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Table of Contents

Executive Summary ........................................................................................................................ 3

1 Introduction ............................................................................................................................. 4

2 Use Patterns ............................................................................................................................ 5

2.1 Label Requirements Related to Spray Drift ..................................................................... 6

2.2 Typical Uses ..................................................................................................................... 7

2.3 Use of Aerial Application ................................................................................................ 7

3 Context .................................................................................................................................... 9

3.1 Incident Rates ................................................................................................................. 10

3.2 Stewardship .................................................................................................................... 11

4 Methods and Inputs ............................................................................................................... 12

4.1 Approach ........................................................................................................................ 13

4.2 Drift Modeling ................................................................................................................ 14

4.3 Hazard Inputs ................................................................................................................. 16

4.4 Exposure Inputs .............................................................................................................. 18

4.6 Risk Reduction Options ................................................................................................. 21

5 Results ................................................................................................................................... 23

5.1 Drift Estimates ................................................................................................................ 24

5.2 Risk Estimates From Inhalation Exposure ..................................................................... 29

5.3 Combined Risk Estimates From Lawn Deposition Adjacent to Applications ............... 32

6 Issues For Consideration ....................................................................................................... 39

7 Conclusions and Recommendations ..................................................................................... 41

Appendix A: Summary of Label Use Patterns 

Appendix B: Lorsban 75WP Label Excerpt 

Appendix C: Summary of Use Information 

Appendix D: AgDrift Screen Shot 

Appendix E: Results of Drift Modeling 

Appendix F: Inhalation Risk Calculations 

Appendix G: Risk Calculations From Deposited Residues on Lawns 
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Executive Summary

This analysis supplements the June 2011 Chlorpyrifos Preliminary Human Health Risk 

Assessment for Registration Review (HHRA) where limited monitoring data indicate risks to 

bystanders.1 Bystanders are those who live on, work in or frequent areas adjacent to treated 

fields. Spray drift can be characterized as the movement of aerosols and volatile components 

away from the treated area as a result of the application process. Bystanders can be exposed to 

spray drift directly or by contact with resulting deposited residues. Spray drift of chlorpyrifos 

was examined using Tier I and II spray drift models to evaluate the impact of varied application 

conditions.2 The degree of such impacts is governed by many processes (e.g., application 

method, nozzles used, release height) and the conditions at the time of application (e.g.,

windspeed and direction). Timing and frequency of exposures are also important. Chlorpyrifos 

is generally not applied multiple times in a year on a per acre basis, so spray drift is sporadic for 

adjacent properties (most applications are once per year). Residues also quickly degrade on plant 

surfaces. As such, single day exposures for bystanders are the focus of this analysis. 

Chlorpyrifos labels indicate sprays should not directly or through drift contact workers or other 

persons. Some also indicate sprays should not drift to structures people occupy, associated 

property, parks or recreation areas. Buffer zones up to 150 feet from the field edge are also 

required to protect aquatic areas. Ensuring these provisions are adhered to is primarily the 

responsibility of the user, which is reinforced through training, compliance assistance, and 

enforcement actions, if needed. The degree of drift in field situations is difficult for users to 

ascertain at times because observing drift to prevent all deposits and potential exposure situations 

can be complex and at times physically impossible. These issues have been discussed extensively 

in efforts to develop good management practices and spray drift labeling language.3 

This analysis focuses on chlorpyrifos applications that comply with application rates and 

methods identified on product labeling. As explained below, such applications may still result in 

drift. This analysis did not focus on circumstances leading to the majority of reported drift 

incidents since it is EPA's assessment that the majority of reported incidents resulted from 

applications that were plainly not in compliance with label requirements. 

Results indicate spray drift from application of chlorpyrifos using current label requirements 

generally results in risk estimates of concern for locations immediately adjacent to treated fields. 

While risk estimates are of concern adjacent to a field edge for all application methods, 

implementing buffer zones as appropriate for residential areas (e.g., similar to those in place to 

address aquatic risk concerns) could alleviate many of the potential human health risks.4

 An 

additional analysis shows shorter buffers coupled with drift reduction technologies and practices 

could further alleviate risks in some cases (e.g., lower application rates, larger droplets, and 

larger swath displacement). 

 

1 www.regulations.gov (docket ID EPA-HQ-OPP-2008-0850-0025) 2

 Peer reviewed modeling approaches were used http://www.epa.gov/scipoly/sap/tools/atozindex/spray.htm and, 

http://www.epa.gov/pesticides/science/residential-exposure-sop.html. 3 http://www.epa.gov/pesticides/factsheets/spraydrift.htm provides links to pertinent sources of information 4 http://www.cdms.net/ldat/ld02A011.pdf (pg 3) as an example 
4 of 60 

 

1 Introduction 

Chlorpyrifos is an organophosphate (OP) insecticide, acaricide, and miticide that controls many 

foliar and soil borne insect pests.5 Chlorpyrifos was first registered in 1965 for use on a variety 

of food and feed crops. As chlorpyrifos use expanded in agriculture, it also grew in the 

residential marketplace. Residential use has since diminished because such uses, for the most 

part, except those with a low exposure potential, were voluntarily cancelled and removed from 

labels in 2001. Even given this trend, exposures can occur in residential environments or other 

areas frequented by the general public through spray drift. Exposures can also occur as a result of 

volatilization of chlorpyrifos from agricultural crops or other areas after application. These 

exposure pathways were addressed in the 2011 HHRA using empirical monitoring data. This 

analysis supplements the previous risk assessment by using spray drift models to estimate the 

potential exposure from a number of different chlorpyrifos application scenarios. This approach 

allows for a broader understanding of the potential for risk associated with chlorpyrifos spray 

drift. 

Off-target movement of chlorpyrifos can occur via many types of pathways and its magnitude is 

governed by many processes. Sprays that are off-target can directly lead to exposure. They can 

also deposit on surfaces where contact with residues can lead to exposure (e.g., children playing 

on lawns next to treated fields). The potential exposure and risk estimates from these residues 

can be calculated using drift modeling and methods employed for typical residential risk 

assessments. There is precedent for using this approach as it mirrors the methods used in a 

response to a petition to cancel 14 pesticides as well as methods used to develop buffer zone 

estimates for use of two organophosphate insecticides on orchard crops in the Pacific 

Northwest.6

 

Volatilization can occur during or after application. It can result from aerosols evaporating 

during application, while deposited sprays are still drying, or after application as dried deposited 

residues volatilize (e.g., possibly via co-distillation). This document addresses only those 

exposures associated with spray drift and whatever volatilization is anticipated to occur during 

application. 

AgDRIFT (V2.1.1) and AgDISP (V8.26) were used to provide deposition values for residential 

lawns, as a fraction of the application rate, at different distances downwind of a treated field. 

AgDRIFT (V2.01) was used to estimate air concentrations at different distances downwind of a 

treated field. Distances up to 125 feet away were considered in both of these analyses. Both the 

drift and exposure methods used to quantify the potential risks from pesticide spray drift were 

previously peer reviewed through the FIFRA Scientific Advisory Panel).6

 

5 http://www.cdms.net/manuf/mprod.asp?mp=11&lc=0&ms=3691&manuf=11 (see Dursban or Lorsban labels) 6 http://www.epa.gov/scipoly/sap/tools/atozindex/residentexp.htm, 

http://www.epa.gov/scipoly/sap/meetings/2009/100609meeting.html, and 

http://www.epa.gov/scipoly/sap/tools/atozindex/spray.htm
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In addition to spray drift deposition and air concentration determinations, other aspects of this 

analysis are based on methods commonly used for evaluating risks from pesticides used on turf 

because the risk concern is based on drift depositing on lawns adjacent to treatment sites. This 

scenario is utilized because it represents the highest potential for exposure associated with spray 

drift and it also considers different human lifestages, including those associated with children at 

different developmental stages.7

 Data from a chlorpyrifos study that determined turf residue 

levels and dissipation rates after application were also available.8

 These data were used in 

conjunction with the standard residential methods to estimate exposure from treated turf. Finally, 

the endpoints and points of departure (PODs) used for this analysis are similar to those used in 

the 2011 HHRA. The PODs used were defined based on route-specific studies that can be 

considered of high quality and suitable for risk assessment purposes. In some cases, PODs differ 

slightly from the 2011 HHRA because these values are more appropriate for evaluating 

infrequent, single day exposures like those anticipated with spray drift.9 

Section 2, Use Patterns provides an overview of how chlorpyrifos is used with a specific focus 

on spray drift. Section 3, Context includes information on related topics such as the nature and 

frequency of incidents and efforts to develop best management practices for spray drift that must 

be considered when interpreting the results of this analysis. Section 4, Methods and Inputs

provides more details on the specific calculations and values used to define risks from 

chlorpyrifos spray drift. The calculated risk estimates are provided in Section 5, Results. Issues 

that should be considered, specific to how the risk estimates from spray drift were calculated, are 

presented in Section 6, Issues for Consideration. Section 7, Conclusions and 

Recommendations, presents the conclusions of this assessment and describes potential 

mitigation measures that could be adopted and their impact on the calculated risk estimates. 

2 Use Patterns 

Chlorpyrifos is a broadly used organophosphate insecticide currently registered for the control of 

various insects. Registered use sites include: food crops including fruits, nuts, vegetables, and 

grains and non-food crops such as golf course turf, industrial sites, greenhouses, nurseries, sod 

farms, and wood products. Public health uses include aerial and ground-based fogger treatments 

to control adult mosquitoes. There is a wide range of currently registered chlorpyrifos application 

rates. In general, current maximum chlorpyrifos application rates do not exceed 4 lb ai/a 

nationwide; however, single application rates greater than 4 lb ai/a are currently permitted for 

some specific use patterns. For example, a single chlorpyrifos application of 6 lb ai/a is permitted 

on citrus in a limited number of counties in California. In addition there are also spot or trunk 

drench applications that may result in single application rates higher than 4 lb ai/a. A summary 

of the chlorpyrifos use patterns including application rates is presented in Appendix A. 

Other information related to how chlorpyrifos is used germane to the exposure potential from 

spray drift and characterizing potential mitigation options is presented below. Specifically, 

 

7 http://www.epa.gov/pesticides/science/residential-exposure-sop.html 8

 (Stafford et al,1999) Determination of Dislodgeable Foliar Residues on Turf Treated With Formulations 

Containing Chlorpyrifos (EPA MRID 44829601). 

9

 Should changes in the hazard evaluation occur they will be reflected in this analysis as appropriate (e.g., impact of 

findings of 2012 FIFRA SAP, http://www.epa.gov/scipoly/sap/meetings/2012/041012meeting.html). 
6 of 60 

Section 2.1 summarizes the requirements to ensure applications are made using a best 

management practices approach. Typical chlorpyrifos use practices are presented in Section 2.2.

Section 2.3 discusses the significance of aerial application as a method for using chlorpyrifos 

(e.g., prevalence on certain crops). 

2.1 Label Requirements Related to Spray Drift 

Current chlorpyrifos labels provide guidance for users on how to reduce the potential for spray 

drift under actual use conditions. Many of these criteria have long been recognized in the 

scientific literature as key factors related to how changes in application technology will impact 

spray patterns and the subsequent drift. The Dow AgroSciences product Lorsban Advanced label 

has been used to illustrate this guidance (EPA Reg. No. 62719-591). All current chlorpyrifos 

labels contain similar labeling language. This guidance serves as the basis for the drift modeling 

described below. The label language under the section, Spray Drift Management, is included as 

Appendix B. A few key elements are summarized below. 

The label prohibits drift from contacting people, the structures they occupy, and associated 

property at any time. The label also indicates avoiding drift is the responsibility of the applicator 

and that they should consider equipment and weather related factors when making applications. 

Buffer zones are also specified for applications around aquatic areas as described in Table 1. 

 

 Table 1. Current Buffer Zones for Chlorpyrifos Around Aquatic Areas 

Application Method Required Buffer Zone 

(feet) 

Groundboom 25 

Chemigation 25 

Airblast 50 

Aerial (fixed wing or helicopter) 150 

The Lorsban label also provides best management practices to reduce spray drift. Guidance is 

provided that describes how applicators should consider the conditions of the site when deciding 

how and when to make an application (e.g., presence of possible atmospheric inversion 

conditions, location of sensitive sites such as residences relative to site location). Additionally, 

the label provides information for specific application methods. Some examples include: 

• For Aerial Applications - Nozzles must produce a medium or coarser droplet size (255 

to 340 microns volume median diameter) per ASABE Standard 572 under application 

conditions and applications must not be made at a height greater than 10 feet above the 

top of the target plants unless required for aircraft safety. 

•For Groundboom Applications - Choose only nozzles and pressures that produce a 

medium or coarse droplet size (255 to 400 microns volume median diameter), per 

ASABE Standard 572 and do not apply product when wind speed exceeds 10 mph. 
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•For Orchard Airblast Applications - Apply only when wind speed is 3 to 10 mph and 

spray the outside rows of orchards from outside in, directing the spray into the orchard 

and shutting off nozzles on the side of the sprayer away from the orchard. 

2.2 Typical Uses 

This section provides use information such as the application rate and number of applications for 

national-level total chlorpyrifos used (in all formulations and with all application methods 

combined) on use sites where information was available. Details are available in Appendix C. 

Approximately 8 million pounds of chlorpyrifos are used annually in agriculture. Total 

chlorpyrifos usage varies widely with average percent crop treated (PCT) - a measure of the area 

treated with chlorpyrifos in the survey years (2006-2010, unless otherwise noted) - as low as 1% 

for several crops and as high as 62 % (for apples) (Appendix C). The five crops with the highest 

PCT are apples (62% PCT), broccoli (55%), walnuts (46%), onions (45%), and cauliflower 

(41%). 

Corn and soybean are the two crops with highest total amount of chlorpyrifos used in terms of 

average pounds applied – both show over 1,000,000 lb used across the years (Appendix C). 

Crops that have low total chlorpyrifos usage (arbitrarily defined as less than 20,000 pounds used, 

on average) but show relatively large area treated (arbitrarily defined as greater than 25% 

average percent crop treated, or PCT) include strawberries, asparagus, and cauliflower. 

Nineteen crops (out of a total of 39 crops surveyed) show average application rates that are 

approximately 1 lb ai/a. These crops are apples, almonds, broccoli, cabbage, cauliflower, 

cherries, grapefruit, hazelnuts, lemons, oranges, peaches, peanuts, pears, plums/prunes, 

pumpkins, squash, sweet corn, tobacco, and walnuts. The frequency of application, on average, 

for most crops is one time per year. In a few crops, the annual average frequency of application 

is approximately two times per year. This information supports the supposition that focusing on 

single day exposures on a per acre basis from spray drift is an appropriate premise.

2.3 Use of Aerial Application 

The usage information on aerial applications was obtained from a private marketing research 

database that stores results of annual market surveys that cover the continental United States and 

the majority of crops produced (Table 2).10 These should be considered in the context of the 

percent crop treated information described above in Section 2.2. The surveys utilize sampling 

procedures that result in statistically valid results for most crops. However, due to limited sample 

size, precision is reduced for some crops and for crops with limited use of chlorpyrifos. Data 

from 2006 to 2010 were used in this analysis, and the results presented are an average of the five 

years of data. The rate range information for each crop was obtained by querying the proprietary 

source database. 

