A for all chlorpyrifos soil treatments on 

grape east of the continental divide. 

2. Turf labels do not restrict the number of chlorpyrifos applications per year, nor provide a 

minimum retreatment interval. The registrants agreed to update the label to reflect a maximum 

single application rate of 3.76 lb a.i./A with no more than two applications per year. Therefore, 

7.52 lb a.i./A would be the highest yearly application of chlorpyrifos permitted on turf. 

3. The registrants have also agreed to update the labels to restrict the amount of chlorpyrifos that 

may be applied per year in terms of a.i./A by use site rather than in terms per season or crop 

cycle. 
39 

4. The registrants have agreed to reduce the number of chlorpyrifos applications for some crops 

such as tart cherries. 

Although the current chlorpyrifos labels do not yet reflect the revisions agreed to by the registrants and 

reflected in the Master Use Summary Document, the use summary document is being used to define the 

use profile for chlorpyrifos for the purposes of updating the registration review DWA for chlorpyrifos. 

As mentioned above, the uncertainties associated with the use of chlorpyrifos use on grapes and turf have 

been resolved, and as a result, these crops use are no longer expected to result in the highest chlorpyrifos 

or chlorpyrifos-oxon concentrations as previously reported in the preliminary assessment. 

Despite the on-going label clarification efforts, there are still a number of uncertainties associated with the 

current chlorpyrifos use scenarios included on the Master Use Summary Document. ATTACHMENT 

1 summarizes the remaining Master Use Summary Document uncertainties including assumptions made 

in the absence of information, if the use was assessed as part of the preliminary DWA, or this update, and 

the potential impact of the use relating to drinking water exposure. In general, reasonable assumptions 

could be made for agricultural crop use sites; however, for some use sites (e.g., commercial/institutional/ 

industrial premises/equipment), the use could not be reasonably assessed based on missing information, 

including single and yearly application rates. For these use sites, realistic assumptions could be made that 

result in drinking water exposure scenarios that are higher than those presented in this updated DWA. 
40 

APPENDIX 2: Spray Drift

In June of 2012, EPA finalized its evaluation of the potential risks from spray drift of chlorpyrifos.46

Results of this assessment indicated spray drift from application of chlorpyrifos using current (in 2012) 

label requirements generally resulted in risk estimates of concern for locations immediately adjacent to 

treated fields. To address these risks, buffer zones and drift reduction technologies (i.e., larger droplet 

sizes) for sensitive sites47 were implemented, in addition to restricting all aerial applications to 2.0 lb 

a.i./A or less except when chlorpyrifos is used to treat Asian citrus psyllid. In this situation, chlorpyrifos 

application may be applied at a rate of up to 2.3 lb a.i./A by aerial equipment. 

The buffer zones and drift reduction technologies only apply to sensitive sites and do not protect aquatic 

environments; therefore, were not considered as part of the exposure modeling for drinking water in this 

update. Nevertheless, the aerial application rate restriction of 2.0 lb a.i./A (2.3 lb a.i./A for Asian citrus 

psyllid) is an across the board restriction and; therefore, was considered as part of this update and is 

reflected in the Chlorpyrifos Master Use Summary Document. 

Spray drift estimates were updated to reflect the most recent offsite deposition guidance48,49 and 

considered the currently labeled buffer restrictions [25 ft. (ground), 50 ft. (air-blast), 150 ft. (aerial)] for 

aquatic water bodies. However, this updated analysis does not consider the court ordered spray drift 

buffers [60 ft. (ground and air-blast) and 300 ft. (aerial)] required for salmon bearing steams, as these 

buffers are only required in three states, California, Oregon, and Washington and are not required as part 

of the labeling under the Federal Insecticide, Fungicide, and Rodenticide Act. 

 

46 Dawson, J., Bohaty, R., Mallampalli, N. Evaluation of the Potential Risks from Spray Drift and the Impact of 

Potential Risk Reduction Measures, June 20, 2012 PC 059101 DP 399483 and 399485.

47 Sensitive sites are areas frequented by non-occupational bystanders (especially children). These include residential 

lawns, pedestrian sidewalks, outdoor recreational areas such as school grounds, athletic fields, parks and all property 

associated with buildings occupied by humans for residential or commercial purposes. Sensitive sites include homes, 

farmworker housing, or other residential buildings, schools, daycare centers, nursing homes, and hospitals. Nonresidential agricultural buildings, including barns, livestock facilities, sheds, and outhouses are not included in this 

prohibition. 

48 U.S. Environmental Protection Agency, Brady, D. Guidance on Modeling Offsite Deposition of Pesticides via 

Spray Drift for Ecological and Drinking Water Assessments, December 20, 2013 

49 U.S. Environmental Protection Agency, White, K., Khan, F., Peck, C., Corbin, M. Guidance on Modeling Offsite 

Deposition of Pesticides via Spray Drift for Ecological and Drinking Water Assessments, December 19, 2013 
41 

APPENDIX 3: Chlorpyrifos and Chlorpyrifos-oxon Volatility 

While laboratory studies suggest that volatilization is not likely to play a significant role in the dissipation 

of chlorpyrifos in the environment, field data suggest otherwise. Chlorpyrifos has been detected in air 

samples and as a result, EPA requested a field volatility study50 as part of the data call-in requirements for 

the registration review of chlorpyrifos. EPA reviewed two field volatility studies (summarized below) that 

indicate volatilization of chlorpyrifos and/or chlorpyrifos-oxon from treated crops is a pathway of 

dissipation in the environment that may result in exposure to vapor phase or redeposited chlorpyrifos and 

chlorpyrifos-oxon downwind of a treated field. The two studies were conducted at rates much lower than 

the current maximum single broadcast application. While the absolute flux for chlorpyrifos observed in 

the potato study is higher than the alfalfa study, the flux profiles51 are similar in both studies. 

Study 1: Alfalfa 

Dow AgroSciences (DAS) recently submitted a field volatility study that measured both vapor phase 

chlorpyrifos and chlorpyrifos-oxon in air samples following an application of a low VOC (volatile 

organic compounds or volatile organic chemicals) formulation52,53,54 of chlorpyrifos to alfalfa. 

Approximately 30% of the applied chlorpyrifos was emitted from the treated field in the first 24 hours 

(28% considering chlorpyrifos only; 30% considering chlorpyrifos and chlorpyrifos-oxon combined). The 

flux profile for chlorpyrifos is similar to those generally observed for fumigants in that there is a peak 

emission shortly after application during the warmer part of the day. The study measured chlorpyrifos for 

a period of 72 hours following application. 

Study 2: Potato 

A field volatility study published in the open literature was conducted with the application of a non-low 

VOC formulation of chlorpyrifos applied to potatoes.55,56 This study only measured parent chlorpyrifos 

 

50 EPA MRID 48883201: Direct Flux Measurement of Chlorpyrifos and Chlorpyrifos-Oxon Emissions Following 

Applications of Lorsban Advanced Insecticide to Alfalfa; Authors: Aaron Rotondaro and Patrick Havens; Sponsor: 

Dow AgroSciences LLC, 9330 Zionsville Road Indianapolis, IN 46268-1054, 2012. 51 A flux profile is the emissions from a treated field over a defined period of time (i.e., an hourly time series of flux 

estimates during a period of measurement following application). 

52 California's Department of Pesticide Regulation (Cal DPR) defines a low VOC pesticide formulation when the 

total emission potential (see footnote 53) is 25% or less (see footnote 54). The emission rate corresponds to total 

VOC emissions and not specially one component of the formulation (i.e., the active ingredient). EPA does not 

currently define low VOC pesticide formulations. 