 

10 A similar analysis was conducted in order to evaluate the import of ground applications. A table analogous to 

Table 2, excerpted from that memo, is included as part of Appendix C for informational purposes. It is not 

included here since ground applications are predominant and they do not represent the most significant risk 

concern, as will be detailed below. 
8 of 60 

The application method rate range data was summed over the five years for each rate range in 

which applications were reported and the percentage of applications in each rate range was 

calculated for aerial applications. The maximum observed rate for aerial applications is the last 

column in Table 2. The maximum label rates may be higher than these maximum observed so it 

is possible that higher rates might have been used. However the maximums reported were the 

highest rates observed over a five year period so a significant number of applications at higher 

rates are unlikely. 

The approximate percentage of the crop treated by air was calculated. This calculation assumes 

that the average number of applications were the same for aerial applications as for all 

applications. This assumption is justified because the average number of applications for most 

crops is once per year. 

For most crops the acreage treated with aerially applied chlorpyrifos represents only a small 

percentage (<10%) of the total crop acreage. Nevertheless, for some crop aerial applications are 

important (e.g., 80% of sunflower chlorpyrifos applications are made by air). Nine percent of 

asparagus acres were estimated to have been treated by air. An estimated five percent of 

sunflowers and sweet corn were treated with aerial applications of chlorpyrifos and for all other 

crops less than five percent of planted acres received aerial applications of chlorpyrifos. 

Maximum observed application rates varied significantly among crops, with some receiving 

maximum application rates of one pound of active ingredient per acre while maximum 

application rates for lemons and oranges were 5.7 and 6 pounds per acre respectively. Citrus 

crops (alone) have an additional label, limited for use only in the San Joaquin Valley of 

California (Fresno, Tulare, Kern, Kings, and Madera counties), that permits use of rates up to 6 

lb ai/a; all other citrus has a maximum application rate of 4 lb ai/a.

Table 2. Aerial Applications of Chlorpyrifos to Crops (2006-2010) 

Crop 

% of 

Applications 

Applied by 

Air 

% of Total 

Crop 

Acreage 

Treated by 

Air 

Average Lbs 

AI Year 

Applied by 

Air 

Average 

Application 

Rate (lb ai/a) 

for Aerial 

Applications 

Maximum 

Rate (lb ai/a) 

Observed for 

Aerial 

Applications 

(rounded up) 

Alfalfa 31 1 130,000 0.5 1.0 

Almonds 14 3 60,000 1.9 2.0 

Apples 5 3 15,000 1.0 2.0 

Asparagus 24 9 4,000 1.0 1.0 

Beans (Snap) <1 <1 <100 0.8 0.8 

Broccoli <1 <1 <100 1.0 1.0 

Cabbage <1 <1 <100 1.0 1.0 

Cauliflower 1 1 200 0.9 1.0 

Cherries 2 1 700 0.9 1.0 

Corn 2 <1 20,000 0.8 2.0 

Cotton 8 <1 40,000 0.8 1.0 

Cucumbers None 

Dry Beans 17 <1 2,000 0.5 1.0 

Grapefruit 2 <1 700 1.5 1.5 
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Crop 

% of 

Applications 

Applied by 

Air 

% of Total 

Crop 

Acreage 

Treated by 

Air 

Average Lbs 

AI Year 

Applied by 

Air 

Average 

Application 

Rate (lb ai/a) 

for Aerial 

Applications 

Maximum 

Rate (lb ai/a) 

Observed for 

Aerial 

Applications 

(rounded up) 

Grapes, 

Raisin None 

Grapes, Table <1 <1 150 1.0 1.0 

Grapes, Wine None 

Hazelnuts 32 4 1,000 1.0 2.0 

Lemons 4 2 3,000 2.7 5.7 

Onions <1 <1 <100 1.0 1.0 

Oranges 7 2 30,000 1.8 (2.5) 6.0 

Peaches 5 1 2,000 1.1 3.0 

Peanuts 2 <1 2,500 1.4 1.8 

Pears 3 1 800 2.0 2.0 

Peas (Fresh) None 

Pecans 15 4 40,000 0.9 (1.5) 2.0 

Peppers 7 <1 <100 0.3 0.3 

Plums/Prunes None 

Potatoes 8 <1 200 1.0 1.0 

Pumpkins None 

Sorghum 18 <1 2,000 0.5 0.8 

Soybeans 16 1 600,000 0.4 (0.8) 1.0 

Squash 1 <1 <100 3.0 3.0 

Strawberries None 

Sugar Beets 13 1 10,000 0.6 1.2 

Sunflowers 80 5 50,000 0.5 (0.7) 1.0 

Sweet Corn 43 5 30,000 0.6 2.0 

Tobacco None 

Walnuts 6 3 25,000 1.9 (2.0) 3.0 

Wheat, Spring 38 1 50,000 0.4 (0.5) 1.0 

Wheat, 

Winter 30 1 110,000 0.4 (0.5) 1.0 

Note: For some crops there are single/very few observations so this should be considered in the 

interpretation of the information presented in this table. 

3 Context 

In late 2009, a policy paper focusing on the development of updated methods for conducting risk 

assessments for workers and for those who live in proximity to agricultural pesticide use sites 

was released.11 Status updates of this policy have also been presented at several meetings of the 

Pesticide Program Dialogue Committee (PPDC). A public comment period was utilized to solicit 

input from stakeholders.12 A key aspect of this policy is that the Agency committed to 

 

11 http://www.epa.gov/pesticides/health/worker-rsk-assmnt.html, also see www.regulations.gov docket ID EPAHQ-OPP-2009-0889-0002 12For example, refer to http://www.epa.gov/oppfead1/cb/ppdc/2011/april/april2011.html 
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developing an approach for characterizing potential exposure and risk estimates associated with 

off-target chemical movement via spray drift. The plan for implementing this policy is through 

the Registration Review process with an initial focus on uses with a perceived high risk potential. 

There are many ways the potential risk associated with pesticide spray drift can be considered in 

the regulatory process. It is important to consider all mitigation alternatives in order to be 

expedient, thorough, and cost effective (e.g., changes to application rates, changes in application 

parameters, buffer zones). For example, if a pesticide can be used to treat lawns directly without 

a risk estimate of concern, then calculating risks via spray drift, given similar application rates, 

may not be needed because the risks from drift could be the same or lower than that associated 

with the direct application to lawns. In other cases, like with chlorpyrifos, uses in the residential 

marketplace are restricted. In these situations, many factors are important for describing the 

potential for risks via drift including: application methods for particular crops, prevalence of use 

on a particular crop or application method, need for a pesticide relative to the pest of concern, 

environmental fate characteristics of a pesticide, and the toxicological characteristics of the 

pesticide. Many of these factors were considered in this analysis and are described. 

In addition to label stipulations that dictate how a pesticide can be used and the factors that can 

impact exposures via drift (described above in Section 2.1), other relevant information should be 

considered including a discussion of incident rates and causes. Incidents are important for 

characterizing the results of this analysis and are summarized based on the 2011 human health 

risk assessment in Section 3.1. The Agency and stakeholders have also been working to develop 

guidance related to managing spray drift using a best practices approach as described below in 

Section 3.2.

13 These efforts have prompted methods development for evaluating the performance 

of drift reduction technologies, an important basis for developing viable mitigation options. 

3.1 Incident Rates 

The conclusions of the most recent evaluation of the incidents associated with chlorpyrifos use 

indicate incidents have declined substantially among residential users. This would be expected 

given that most residential uses, except products that are known to produce lower levels of 

exposure, were voluntarily cancelled and removed from labels at the end of 2001.14 At the same 

time, occupational incident rates have remained fairly constant over time. The conclusions that 

were made associated with the 2011 HHRA indicate that the overall numbers and severity of 

incidents associated with chlorpyrifos use do not represent an immediate public health concern 

(e.g., serious non-reversible effects or deaths have not been seen as a result of chlorpyrifos drift). 

For the most part, they also have been caused by some manner of accident, operator error, or 

misuse (e.g., direct drift onto individuals in adjacent properties). These incidents differ from the 

drift calculations contained in this analysis because this analysis is based on the premise of label 

compliance. 

An evaluation of the National Institute for Occupational Safety and Health (NIOSH) Sentinel 

Event Notification System for Occupational Risks (SENSOR) information indicates issues 

 

13 http://www.epa.gov/pesticides/factsheets/spraydrift.htm 14 Recore and Oo (6/27/11) Chlorpyrifos: Tier II Incident Report (D388406) 
11 of 60 

associated with application appear to be the leading cause of the reported incidents involving 

chlorpyrifos, and responsible for 46% of those incidents reported from 1998 to 2007. The 

California Pesticide Illness Surveillance Program (PISP) also reported incidents associated with 

chlorpyrifos and it appears that drift from adjacent fields may be the cause of most of the 

reported incidents, unlike the SENSOR results. Spray drift is responsible for 56% of the cases 

reported to PISP from 1999 to 2008 (Figure 1). These incidents appear to be predominantly 

caused by drift contacting workers in fields adjacent to application events, which is a misuse 

based on current labels. An example includes a large 2007 incident (i.e., impact on large number 

of people) in Tulare County California associated with an airblast application of chlorpyrifos to 

almonds that impacted 28 workers who were working in an adjacent vineyard. 

Figure 1. Chlorpyrifos CA PISP Occupational Incident Summary 

A separate published analysis of drift incidents developed by NIOSH SENSOR investigators was 

also considered. This analysis indicated chlorpyrifos has a relatively high rate of incidents due to 

drift compared to the other pesticides addressed in the analysis.15 The authors indicated 49 out of 

1809 total cases (i.e., incidents) across all pesticides considered, where the cause was related to a 

single pesticide, could definitively be associated with exposure to chlorpyrifos. Ten of these 

were defined as being of moderate to high severity. Additionally, the authors noted the Tulare 

County incident described above was one of the 10 largest (i.e., most impacted people) incidents 

that occurred between 1998 and 2006 associated with spray drift. 

3.2 Stewardship 

As mentioned previously, the issue of spray drift, including developing a workable strategy for 

ensuring proper stewardship by users, has been a longstanding issue. These efforts have been 

formalized with the development of a draft PR notice (2009-X: Draft Pesticide Drift Labeling) 

which provides guidance to pesticide registrants on how to minimize drift and to protect people, 

non-target organisms, and the environment from adverse effects that may be caused by off-target 

 

15 Lee et al (2011) Acute Pesticide Illnesses Associated with Off-Target Pesticide Drift from Agricultural 

Applications — 11 States, 1998–2006, available at the following: 

http://ehp03.niehs.nih.gov/article/info%3Adoi%2F10.1289%2Fehp.1002843 
12 of 60 

pesticide drift.16 Current chlorpyrifos labels in many ways reflect the guidance outlined in the PR 

Notice 2009-X: Draft Pesticide Drift Labeling (see Appendix B). This includes overall guidance 

and recommendations for users to evaluate field and atmospheric conditions prior to and during 

application to ensure drift potential is minimized, particularly if there are areas nearby where 

people live or that could be considered sensitive. 

The draft PR Notice also outlines a plan for developing a Drift Reduction Technology (DRT) 

program. DRTs represent many possible application technologies that offer the potential to 

reduce drift from pesticide applications. Even though some of these techniques are widely 

recognized for reducing drift potential, limited information exists to quantify their actual 

effectiveness. The DRT provides application equipment and spray adjuvant manufacturers with a 

test method and a process for voluntarily testing and validating technologies for drift reduction 

potential. Tested technologies that are proven to significantly reduce drift will be assigned a 

rating and listed on the Agency’s website. Pesticide registrants will then be able to choose to 

recommend or require through pesticide product labels the use of validated DRTs for product 

application as a drift mitigation measure. EPA would consider label DRTs in its risk assessment 

and risk management decisions for the registration of these products. Labeling that cites DRTs 

could provide applicators who employ them more flexibility for modifying equipment and 

techniques in order to reduce drift potential for the specific use scenario. In effect, use of DRTs 

is a performance based approach that lets users employ the means at their disposal to reduce 

drift. Note: DRTs are described in detail in the draft PR Notice if further information is desired. 

Managing the drift potential from applications of chlorpyrifos is a key concern. In the PR Notice 

example, different application parameters are associated with different possible buffer distances. 

Such application parameters include varying the droplet size, allowing for different wind speeds 

at application, and fixing boom size relative to the wingspan of a plane or the helicopter rotor. 

The evaluation of drift potential for chlorpyrifos and the associated risk estimates were 

developed in a manner that is consistent with the draft PR Notice and the DRT performancebased construct. A series of possible drift reduction measures and the associated impacts were 

evaluated as part of this analysis as potential refinements to existing chlorpyrifos labels and may 

also be used as a guide for the development of data consistent with the DRT approach. 

Finally, many of the approaches that are currently being implemented as part of the overall 

strategy for reducing risk estimates associated with fumigants could also be effective for spray 

drift concerns.17 This is especially true of some of the qualitative measures like enhanced 

training, site specific management plans, and record keeping requirements. 

4 Methods and Inputs 

The approach used to evaluate the drift potential and associated risks for chlorpyrifos is based on 

standard methods and inputs. Section 4.1 describes the overall approach used for this spray drift 

assessment. Section 4.2 describes the models used, inputs, and limitations used to define the 

degree of drift associated with each application method evaluated. Section 4.3 summarizes the 

 

16 Available at www.regulations.gov (docket ID EPA-HQ-OPP-2009-0628-0002), also refer to (docket ID EPAHQ-OPP-2009-0628-0003) which provides examples to aid with interpretation of the PR Notice 17 http://www.epa.gov/opp00001/reregistration/soil_fumigants/implementing-new-safety-measures.html 
13 of 60 

toxicological characteristics of chlorpyrifos. Section 4.4 describes the values and methods used 

to calculate the exposures, once the drift potential was defined, for risk assessment purposes. 

Similarly, Section 4.5 describes the values and methods used for risk calculation purposes. 

Finally, Section 4.6 describes the possible DRTs that were considered as viable measures for 

reducing risk estimates and how they were integrated into the analysis in order to illustrate their 

potential impacts. 

4.1 Approach 

Pesticide spray drift can potentially impact those who are in proximity to application events 

through a variety of possible exposure pathways. In order to evaluate the drift potential and 

associated risks, an approach based on drift modeling coupled with techniques used to evaluate 

residential uses of pesticides was utilized. Essentially, a residential turf assessment based on 

exposure to deposited residues has been completed for each scenario, but the source term used to 

define these residues was determined in a different manner and is based on the amount of spray 

drift that may occur as illustrated in Figure 2. 

Figure 2. Conceptual Model of Exposure Pathway Associated With Spray Drift 

In this case, drift modeling was completed for a variety of application scenarios including 

different application equipment, spray types, and windspeeds. This approach is also protective of 

other possible types of pathways because the exposures used as the basis for these calculations 

are protective of other possible exposure situations (i.e., children’s exposure on treated turf 

yields significantly higher estimates than other possible scenarios). It also is a logical exposure 

pattern that would reasonably be expected to occur with a spray drift event, given that children 

could play on lawns adjacent to treated fields. Along with these types of exposures, airborne 

concentrations of chlorpyrifos were also defined and used to estimate risks from inhalation 

exposure. For this calculation, concentrations were defined in the breathing zone (area around 

the nose, ~ 3 to 5 ft above ground for this analysis) at the edge of the 50’ wide lawn closest to the 

treated field. Chlorpyrifos is generally not applied multiple times in a year on a per acre basis, so 
14 of 60 

spray drift is only anticipated sporadically on adjacent properties. As such, there is a focus in this 

assessment on single day exposures for individuals who may live on or frequent such properties. 