53 Emission potential is based on Thermogravimetric Analysis; Oros, D., Spurlock, F. California Department of 

Pesticide Regulation, ESTIMATING PESTICIDE PRODUCT VOLATILE ORGANIC COMPOUND OZONE 

REACTIVITY. PART 1: SPECIATING TGA -BASED VOLATILE ORGANIC COMPUND EMISSIONS USING 

CONFIDENTIAL STATEMENTS OF FORMULA, January 27, 2011 

http://www.cdpr.ca.gov/docs/emon/pubs/ehapreps/analysis_memos/2286_segawa.pdf 

54 Proposed regulation can be found at: http://www.cdpr.ca.gov/docs/legbills/rulepkgs/12-001/text.pdf 55 EPA MRID 48998801: Volatilization of the Pesticides Chlorpyrifos and Fenpropimorph from a Potato Crop; 

Authors: Minze Leistra, Johan H. Smelt, J. Hilbrand Weststrate, Frederik VanDenBerg, and Rene Aalderink; 

Sponsor: This work was carried out within the framework of the EU APECOP project Effective Approaches for 

Assessing the Predicted Environmental Concentrations of Pesticides (QLK4-CT-1999-01338) and of Research 

Program 416, Pesticides and the Environment, of the Dutch Ministry of Agriculture, Nature and Food Quality; 

Citation: Leistra, M; Smelt, J. H.; Weststrate, J. H.; Van Den Berg, F; Aalderink, R. Environ. Sci. Technol. 2006,

40, 96-102. 56 Since the raw data for this study could not be obtained, the flux rates could not be independently verified by EPA 

and, thus, evaluation of experimental details and associated data quality review of this study is not as rigorous as that 
42 

and did not measure concentrations of chlorpyrifos-oxon. Approximately 71% of the applied chlorpyrifos 

was estimated to volatilize from the treated field within 24 hours following application, assuming 

continuous flux.57 

While volatility has been observed to be a major route of dissipation of chlorpyrifos in the environment, 

the extent of deposition following volatilization and the area of deposit off a treated field is unknown. As 

a conservative approach, all the applied chlorpyrifos is assumed to be available for runoff, spray drift, and 

erosion in this update. The reported EDWCs may be higher than concentrations that would be found in 

the environment because volatilization is not accounted for in model simulations. Volatility is the likely 

reason chlorpyrifos is detected in remote regions or in precipitation collected from locations far from 

potential applications sites. In addition, in some cases chlorpyrifos monitoring is conducted from 

irrigation canals which discharge to streams and rivers and chlorpyrifos is not observed in the irrigation 

water yet is samples of river water reveal concentrations of chlorpyrifos. This may be the result of 

volatilization followed by redeposition. 

 

 

associated with the alfalfa study. The results from this study are presented in this assessment to provide another line 

of evidence of the potential volatility of chlorpyrifos, as demonstrated in the registrant submitted study, and to help 

describe the potential variability in chlorpyrifos flux rates due to different study conditions (e.g., crop canopy, 

formulation, and weather). 

57 Sampling did not occur at night; therefore, in order to develop a 24 hour flux profile. EPA developed a flux rate 

for the missing sampling periods by averaging the flux rate prior to and after the time period when sample collection 

did not occur. 
43 

APPENDIX 4: NAFTA Kinetic Analysis 

Aerobic Soil Metabolism 
44 
45 
46 

 
47 

Anaerobic Aquatic Metabolism 

 
48 

Anaerobic Soil Metabolism 
1

Attachment 1. Chlorpyrifos Use Summary

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)

3

REI (hours)

3

MRI (days)

3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC2

lb a.i./A

Per 

Year

Per 

CC2

AGRICULTURAL FARM 

PREMISES

Livestock housing 

and holding areas 

(such as hog 

barns, empty 

chicken houses, 

dairy areas, 

milkrooms, calf 

hutches, calving 

pens and parlors).



Indoor 

general 

surface spray

backpack 

sprayer; high 

and low sprayer 

(pressure or 

volume)

0.075 lb a.i./ 

1000 ft sq

1.2 

EC, ME

[14.4]

NS NA 12 NA NA NS NS

Only permitted 

for use in 

poultry houses

ALFALFA

 At plant groundboom 1.0 

G

1.0 1.0 [1]

NS 1 21 24 [10]NS

Missouri 

only

Lower PHI 

permitted for 

EC rates 0.33 lb 

a.i./A (7 d) and 

0.67 lb a.i./A 

(14 d) e.g. Reg. 

No. 62719-591

Stand is in 

production 3-5 

years. Planted 

1⁄4” to 1⁄2” deep. 

 Foliar

aerial or 

ground/ 

broadcast, 

chemigation

1.0 

EC

[4.0]

NS 4.0 [4]NS 4 21 24 10

Lower PHI 

permitted for 

EC rates 0.33 lb 

a.i./A (7 d) and 
2

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

0.67 lb a.i./A 

(14 d) e.g., Reg. 

No. 62719-591

Multiple 

harvests (or 

cuttings) per 

year when used 

for feed/fodder 

and 1 harvest 

per year when 

grown for seed. 

Cuttings occur 

about every 30 

days.

Only 1 crop 

cycle per year 

but up to 9 

cuttings, varies 

by geography.

Total 1.0 5.0 5.0 [5]

NS

5 21 24 [10]

NS

Represents 

Missouri 

scenario 

otherwise 4.0 lb 

a.i./A per is 

max.

ALMOND



dormant/

delayed 

dormant;

broadcast

aircraft, airblast 2.0 

WDG, WP 2.0 NA 1 NA NA 24 10

Restricted 

use in 

California.

 foliar

; aircraft, airblast 2.0 6.0 NA3 NA 14 10
3

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

broadcast WDG,WP



pre-plant, 

foliar;

trunk 

spray/drenc

h or pre-

plant dip

handheld, 

backpack, 

drench/dip, 

handgun, and 

low pressure 

hand wand

2.5

(3.0/100 gal)

WDG

2.5 NA1 NA 14 NS



Dormant/ 

delayed 

dormant; 

foliar; 

orchard 

floors 

broadcast 

ground boom, 

handgun, 

chemigation

4.0

EC* 4.0 NA

2 NA 14 10

Restricted 

use in 

California. 

Only one 

dormant 

application 

can be made.

Total -- 4.0 14.5 NA7 NA 14 NS

Excludes 

nursery 

applications 

(See general 

“Fruits” listing)

APPLE



dormant/

delayed 

dormant;

broadcast

aircraft, airblast

2.0 

EC

2.0

WDG

1.5

WP

22.011 NA 24/ 

4 d 10d

Reflects spray 

drift mitigation 

measures.



pre-plant, 

foliar;

trunk 

spray/drenc

h or pre-

plant dip;

handheld, 

backpack, 

drench/dip, 

handgun, and 

low pressure 

hand wand

1.5

(1.5 lb ai/100 

gal)

WDG 

1.5 NA11 28 4d NS

Use 

permitted in 

states east of 

the Rockies 

except 

Mississippi.
4

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)

3

REI (hours)

3

MRI (days)

3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC2

lb a.i./A

Per 

Year

Per 

CC2

ground

Total 2.0 3.5 2

ASPARAGUS 

Foliar, preharvest; 

broadcast

aircraft, ground 

boom

1.0 

EC, WDG 1.0 1.0 1 1 1 24 10



Postharvest, 

broadcast

aircraft, ground 

boom

1.0 

EC, WDG 2.0 2.0 2 1 1 24 10

granular soil 

band treatment 

ground boom

1.5 

G

3.0 3.0 2 2 180 24 [10]

NS

Permitted in 

California, 

the Midwest, 

and the 

Pacific 

Northwest 

19713-505, 

19713-521, 

5481-525, 

62719-34, 

83222-34

Do not apply 

more than 3.0 lb 

a.i./A between 

harvests.

Total 1.5 

G

3.0 G

2.0

3.0 G

2.0 3 3 1 24 10

BEANS



Preplant; 

Seed 

treatment

Seed Treatment

0.016-0.348

0.000798 lb

ai/lb seed 

ME

0.013-0.272

0.000625 lb

ai/lb seed 

NS [0.348]

NS NS [1]NS NS NS NS

ME is SLN 

only for ID

Italics highlight 

the range of 

application 

rates depending 

on the number 

of seeds per lb 

and the number 
5

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

WP

0.012-0.253

0.00058 lb

ai/lb seed 

EC

of seeds planted 

per acre. 

Seeding rate 

information 

provide by 

BEAD.

4

BEEF/RANGE/ 

FEEDER 

CATTLE 

(MEAT)/

DAIRY 

CATTLE (NON-

LACTATING)

Summer, late 

fall, spring; 

impregnated 

collar/tag

Animal 

treatment (ear 

tag)

0.0066

lb/animal

[0.0099 ]

NS

NA3 NA NS NS NS

Reg. No. 

39039-6

Cattle ear tags 

are assumed to 

last 4-6 months 

Two tags per 

animal at 

0.0033 lb 

a.i./tag in the 

summer and 

one tag per 

animal at 

0.0033 lb a.i./A.

BEETS 

(UNSPECIFIED; 

TABLE OR 

SUGAR)

“grown for seed”



At plant, soil 

band 

treatment

Ground boom 1.0 

EC NS

1 NS1 24

Allowed in 

Oregon

Court 

ordered 

buffer of 60 

ft for ground 

chlorpyrifos 

application 

is required 

for “affected 

waterways”.

Minimum 

Incorporation: 2 

inches
6

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2



Preplant, soil 

incorporated 

treatment

Broadcast/ 

ground boom

1.9

EC

NS

(2.8 ID) NS

1 NS

Allowed in 

Oregon and 

Idaho

OR-09007; 

62719-591

ID-090002; 

62719-591

Total 1.9 NS NS NS NS 24

One or the other 

type of 

application.

SUGAR BEETS



Preplant, soil 

incorporated 

treatment

Broadcast/ 

ground boom

1.0 

EC

2.0 G

3.0 2.01

1

NA 24 10

Minimum 

Incorporation: 1 

inch



At plant, soil 

band 

treatment

Broadcast/ 

ground boom

1.0

EC, WDG

2.0 G

3.0 2.011 30 24 10



Postplant, 

soil band

Broadcast/ 

ground boom

2.0 G

3.02.011 30 24 10



Post-

emergence 

band 

treatment; 

broadcast

Broadcast/ 

ground boom

1.0 

EC, WDG

3.0 1.031 30 24 10

 broadcast

Aircraft, ground 

boom, 

chemigation

1.0 

EC, WDG

3.0 1.031 30 24 10

EC is not for 

use in MS

Total

1.0 

EC

2.0 G

4.0 [4.0]

NS3

[3]

NS 30 24 10

One granular 

application at 

2.0 a.i./A and 

two liquid 

applications at 

1.0 a.i./A per 
7

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

year. Also 

assumed per 

crop cycle.

CARROT 

Grown for Seed 

(INCLUDING 

TOPS)



Foliar pre-

bloom 

broadcast

aircraft, ground 

boom

0.94 

EC 0.94

1117 24 NA

Oregon and 

Washington 

Court 

ordered 

buffer of 60 

ft for ground

and 300 ft 

for aerial 

application 

is required 

for “affected 

waterways”.

OR090011

SLN Expires: 

12/31/2018

WA090011 

SNL Expires: 

12/31/2016

Carrots take 

two years to 

produce seed. 

All commercial 

production of 

the carrot 

(vegetable) 

takes place in 

the first year 

when the plant 

is nowhere near 

blooming.

CHERRIES



dormant/

delayed 

dormant;

broadcast

aircraft, airblast

2.0

WDG, EC

1.5

WP

2.0 NA1 NA NS 24 10



foliar;

broadcast 

airblast 4.0

EC 10.0 NA

5 NA 14 24 10

Tart cherry only

aircraft 2.0 Reflect

s spray 

drift mitigation
8

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2



Foliar, post 

harvest;

trunk 

spray/drenc

h 

handheld, 

backpack, 

drench/dip, 

handgun, and 

low pressure 

hand wand

2.5

(3.0/100 gal)

WDG, EC

2.5 NA1 NA2 24 [10]

NS

Only some 

labels specify a 

10 d MRI. 

Total

--

4.0

4.5 

(sweet) 14.5 

(tart 

only)

6

Excludes 

nursery 

applications 

(See general 

“Fruits” listing)

The foliar 

applications

only apply to 

tart cherries, 

thus, sweet 

cherry scenarios (e.g., Pacific 

NW) annual 

application rate 

would be 4.5 lb 

total a.i./year.

CHRISTMAS 

TREE 

PLANTATIONS



foliar;

broadcast

helicopter, 

orchard blast

1.0

EC, WDG, WP 3.0 NA

3 NA [0]

NS 24

7

Aerial 

applications 

via 

helicopter 

are only 

permitted in 

Washington 

and Oregon.
9

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2



post harvest;

Stump 

Treatment

handheld, 

backpack, 

drench/dip, 

handgun, and 

low pressure 

hand wand

2.5

(3.0/100 gal)

EC, WDG

2.5 NA1 NA NA7

Total 2.5 5.54

CITRUS 



foliar;

broadcast

airblast, ground 

boom

6.0 

WP, WSP, EC 7.5 NA

2 NA

35 

(21 

for 

low 

rate

s)

5d

30 

(10 

for 

low 

rates )

6.0 lb a.i. /A 

is only 

permitted in 

California 

and Arizona.

The max 

single rate in 

other states 

is restricted 

to 4 lb a.i./A.

 aircraft 2.3

WP, WSP, EC 21

5 10

Florida, 

California, 

and 

potentially 

Texas

Aerial 

application used 

to control 

psyllid, the 

vector for citrus 

greening.

Reflects spray 

drift mitigation



foliar; 

orchard 

floors 

broadcast

ground boom, 

chemigation, 

handheld, 

backpack, 

drench/dip, 

handgun, and 

1.0

G*, WSP, EC 3.0 NA

3 NA 28 24/ 

5 d 10
10

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

low pressure 

hand wand

Total -- 6.0 10.55

Registered 

labels permit 

both foliar and 

soil applications 

in the same 

orchard.

Total excludes 

nursery 

applications 

(See general 

“Fruits” listing)

CLOVER 

(GROWN FOR 

SEED)

 Preplant Ground boom 1.9 

EC 1.9 1.9

11 NS 24 NA

Use only

permitted in 

Oregon.

OR-0900100; 

master label: 

62719-591



Post-Plant 

Foliar

aircraft and 

ground boom

Either a 

preplant or post 

plant 

application is 

allowed.

COLE CROPS 

(EXCLUDES 

CAULIFLOWE

R AND 



Preplant, soil 

incorporated 

treatment

Ground boom

2.0

EC, WDG, G 4.0 2.0

2

1

30 24 10

Min. 

incorporation: 

2 inches

BRUSSELS 

SPROUTS)



At plant, soil 

band 

treatment

Ground boom1

One granular 

application 

permitted per 

year.

 Post plant Ground boom 1 
11

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2



Foliar 

Established 

Plantings, 

soil sidedress 

treatment

Ground boom1



Foliar, 

broadcast

Aircraft, ground 

boom, 

chemigation

1.0

EC, WDG, WP 4.0 3.0

43 21 10

Multiple crops 

per year are 

possible in 

some locations.

Total 8.056

4

Some labels 

restrict the 

yearly 

application rate 

to 3 lb a.i./A.

The maximum 

number of crops 

per year is 2.

BRUSSELS 

SPROUTS



At plant, soil 

band 

treatment

Ground boom

2.0

EC; G

2.0 [2.0]

NS



21 21 24 10

Preplant, soil 

incorporated 

treatment

Ground boom

Minimum 

incorporation is 

2 inches



Postplant, 

soil 

application

Ground boom 2.25 EC, G 2.25 [2.25]

NS



Foliar 

broadcast

Aircraft, 

Ground boom

1.0

EC

[5.3]

NS 3.0 NS

3 10

83222-20, 

84930-7, 

86363-3 specify 

a 7 day MRI. 