4.2 Drift Modeling 

Tier I spray drift analysis for aerial, ground, and orchard air blast applications of chlorpyrifos 

were completed using AgDRIFT18 (v2.1.1) to investigate the deposition pattern of chlorpyrifos 

downwind of a treated field.19 The AgDRIFT spray drift model is a Microsoft Windows-based 

computer program provided to the U.S. Environmental Protection Agency’s Office of Pesticide 

Programs as a product of the Cooperative Research and Development Agreement (CRADA) 

between EPA’s Office of Research and Development and the Spray Drift Task Force (SDTF). 

AgDRIFT predicts the motion of spray material released from aircraft, including the mean 

position of the material and the position variance about the mean as a result of turbulent 

fluctuations. AgDRIFT has undergone extensive validation including evaluation by a FIFRA 

Scientific Advisory Panel.20, 21 

Tier I AgDRIFT is a regression model developed from SDTF data including more than 300 

applications made in 10 field studies covering a range of application practices for each type of 

application (i.e., aerial, ground, and orchard air blast applications). AgDRIFT has been formally 

validated by comparing its predicted outputs to 180 SDTF field trials. These data were generated 

for aerial applications to a distance of about 800 meters downwind of the application field edge. 

These field trials were conducted using pesticide (i.e., dissolved or emulsifiable) in a liquid spray 

and therefore they may not fully represent spray drift resulting from encapsulated or granular 

based pesticide formulations. If these formulations (e.g., dispersible capsules or dispersible 

granular) are applied using a liquid carrier and the droplet size distribution is the same as those 

droplet size distribution included in AgDRIFT the resulting spray drift values are assumed to be 

the same. Granular formulations have different drift patterns than for liquid sprays, and as such 

need to be considered in a separate analysis. However, from a human health perspective, off-site 

movement of granular products would result in lower risk estimates than those for liquid 

products (e.g., less drift occurs and there is less exposure uptake for granules). 

Deposition rates were determined as a fraction of the application rate (i.e., how much of the 

target application rate is predicted to be deposited at various distances downwind of the treated 

field). This fraction of the application rate was adjusted based on the range of currently approved 

application rates (1 to 6 lb ai/a) for various crops to determine the average effective deposition 

 

18 A User’s Guide for AgDRIFT 2.1.1: A Tiered Approach for the Assessment of Spray Drift Pesticides (February 

2003). AgDRIFT V2.01 was used to model inhalation exposure concentrations. 19 AgDRIFT and AGDISP models: Models are available through Harold Thistle, US Forestry, hthistle@fs.fed.us. 20 U.S. Environmental Protection Agency. Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) Scientific 

Advisory Panel: Estimating Drinking Water Exposure as a Component of the Dietary Risk Assessment; Spray 

Drift Program, December 10-11, 1997. 21 U.S. Environmental Protection Agency. Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) Scientific 

Advisory Panel: Burholderia cepacia: Risk Assessment of a Biopesticide with Affinities to a Human 

Opportunistic Pathogen; A Consultation on Protocol Design to Assess Acute Neurotoxicity Studies following 

Oral Administration of Pesticides; Higher Tier Ecological Risk Assessment for Chlorfunapyr; Spray Drift - 

Review of Proposed Pesticide Deposition Curves to Adjacent Areas, July 20-23, 1999. 
15 of 60 

rate (lb ai/a) at various distances downwind of the treated field for each respective crop use. 

Input parameters used in the Tier I spray drift analysis are provided in Table 3. 

Table 3. Tier I AgDRIFT Input Parameters 

Parameter Value Comments 

Aerial 

Equipment Air Tractor AT-401 AgDRIFT default option 

Release Height 10 ft AgDRIFT default values 

Wind Speed 10 mph 

AgDRIFT default values / Chlorpyrifos labels (e.g., EPA Reg. 

No. 62719-591) restricts applications to periods when the 

wind speed is between 3-10 mph. 

Surface Roughness 0.0075 m (0.3 in) Default 

Temperature Not specified AgDRIFT Tier I ground models are based on regression 

equations developed on empirical data. 

Swath Displacement 

0.3702 (F2M) 

0.2781 (M2C) 

0.2149 (C2VC) 

AgDRIFT default values/ Chlorpyrifos labels (e.g., EPA Reg. 

No. 62719-591) restricts applications to droplet sizes greater 

than 255 μM. 

Droplet Size F2M, M2C, C2VC 

Chlorpyrifos labels (e.g., EPA Reg. No. 62719-591) restrict 

applications to droplet sizes greater than 255 μM; therefore, 

only droplet distributions with a mean diameter (Dv0.5) ≥ 255 

μM were selected for modeling. 

Fine to Medium (F2M): Droplet size (Dv0.5) = 255 μM 

Medium to Coarse (M2C): Dv0.5 = 341 μM 

Coarse to Very Coarse (C2VC): Dv0.5 = 439 μM 

Ground1

Equipment Low Boom (LB) 

High Boom (HB) AgDRIFT default options 

Release Height LB: 0.508 m (20 in) 

HB: 1.27 m (50 in) AgDRIFT default values 

Application Efficiency LB: 99.27 

HB: 99.22 AgDRIFT default values 

Wind Speed Not specified AgDRIFT Tier I ground models are based on regression 

equations developed on empirical data. 

Surface Roughness Not specified AgDRIFT Tier I ground models are based on regression 

equations developed on empirical data. 

Temperature Not specified AgDRIFT Tier I ground models are based on regression 

equations developed on empirical data. 

Swath Width 13.72 m (45 ft) AgDRIFT default value 

Droplet Size F2M/C 

Chlorpyrifos labels (e.g., EPA Reg. No. 62719-591) restrict 

applications to droplet sizes greater than 255 μM; therefore, 

only droplet distributions with a mean diameter (Dv0.5) ≥ 255 

μM were selected for modeling. 

Fine to Medium/Coarse (F2M/C): Droplet size (Dv0.5) = 341 μM (see AgDrift GUI screenshot in Appendix D) 

1. Regression equations were developed from SDTF field study results with ground boom equipment. 

Orchard Air Blast1

Equipment Not specified AgDRIFT Tier I orchard air blast model are based on 

regression equations developed on empirical data. 

Release Height Not specified AgDRIFT Tier I orchard air blast model are based on 

regression equations developed on empirical data. 

Application Efficiency 

Normal: 99.85 

Dense: 98.01 

Sparse: 97.69 

Vineyard: 99.73 

AgDRIFT default/ Chlorpyrifos labels (e.g., EPA Reg. No. 

62719-591) permits all these types of applications. 
16 of 60 

Parameter Value Comments 

Orchard: 98.63 

Wind Speed Variable AgDRIFT Tier I orchard air blast model are based on 

regression equations developed on empirical data. 

Surface Roughness Not specified AgDRIFT Tier I orchard air blast model are based on 

regression equations developed on empirical data. 

Temperature Variable AgDRIFT Tier I orchard air blast model are based on 

regression equations developed on empirical data. 

Swath Displacement Not specified AgDRIFT Tier I orchard air blast model are based on 

regression equations developed on empirical data. 

Droplet Size Not specified AgDRIFT Tier I orchard air blast model are based on 

regression equations developed on empirical data. 

Orchard Type2 Normal, Dense, Sparse, 

Vineyard, and Orchard 

AgDRIFT default/ Chlorpyrifos labels (e.g., EPA Reg. No. 

62719-591) permits all these types of applications 

1. Regression equations were developed from SDTF field study results with orchard blast equipment. 

2. Normal (Stone and Pome Fruit, Vineyard): This composite orchard combines grape and apple orchards 

Dense (Citrus, Tall Trees): This composite orchard combines almond, orange, grapefruit, small grapefruit (mist 

blower) and pecan orchards. 

Sparse (Young, Dormant): This composite orchard combines small grapefruit and dormant apple orchards. 

Orchard: This composite orchard combines apple, almond, orange, grapefruit, small grapefruit, pecan, and 

dormant apple orchards. 

Vineyard: This composite curve combines grape air blast sprayer applications and may not apply to other 

application equipment. 

 

4.3 Hazard Inputs 

Chlorpyrifos inhibits the enzyme acetylcholinesterase which leads to accumulation of 

acetylcholine and ultimately to neurotoxicity. In previous risk assessments, including the 2011 

risk assessment, the Agency concluded that data on the inhibition of cholinesterase (ChE) 

provided the most sensitive dose-response data for use in deriving points of departure (POD) for 

all durations, routes of exposure, and lifestages. The 2011 risk assessment included the typical 

scenarios used for risk assessment [acute dietary, chronic dietary, short-term (1-30 days), 

intermediate-term (1 month-6 months), and long-term (>6 months)]. This spray drift assessment 

relies on the endpoint selection from the 2011, with refinements to account for the focus on 

single day exposures from spray drift. Specifically, revisions were made to provide a more 

appropriate match between the duration of the toxicology endpoints to the duration of exposure. 

It is noted below where values varied from the 2011 risk assessment and the rationale for 

modifying them. 

The toxicity database of laboratory animal studies spans multiple routes of exposure (oral, 

dermal, and inhalation), animal species, lifestages, and durations. The database consists of 

studies that address different durations of exposure from a single exposure day (acute) to 

subchronic and chronic toxicity. The metabolism and pharmacokinetics of chlorpyrifos are wellcharacterized due to a variety of studies in different species and lifestages. The studies used to 

complete this assessment are of high quality and provide information that are appropriate for 

evaluating risks associated with single day exposures which are the focus of this assessment. A 

comparative cholinesterase assay (CCA) provides information on comparative sensitivity in adult 

and juvenile rats from acute and repeated exposures to chlorpyrifos. The POD for acute dietary 

risk was defined using the CCA study. The POD was derived using a benchmark dose (BMD) 
17 of 60 

approach; details of the BMD analysis can be found in the 2011 risk assessment. This POD was 

also considered appropriate for children’s mouthing behavior, as described later in this 

document, for a single day duration of exposure and is thus used here. 

Dermal exposures were evaluated in this assessment using a POD derived from a dermal toxicity 

study where sacrifices occurred at 4 and 21 days of dosing. It is notable that the results from the 

4 day sacrifice are similar to those from 21 days of dosing. In addition, a single dose dermal 

administration study conducted in human volunteers (Nolan, et al, 1982)22 indicates that effects 

can occur with only a single dermal dose. This means that the resulting risks using the 4-day 

study can be reasonably characterized as being representative of single day dermal risk estimates. 

Finally, inhalation risks were evaluated in the 2011 risk assessment using the POD derived from 

an acute inhalation toxicity study. In the previous assessment the POD was a HEC (Human 

Equivalent Concentration) calculated based on a 24 hour basis, but realistic exposure durations 

are much shorter, so the HEC was revised using a 2 hour duration. This 2 hour period was 

selected because it both represented a dosing time in the study and the potential duration of 

exposure from spray drift. Note: The impact of using a 2 hour duration is discussed in more 

detail below, including how the exposure source is considered after the first hour of application 

given how the drift estimates are modeled.

The endpoints and PODs used for this analysis are summarized in Table 4. A 1x FQPA safety 

factor (SF) was used in all cases, except for the 10X FQPA database uncertainty factor (UF) that 

was applied, to account for LOAEL to NOAEL extrapolation in the acute inhalation study 

because a NOAEL was not determined (LOAEL = Lowest observed adverse effect level and 

NOAEL = No observed adverse effect level). As discussed in the 2011 risk assessment, 

benchmark dose modeling of the acute inhalation study results was attempted, but the doseresponse data were not amenable for this type of analysis. 

Table 4. Toxicological Doses, Endpoints and Points of Departure for Chlorpyrifos Drift 

Risk Assessment 

Exposure 

Scenario

Point of Departure 

(mg/kg/day) 

Study and Toxicological 

Effects 

Acute Dietary (all 

populations) 

[Also used in this case to 

represent single day 

Incidental Oral 

 exposures] 

BMDL10 = 0.36 

UFA = 10x 

UFH = 10x 

FQPA SF = 1x 

Residential LOC for MOE=100 

Inhibition of RBC ChE in male and 

female rat pups. 

Weight of evidence from several 

acute oral studies: 

• CCA Study (MRID 

48139301) in the rat – PND 

11 males and females 

 

22 This study was reviewed by Human Studies Review Board in 2009. Materials are available at: 

http://www.epa.gov/osa/hsrb/jun-24-25-2009-public-meeting.htm. Additionally it should be noted that a 2008 

FIFRA Scientific Advisory Panel review indicated that this study provides useful information but is not 

appropriate for defining PODs http://www.epa.gov/scipoly/sap/meetings/2008/september/sap0908report.pdf . 
18 of 60 

Exposure 

Scenario

Point of Departure 

(mg/kg/day) 

Study and Toxicological 

Effects 

• Data on PND17 males , 

Moser et al.( 2006) 

• Qualitative support from 

Timchalk et al. (2006) and 

Zheng et al. (2000) studies 

Dermal Short- 

(1 – 30 days) and 

Intermediate-Term (1 to 

6 months) 

[Also used in this case to 

represent single day 

dermal exposures] 

NOAEL = 5 mg/kg/day 

UFA = 10x 

UFH = 10x 

FQPA SF = 1x (residential) 

Residential LOC for MOE=100 

Plasma and RBC ChE inhibition. 

21-day dermal study 

(NOAEL) and 4 day probe 

study (LOAEL) at 10 

mg/kg/day in adult rats 

(MRID 40972801). 

Acute Inhalation 

[A 2 hour HEC has been 

calculated which better 

reflects actual exposure 

conditions and the 

available dosing regimen 

from the study.] 

Inhalation LOAEL = 3.7 mg/m3 

HEC = 2.48 mg/m3 

UFA = 3x 

UFH = 10x 

FQPA UFDB = 10x (LOAEL to 

NOAEL extrapolation (residential)

Residential LOC for MOE=300 

Lung ChE inhibition. 

Special acute inhalation 

study (MRID 48139303). 

(Aerosol) 

[2, 4, and 6 hour sacrifice 

data were used to define the 

2 hour HEC] 

4.4 Exposure Inputs 

The exposure aspects of this analysis were completed based on the algorithms and input values 

specified in the recently revised (2012) Standard Operating Procedures For Residential Risk 

Assessment (SOPs). These are publicly available and address many broad issues pertinent to the 

development of risk assessments for pesticides used in a residential environment.23 These SOPs 

have been extensively peer reviewed and information on this process is also publicly available.24 

The calculations in this analysis were developed by considering the variety of possible pathways 

and all pertinent routes of exposure that could occur associated with spray drift. As a result of 

this process, two pathways were identified and used to evaluate the potential risks associated 

with spray drift including (1) inhalation exposures at discrete distances downwind of a treated 

field during application and (2) exposures from lawns adjacent to treated fields where drift 

occurs.

Inhalation exposure calculations were based on modeled air concentrations of chlorpyrifos in a 

vertical plane at specified distances downwind from the edge of a treated field. These represent 1 

 

23 http://www.epa.gov/pesticides/science/residential-exposure-sop.html and 

http://www.epa.gov/pesticides/science/EPA-OPP-HED_Residential%20SOPS_Feb2012.pdf 24 http://www.epa.gov/scipoly/sap/meetings/2009/100609meeting.htm, 

http://www.epa.gov/scipoly/sap/meetings/1999/092199_mtg.htm, and 

http://www.epa.gov/scipoly/sap/meetings/1997/090997_mtg.htm 
19 of 60 

hour time weighted average concentrations during application and can be defined only for aerial 

applications. In this case these outputs were used to estimate breathing zone exposure 

concentrations. Specifically, these concentrations were estimated using Tier II in the AgDRIFT 

model (V2.01) with varied spray/application rates. The only modifications to the Tier II inputs 

were altering the volatile and nonvolatile components of the spray solution variables to account 

for the specific application rates and chlorpyrifos products considered in this assessment. 