All other labels 
12

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

specify a 10 day 

MRI.

The PHI stated 

84930-7 is 

conflicting [p. 4 

(21 days and p. 

19 (30 days)]

Total 2.3 5.3 NS 21 247

Assume one 

application of 

either at plant, 

preplant, or 

postplant 

followed with 

additional foliar 

applications.

CAULI-

FLOWER



At plant, soil 

band 

treatment

Ground boom

2.0 

EC

2.3 G

2.0 

EC 2.25 G

NS [1]

NS

1 21

3d

10

Only one 

granular 

application.



Preplant, soil 

incorporated 

treatment

Ground boom 2.3 G

2.0 

EC

2.3 NS [1]

NS

1

30, 

EC,

21 G

Minimum 

incorporation is 

2 inches



Postplant, 

soil 

application

Ground boom



Foliar 

broadcast

aircraft, ground 

boom

1.0 

EC

[5.3]

NS 3.0 NS

3 21 10

Total 2.3 5.3 [5.3]

NS NS [4]NS 21 24 10

Assume one 

application at 

either plant, 

preplant, or 
13

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

postplant 

followed with 

additional foliar 

applications.

COMMERCIAL

/INSTITUTION-

AL/ 

INDUSTRIAL 

PREMISES/ 

EQUIP. 

(INDOOR)

Non-food areas of 

manufacturing, 

industrial, and 

food processing 

plants;

warehouses; ship 

holds; railroad 

boxcars.

Broadcast Product 

Container

0.4373 lb 

a.i./100 sq ft

190.5 G

NS NA NS NA NA NS NS For treatment of 

fire ants

Crack and 

Crevice/Void

Sprayer/ 

Injection

0.0625 lb 

a.i./1000 sq ft

2.7 

ME

NS NA NS NA NA NS NS 499-419

Crack and 

Crevice/Spot

Sprayer/ 

Injection

0.0424 lb/gal 

ME NS NA NS NA NA NS

7

COMMERCIAL

/INSTITUTION

AL 

/INDUSTRIAL 

PREMISES/EQ

UIP. 

(OUTDOOR)

Outdoor 

commercial use 

around non-food 

areas of manufact-

uring, industrial, 

Soil 

broadcast

Low and High 

Pressure, 

Backpack, 

Handgun 

Sprayers

0.0247 lb 

a.i./1000 sq ft

1.1 

ME

NS NA NS NA NA NS NS

Directed 

spray

0.1132 lb 

a.i./1000 sq ft

4.9 

ME

NS NA NS NA NA NS NS

Specific to: 

Inside and 

outside 

dumpsters and 

other trash 

holding 

containers, trash 

corrals and 
14

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

and food 

processing plants; 

warehouses; ship 

holds; railroad 

boxcars

other trash 

storage areas.

Crack and 

Crevice/void/

general 

outdoor

0.0424 lb/gal 

ME NS NA NS NA NA NS

7

CONIFERS 

AND 

DECIDUOUS 

TREES; 



?

foliar;

broadcast Ground boom 1.0 EC

3 NA6 NA7 247

PLANTATION, 

NURSERY



?

foliar; stump 

treatment

backpack, 

drencher, low 

pressure hand 

wand

0.3 

EC 0.3 NA

1 NA7 247

Total 1.03 NA6 NA7 247

The total 

number of 

applications 

assumed is 

either 3 foliar 

applications or 

2 foliar 

applications 

with one stump 

treatment.

CORN (ALL)

 Preplant

ground/ soil 

incorporated

conservation 

tillage, in 

furrow, 

broadcast, 

chemigation, 

3.0 

EC

2.0 G

3.0 3.0 NS3 NA

24/ 

5 

EC

10

19713-520, 

19713-599, 

33658-26, 

34704-857, 

72693-11, 

83222-20
15

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

soil band The minimum 

incorporation 

depth is 2 

inches.

soil 

incorporated 

aerial

conservation 

tillage

2.0

EC, G



ground/ 

conservation 

tillage, in 

furrow, 

broadcast, 

chemigation, 

soil band

1.0

EC

2.0 G

3.0 3.0 NS3 21 10 19713-520



Storage or 

preplant seed 

treatment

Seed treatment

0.001-0.021

0.000625 lb 

a.i./ lb seed 

WP

0.1-1.9

0.058 lb a.i./ lb 

seed 

FC

[?]

NS

[1.9]

NS

[?]

NS

1 NS NS NS

Italics highlight 

the range of 

application 

rates depending 

on the number 

of seeds per lb 

and the number 

of seeds planted 

per acre. 

Seeding rate 

information 

provide by 

BEAD.

4

 At plant soil 

incorporated, 2.0

[?]

NS 3.0 [?]NS

3 21 24 10
16

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

conservation 

tillage

G



Post 

emergence

Aerial or 

ground, 

broadcast, 

chemigation

1.5 

EC

1.0 

WDG

NS 3.0 NS3 21

24/ 

5d 

(EC

10

A brush on max 

single rate is 

permitted at 1.0 

lb ai/a (72693-

11)

 Foliar

Aerial or 

ground/ 

broadcast, 

granule, seed 

and 

chemigation

1.5 

EC 3.0 3.0 NS3 21 10

Total 3.0 8.1 8.1 NS4 21 10

Two granular 

applications are 

allowed with a 

maximum 

single rate of 

1.0 lb a.i./A or 

one granular 

application at 2 

lb a.i./A.

Total with seed 

treatment

PHI: 21 d 

except 

Delaware and 

Florida (7 d)

COTTON



Storage or 

preplant seed 

treatment

Seed treatment

0.8-2.2

0.00116 lb/lb 

seed 

[2.2] 

NS

[2.2] 

NS

[1]

NS

1 NS NS NS

264-932

Rates in italics 

highlight the 
17

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

EC potential range 

of application 

rates depending 

on the number 

of seeds per lb 

and the number 

of seeds planted 

per acre. 

Seeding rate 

information 

provide by 

BEAD.

2

 Foliar

aerial, 

chemigation, 

ground boom 

1.0 

EC, WDGP

3 3.033 14 24 10

Except MS

Total1.0 3.2 3.233 14 24 10

1.6 lb a.i./A is 

max single rate 

(seed treatment)

Total with seed 

treatment

1 crop cycle per 

year assumed

CRANBERRY

 Foliar

aircraft, ground 

boom/ 

broadcast and 

chemigation

1.5 

EC, WDG 3.0 NA

2 NA 60 24 10

Not for use 

in 

Mississippi.

Do not apply to 

bogs when 

flooded.

CUCUMBER



Storage or 

preplant seed 

treatment

Commercial

seed treatment

0.4

0.00058 lb/lb 

seed

EC

NS 0.121 NS NS NS

Seeding rate 

information 

provide by 

BEAD.

2

264-932, 
18

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

62719-221, 

CA040004

Per registrant 2 

CCs per year

FIGS 



dormant/

delayed 

dormant; 

soil 

application

ground boom 2.0

WDG, EC 2.0 NA

1 NA 2174d NS

Use is 

restricted to 

California 

only.

Incorporation to 

3 inches is 

suggested but 

not required 

following 

application.

FILBERTS/ 

HAZELNUT



dormant/ 

delayed 

dormant;

broadcast

aircraft, airblast 2.0 

WP 2.0 NA

1 NA 14

24

10



foliar;

broadcast aircraft, airblast 2.0WDG, WP, EC 6.0 NA

3 NA 14 10

Some labels 

specify a 

retreatment 

interval of 10 

days.

Total 2.0 6.0 NS 3.0 NA 14 24 10

Excludes 

nursery 

applications 

(See general 

“Fruits” listing)

FOOD 

PROCESSING 

PLANT 

PREMISES 

(NONFOOD 

CONTACT)

When 

needed, crack 

and crevice 

treatment, 

spot 

treatment

0.0424 lb/ gal 

ME NS NA NS NA NA NS

7

53883-264,

84575-3 

Spot Treatment: 

Do not exceed 

two square feet

per individual 

spot.
19

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

FOREST 

PLANTINGS 

(REFORESTAT

ION 

PROGRAMS)

(TREE FARMS, 

TREE 



Foliar, 

broadcast ground boom 1.0 EC 6.0 NA

6 NA

24

7

PLANTATION, 

ETC.)



Foliar, stump 

treatment

direct spray,

drencher

0.34 

EC 6.0 NA [18]NS NA

7

FOREST 

TREES 

(SOFTWOODS, 

CONIFERS)



Foliar, 

broadcast

ground boom, 

drencher

0.61

EC 3.6 NA NS NA 24

7



Foliar, stump 

treatment direct spray

[3.6]

2.4 lb a.i./100 

gal 

EC

3.6 NA NS NA7

Application rate 

is provided as a 

dilution factor.

FRUITS&

NUTS

Non-bearing (not 

to bear fruit 

within 1 year) 

fruit trees in 

nurseries 

(includes: 

almonds, citrus, 

filbert, apple, 

cherry, nectarine, 

peach, pear, plum, 

prune).



Foliar-Non-

bearing 

nursery 

broadcast

High/low 

volume spay/ 

hand held 

sprayer/power

sprayer

4.0 

EC 4.0 NA NS NA 14 NS

7

For nectarines 

and peaches, 

the use is 

restricted to one 

application of 

no more than 3 

lb a.i./A per cc. 

For apples, the 

max rate is 2 lb 

a.i./A per crop cycle and the 

use is restricted 

to 1 application 

(either canopy
20

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

or trunk drench) 

per year. 

Example label, 

62719-254



Foliar-Non-

bearing 

nursery trunk 

drench

drencher, high 

and low 

pressure sprayer

2.0

WDG

2.0 NA NS1 147

Total 4.0 6.0

Maximum 

Single Rates: 

3.0 (nectarines 

and peaches)

2.0 (apples)

Maximum 

Yearly Rates: 

3.0 (nectarines 

and peaches)

2.0 (apples)

GINSENG 

(MEDCINAL)



Preplant, 

post-

emergence

Ground, soil 

broadcast

2.0 G

2.0 NA1 NA 365 24 NA

Permitted in 

Michigan 

and 

Wisconsin

MI110006,WI1

10003)

Minimum 

incorporation: 4 

inches 

Application 

should be 

followed by 

rainfall or 

overhead 

watering.

Valid until June 

29, 2016.
21

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

GOLF COURSE 

TURF

When 

needed, soil 

broadcast/ 

spot 

treatment

Ground, low 

pressure

1.0

EC 2.0 NA

2 NA

24

NS

Foliar, 

broadcast, 

Ground boom, 

handgun, low 

pressure and 

backpack

1.0 

EC, G, B

2.0 NA2 NA

NS Chemigation 

not allowed for 

the EC 

formulation. Tractor drawn 

spreader, push 

type spreader, 

belly grinder

1.0 G

[24]

NS

7

Mound 

treatment

Granule 

applicator

1.0G

2.0 NS2 NS NS7

Total 2.0 2.0 NA2 NA NS NS

GRAPES



Dormant/ 

Delayed 

Dormant 

(pre-bloom)

Ground boom, 

broadcast, 

drench

high/low spray

volume

1.0 

WDG, EC 1.0

11 NA 35

24

NS

East of the 

continental 

divide only.

Do not use in 

conjunction 

with soil 

surface 

applications for 

grape borer 

control.



2.0

EC 2.0

11NA 35

Permitted in 

Colorado, 

Idaho, and 

Washington

CO080008, 

ID090004, 

WA090002

Master label: 

62719-591

 Foliar Ground/ 2.25 2.25

11 NA 35 NS Permitted 
22

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

broadcast, basal 

spray and 

drench (soil 

treatment)

EC east of the 

continental 

divide.



1.0 

EC 3.0

33 NA 35 NS California CA080010



Postharvest, 

dormant/ 

delayed 

dormant

Ground boom, 

broadcast

2.0 

EC 2.0

11 NA NS NS California CA080009

Total 2.25 2.251 35 24NS

Permitted 

east of the 

continental 

divide.

2.0 5.04 NS NS California

GRASS 

FORAGE/ 

FODDER/HAY



Foliar, 

broadcast

Aircraft, ground 

boom, 

chemigation

1.0 

EC 3.0 NA

3 NA NS 24

Permitted in 

Nevada, 

Oregon, 

Washington, 

and Idaho

NV080004, 

NV940002, 

OR090009, 

WA090010,

ID090003

GREENHOUSE



early 

evening, 

aerosol, fog 

or fumigation

Total release 

fogger

0.029 

0.0066 lb 

a.i./1000 sq. ft

PL

NS NA NS NA NS NS2

HOUSEHOLD/

DOMESTIC 

DWELLINGS 

INDOOR 

PREMISES

 When needed Bait station 0.0003 lb/bait 

station NS NA NS NA NA NS NS 9688

-67

HYBRID 

COTTONWOO



Foliar, 

dormant, 

High volume 

(dilute)

1.9 

EC

[2.0]

NS 6.0 [1]NS

3 247 Washington WA090004
23

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

D/ POPLAR 

PLANTATIONS

delayed 

dormant; 

broadcast

Low volume 

(concentrate)

Energy wood 

plantations may 

be harvested as 

often as every 2-3 years; 

pulpwood 5-10 

years; and saw

timber 15-20 

years. 

(Arkansas 

production 

guide). In 

Washington the 

crop takes 2-8 

years

LEGUME 

VEGETABLES



Preplant, soil 

treatment Ground boom 1.0 EC, WDG 1.0 NA

1 NANS

24

NA No MRI 

because 

application only 

once a year



At planting, 

soil treatment Ground boom 1.0 EC, WDG 1.0 NA

1 NANS NA

Total 1.0 1.0 NA1 NA NS 24 NS

Assumed either 

a preplant or an 

at plant 

treatment.

MINT/ 

PEPPERMINT/ 

SPEARMINT



Preplant soil 

incorporated

Aerial or 

ground/ 

broadcast

2.0 

EC, WDG

[2.0]

NS 2.0 [1]NS

1 90 24 NA No use in 

Mississippi.

19713-599, 

33658-26, 

34704-857, 

67760-28, 

84229-25, 

84930-7, 

OR940027
24

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

MRI NA due to 

once per crop cycle

application



Post-

emergence, 

Postharvest, 

Foliar

Chemigation, 

ground/ airblast

2.0 

EC

2.02.0 [1]

NS

2 90 NS No use in 

Mississippi.

Postharvest 

application 

retreatment not 

specified on 

some labels.

Total 2.0 4.0 4.0 2.03 90 24 NS

Labels allow 

one growing 

season 

application 

including pre-

plant and one 

post-harvest 

application per 

season.

MOSQUITO 

CONTROL; 

HOUSEHOLD/

DOMESTIC 

DWELLINGS 

OUTDOOR 

PREMISES;

RECREATION

AL AREAS



When 

needed; 

broadcast

Ultra low 

volume air and 

ground

0.01

EC 0.26 NA 26 NS NA NS 24 h

In Florida: 

Do not apply 

by aircraft 

unless 

approved by 

the Florida 

Dept of Ag.

Aerial 

applications 

may be made at 

altitudes 

ranging from 

75-300 ft (see 

labels for 

specifics).

For use by 

federal, state, 

tribal or local 

government 

officials or by 
25

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

persons 

certified in the 

appropriate 

category or 

authorized by 

the state or 

tribal lead 

regulatory 

agency.