Vertical flux planes were considered at different distances ranging from the edge of a treated 

field to 125 feet downwind of the field. This analysis is only possible for aerial applications 

because both the ground boom and airblast aspects of AgDRIFT are empirical in nature, thus 

making upper tier analyses, which provide this type of output, not possible. In order to account 

for dilution, a dissipation rate of 25 percent per hour was used. This is protective as defined by 

an analysis conducted using the well-mixed box model, which is described in the residential 

SOPs. Exposure concentrations were used to compare to the acute inhalation HEC presented in 

Table 4 to calculate risks. 

The calculations for the second pathway included in this analysis are based on the premise that 

chlorpyrifos residues drift away from a treated area, are deposited downwind (e.g., on a lawn) 

and, then serve as a potential source of exposure. Once the amount of drift has been quantified, 

the resulting levels are considered like any pesticide intended for use on lawns. In this 

assessment, agricultural application rates are adjusted by the amount of drift averaged over a 50 

foot wide lawn. These lawns are considered at different distances up to 300 feet (125 reported) 

downwind from a treated field (closest edge to the treated field defines the distance). In this 

assessment, dermal exposures were added to non-dietary incidental ingestion exposure sources to 

calculate total risks because the toxicological endpoint was similar for all routes of exposure 

(i.e., cholinesterase inhibition). 

When risks associated with lawn pesticides are calculated, if residue data referred to as turf 

transferable residues (TTRs) are available, they are used as the basis of the calculation. If TTRs 

are not available, they are estimated using an established default methodology as described in the 

SOPs. TTR data, generated when chlorpyrifos use on turf was allowable, are available in this 

case and have been used directly as prescribed in the SOPs. The chlorpyrifos TTR data were 

used in the 2011 risk assessment to evaluate other scenarios involving possible contact with 

treated turf, including deposits resulting from the mosquito adulticide use of chlorpyrifos and its 

use on golf courses. The data have been summarized and used for the purposes of this 

assessment in a manner similar to what was done in the 2011 risk assessment. 

The available TTR study (MRID 44829601) was conducted in three states including California, 

Indiana, and Mississippi. This study examined the residues of chlorpyrifos on turf after 

application of Dursban® Pro (emulsifiable concentrate), Dursban® 50W (wettable powder), 

Dursban® 2.5G (granular) and Dursban® 1F (flowable granular). Single applications of the test 

products were made to the treatment plots using tractor mounted boom sprayers for the liquid 

applications. The liquid applications were made at a nominal application rate of 4 lb ai/a.25 

Duplicate samples were collected using the California roller technique at the following intervals: 

 

25 In the calculations, residue levels from this study are adjusted based on the amount of drift and the varied 

application rates considered in the assessment. 
20 of 60 

one day prior to the application, just after the application (2.5 hours), and days 1, 2, 4, and 7 after 

application. Samples were analyzed for residues of chlorpyrifos.26 The overall average 

concurrent recovery was 98% ± 3%. The LOD and LOQ were reported as 0.001 μg/cm2 and 

0.003 μg/cm2, respectively. The field study samples did not require correction for field 

fortification recovery. Average field fortification recoveries (corrected for concurrent recovery), 

at each of three fortification levels were greater than 90% at all sites. Dursban® Pro, a liquid 

formulation, results are presented in Table 5. The results for this formulation are presented 

because they represent the highest relative levels of residues resulting from the products used in 

this study. The chlorpyrifos dissipation half-life, at all sites, was approximately 14 hours or less. 

Table 5. Chlorpyrifos (Dursban Pro EC) TTR Data Collected Using California 

Roller Method 

Site Target App Rate 

(lb ai/A) 

Deposition At 

Appl. Rate 

(μg/cm2) 

Day of 

Application 

Mean TTR 

(μg/cm2) 

TTR as % App. 

Rate 

CA 3.80 42.60 0.124 0.29 

IN 3.98 44.62 0.090 0.20 

MS 3.83 42.93 0.146 0.34 

average 3.87 43.38 0.120 0.28 

4.5 Risk Assessment

As there is a wide variety of use scenarios described on chlorpyrifos labels, all calculations in 

this assessment were completed using an approach that groups currently registered chlorpyrifos 

application rates and crops into appropriate categories. The use information included in this 

document is presented in order to provide context for the groupings. The application rates listed 

for the individual groupings represent the maximum single application rate for the crops in that 

grouping (see Table 6). 

Table 6. Chlorpyrifos Application Groupings 

Single Application Rate of 

Chlorpyrifos lb ai/a 

Example 

Use Site 

Comments 

6 Citrus Use only permitted in specific 

counties in Arizona and California 

3.5 or 4 other citrus, grass grown for seed Use permitted nationwide 

2.3 Citrus 

Aerial application used to control 

psyllid, the vector for citrus 

greening1

 (pest present in Florida 

and possibly California and Texas) 

2 nursery and orchard trees, tree fruit, 

nuts Use permitted nationwide 

1 alfalfa, asparagus, sorghum, Use permitted nationwide 

 

26 Chlorpyrifos oxon was not measured but this would not impact the results of this analysis because only the values 

immediately following application were considered in this assessment. 
21 of 60 

strawberry, and sugarbeet 

1. Based on recent communications between EPA/OPP/PRD and DAS, et al. (May 17, 2012) 

In addition to these groupings, calculations were further delineated by application method and 

the types of spray patterns and spray conditions used. These are based on the pre-defined options 

incorporated into the AgDRIFT model, and they include:27

• Orchard Airblast (normal, dense, sparse, and vineyard foliage/canopy levels)28

• Aerial [spray droplet patterns/sizes include fine to medium (Dv0.5 = 255 μM), medium 

(Dv0.5 = 294 μM), medium to coarse (Dv0.5 = 341 μM), coarse to very coarse (Dv0.5 = 439 

μM)] 

• Groundboom [low (20 in) and high (50 in) booms, fine to medium/coarse spray pattern 

(Dv0.5 = 341 μM)] 

As described in detail above, two types of calculations were completed in this analysis. All of the 

calculations follow the guidance contained in the residential SOPs and the drift/deposition 

outputs described above. The appendices of this document contain the detailed algorithms and 

inputs used for this analysis, as well as the results. 

4.6 Risk Reduction Options 

The concept behind the development of the DRTs and the overall guidance of the PR notice for 

labeling related to spray drift described above is that pesticide applicators can control drift 

through the use of specific equipment and application parameters. These parameters include 

spray nozzle size, application pressure, vehicle type and configuration, release height, 

formulation choice, use of additives such as surfactants, and considering terrain as well as 

atmospheric conditions at the time of application. Additional spray drift modeling was completed 

for several droplet size distributions to investigate the impact that the aircraft, wind speed, swath 

displacement (the horizontal offset distance between the flight line and the target area), and crop 

canopy have on the deposition pattern of chlorpyrifos downwind of treated fields. These 

represent implementable means that applicators could potentially use to reduce drift 

Tier II modeling for ground and orchard applications was not completed as AgDRIFT does not 

have the capability to refine the spray drift estimates for these application types; however, Tier II 

spray drift analysis can and was completed using AgDRIFT for aerial applications. As a Tier II 

assessment tool, AgDRIFT is a parameterized model that can be used to investigate specific 

aerial application parameters. For chlorpyrifos, aerial application parameters investigated 

 

27 Note: Orchard airblast and groundboom are only available for Tier I analysis. A “medium” droplet size (Dv0.5 = 

294 μM) is only attainable for analysis in Tier II. 28 Normal (Stone and Pome Fruit, Vineyard): This composite orchard combines grape and apple orchards 

Dense (Citrus, Tall Trees): This composite orchard combines almond, orange, grapefruit, small grapefruit (mist 

blower) and pecan orchards. 

Sparse (Young, Dormant): This composite orchard combines small grapefruit and dormant apple orchards. 

Orchard: This composite orchard combines apple, almond, orange, grapefruit, small grapefruit, pecan, and 

dormant apple orchards. 

Vineyard: This composite curve combines grape air blast sprayer applications and may not apply to other 

application equipment. 
22 of 60 

included: aircraft (fixed and rotary winged), wind speed (10 and 5 mph), and swath displacement 

(default value based on droplet size see Table 3 and 100%). AgDRIFT input values for the Tier 

II analyses are provided in Table 7. 

Table 7. Tier II AgDRIFT Input Parameters 

Parameter Value Comments 

Aerial 

Equipment Air Tractor AT-401 

WASP Helicopter 

There are no aircraft restrictions on chlorpyrifos labels (e.g., EPA 

Reg. No. 62719-591); therefore, one fixed and one rotary winged 

aircraft was chosen. The default airplane (fixed wing) used in the 

Tier I analysis was used for consistency between analyses. One of 

the two default Tier II options for helicopter (rotary wing) was 

selected by the assessor. 

Release Height 10 ft Chlorpyrifos labels (e.g., EPA Reg. No. 62719-591) restrict 

applications to 10 ft above the crop canopy. 

Wind Speed 10 mph 

5 mph 

Chlorpyrifos labels (e.g., EPA Reg. No. 62719-591) limit 

applications to time periods when the wind speed is between 3 and 

10 mph. 

Surface 

Roughness 0.0075 m (0.3 in) AgDRIFT default value 

Temperature 86 °F AgDRIFT default value 

Swath 

Displacement 

0.3702 and 1 (F2M) 

0.3351 and 1(M) 

0.2781 and 1 (M2C) 

0.2489 (C) 

0.2149 and 1 (C2VC) 

0.2005 (VC) 

While an upwind swath displacement is recommended on 

chlorpyrifos labels (e.g., EPA Reg. No. 62719-591) a specific 

displacement value is not prescribed. The default Tier I value was 

selected by the assessor for consistency with the Tier I analysis. An 

alternative swath displacement of 100% was selected by the assessor 

to evaluate the impact of swath displacement. 

Droplet Size F2M, M, M2C, C, 

C2VC 

Chlorpyrifos labels (e.g., EPA Reg. No. 62719-591) restrict 

applications to droplet sizes greater than 255 μM; therefore, only 

droplet distributions with a mean diameter (Dv0.5) ≥ 255 μM were 

selected for modeling. These droplet sizes are consistent with the 

Tier I analysis. 

Nonvolatile Rate 

1.49 lb/a 

1.35 lb/a 

Chlorpyrifos label EPA Reg. No. 62719-591 (59.8% other 

ingredients /40.2% a.i. x 1 lb ai/a = 1.49 lb/a other ingredients based 

on data provided on the label as shown below). 

Chlorpyrifos label EPA Reg. No. 66222-19 (57.5% other ingredients 

/42.5% a.i. x 1 lb ai/a = 1.35 lb/a other ingredients based on data 

provided on the label as shown below) 
23 of 60 

Parameter Value Comments 

Aerial 

Spray Volume 2 gal/a Minimum required spray volume 

Carrier Type Water Chlorpyrifos labels (e.g., EPA Reg. No. 66222-19) 

Fine to Medium (F2M): Average Droplet size (Dv0.5) = 255 μM 

Medium (M): Dv0.5 = 294 μM 

Medium to Coarse (M2C): Dv0.5 = 341 μM 

Coarse (C) Dv0.5 = 385 μM 

Coarse to Very Coarse (M2C): Dv0.5 = 439 μM 

Very Coarse (VC): Dv0.5 = 478 μM 

Other input parameters were not changed or adjusted based on standard AgDRIFT recommendation via program 

prompts. 

The Tier I and Tier II analysis for aerial applications are based on bare ground applications. A 

Tier III analysis for aerial applications to investigate the effect that a crop canopy may have on 

the deposition pattern downwind of a treated field following an aerial application of chlorpyrifos 

was contemplated. However, the use of Tier III results are limited primarily for the following 

reasons: 1) canopy simulations in AgDISP are based on theoretical calculations and the results 

have not be validated (compared to field data); and 2) AgDISP simulations represent canopy 

structures that are expected to be different from chlorpyrifos use sites (e.g., AgDISP simulations 

are based on a uniformly closed canopy which is generally not expected for tree crops in an 

orchard setting). These limitations were discussed with and acknowledged by the model 

developer, Dr. Harold Thistle with the U.S. Forest Service.29 Tier III results are not presented in 

this document. 

5 Results 

The results of the analyses completed to evaluate the potential risks from chlorpyrifos spray drift 

are presented below. Section 5.1 describes the different spray drift modeling outputs that were 

calculated for the current label prescribed application conditions as well as those that were 

calculated representing potential risk mitigation options. Section 5.2 presents the inhalation risk 

estimates that were calculated. Section 5.3 presents the risk estimates associated with contact of 

residues which potentially deposit on lawns adjoining treated fields. 

 

29 Personal communication on May 30, 2012 
24 of 60 

5.1 Drift Estimates 

The spray drift deposition curves for the Tier I analysis for aerial applications are shown in 

Figure 3. This analysis includes fine to medium [average droplet size (Dv0.5) = 255 μM, which 

represents the current label], medium to coarse (Dv0.5 = 341 μM) and coarse to very coarse (Dv0.5

= 439 μM) droplet sizes. The estimated drift concentrations over a 50’ wide lawn for various 

distances downwind from the treated field are provided in Table 8. These estimated drift 

concentrations are shown for a range of chlorpyrifos application rates (1 to 6 lb ai/a). 

Figure 3. Tier I Spray Drift Analysis: Aerial Deposition Curves for Three Different Droplet 

Sizes 

Table 8. Tier I Spray Drift Analysis: Average Deposition Concentrations (lb ai/a) for a 50’ 

Wide Lawn Starting at Various Distances Downwind From a Field Treated with 

Chlorpyrifos Using Aerial Equipment 

Application 

Rate 

(lb ai/a) 

Droplet 

Size 

Distance Downwind From Treated Field (feet) 

0 10 25 50 75 100 125 150 200 250 300 

Average Deposition Concentrations (lb ai/a) 

for a 50’ Wide Lawn 

6 

F2M 1.64 1.23 1.02 0.77 0.58 0.46 0.38 0.32 0.25 0.20 0.17 

M2C 1.38 0.91 0.70 0.49 0.34 0.26 0.21 0.18 0.13 0.10 0.08 

C2VC 1.23 0.71 0.50 0.31 0.22 0.17 0.13 0.11 0.08 0.06 0.05 

4 

F2M 1.10 0.82 0.68 0.51 0.38 0.30 0.25 0.22 0.16 0.13 0.11 

M2C 0.92 0.60 0.46 0.32 0.22 0.17 0.14 0.12 0.08 0.07 0.05 

C2VC 0.82 0.48 0.33 0.21 0.15 0.11 0.22 0.07 0.05 0.04 0.03 

2.3 

F2M 0.63 0.47 0.39 0.29 0.22 0.18 0.14 0.12 0.09 0.08 0.06 

M2C 0.53 0.35 0.27 0.19 0.13 0.10 0.08 0.07 0.05 0.04 0.03 

C2VC 0.47 0.27 0.19 0.12 0.08 0.06 0.05 0.04 0.03 0.02 0.02 

2 

F2M 0.55 0.41 0.34 0.26 0.19 0.15 0.13 0.11 0.08 0.07 0.06 

M2C 0.46 0.30 0.23 0.16 0.11 0.09 0.07 0.06 0.04 0.03 0.03 

C2VC 0.41 0.24 0.17 0.10 0.07 0.06 0.04 0.04 0.03 0.02 0.02 

0

0.1

0.2

0.3

0.4

0.5

0.6

0 50 100 150 200 250 300

Fraction of Applied

Distance Downwind From Treated Fields

AT401, F2M, 10 mph, 37% SD

AT401, M2C, 10 mph, 28% SD

AT401, C2VC, 10 mph, 21% SD
25 of 60 

1a F2M 0.27 0.20 0.17 0.13 0.10 0.08 0.06 0.05 0.04 0.03 0.03 

M2C 0.23 0.15 0.12 0.08 0.06 0.04 0.03 0.03 0.02 0.02 0.01 

C2VC 0.20 0.12 0.08 0.05 0.04 0.03 0.02 0.02 0.01 0.01 0.01 

Fine to Medium (F2M): Avg. Droplet size (Dv0.5) = 255 μM, Medium to Coarse (M2C): Dv0.5 = 341 μM, Coarse to 

Very Coarse (C2VC): Dv0.5 = 439 μM 

The double box indicates the current aquatic buffer distance of 150 feet. 

a. The average deposition concentration for a 50’ wide lawn at each of the distances downwind. This is equivalent 

in terms of the average fraction of the applied that deposits over the same area [e.g., 0.27 lb ai/a is equivalent to a 

fraction applied of 0.27 (or 27% of the agricultural application rate)].