NECTARINE



dormant/

delayed 

dormant

broadcast

airblast, 

handgun

3.0

WDG, EC

3.0 NA1 NA NS

24/

4d

10

83222-20 others 

at 2 lb a.i./a

Aircraft 2.0

WDG, EC

Updated to 

reflect spray 

drift mitigation.



pre-plant, 

foliar;

trunk 

spray/drenc

h or pre-

plant dip

Handgun, low 

pressure 

backpack, dip

2.5

(3.0/100 gal)

WDG, EC

2.5 NA1 NA 145

There is no 

application 

retreatment 

interval 

specified on 

some of the 

label. The 

application rate 

is provided as a 

dilution factor.

Total 3.0 5.5 NA2 NA

Some labels 

limit the 

amount a.i./A 

per year. 

Multiple types 

of applications 

can occur such 
26

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

as preplant, 

trunk drench 

and dormant, 

delayed 

dormant 

applications. 

Excludes 

nursery 

applications 

(See general 

“Fruits” listing)

NONAGRICUL

TURAL 

OUTDOOR 

BUILDINGS/ST

RUCTURES

to and around 

outside surfaces 

of nonresidential 

buildings and 

structures. 

Permitted areas of 

use include 

fences, pre-

construction 

foundations, 

refuse dumps, 

outside of walls, 

and other areas 

where pests 

congregate or 

Outdoor 

general 

surface/ Band 

(may be 

better if 

called 

perimeter)

Ground sprayer/ 

band sprayer

1.0 

EC NS NA NS NA NA NS NS
27

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

have been seen

NURSERY-

STOCK: : 

Ornamental 

nursery stock 

annuals, 

perennials and 

woody plants 

being grown in 

the field, in ball 

and burlap or in 

containers 

outdoor and in 

greenhouses

Dormant/ 

Delayed 

Dormant

high spray 3.0

EC 3.0 NA

1 NA 24 NS

Preplant

Ground boom, 

soil 

incorporated

4.0

EC, WP NS NA NS NA

foliar, soil 

directed

Tractor drawn 

spreader, push 

type spreader, 

belly grinder, 

gravity fed 

backpack, 

spoon

1.1 G

Total 4.0 CBD3

ONIONS



Post plant 

(seeding) 

Broadcast

Ground boom 1.0 

EC 1.0

NS

2

NS 60 24 NS



At plant, soil 

drench or 

basal spray

Ground boom 1.0 

EC, WDG, G 1.0 1 2 inch incorporation
28

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

Total 2.0 2.02 60 24 NS

ORNAMENTAL 

AND/OR 

SHADE TREES,

HERBACEOUS 

PLANTS



Foliar 

broadcast

Ground boom, 

air blast, 

handgun, low 

and high 

pressure hand 

wands

2.0 

EC, WP

1.0 

G, B

2.0 NA [2]

NS NA NS

24

NS

Some labels 

include a MRI 

of 7 days.



Dormant 

/Delayed 

Dormant

Handgun, low 

pressure and 

backpack

3.0 

EC 3.0 NA

1 NA NS7

Low volume 

spray permitted 

for concentrated 

solutions and 

lower rates.

ORNAMENTAL 

LAWNS AND 

TURF, SOD 

FARMS (TURF)



When 

needed, 

broadcast, 

soil or spot 

treatment

ground boom 

(WP only), high 

pressure hand 

wand

3.76

EC, WP 7.52 NA2 NA NS 24 NS

 NS

Tractor drawn 

spreader, push 

type spreader, 

belly grinder

1.0 B

2.0 NA2 NA NS 24 NS Bait is used for 

fire ant control.

ORNAMENTAL 

NON-

FLOWERING 

PLANTS



Foliar, 

broadcast, 

soil drench

Chemigation, 

ground boom, 

low and high 

pressure 

handwand, 

handgun, 

backpack 

sprayer, 

sprinkling can

0.007/gal 

ME NS NA 12 NA NA 24 NS

Application rate 

provided as a 

dilution factor.

Restricted 

use—

occupational 

only

ORNAMENTAL Foliar Ground boom, 2.0 

2.0 NA [1] NA NS 24 NS Several labels 
29

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

WOODY 

SHRUBS AND 

VINES

broadcast air blast, 

handgun, low 

and high 

pressure 

sprayer, 

backpack

EC, WDG

0.01 lb/gal 

EC

0.01 

lb/gal

NS do not restrict 

the application 

rate in lb a.i./A. 

Examples 

include 16.5 

lb/100 gal (228-

625) and 1.0 

lb/100 gal (829-

280).

Dormant/ 

delayed 

dormant

1.0 

EC

0.005 lb/gal 

EC

1.0 NA [1]

NS NA

Preharvest

Tractor drawn 

spreader, push 

type spreader, 

belly grinder

6.0 G

6.0 NA [1]

NS NA

Preplant, 

potted, 

bailed-and 

burlapped, 

containerized

groundboom, 

handgun, low 

and high 

pressure 

sprayer, 

backpack, 

drench

1.0

EC NS

1 NS1

Pretransplant groundboom 4.0 

WP

[48.0]

NS

4 124

Total

6.0G

4.0

WP

CBD CBD

PEACH

 dormant/ airblast 3.0 3.0 NA

1 NA 10 24/ NS 83222-20 (all 
30

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

delayed 

dormant

broadcast

EC

2.0

WDG

4d other labels 

restrict to 2 lb 

ai/a)

aircraft,

2.0

EC

2.0

WDG

NS

Updated to 

reflect spray 

drift mitigation.



Post-harvest

broadcast

airblast

2.5

(3.0/100 gal)

EC

2.5

NA1 NA NA NS

Permitted in 

Georgia and 

South 

Carolina

GA0400001, 

SC040001

SLN Expires:

aircraft

2.0

(3.0/100 gal)

EC

2.0

GA0400001, 

SC040001

SLN Expires:

Updated to 

reflect spray 

drift mitigation



pre-plant, 

foliar;

trunk 

spray/drenc

h or pre-

plant dip;

ground

handheld, 

backpack, 

drench/dip, 

handgun, and 

low pressure 

hand wand

2.5

(3.0/100 gal)

WDG

2.5 NA1 NA 145 NS

Some labels do 

not specify 

minimum 

retreatment 

interval. 

Total

3.0 5.5 NA3 NA NA 24 NS It is possible 

that multiple 

types of 

applications can 

occur such as 

soil, foliar 

and/or post-

harvest and 

3.0 8.0 NA3 NA NA 24 NS

Permitted in 

Georgia and 

South 

Carolina
31

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

dormant/ 

delayed 

dormant 

applications.

Excludes 

nursery 

applications 

(See general 

“Fruits” listing)

PEANUT

 Preplant

Aerial or 

ground/ 

broadcast

2.0 

EC, WDG

[4.0]

NS 4.0 [2]NS

2 NA 24 10

Do not apply 

aerial in 

Mississippi Assumes one 

crop cycle per 

year.



At plant, 

postplant

4.0 G[4.0]

NS 4.0

22 21 24 10

 At pegging

2.0 G

EC, WDG

[4.0]

NS 4.0

2

[2]

NS 21 24 10

Total

4.0 G

2.0 

EC, WDG

4.0 4.022 10 24 10

PEAR



dormant/

delayed 

dormant

broadcast

aircraft, airblast 2.0

WDG, EC 2.0 NA

1 NA NA 24 NA

Restricted 

use in 

California. 

83222-20 

allows 3.0 lb 

a.i./ A; 

however, this 

does not match 

the 2001 RED.



Post-harvest

broadcast aircraft, airblast

2.0

WDG, EC 2.0 NA1 NA NA 24 NS

Permitted in 

California, 

Oregon and 

Washington.
32

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

Total 2.0

WDG, EC 4.0 NA

2 NA NA 24 NS

Multiple types 

of applications 

may occur in 

within a year in 

California, 

Oregon and 

Washington 

such as a post-

harvest 

application and 

a dormant, 

delayed 

dormant.