Tier I results are presented in Figure 4 and 
26 of 60 

Table 9 for fine to medium droplet sizes for applications using ground boom application 

equipment with high and low spray booms. The results suggest that potential spray drift exposure 

is higher near the field when a high boom is used as compared to a low boom; however, once 

several feet (≥10 ft) downwind the exposure resulting from the use of either boom is about the 

same. 

Figure 4. Tier I Spray Drift Analysis: Deposition Curves Resulting From the Application of 

Chlorpyrifos Using Ground Equipment 

0

0.2

0.4

0.6

0.8

1

0 50 100 150 200 250 300

Fraction of Applied

Distance Downwind From Treated Fields

High Boom Low Boom
27 of 60 

Table 9. Tier I Spray Drift Analysis: Average Deposition Concentrations (lb ai/a) for a 50’ 

Wide Lawn Starting at Various Distances Downwind From a Field Treated with 

Chlorpyrifos Using Ground Equipment (high and low boom options) 

Application 

Rate 

(lb ai/a) 

Boom 

Height 

Distance Downwind From Treated Field (feet) 

0 10 25 55 75 100 125 150 200 250 300

Average Deposition Concentrations (lb ai/a) 

for a 50’ Wide Lawn 

6 High 1.63 0.11 0.08 0.05 0.04 0.04 0.03 0.03 0.02 0.02 0.02 

Low 1.37 0.07 0.05 0.03 0.03 0.02 0.02 0.02 0.01 0.01 0.01 

4 High 1.08 0.07 0.05 0.04 0.03 0.02 0.02 0.02 0.01 0.01 0.01 

Low 0.91 0.04 0.03 0.02 0.02 0.02 0.01 0.01 0.01 0.01 0.01 

2 High 0.54 0.04 0.03 0.02 0.02 0.01 0.01 0.01 0.01 0.01 0.01 

Low 0.46 0.02 0.02 0.01 0.01 0.01 0.01 0.01 0.00 0.00 0.00 

1a High 0.27 0.02 0.01 0.01 0.01 0.01 0.01 0.00 0.00 0.00 0.00 

Low 0.23 0.01 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 

Low Boom 0.508 m (20 in), High Boom 1.27 m (50 in) 

Fine to Medium/Coarse (F2M/C): Avg. Droplet size (Dv0.5) = 341 μM 

The double box indicates the current aquatic buffer distance of 25 feet. 

a. The average deposition concentration for a 50’ wide lawn at each of the distances downwind. 

This is equivalent in terms of the average fraction of the applied that deposits over the same area 

[e.g., 0.27 lb ai/a is equivalent to a fraction applied of 0.27 (or 27% of the agricultural application 

rate)]. 

b. Data are reported for the 90th percentile.

Finally, Tier I results are presented in Figure 5 and Table 10 for fine to medium droplet sizes for 

applications using orchard airblast application equipment. These results show that the highest 

exposure from spray drift is when chlorpyrifos applications are made to sparsely vegetated or 

dormant orchards. This is consistent with the fact that canopy density and spray interception 

likely correlates to potential reductions of spray drift. 

Figure 5. Tier I Spray Drift Analysis: Deposition Curves Resulting from the Application of 

Chlorpyrifos Using Orchard Blast Equipment in Various Orchard Types 

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0 50 100 150 200 250 300

Fraction of Applied

Distance Downwind From Treated Fields

Normal (Stone and Pome Fruit, 

Vineyard)

Dense (Citrus, Tall Trees)

Sparse (Young, Domant)
28 of 60 

Table 10. Tier I Spray Drift Analysis: Average Deposition Concentrations (lb ai/a) for a 50’ 

Wide Lawn Starting at Various Distances From a Field Treated with Chlorpyrifos Using 

Orchard Blast Equipment in Various Orchard Types 

Application 

Rate 

(lb ai/a) 

Crop 

Canopy 

Distance Downwind From Treated Field (feet) 

0 10 25 50 75 100 125 150 200 250 300 

Average Deposition Concentrations (lb ai/a) 

for a 50’ Wide Lawn 

6 

Normal 0.03 0.01 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 

Dense 0.44 0.16 0.06 0.03 0.04 0.03 0.02 0.02 0.01 0.01 0.01 

Sparse 1.70 0.48 0.27 0.12 0.06 0.04 0.03 0.02 0.01 0.01 0.00 

Vineyard 0.12 0.02 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 

Orchard 0.80 0.24 0.15 0.07 0.05 0.03 0.02 0.02 0.01 0.01 0.01 

4 

Normal 0.02 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 

Dense 0.29 0.11 0.04 0.02 0.03 0.02 0.02 0.01 0.01 0.01 0.01 

Sparse 1.13 0.32 0.18 0.08 0.04 0.03 0.02 0.01 0.01 0.00 0.00 

Vineyard 0.08 0.02 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 

Orchard 0.53 0.16 0.10 0.05 0.03 0.02 0.02 0.01 0.01 0.01 0.01 

2 

Normal 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 

Dense 0.15 0.05 0.02 0.01 0.01 0.01 0.01 0.01 0.00 0.00 0.00 

Sparse 0.57 0.16 0.09 0.04 0.02 0.01 0.01 0.01 0.00 0.00 0.00 

Vineyard 0.04 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 

Orchard 0.27 0.08 0.05 0.02 0.02 0.01 0.01 0.01 0.00 0.00 0.00 

1a 

Normal 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 

Dense 0.07 0.03 0.01 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 

Sparse 0.28 0.08 0.05 0.02 0.01 0.01 0.00 0.00 0.00 0.00 0.00 

Vineyard 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 

Orchard 0.13 0.04 0.02 0.01 0.01 0.01 0.00 0.00 0.00 0.00 0.00 

Normal (Stone and Pome Fruit, Vineyard): This composite orchard combines grape and apple orchards 

Dense (Citrus, Tall Trees): This composite orchard combines almond, orange, grapefruit, small grapefruit (mist 

blower) and pecan orchards. 

Sparse (Young, Dormant): This composite orchard combines small grapefruit and dormant apple orchards. 

Orchard: This composite orchard combines apple, almond, orange, grapefruit, small grapefruit, pecan, and dormant 

apple orchards. 

Vineyard: This composite curve combines grape air blast sprayer applications and many not apply to other 

application equipment. 

The double box indicates the current aquatic buffer distance of 50 feet. 

a. The average deposition concentration for a 50’ wide lawn at each of the distances downwind. This is equivalent 

in terms of the average fraction of the applied that deposits over the same area [e.g., 0.27 lb ai/a is equivalent to a 

fraction applied of 0.27 (or 27% of the agricultural application rate)].

The spray drift deposition curves for the Tier II analysis for aerial chlorpyrifos applications are 

shown in Figure 6 for a medium droplet size (Dv0.5 = 295 μM). Included in Appendix E are the 

results for fine to medium droplet size (Dv0.5 = 255 μM), medium to coarse (Dv0.5 = 341 μM) and 

coarse to very coarse (Dv0.5 = 439 μM) droplet sizes (Figures E.1, E.2 and E.3, respectively). 

For all the droplet size spectra analyzed, the fraction of chlorpyrifos applied that is expected to 
29 of 60 

be deposited over a 50’ wide lawn for various distances downwind from the treated field are 

provided in Table 11.

30 

Figure 6. Tier II Spray Drift Analysis: Deposition Curves for a Medium Droplet Size 

Following Chlorpyrifos Application Using Several Different Aerial Application 

Configurations 

Table 11. Tier II Spray Drift Analysis: Average Deposition Concentrations (lb ai/a) for a 

50’ Wide Lawn Starting at Various Distances From a Field Treated with Chlorpyrifos 

Using Several Different Aerial Application Configurations and a Medium Droplet Size 

Configuration 

Distance Downwind From Treated Field (feet) 

0 10 25 50 75 100 125 150 200 250 300 

Average Fraction of Applied Deposited on a 

50’ Wide Lawn Downwind of a Treated Field1 

AT401, F2M, 10 mph, 37% SD 0.28 0.21 0.18 0.14 0.10 0.09 0.07 0.06 0.05 0.04 0.04 

WASP, F2M, 10 mph, 37% SD 0.27 0.21 0.17 0.11 0.09 0.07 0.06 0.05 0.04 0.03 0.03 

AT401, F2M, 5 mph, 37% SD 0.19 0.16 0.12 0.09 0.07 0.06 0.05 0.05 0.04 0.03 0.03 

AT401, F2M, 10 mph, 100% SD 0.16 0.14 0.12 0.09 0.08 0.07 0.06 0.05 0.04 0.04 0.03 

AT401, F2M, 5 mph, 100% SD 0.10 0.09 0.08 0.06 0.06 0.05 0.05 0.04 0.03 0.03 0.02 

WASP, F2M, 5 mph, 100% SD 0.08 0.07 0.06 0.05 0.04 0.04 0.03 0.03 0.02 0.02 0.01 

AT401, M, 10 mph, 37% SD 0.24 0.18 0.15 0.11 0.08 0.07 0.05 0.05 0.04 0.03 0.03 

WASP, M, 10 mph, 37% SD 0.22 0.16 0.13 0.09 0.06 0.05 0.04 0.04 0.03 0.02 0.02 

AT401, M, 5 mph, 37% SD 0.16 0.13 0.10 0.06 0.05 0.04 0.04 0.04 0.03 0.02 0.02 

AT401, M, 10 mph, 100% SD 0.13 0.11 0.09 0.07 0.06 0.05 0.04 0.04 0.03 0.03 0.02 

AT401, M, 5 mph, 100% SD 0.08 0.07 0.06 0.05 0.04 0.04 0.03 0.03 0.02 0.02 0.02 

WASP, M, 5 mph, 100% SD 0.06 0.05 0.04 0.04 0.03 0.03 0.02 0.02 0.02 0.01 0.01 

AT401, M2C, 10 mph, 28% SD 0.24 0.16 0.12 0.09 0.06 0.05 0.04 0.03 0.03 0.02 0.02 

 

30 To obtain the estimated chlorpyrifos concentrations (lb ai/a), as presented for Tier I analysis, the fraction of 

applied should be multiplied by the range of chlorpyrifos application rates (1 to 6 lb ai/a). 

0

0.1

0.2

0.3

0.4

0.5

0.6

0 50 100 150 200 250 300

Fraction of Applied

Distance Downwind From Treated Fields (feet)

M, AT401, 10 mph, 37% SD 

M, WASP, 10 mph, 37% SD

M, AT401, 5 mph, 37% SD 

M, AT401, 10 mph, 100% SD

M, AT401, 5 mph, 100% SD

M, WASP, 5 mph, 100% SD 
30 of 60 

Configuration 

Distance Downwind From Treated Field (feet) 

0 10 25 50 75 100 125 150 200 250 300 

Average Fraction of Applied Deposited on a 

50’ Wide Lawn Downwind of a Treated Field1 

WASP, M2C,10 mph, 28% SD 0.21 0.14 0.11 0.07 0.05 0.04 0.03 0.03 0.02 0.02 0.01 

AT401, M2C,5 mph, 28% SD 0.15 0.11 0.08 0.05 0.04 0.03 0.03 0.02 0.02 0.02 0.01 

AT401, M2C,10 mph, 100% SD 0.10 0.08 0.07 0.05 0.04 0.03 0.03 0.03 0.02 0.02 0.01 

AT401, M2C,5 mph, 100% SD 0.05 0.04 0.04 0.03 0.03 0.02 0.02 0.02 0.02 0.01 0.01 

WASP, M2C, 5 mph, 100% SD 0.04 0.03 0.03 0.02 0.02 0.02 0.01 0.01 0.01 0.01 0.01 

AT401, C, 10 mph, 25% SD 0.22 0.14 0.10 0.07 0.05 0.04 0.03 0.03 0.02 0.02 0.01 

WASP, C, 10 mph, 25% SD 0.19 0.12 0.09 0.05 0.04 0.03 0.02 0.02 0.01 0.01 0.01 

AT401, C2VC, 10 mph, 21% SD 0.21 0.12 0.09 0.06 0.04 0.03 0.02 0.02 0.01 0.01 0.01 

WASP, C2VC, 10 mph, 21% SD 0.17 0.10 0.07 0.04 0.03 0.02 0.02 0.02 0.01 0.01 0.01 

AT401, C2VC, 5 mph, 21% SD 0.12 0.08 0.05 0.03 0.02 0.02 0.02 0.01 0.01 0.01 0.01 

AT401, C2VC, 10 mph, 100% SD 0.06 0.05 0.04 0.03 0.02 0.02 0.02 0.02 0.01 0.01 0.01 

AT401, C2VC, 5 mph, 100% SD 0.03 0.03 0.02 0.02 0.02 0.01 0.01 0.01 0.01 0.01 0.01 

WASP, C2VC, 5 mph, 100% SD 0.02 0.02 0.02 0.01 0.01 0.01 0.01 0.01 0.01 0.00 0.00 

AT401, VC, 10 mph, 20% SD 0.20 0.11 0.07 0.05 0.03 0.02 0.02 0.02 0.01 0.01 0.01 

WASP, VC, 10 mph, 20% SD 0.16 0.09 0.06 0.04 0.03 0.02 0.02 0.01 0.01 0.01 0.01 

1. To obtain the estimated chlorpyrifos concentrations (lb ai/a), as presented for Tier I analysis, the fraction of applied should 

be multiplied by the range of chlorpyrifos application rates (1 to 6 lb ai/a). 

Fine to Medium (F2M): Average Droplet size (Dv0.5) = 255 μM 

Medium (M): Dv0.5 = 294 μM 

Medium to Coarse (M2C): Dv0.5 = 341 μM 

Coarse (C) Dv0.5 = 385 μM 

Coarse to Very Coarse (M2C): Dv0.5 = 439 μM 

Very Coarse (VC): Dv0.5 = 478 μM 

The double box indicates the current aquatic buffer distance of 150 feet. 

The results suggest that swath displacement and wind speed have the most impact, of all the 

parameters tested, on reducing the amount of chlorpyrifos spray drift downwind of a treated 

field. A comparison of the different droplet sizes also shows that increasing the size of the spray 

droplet reduces the spray drift as well. This is also supported by the Tier I analysis. 

5.2 Risk Estimates From Inhalation Exposure 

The risk estimates associated with potential inhalation exposures are presented in this section 

(Table 12). Note: Detailed calculations are included in Appendix F. The toxicological input 

for this calculation is a Human Equivalent Concentration (HEC) based on an acute rat inhalation 

study with multiple sampling times on day of dosing that was used to calculate a 2 hour HEC 

(2.48 mg/m3

). A no observed adverse effect level (NOAEL) was not determined in the rat 

inhalation study, as a result, the total uncertainty factor considered appropriate for identifying 

risks of concern is 300 (i.e., MOEs < 300 present a risk estimate of concern). 

In the 2011 risk assessment a 24 hour exposure period was used, which was a reasonable 

approach given that the source of exposure was ambient air and emissions occurred over a longer 

period of time than would be expected for typical spray drift exposure situations. The HEC used 
31 of 60 

was also based on a 24 hour period. Inhalation exposures from spray drift have instead been 

evaluated based using a 2 hour duration in order to better reflect how they would likely occur. 

This also required that an updated HEC based on a 2 hour exposure period be calculated as 

described above. The exposure considerations related to this approach are discussed below. This 

study was completed using small aerosols (~2 microns). 

Air concentrations in the breathing zone were calculated using the Tier II option in AgDRIFT 

(V2.01). AgDRIFT provides air concentrations at specified distances downwind of a treated field 

in a vertical flux plane but this capability is limited only to aerial applications. These values are 1 

hour time-weighted averages and have a certain degree of conservatism associated with them 

because in AgDRIFT the wind vector (i.e., speed and direction) remains constant at all times and 

this analysis was based on a 10 mph windspeed, the highest allowable under current chlorpyrifos 

labels which results in the highest possible air concentrations. It also calculates air 

concentrations for the range of droplet sizes included in the particular spectra used as the basis 

for the model run. In all cases, droplets less than approximately 10 microns account for a very 

small percentage of the overall amount of droplets produced for any spectra that would be used 

for modeling of chlorpyrifos drift. The dichotomy between how the data used as the basis for the 

HEC and the airborne exposure concentrations should be considered when interpreting the 

associated risk estimates (i.e., they are conservative because only a small percentage of the 

airborne exposure concentration is made up of droplets which could reach the lung). 

For further consideration relative to the application methods evaluated, especially those that take 

more time to complete (i.e., groundboom and airblast applications), wind vectors would be 

expected to change to some extent. In order to reflect actual anticipated exposures over 2 hour 

periods and account for expected changes in atmospheric conditions an approach to factor 

dilution over time was used based on the 1 hour concentrations as a starting point. The 1 hour 

values were amortized using a dilution factor of 25 percent per hour over the 2 hour exposure 

period. This value, especially when coupled with the premise inherent in AgDRIFT of a 

constant wind vector, is intended to represent possible conditions but also be conservative (e.g., 

20 flight passes for aerial applications which could take a substantial time period and a constant 

windspeed and vector). Values that represent a higher degree of dilution were considered but not 

utilized because some atmospheric conditions could potentially impede dilution such as 

atmospheric inversions or diametric changes in wind direction. However, to be thorough, the 

impact of conditions where more dilution would be expected was also investigated and these 

were found not to impact the results in a manner that would alter the conclusions of the 

assessment. 

Finally, it is not appropriate to combine this exposure with those described below in Section 5.3

because the exposure conditions differ (e.g., duration, time/location issues), there are different 

uncertainties associated with each pathway, and the HEC in this case is based on lung 

cholinesterase inhibition using very small droplets (~ 2 microns) which differs from the other 

types of exposures. 

Single day risk estimates based on the current label directives for managing spray drift are of 

concern for most scenarios at the 4 and 6 lb ai/a rates even at 125 feet from the edge of a treated 

field. Some scenarios are of concern at application rates of 2 and 2.3 lb ai/a at 75 feet from the 
32 of 60 

edge of a treated field when using medium to coarse nozzles. If larger droplets are used risks are 

not of concern at shorter distances. At the lower application rate of 1 lb ai/a risks estimates are 

not of concern at the field edge for larger droplets and not of concern at 10 feet for medium to 

coarse droplets. There are possible techniques that applicators can use to reduce drift from 

treated fields. These are discussed below in Section 6 but due to a lack of information further 

refinements to these calculations have not been attempted. 

Table 12. Inhalation Risk Estimates Associated With Spray Drift at Differing Distances 

From Edge of Treated Field 

Flux Plane 

Distance (ft) 

Results Based On 2 Hr Amortized Concentration 

Medium/Coarse Droplets Coarse/Very Coarse Droplets 

ng/m3 MOE ng/m3 MOE 

6.0 lb ai/ A - Citrus [CA/AZ] 

0 46875 53 34375 72 

10 39063 63 26563 93 

25 31875 78 20313 122 

50 26250 94 15625 159 

75 20000 124 11250 220 

100 16250 153 9375 265 

125 13750 180 7813 317 

4 lb ai/ A - Nursery and Orchard Trees (except apple), Tree Fruit, Tree Nuts 

0 32813 76 23438 106 

10 27500 90 18438 135 

25 23125 107 14375 173 

50 18750 132 11250 220 

75 14375 173 8750 283 

100 12500 198 7500 331 

125 10625 233 5938 418 

2.3 lb ai/ A - psyllid, the vector for citrus greening1

0 20625 120 14375 173 

10 16875 147 11250 220 

25 14375 173 8750 283 

50 11875 209 7500 331 

75 10000 248 5625 441 

100 8125 305 5000 496 

125 7500 331 4375 567 

2 lb ai/ A - Nursery and Orchard Trees (except apple), Tree Fruit, Tree Nuts 

0 18125 137 12500 198 

10 15000 165 10000 248 
33 of 60 

Flux Plane 

Distance (ft) 

Results Based On 2 Hr Amortized Concentration 

Medium/Coarse Droplets Coarse/Very Coarse Droplets 

ng/m3 MOE ng/m3 MOE 

25 13125 189 8125 305 

50 11250 220 6875 361 

75 8750 283 5000 496 

100 8125 305 4375 567 

125 6875 361 3750 661 

1 lb ai/ A - Alfalfa, Asparagus, Sorghum, Strawberry, Sugarbeet 

0 10000 248 6875 361 

10 8125 305 5000 496 

25 7500 331 5000 496 

50 6250 397 3750 661 

75 5625 441 3125 794 

100 5000 496 2500 992 

125 4375 567 1875 1323 

MOEs<300 would indicate a risk concern 

1. Pest present in Florida and possibly California and Texas

5.3 Combined Risk Estimates From Lawn Deposition Adjacent to Applications 

The risk estimates associated with deposition of residues that could potentially result in 

exposures akin to those experienced from intentionally treated turf are presented in this section 

(Table 13). These have been calculated using the Tier I option in the AgDRIFT model and the 

droplet spectra that are allowable per current chlorpyrifos labels. All of the results for orchard 

airblast and groundboom results are allowable under existing labels. Note: Cells indicating risk 

estimates of concern have been highlighted for ease of review. Also, detailed calculations are 

included in Appendix G. 

The results are based on the premise that if a residence with a 50 foot wide lot exists next to a 

treated field spray drift could result from an application such that residues could be deposited 

across that lot on the lawn. Children could play on that contaminated turf resulting in exposure. 

This type of exposure has been assessed using the residential SOPs as described above. The only 

difference between these calculations that quantify exposure due to chlorpyrifos spray drift 

landing on residential lawns and an evaluation of a pesticide intended for use on lawns is how 

the exposure concentration is determined. The amount deposited on lawns in this approach is 

based on the agricultural application rate which was then adjusted for the average amount of 

spray drift deposition anticipated for the scenario across the modeled lawn (50’ wide). In 

addition to results included in Table 13 that are based on AgDrift Tier I, additional scenarios 

have been evaluated using AgDrift Tier II including considering medium, coarse, and very 

coarse sized droplets and the impact of using potential spray drift reduction measures (Table 14). 

In all cases, exposures were considered for lawns where the nearest side of the property was 
34 of 60 

directly adjoining the treated field (at field edge) up to 125 feet downwind of a treated field (see 

Figure 2). The toxicological points of departure for this analysis are route specific and highly 

refined. Dermal and non-dietary risk estimates were combined because the toxicity endpoint for 

each route of exposure is cholinesterase inhibition. The total applicable uncertainty factor is 100 

so MOEs < 100 would be of concern. 

The risk estimates presented in Table 13 based on AgDrift Tier I indicate that the major risk 

concern is from aerial applications. 31 Risk estimates from ground boom and orchard airblast 

applications are not of concern past 25 feet downwind from a field edge for all situations 

considered, even at higher application rates, except for a couple of airblast application scenarios 

representing sparse orchard canopy situations. For aerial applications, risks are of concern up to 

125 feet downwind from a treated field. Risks are reduced if lower application rates are 

considered. Also, the impact of changing nozzle types resulting in coarser sprays, which drift 

less, reduces risks from aerial applications. 

Table 13. Risk Estimates Associated With Spray Drift Deposition Based On AgDrift Tier 1 

From All Pertinent Application Methods 

Application 

Scenario 

(Rep. Crop) 

Appl. 

Rate 

(lb ai/A) 

Nozzle/ 

Spray Type 

Day (0) Highest Measured 

TTR (ug/cm2) MOEs At Various Distances Downwind From Treated Fields 

Source Appl. 

Rate 

Day 0 

Levels 

At 

Edge 

10 

Feet 

25 

Feet 

50 

Feet 

75 

Feet 

100 

Feet 

125 

Feet 

Aerial

Tier I 

[Citrus 

(CA/AZ)] 

6.0 

Fine to 

Medium 

Pro - MS 3.83 0.146 10 13 15 20 27 34 42 

Mean-All 

sites 3.87 0.120 12 16 19 25 33 42 51 

Medium to 

Coarse 

Pro - MS 3.83 0.146 11 17 22 32 46 60 75 

Mean-All 

sites 3.87 0.120 14 21 28 40 57 74 93 

Coarse to 

Very Coarse 

Pro - MS 3.83 0.146 13 22 31 50 72 93 121 

Mean-All 

sites 3.87 0.120 16 27 39 61 88 114 148 

Tier I 

[Tree Fruits, 

Nuts, 

Orchards, 

Nursery] 

4.0 

Fine to 

Medium 

Pro - MS 3.83 0.146 14 19 23 31 41 51 63 

Mean-All 

sites 3.87 0.120 18 23 28 38 50 63 77 

Medium to 

Coarse 

Pro - MS 3.83 0.146 17 26 34 48 70 90 113 

Mean-All 

sites 3.87 0.120 21 32 41 59 86 111 139 

Coarse to 

Very Coarse 

Pro - MS 3.83 0.146 19 33 47 75 108 140 181 

Mean-All 

sites 3.87 0.120 23 40 58 92 133 172 222 

Tier I 

[psyllid, the 

vector for 

citrus 

greening 

(CA/FL/TX)] 

2.3 

Fine to 

Medium 

Pro - MS 3.83 0.146 25 33 40 53 71 89 109 

Mean-All 

sites 3.87 0.120 31 41 49 65 87 110 134 

Medium to 

Coarse 

Pro - MS 3.83 0.146 30 45 59 84 121 156 196 

Mean-All 

sites 3.87 0.120 36 55 72 103 149 192 241 

 

31 Note that aggregate exposures that also consider other sources of possible chlorpyrifos exposure (e.g., food and 

water) have not been incorporated into these risk estimates presented herein. These will be addressed in the 

registration review risk assessment for chlorpyrifos where all other pertinent aggregate exposure estimates will 

be presented and discussed. 
35 of 60 

Application 

Scenario 

(Rep. Crop) 

Appl. 

Rate 

(lb ai/A) 

Nozzle/ 

Spray Type 

Day (0) Highest Measured 

TTR (ug/cm2) MOEs At Various Distances Downwind From Treated Fields 

Source Appl. 

Rate 

Day 0 

Levels 

At 

Edge 

10 

Feet 

25 

Feet 

50 

Feet 

75 

Feet 

100 

Feet 

125 

Feet 

Coarse to 

Very Coarse 

Pro - MS 3.83 0.146 33 57 82 130 188 243 315 

Mean-All 

sites 3.87 0.120 41 70 101 159 230 298 387 

Tier I 

[Tree Fruits, 

Nuts, 

Orchards, 

Nursery] 

2 

Fine to 

Medium 

Pro - MS 3.83 0.146 29 38 46 61 82 103 125 

Mean-All 

sites 3.87 0.120 35 47 57 75 100 126 154 

Medium to 

Coarse 

Pro - MS 3.83 0.146 34 52 67 97 139 180 226 

Mean-All 

sites 3.87 0.120 42 64 83 119 171 221 278 

Coarse to 

Very Coarse 

Pro - MS 3.83 0.146 38 66 94 149 216 279 362 

Mean-All 

sites 3.87 0.120 47 81 116 183 265 343 445 

Tier I 

Alfalfa, 

Asparagus. 

Sorghum, 

Strawberry, 

Sugarbeet 

1 

Fine to 

Medium 

Pro - MS 3.83 0.146 57 76 92 122 163 205 250 

Mean-All 

sites 3.87 0.120 70 94 113 150 201 252 307 

Medium to 

Coarse 

Pro - MS 3.83 0.146 68 104 135 193 279 360 452 

Mean-All 

sites 3.87 0.120 83 127 166 237 342 442 555 

Coarse to 

Very Coarse 

Pro - MS 3.83 0.146 76 132 188 298 431 558 724 

Mean-All 

sites 3.87 0.120 94 162 232 367 530 686 890 

Airblast

Tier I 

[Citrus 

(CA/AZ) ] 

6 

Normal 

Pro - MS 3.83 0.146 485 1350 1907 3023 4168 5223 6445 

Mean-All 

sites 3.87 0.120 596 1659 2344 3715 5123 6419 7921 

Dense 

Pro - MS 3.83 0.146 36 97 264 531 399 531 685 

Mean-All 

sites 3.87 0.120 44 119 324 653 491 653 841 

Sparse 

Pro - MS 3.83 0.146 9 33 57 132 247 387 589 

Mean-All 

sites 3.87 0.120 11 40 70 163 303 476 724 

Vineyard 

Pro - MS 3.83 0.146 135 672 1149 2218 3387 4500 5810 

Mean-All 

sites 3.87 0.120 166 825 1413 2725 4163 5531 7140 

Tier I 

[Citrus] 3.5 

Normal 

Pro - MS 3.83 0.146 832 2314 3270 5182 7146 8954 11049 

Mean-All 

sites 3.87 0.120 1022 2843 4019 6369 8782 11004 13579 

Dense 

Pro - MS 3.83 0.146 61 166 452 911 685 911 1174 

Mean-All 

sites 3.87 0.120 75 203 555 1119 842 1119 1442 

Sparse 

Pro - MS 3.83 0.146 16 56 98 227 423 664 1009 

Mean-All 

sites 3.87 0.120 19 69 120 279 520 816 1240 

Vineyard 

Pro - MS 3.83 0.146 232 1151 1970 3802 5807 7715 9960 

Mean-All 

sites 3.87 0.120 285 1415 2422 4672 7136 9482 12241 

Tier I 

[Tree 

Fruits/Nuts/O

rchards, 

Nursery] 

2 

Normal 

Pro - MS 3.83 0.146 1456 4049 5722 9069 12505 15669 19336 

Mean-All 

sites 3.87 0.120 1789 4976 7033 11145 15368 19257 23763 

Dense 

Pro - MS 3.83 0.146 107 290 791 1594 1198 1594 2054 

Mean-All 

sites 3.87 0.120 131 356 972 1958 1473 1958 2524 

Sparse 

Pro - MS 3.83 0.146 28 98 172 397 740 1162 1766 

Mean-All 

sites 3.87 0.120 34 120 211 488 910 1428 2171 
36 of 60 

Application 

Scenario 

(Rep. Crop) 

Appl. 