Excludes 

nursery 

applications 

(See general 

“Fruits” listing)

PEAS



Preplant Seed 

treatment Seed Treatment

0.30

0.000625 lb/lb 

seed 

WP

0.28

0.00058 lb/lb 

seed 

EC

NS NS NS NS NS NS NS

There is a range 

of potential 

application 

rates depending 

on the number 

of seeds per lb 

and the number 

of seeds planted 

per acre. 

Seeding 

information 

provide by 

BEAD.

2
33

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

PECANS



dormant/

delayed 

dormant

broadcast

aircraft, airblast 2.0

EC, WDG 2.0 NA

1 NA 14

24

10 66222

-19 and 

66222-233



foliar;

broadcast

airblast 4.

3

EC, WDG

6.3 NA3 NA 14 10

Some labels 

require a 28 d 

PHI

aircraft 2.0

EC, WDG

Updated to 

reflect spray 

drift mitigation.



foliar; 

orchard 

floors 

broadcast

Ground boom, 

chemigation

4.3

EC, WDG 4.

3 NA2 NA 14 10

Total 4.3 12.6 NA6 NA 14 24 10

Considers 

multiple type of 

applications (e.g., dormant, 

foliar broadcast, 

and orchard 

floor) but excluding 

nursery 

For nursery 

applications 

(See general 

“Fruits” listing)

PEPPER

 Foliar Ground 

broadcast

1.0 

WDG

[8]

NS 8.0

[8]

NS

87 24 10 Permitted in 

Florida

FL040005; 1 

crop cycle per 

year.

PINEAPPLE

 Postplant Ground boom, 2.0 

6.0 6.03 NA 365 24 30 Permitted in HI090001 
34

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

broadcast EC Hawaii SNL Expires: 

March 29, 

2014.

Do not make 

applications 

beyond three 

months after 

planting. 

PLUM/

PRUNE



dormant/ 

delayed 

dormant;

broadcast

Aircraft, 

airblast

2.0

EC, WDG 2.0 NA

1 NA NA

24/

4d

10



foliar;

trunk 

spray/drenc h

handheld, 

backpack, 

drench/dip, 

handgun, and 

low pressure 

hand wand

2.5

3.0/100 gal

WDG

2.5 NA1 NA NA 10

Total 2.5 4.5 NA

2 NA

Excludes 

nursery 

applications 

(See general 

“Fruits” listing)

POULTRY 

LITTER



When 

needed,

animal 

bedding/litter 

treatment. 

Sprayer

0.07126 

a.i./1000 sq ft

3.1 

ME

NS NA NS NA NA NS 53883

-264, 

84575-3

PUMPKIN



Preplant Seed 

treatment Seed treatment

0.3

0.00058 lb /lb 

seed

[0.3]

NS

[1]

NS

[1]

NS

1 NS NS NS

California 

maximum 

single rate 

There is a range 

of potential 

application 
35

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

WP 0.000625 lb 

a.i./lb.

rates depending 

on the number 

of seeds per lb 

and the number 

of seeds planted 

per acre. 

Seeding 

information 

provide by 

BEAD.

4

RADISH

 Foliar Broadcast

ground

1.0 

EC NS

1 NS1 NS 24 NS permitted in 

Oregon

OR090012 on 

radish grown 

for seed.

Label valid 

until December 

31, 2012. (per 

registrant SLN 

still valid)

 Preplant

Soil 

incorporation

ground

3.0 

EC 12.0

341 NS NS 10



At plant/post-

plant

In furrow 

drench/ 

treatment

3.0 

EC

2.8 G

[15.0]

NS

3

[5]

NS

1

30, 

EC,

7, G

24 10

Only one 

granular 

application 

permitted.

Total 3.0 [22.0]

NS

2

[9]

NS

Only one 

preplant or at 

plant 

application is 

assumed.
36

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

RIGHTS OF 

WAY, ROAD 

MEDIANS

When 

needed, soil 

broadcast

Granular or low 

pressure wand

1.0 

EC, G, Bait

[2.0]

NS NA

2 NA NA NS7

Apply when 

needed

RUTABAGA

 Preplant

Chemigation, 

Groundboom

2.4

EC, WDG [4.8]

NS

2.4

[2]

NS

1 30 24 10

Aerial 2.0

EC, WDG 2.0

Updated to 

reflect spray 

drift mitigation.



At plant/post-

plant

In furrow 

drench/ 

treatment

2.4

EC, G WDG 4.8 2.4 [2]NS

17 24 10

Disallowed 

in California 

and Arizona.

Two crop 

cycles per year

Total 2.4 [9.6]

NS 4.8 [4]NS

2 24 10

SEWER 

MANHOLE 

COVERS AND 

WALLS

When needed Low pressure

0.31 

lb/manhole 

RTU

NS NA NS NA NA NA NS 3 pints product/ 

manhole

SEED 

ORCHARD 

TREES



foliar;

broadcast Ground boom 1.0EC 3.0

3.0 NS NA 30 247

62719-575, 

62719-615



High volume 

sprayer

2.5

0.01

a.i./tree

0.02 EC

2.5 NS [1]

NS NA 30 24

7

Cone worm 

treatment 

(62719-575 and 

62719-615)

Treatment of 

1000 trees per 

acre would 

results in an 

single 

application rate 

of 10 lb a.i./a.
37

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

DAS: 1000 is a 

bit high, 

typically for 

orchards 312 

trees per acre



foliar; stump 

treatment

backpack, 

drencher, low 

pressure hand 

wand,

0.3

EC 0.3

1.0 NS NA 30 247

62719-575, 

62719-615

Total 1.0 5.83 NS NA 30 247

The total 

number of 

applications 

assumed is 

either three

foliar 

applications or 

two foliar 

applications 

with one stump 

treatment.

SORGHUM 

GRAIN



Seed 

Treatment Seed treatment

[0.0009]

0.01-

0.0024 lb ai/ 

100 lbs seed 

EC

0.01 0.01 [1]

NS

1 NA NS NS

264-932



Preplant Soil 

Directed

Ground 

Spreader/T 

Band

1.5G

1.5 1.5 [1]

NS

1 60 24 10



Foliar/Post 

emergent

Ground, Aerial, 

Chemigation

1.0 

EC, WDG 1.5 [1.5]NS

[1]

NS

3 30 24 10 PHI varies 

across labels

Total 3.33.01 3.01 [3]3 30 24 10 One crop cycle 
38

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

G

1.0

EC, WDG

CBD per year.

SOYBEAN



foliar , post-

emergence 

soil broadcast

broadcast 

ground, aerial, 

chemigation

1.0 

EC, WDG

3.0 3.033 28 24 14 One crop 

cycle

per year.



At plant/post 

plant 

treatment;

soil band

ground boom

2.2G

1.0 EC

3.0 3.0 1 (G), 

3 (EC)

1 (G), 

3 

(EC)

28 24 10

Total

1.0

EC, WDG

2.2G

3.0 3.033

One crop cycle 

per year.

STRAW-

BERRIES 

 Pre

-plant

Aerial or 

ground/ 

broadcast

2.0

EC 2.0 NS

1 NS NA 24 10 No use in 

Mississippi 33658

-26

 Foliar

Aerial or 

ground/

broadcast, foliar 

spray

1.0

EC, WDG 2.0 NS

2 NS 21

24

10

Two 

applications (2 

lb ai) for all 

products per cc.

 Post harvest Ground directed 

spray

1.0

EC, WDG 2.0 NS

2 NS 21 14

Total 2.0 4.03

One preplant 

application and 

two foliar 

and/or 

postharvest 

application 
39

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

permitted per 

year.

SUNFLOWER

 At plant

Aerial/ground

2.0 G

3.0 3.0 [1]

NS 1 42

24

10 Per registrant 1 

cc per year

 Preplant 2.0 

EC, WDG

3.0 3.0 [1]

NS 1 42 10 2 inches min incorporation 



Post 

emergent or 

foliar

1.5 

EC, WDG

3.0 3.0 [2]

NS 2 42 10

Total 2.05.0 5.033

Assumed either 

an at plant or 

preplant 

application 

followed with 

two foliar 

applications. 