Rate 

(lb ai/A) 

Nozzle/ 

Spray Type 

Day (0) Highest Measured 

TTR (ug/cm2) MOEs At Various Distances Downwind From Treated Fields 

Source Appl. 

Rate 

Day 0 

Levels 

At 

Edge 

10 

Feet 

25 

Feet 

50 

Feet 

75 

Feet 

100 

Feet 

125 

Feet 

Vineyard 

Pro - MS 3.83 0.146 406 2015 3448 6653 10162 13501 17430 

Mean-All 

sites 3.87 0.120 499 2476 4238 8176 12488 16593 21421 

Tier I 

[Christmas 

Trees, 

Conifer, 

Deciduous 

Nursery, 

Grape] 

1 

Normal 

Pro - MS 3.83 0.146 2912 8098 11445 18137 25010 31339 38671 

Mean-All 

sites 3.87 0.120 3578 9952 14065 22290 30737 38515 47526 

Dense 

Pro - MS 3.83 0.146 213 580 1581 3187 2397 3187 4108 

Mean-All 

sites 3.87 0.120 262 712 1943 3917 2946 3917 5048 

Sparse 

Pro - MS 3.83 0.146 55 196 343 794 1481 2325 3533 

Mean-All 

sites 3.87 0.120 68 240 422 975 1820 2857 4342 

Vineyard 

Pro - MS 3.83 0.146 811 4029 6896 13306 20323 27002 34860 

Mean-All 

sites 3.87 0.120 997 4952 8475 16352 24976 33185 42843 

Groundboom

Tier I 

[Grape (E of 

Cont. 

Divide)] 

6 

Low 

Boom/Fine to 

Med/Coarse 

Pro - MS 3.83 0.146 11 235 327 467 587 687 794 

Mean-All 

sites 3.87 0.120 14 289 402 574 722 844 976 

High 

Boom/Fine to 

Med/Coarse 

Pro - MS 3.83 0.146 10 143 201 292 373 441 515 

Mean-All 

sites 3.87 0.120 12 176 247 359 458 542 633 

Tier I 

[Orchard 

Floor] 

4 

Low 

Boom/Fine to 

Med/Coarse 

Pro - MS 3.83 0.146 17 353 490 701 881 1030 1191 

Mean-All 

sites 3.87 0.120 21 434 602 861 1083 1266 1464 

High 

Boom/Fine to 

Med/Coarse 

Pro - MS 3.83 0.146 14 215 301 439 560 662 773 

Mean-All 

sites 3.87 0.120 18 264 370 539 688 813 950 

Tier I 

[Fig, Peanut, 

Mint, 

Strawberry, 

etc.] 

2 

Low 

Boom/Fine to 

Med/Coarse 

Pro - MS 3.83 0.146 34 706 980 1401 1762 2061 2382 

Mean-All 

sites 3.87 0.120 42 867 1205 1722 2166 2533 2927 

High 

Boom/Fine to 

Med/Coarse 

Pro - MS 3.83 0.146 29 429 603 877 1119 1323 1546 

Mean-All 

sites 3.87 0.120 35 527 741 1078 1375 1626 1900 

Tier I 

[Brussel 

Sprouts, 

Cauliflower, 

Onion, 

Soybean, 

Wheat] 

1 

Low 

Boom/Fine to 

Med/Coarse 

Pro - MS 3.83 0.146 69 1412 1961 2802 3524 4121 4764 

Mean-All 

sites 3.87 0.120 84 1735 2410 3444 4331 5065 5854 

High 

Boom/Fine to 

Med/Coarse 

Pro - MS 3.83 0.146 58 858 1206 1755 2238 2646 3093 

Mean-All 

sites 3.87 0.120 71 1055 1482 2156 2751 3252 3801 

MOEs<100 indicate a risk estimate of concern 
37 of 60 

Additional results were calculated using AgDrift Tier II in order to evaluate risks associated with 

a variety of droplet spectra and to evaluate the impact of potential spray drift reduction measures 

(Table 14). This type of analysis is only feasible for aerial applications due to limitations with 

the AgDRIFT model. Section 4.6 above describes the types of application parameters that were 

considered in detail. Some of the factors are believed to be readily implementable under actual 

field conditions as described in Section 3.2 (e.g., use of different droplet spectra). Others have 

been evaluated as well to identify how sensitive the results would be relative to changes in such 

parameters even though they may be less viable as mitigation measures because they are harder 

to routinely implement (e.g., swath width and windspeed at time of application). 

 To summarize, the possible mitigation measures that were considered include: 

• use of a helicopter (WASP) rather than fixed wing aircraft (AT 401), 

• varied swath displacement (100% of the width of the aircraft shift inward from the field 

edge rather than the standard values for each droplet spectra – e.g., 34% for medium) , 

• use of coarser droplets than the label indicates, specific size ranges are noted, and 

• a reduction in maximum allowable wind speed during application from 10 to 5 mph. 

These were developed in the context of the draft PR Notice guidance for spray drift labeling and 

the DRTs discussed in Section 3.2 above. 

It is clear that applicators can utilize measures that will be effective for reducing spray drift 

levels and that the methods will reduce risk estimates depending upon the situation. Altered 

nozzle size appears to be an effective approach for reducing risks compared to the current label 

that could be readily implementable. 

Table 14. Risk Estimates Associated With Spray Drift Deposition Based On AgDrift Tier II 

From Aerial Application 

Application Scenario 

App 

Rate 

(lb ai/A) 

Nozzle 

Configuration 

Day (0) Highest Measured TTR MOEs At Various Distances Downwind From Treated Fields 

Source Appl. 

Rate (ug/cm2) At Edge 

10 

Feet 

25 

Feet 

50 

Feet 

75 

Feet 

100 

Feet 

125 

Feet 

Tier II (AT 401/10 mph/34%SD) 

6.0 

Medium Pro - MS 3.87 0.146 10 14 18 24 32 40 48 

Tier II (AT 401/5 mph/34%SD) Medium Pro - MS 3.87 0.146 16 20 26 40 51 59 67 

Tier II (AT 401/10 mph/100%SD) Medium Pro - MS 3.87 0.146 21 24 28 36 45 53 60 

Tier II (AT 401/5 mph/100%SD) Medium Pro - MS 3.87 0.146 33 40 46 56 64 71 80 

Tier II (Wasp/10 mph/34%SD) Medium Pro - MS 3.87 0.146 11 15 19 29 40 49 60 

Tier II (Wasp/10 mph/100%SD) Medium Pro - MS 3.87 0.146 24 30 35 46 56 65 75 

Tier II (Wasp/5 mph/34%SD) Medium Pro - MS 3.87 0.146 18 26 35 52 65 75 100 

Tier II (Wasp/5 mph/100%SD) Medium Pro - MS 3.87 0.146 45 52 59 70 82 95 110 

Tier II (AT 401/10 mph/25%SD) Coarse Pro - MS 3.87 0.146 12 19 25 38 53 68 84 

Tier II (Wasp/10 mph/25%SD) Coarse Pro - MS 3.87 0.146 14 22 30 49 69 88 110 

Tier II (AT 401/10 mph/20%SD) Very Coarse Pro - MS 3.87 0.146 13 24 35 57 81 106 136 
38 of 60 

Application Scenario 

App 

Rate 

(lb ai/A) 

Nozzle 

Configuration 

Day (0) Highest Measured TTR MOEs At Various Distances Downwind From Treated Fields 

Source Appl. 

Rate (ug/cm2) At Edge 

10 

Feet 

25 

Feet 

50 

Feet 

75 

Feet 

100 

Feet 

125 

Feet 

Tier II (Wasp/10 mph/20%SD) Very Coarse Pro - MS 3.87 0.146 17 31 45 73 104 136 175 

Tier II (AT 401/10 mph/28%SD) Medium to 

Coarse Pro - MS 3.87 0.146 11 17 22 31 44 55 68 

Tier II (AT 401/5 mph/28%SD) Medium to 

Coarse Pro - MS 3.87 0.146 18 25 34 56 74 86 101 

Tier II (AT 401/10 mph/100%SD) Medium to 

Coarse Pro - MS 3.87 0.146 27 32 39 52 65 76 89 

Tier II (AT 401/5 mph/100%SD) Medium to 

Coarse Pro - MS 3.87 0.146 48 59 68 82 97 110 126 

Tier II (Wasp/10 mph/28%SD) Medium to 

Coarse Pro - MS 3.87 0.146 13 19 25 40 57 71 87 

Tier II (Wasp/5 mph/100%SD) Medium to 

Coarse Pro - MS 3.87 0.146 65 77 87 109 135 160 189 

Tier II (AT 401/10 mph/21%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 13 22 31 48 68 86 109 

Tier II (AT 401/5 mph/21%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 22 34 49 84 114 136 167 

Tier II (AT 401/10 mph/100%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 45 53 63 84 107 127 151 

Tier II (AT 401/5 mph/100%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 78 93 109 134 164 192 222 

Tier II (Wasp/10 mph/21%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 15 27 38 63 88 113 145 

Tier II (Wasp/5 mph/100%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 114 135 156 199 248 295 350 

Tier II (AT 401/10 mph/34%SD) 

4.0 

Medium Pro - MS 3.87 0.146 15 21 26 36 48 60 73 

Tier II (AT 401/5 mph/34%SD) Medium Pro - MS 3.87 0.146 24 30 39 60 77 89 100 

Tier II (AT 401/10 mph/100%SD) Medium Pro - MS 3.87 0.146 31 36 42 55 68 79 90 

Tier II (AT 401/5 mph/100%SD) Medium Pro - MS 3.87 0.146 50 60 69 84 97 107 120 

Tier II (Wasp/10 mph/34%SD) Medium Pro - MS 3.87 0.146 17 23 29 44 60 74 91 

Tier II (Wasp/10 mph/100%SD) Medium Pro - MS 3.87 0.146 36 44 53 68 84 98 112 

Tier II (Wasp/5 mph/34%SD) Medium Pro - MS 3.87 0.146 27 40 53 78 97 112 150 

Tier II (Wasp/5 mph/100%SD) Medium Pro - MS 3.87 0.146 68 79 88 105 123 142 165 

Tier II (AT 401/10 mph/25%SD) Coarse Pro - MS 3.87 0.146 18 28 38 56 80 101 126 

Tier II (Wasp/10 mph/25%SD) Coarse Pro - MS 3.87 0.146 21 33 45 73 103 132 165 

Tier II (AT 401/10 mph/20%SD) Very Coarse Pro - MS 3.87 0.146 20 36 53 86 122 159 204 

Tier II (Wasp/10 mph/20%SD) Very Coarse Pro - MS 3.87 0.146 25 46 67 110 156 205 263 

Tier II (AT 401/10 mph/28%SD) Medium to 

Coarse Pro - MS 3.87 0.146 17 25 33 46 65 83 102 

Tier II (AT 401/5 mph/28%SD) Medium to 

Coarse Pro - MS 3.87 0.146 27 37 50 85 111 129 151 

Tier II (AT 401/10 mph/100%SD) Medium to 

Coarse Pro - MS 3.87 0.146 41 48 58 78 98 114 134 

Tier II (AT 401/5 mph/100%SD) Medium to 

Coarse Pro - MS 3.87 0.146 72 89 102 123 145 165 189 

Tier II (Wasp/10 mph/28%SD) Medium to 

Coarse Pro - MS 3.87 0.146 19 28 37 60 86 106 131 

Tier II (Wasp/5 mph/100%SD) Medium to 

Coarse Pro - MS 3.87 0.146 98 115 130 164 203 240 284 

Tier II (AT 401/10 mph/21%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 19 32 46 72 102 129 163 

Tier II (AT 401/5 mph/21%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 33 51 73 126 170 204 250 

Tier II (AT 401/10 mph/100%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 67 80 95 126 160 190 226 

Tier II (AT 401/5 mph/100%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 117 139 163 200 246 288 332 

Tier II (Wasp/10 mph/21%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 23 40 57 94 132 170 218 

Tier II (Wasp/5 mph/100%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 171 203 233 298 371 442 524 

Tier II (AT 401/10 mph/34%SD) 

2.3 

Medium Pro - MS 3.87 0.146 29 39 47 63 85 106 128 

Tier II (AT 401/5 mph/34%SD) Medium Pro - MS 3.87 0.146 43 55 72 107 135 155 176 

Tier II (AT 401/10 mph/100%SD) Medium Pro - MS 3.87 0.146 54 62 73 95 118 137 157 

Tier II (AT 401/5 mph/100%SD) Medium Pro - MS 3.87 0.146 87 105 121 146 168 185 208 

Tier II (Wasp/10 mph/34%SD) Medium Pro - MS 3.87 0.146 31 42 53 79 107 130 159 
39 of 60 

Application Scenario 

App 

Rate 

(lb ai/A) 

Nozzle 

Configuration 

Day (0) Highest Measured TTR MOEs At Various Distances Downwind From Treated Fields 

Source Appl. 