Onecrop cycle

per year

SWEET 

POTATO



Preplant, soil 

broadcast

Aircraft, ground 

boom

2.1

G, EC, WDG

2.1 NS11 125 24

LA090002,

MS080007, 

NC090001 

permits 60 

PHI

Aircraft 2.0

G, EC, WDG

Updated to 

reflect spray 

drift mitigation.

TOBACCO

 Preplant Aircraft, ground 

boom

2.0

EC, G, WDG 2.0 NS

117 24 NA

TRITICALE



Storage 

Commercial 

Slurry Seed 

Treatment

Seed treatment

0.003

0.0024 lb ai/ 

100 lbs seed 

EC

[0.003] NS[1]

NS

[1]

NS

[1]

NS NA

[10 ]

NS

[10]

NS

264-932

Seeding 

information 

provide by 

BEAD.

4
40

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

One crop cycle 

per year.

TURNIP

 Preplant

soil 

incorporation/ 

ground boom, 

handgun

2.3 

G, WDG

[4.6]

NS 2.3 [2]NS

1 30 24 10

Minimum 

incorporation: 

2 inches.

 Postplant

Soil 

incorporation/ 

ground boom, 

handgun

2.3

G, WDGP

[4.6]

NS 2.3 [2]NS 1 30 24 10

Minimum 

incorporation: 

2 inches.

Total 2.3 4.6 2.321 30 24 10

Assumed either 

a preplant or 

postplant 

application.

Twocrop 

cycles per year

UTILITIES

For use in and 

around 

telecommunicatio

ns, power, utilities 

and railroad 

systems 

equipment: 

Buried cables, 

cable television 

pedestals, cables, 

pad-mounted 

electric power 

transformers, 

telephone cables, 

When 

needed, 

broadcast

Product 

container

190.5 G

0.44 lba.i./100 

sq ft

(see 

comments)

NS NS NS NS NS NS NS

Applications 

permitted as 

needed. Reg. 

Nos. 13283-14, 

13283-17

Broadcast 

product onto the 

ground 

covering the 

area of the pad 

location, plus a 

two foot 

perimeter 

around the 

outside of the 
41

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

underground 

vaults, 

telecommunicatio

ns equipment, 

power and utilities 

equipment 

pad location.

WALNUTS



dormant/

delayed 

dormant;

broadcast

Aircraft, 

airblast

2.0

EC, WDG 2.0 NA

1 NA 14

24

10 62719

-301 (12 

lb a.i./A)



foliar;

broadcast

aircraft, 

airblast, 

chemigation

2.0

EC, WDG 4.0 NA

2 NA 14 10

Some labels do 

not specify 

retreatment 

interval.



foliar; 

orchard 

floors 

broadcast

Ground boom, 

chemigation

4.0

EC, WDG 4.0 NA

1 NA 14 10

Total 4.0 10.04

Excluding 

nursery 

applications; 

includes 

dormant, foliar 

broadcast, and 

orchard floor.

For nursery 

applications 

(See general 

“Fruits” listing)

WIDE AREA/ 

GENERAL 



when needed, 

Broadcast Ground sprayer 0.5084 lb ai/100 gal 

[1.02]

NS NA

2 NA NA NS NS 66222-19 
42

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation

1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)3REI (hours)3MRI (days)3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC

2

lb a.i./A

Per 

Year

Per 

CC

2

OUTDOOR 

TREATMENT 

For ants and other 

misc. pests.

EC

when needed, 

Drench Drench

1 NS NA NS NA NA NS 228-624

[1]

8.2 lb a.i/100 

gal EC

NS NA NS NA NA NS 228-625 

Total [1] NS NA NS NA NA

WHEAT



Slurry Seed 

Treatment Seed treatment

0.003

0.0024 lb ai/ 

100 lbs seed 

EC

[0.006]

NS

1

[2]

NS

1 NA NA NA

Only for use 

in AZ, CA, 

CO, ID, KS, 

MN, MO, 

NE, NM, 

NV, ND, 

OK, OR, 

SD, TX, UT, 

WA and WY

Seeding 

information 

provide by 

BEAD.

4



Foliar, soil 

treatment

Ground, 

broadcast

0.5

EC

[8.0]

NS 4.0 [2]NS

1

14/

28

24 

14

PHI: 14 forage 

or hay, 28 grain 

or straw



Post-

emergence 

foliar

Ground, Aerial, 

Chemigation

1.0 

EC

[4.0]

NS 2.0 [4]NS

2

14/

28 NS

Label states 1.0 

lb ai/A for 

cereal leaf 

beetles and then 

state max rate 

0.5 lb ai/A in 

restriction). 

Some labels 

restrict no more 

than 2 

applications per 

crop/season

PHI 14 forage 

or hay, 28 grain 

or straw

Total [1]

4.0

[12.006 ]

[6.003]

5.0

[8]

NS

[4] 2MO otherwise 

2.0 plus seed 
43

Crop/Site

Residential

Agricultural

Forestry

Timing;

Application 

Type 

Method/

Equipment

Maximum 

Single 

Application 

Rate by 

Formulation1

(lb a.i./A)

Maximum 

Application Rate

Maximum 

Application 

Number 

PHI (days)

3

REI (hours)

3

MRI (days)

3

Geographic 

Restrictions Comments

Per 

Year

lb 

a.i./A

Per 

CC2

lb a.i./A

Per 

Year

Per 

CC2

EC treatment

WOOD 

PROTECTION 

TREATMENT 

TO 

BUILDINGS/

PRODUCTS 

OUTDOOR

When 

needed, 

Wood 

surface 

treatment

Low pressure 

handwand, 

backback 

sprayer, 

paintbrush

16.65 

lb/10,000 sq ft

0.17 lb a.i./gal

EC

NS NA NS NA NS NS NS

0.08 lb ai/gal

EC, RTU EC, 

ME

NS NA NS NA NS NS NS

Apply 1 gal per 

100 sq ft of 

wood

1. EC - emulsifiable concentrate; WDG – water dispersible granular in water soluble packet; WP – wettable power in water soluble packet; B – bait (granular), G – granular; ME –

microencapsulated; RTU – ready to use.

2. Reported as per crop cycle or per season

3. PHI – Preharvest interval; REI – reentry interval; MRI – Minimum retreatment interval

4. Becker, J.; Ratnayake, S. Acres Planted per Day and Seeding Rates of Crops Grown in the United States, U.S. EPA OPP/BEAD, 2011; example calculations provided below:

Beans: 0.00058 lb a.i./lb seed / 960 seeds/lb seed x 418,176 seeds/A [pgs. 19, 81 (beans, succulent)]

Corn: 0.000625 lb a.i./lb seed / 1,800 seeds/lb seed x 59,739 seeds/A [pgs. 24, 81 (corn, sweet)]

Cotton: 0.00116 lb a.i./lb seed / 4,500 seeds/lb seed x 85,00 seeds/A [pgs. 13, 81]

Cucumber: 0.00058 lb a.i./lb seed / 12,000 seeds/lb seed x 80,418 seeds/A [pgs. 25, 81]

Peas: 0.000625 lb a.i./lb seed / 1,361 seeds/lb seed x 653,400 seeds/A [pgs. 34, 82]

Pumpkin: 0.00058 lb a.i./lb seed / 1,600 seeds/lb seed x 7,260 seeds/A [pgs. 37, 82]

Sorghum: 0.001 lb a.i./lb seed / 11,000 seeds/lb seed x 100,000 seeds/A [pgs. 16, 39]

Triticale: 0.003 lb a.i./100 lb seed / 109 lb seed/A [pg.16]

Wheat: 0.003 lb a.i./100 lb seed /116 lb seed/A [pg. 16]

[ ] indicate assumptions that are made when the information is not specified but can be inferred