Rate (ug/cm2) At Edge 

10 

Feet 

25 

Feet 

50 

Feet 

75 

Feet 

100 

Feet 

125 

Feet 

Tier II (Wasp/10 mph/100%SD) Medium Pro - MS 3.87 0.146 63 77 92 119 146 170 195 

Tier II (Wasp/5 mph/34%SD) Medium Pro - MS 3.87 0.146 50 73 97 138 170 196 230 

Tier II (Wasp/5 mph/100%SD) Medium Pro - MS 3.87 0.146 118 137 153 183 215 247 287 

Tier II (AT 401/10 mph/25%SD) Coarse Pro - MS 3.87 0.146 31 49 66 98 139 176 219 

Tier II (Wasp/10 mph/25%SD) Coarse Pro - MS 3.87 0.146 36 58 78 127 180 230 288 

Tier II (AT 401/10 mph/20%SD) Very Coarse Pro - MS 3.87 0.146 35 62 92 150 212 277 355 

Tier II (Wasp/10 mph/20%SD) Very Coarse Pro - MS 3.87 0.146 43 80 116 191 271 356 457 

Tier II (AT 401/10 mph/28%SD) Medium to 

Coarse Pro - MS 3.87 0.146 29 44 57 80 114 144 178 

Tier II (AT 401/5 mph/28%SD) Medium to 

Coarse Pro - MS 3.87 0.146 47 64 87 147 192 224 263 

Tier II (AT 401/10 mph/100%SD) Medium to 

Coarse Pro - MS 3.87 0.146 72 84 101 136 170 199 233 

Tier II (AT 401/5 mph/100%SD) Medium to 

Coarse Pro - MS 3.87 0.146 126 154 178 214 253 288 328 

Tier II (Wasp/10 mph/28%SD) Medium to 

Coarse Pro - MS 3.87 0.146 33 49 65 104 149 185 228 

Tier II (Wasp/5 mph/100%SD) Medium to 

Coarse Pro - MS 3.87 0.146 171 200 227 284 353 418 493 

Tier II (AT 401/10 mph/21%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 33 56 80 125 177 224 283 

Tier II (AT 401/5 mph/21%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 57 89 127 219 296 354 435 

Tier II (AT 401/10 mph/100%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 116 138 166 219 278 330 393 

Tier II (AT 401/5 mph/100%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 203 242 284 348 428 501 578 

Tier II (Wasp/10 mph/21%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 39 70 98 163 230 295 378 

Tier II (Wasp/5 mph/100%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 298 353 406 519 646 769 912 

Tier II (AT 401/10 mph/34%SD) 

2 

Medium Pro - MS 3.87 0.146 33 45 55 73 98 122 147 

Tier II (AT 401/5 mph/34%SD) Medium Pro - MS 3.87 0.146 50 63 82 123 155 179 202 

Tier II (AT 401/10 mph/100%SD) Medium Pro - MS 3.87 0.146 62 71 84 109 136 158 181 

Tier II (AT 401/5 mph/100%SD) Medium Pro - MS 3.87 0.146 100 121 139 168 193 213 239 

Tier II (Wasp/10 mph/34%SD) Medium Pro - MS 3.87 0.146 36 48 60 91 123 150 183 

Tier II (Wasp/10 mph/100%SD) Medium Pro - MS 3.87 0.146 72 89 106 137 168 196 225 

Tier II (Wasp/5 mph/34%SD) Medium Pro - MS 3.87 0.146 58 84 111 159 195 226 264 

Tier II (Wasp/5 mph/100%SD) Medium Pro - MS 3.87 0.146 135 157 176 211 247 284 330 

Tier II (AT 401/10 mph/25%SD) Coarse Pro - MS 3.87 0.146 36 57 76 113 160 203 251 

Tier II (Wasp/10 mph/25%SD) Coarse Pro - MS 3.87 0.146 41 67 90 146 207 264 331 

Tier II (AT 401/10 mph/20%SD) Very Coarse Pro - MS 3.87 0.146 40 71 106 172 243 318 409 

Tier II (Wasp/10 mph/20%SD) Very Coarse Pro - MS 3.87 0.146 50 93 134 220 312 409 525 

Tier II (AT 401/10 mph/28%SD) Medium to 

Coarse Pro - MS 3.87 0.146 33 50 65 92 131 166 204 

Tier II (AT 401/5 mph/28%SD) Medium to 

Coarse Pro - MS 3.87 0.146 54 74 101 169 221 258 302 

Tier II (AT 401/10 mph/100%SD) Medium to 

Coarse Pro - MS 3.87 0.146 82 97 116 156 196 229 267 

Tier II (AT 401/5 mph/100%SD) Medium to 

Coarse Pro - MS 3.87 0.146 144 177 205 246 291 331 378 

Tier II (Wasp/10 mph/28%SD) Medium to 

Coarse Pro - MS 3.87 0.146 38 57 74 119 172 213 262 

Tier II (Wasp/5 mph/100%SD) Medium to 

Coarse Pro - MS 3.87 0.146 196 230 261 327 406 481 567 

Tier II (AT 401/10 mph/28%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 38 65 92 143 203 258 326 

Tier II (AT 401/5 mph/28%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 65 102 146 252 341 407 500 

Tier II (AT 401/10 mph/100%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 134 159 190 252 320 380 452 

Tier II (AT 401/5 mph/100%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 233 279 326 401 492 576 665 

Tier II (Wasp/10 mph/28%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 45 80 113 188 264 340 435 
40 of 60 

Application Scenario 

App 

Rate 

(lb ai/A) 

Nozzle 

Configuration 

Day (0) Highest Measured TTR MOEs At Various Distances Downwind From Treated Fields 

Source Appl. 

Rate (ug/cm2) At Edge 

10 

Feet 

25 

Feet 

50 

Feet 

75 

Feet 

100 

Feet 

125 

Feet 

Tier II (Wasp/5 mph/100%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 342 406 467 597 743 884 1049 

Tier II (AT 401/10 mph/34%SD) 

1 

Medium Pro - MS 3.87 0.146 66 89 109 145 196 243 295 

Tier II (AT 401/5 mph/34%SD) Medium Pro - MS 3.87 0.146 100 126 165 246 311 358 404 

Tier II (AT 401/10 mph/100%SD) Medium Pro - MS 3.87 0.146 124 143 167 218 272 316 362 

Tier II (AT 401/5 mph/100%SD) Medium Pro - MS 3.87 0.146 201 242 278 335 387 427 478 

Tier II (Wasp/10 mph/34%SD) Medium Pro - MS 3.87 0.146 71 97 121 182 246 300 367 

Tier II (Wasp/10 mph/100%SD) Medium Pro - MS 3.87 0.146 145 177 211 274 335 392 450 

Tier II (Wasp/5 mph/34%SD) Medium Pro - MS 3.87 0.146 115 168 223 318 390 452 529 

Tier II (Wasp/5 mph/100%SD) Medium Pro - MS 3.87 0.146 271 314 353 422 494 567 659 

Tier II (AT 401/10 mph/25%SD) Coarse Pro - MS 3.87 0.146 71 114 153 225 320 406 503 

Tier II (Wasp/10 mph/25%SD) Coarse Pro - MS 3.87 0.146 83 133 180 293 413 528 662 

Tier II (AT 401/10 mph/20%SD) Very Coarse Pro - MS 3.87 0.146 80 142 212 344 487 637 818 

Tier II (Wasp/10 mph/20%SD) Very Coarse Pro - MS 3.87 0.146 99 185 267 440 623 818 1051 

Tier II (AT 401/10 mph/28%SD) Medium to 

Coarse Pro - MS 3.87 0.146 66 101 131 185 262 332 408 

Tier II (AT 401/5 mph/28%SD) Medium to 

Coarse Pro - MS 3.87 0.146 107 148 201 338 442 515 605 

Tier II (AT 401/10 mph/100%SD) Medium to 

Coarse Pro - MS 3.87 0.146 165 194 232 312 392 457 535 

Tier II (AT 401/5 mph/100%SD) Medium to 

Coarse Pro - MS 3.87 0.146 289 354 409 493 581 661 755 

Tier II (Wasp/10 mph/28%SD) Medium to 

Coarse Pro - MS 3.87 0.146 75 114 149 239 343 425 525 

Tier II (Wasp/5 mph/100%SD) Medium to 

Coarse Pro - MS 3.87 0.146 393 459 522 654 812 961 1134 

Tier II (AT 401/10 mph/28%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 75 129 184 287 406 516 652 

Tier II (AT 401/5 mph/28%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 131 204 292 503 682 814 1000 

Tier II (AT 401/10 mph/100%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 267 318 381 505 640 759 905 

Tier II (AT 401/5 mph/100%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 466 558 653 801 984 1152 1329 

Tier II (Wasp/10 mph/28%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 91 160 226 376 529 679 870 

Tier II (Wasp/5 mph/100%SD) Coarse to Very 

Coarse Pro - MS 3.87 0.146 685 812 934 1194 1485 1769 2098 

MOEs<100 indicate a risk estimate of concern 

6 Issues For Consideration 

The available incident data and limited monitoring data included in the risk assessment indicated 

spray drift can be of concern. The analysis in this document supplements the findings in the 2011 

HHRA by using modeling approaches which allow for a broader consideration of the potential 

impacts on risk estimates due to varied application scenarios. This analysis was developed by 

coupling established methods for estimating spray drift and residential exposures. As such, the 

caveats and concerns that can be associated with those techniques also apply herein. 

Even given this premise, there are a significant number of issues that should be considered in the 

interpretation of the results including: 

• The risk estimates calculated are based on the premise that spray drift occurs in a manner 

similar to that predicted and that an exposed person is at the locations and exhibits the 

behaviors mimicked in the risk assessment. These activities are believed to be plausible. 
41 of 60 

Examples could include homebound individuals at a location downwind and lawns 

adjacent to fields that could be contaminated followed by children playing on them. 

• The analysis and resulting recommendations have been developed in a manner consistent 

with guidance in the draft PR Notice for spray drift labeling and the DRTs. The 

evaluation of possible risk mitigation approaches considered information developed in a 

manner consistent with this context. One example may be to develop droplet spectra data 

that evaluates the impact of adjuvants on the spray pattern (e.g., sticking and drift 

reduction agents). 

• Spray drift values are based on the general application of the Tier I output values from 

AgDRIFT and the subsequent higher tier analyses that were completed. There are 

uncertainties associated with all of these approaches which have been discussed 

extensively during the activities of the SDTF and the development of these models. All of 

the associated uncertainties apply to the results of this analysis (please refer to the FIFRA 

SAP reviews cited above). There are additional analyses which could be completed in 

order to elicit how sensitive spray drift levels may be to such changes (e.g., evaluate 

impact of alternative aircraft, evaluate nozzle placement, impacts of surface roughness). 

It should also be noted that in the drift analyses completed in the assessment, wind 

vectors were moving from treated areas to the downwind area of the field 100 percent of 

the time and in most analyses (except some mitigation option analyses that considered 

lower values) windspeed was set to 10 mph which would maximize spray drift levels 

under the model conditions. 

• The residential aspects of the calculation are based on the recently revised SOPs that have 

undergone an extensive review process as cited above. Associated with each calculation 

there is a degree of uncertainty which is described in detail in the SOPs themselves. A 

couple of issues should be noted in the interpretation of the calculated risks. In this case a 

TTR study for chlorpyrifos using multiple formulations in three different locations was 

available. The formulation that provided the highest relative TTR was used for estimating 

risks (Dursban Pro – which is a commonly used liquid formulation). TTR levels in the 

cited study varied by about a factor of two depending upon location and the type of 

formulation. Also, the TTR half-life in all cases was less than 1 day and in most cases 

less than 12 hours. Using this formulation, as compared with granules as an example, 

more closely mimics the exposures that would be expected from liquid spray drift. 

• Aerial application is used on a small percentage of the crops for which chlorpyrifos is 

labeled, with the percent crop treated for most crops on the order of 1 to 2 percent. 

However, when acreage is treated using aircraft, it can account for a substantial number 

of the total applications for that crop on an annual basis (e.g., alfalfa, almonds, apples, 

asparagus). 

• Single day risk estimates were calculated by comparing calculated exposures to PODs 

defined based on animal studies that are of high quality and appropriate for that purpose. 

For many pesticides, defining PODs for single day non-dietary exposure scenarios is 

difficult, but for chlorpyrifos the data exists. For the inhalation exposure pathway, a state 
42 of 60 

of the art study that defined lung cholinesterase as the endpoint was used to establish the 

POD (i.e., the HEC). For non-dietary ingestion a single day POD, the same used for 

defining the aPAD in the 2011 HHRA, was used. It was established based on the results 

of a single dose CCA (comparative cholinesterase assay) study that measured 

cholinesterase inhibition. Finally, 4 day sacrifice data in the same 21 day dermal toxicity 

study used to define the dermal POD in the 2011 HHRA also supports using the existing 

POD also as the basis of a the single day assessment approach. This characterization of 

the dermal study is also supported by a human volunteer dermal study (Nolan et al, 

1992). Finally, the dichotomy between the nominal droplet size used to generate the HEC 

and the airborne exposure concentration should be considered in any evaluation of the 

related risk estimates (i.e., they are conservative because only a small percentage of the 

airborne exposure concentration is made up of droplets which could reach the lung). 

7 Conclusions and Recommendations 

Because it can be demonstrated that spray drift occurs even if applications are compliant with 

labels, spray drift has been further examined to quantify potential risk estimates associated with 

exposure to chlorpyrifos downwind of a treated field. The approaches used as the basis for all 

calculations in this document have been thoroughly vetted through a public peer review process. 

In most cases, the findings indicate risks are a concern adjacent to treated fields and aerial 

applications, out of all application types considered, have the highest associated risk estimates. 

There are several actions which could be taken that would result in lower risk estimates. The 

impacts have been examined quantitatively where feasible. In some cases, differing 

combinations of possible mitigation options were also considered. These include: 

• Reduce maximum application rates to those needed to achieve desired efficacy as 

appropriate. 

• Require that buffer distances, similar to those already in place to address aquatic risk 

concerns, also be required to alleviate potential human health risks in situations where 

deemed appropriate. This would entail altering labels to expand the applicability and 

scope of the existing buffer distances for all areas where drift could result in human 

exposure. 

• Implement drift reduction technologies and approaches consistent with DRTs that can 

alleviate risks including: 

o require larger droplets be used to alter spray patterns and reduce drift (e.g.,

perhaps by requiring larger nozzle sizes by specifying a droplet size distribution 

(i.e., Dv0.5) on the label)) 

o require larger swath displacement from field edge 

• Other possible approaches, consistent with the spirit of those used recently to manage 

potential risks for fumigants, may also be appropriate such as: 

o drift management plans for applicators 
43 of 60 

o specialized training for applicators on drift management issues 

o use of buffer credit system consistent with the concept of DRTs, supported by 

appropriate data 

o place restrictions around sensitive areas such as schools 

o encourage use of technology to manage drift such as GPS for pilots 

• Restrict aerial applications based on risk findings and available mitigation options. 

Data to confirm the efficacy of any DRT measures implemented to reduce the risk estimates 

associated with spray drift from chlorpyrifos should be developed. 
44 of 60 

Appendix A- Summary of Label Use Patterns

Table A1: Summary of Chlorpyrifos Agricultural Uses

Crop or Target

Maximum (Single) 

Application Rate

(lb ai/A)

Application Type/Equipment

Alfalfa 1.0 Aerial, Chemigation, Groundboom, Tractor 

Drawn Spreader

Asparagus 1.0 Aerial, Groundboom

1.5 Soil Ground Band (postharvest) (CA only) 

(Midwest and Pacific Northwest states – 

Amvac)

Beets (Table and Sugar Grown 

for Seed)

2 Soil Ground (preplant, at-plant) (24c)

Brassica Vegetable (Bok Choy, 

Broccoli, Broccoli Raab, 

Brussels Sprout, Cabbage, 

Cauliflower, Chinese Broccoli, 

Collards, Kale, and Kohlrabi)

1.0 Foliar Ground, Aerial

2.25 Soil Ground Spreader or Splitter, T-Band 

(at-plant)

2.4 Soil Band, Broadcast, Sidedress, & 

Injection (at plant, established plant, 

postplant) 

Cauliflower 1.2 oz/1000 ft row Soil Ground, Soil Injected (preplant, atplant, postplant)

Broccoli, broccoli raab, etc. 1.3 - 1.4 oz/1000 ft row Soil Ground, Soil Injected (preplant, atplant, postplant)

Broccoli, Brussels sprout, 

cabbage

1.4 oz/1000 ft row Ground (at-plant) (24c)

Cauliflower 1.3 oz/1000 ft of row Ground (at-plant) (24c)

Bok choy, broccoli raab, 

Chinese broccoli

2.11 Soil Ground (at-plant) (24c)

Carrot (Grown for Seed) 1 Aerial, Groundboom (24c)

Citrus Fruit 6 (AZ and CA) Aerial, Airblast, Groundboom, High 

Volume Spray (dilute), Low Volume 

(concentrate) Ground Sprayer, Broadcast, 

4 (States other than AZ 

and CA) 

Aerial, Airblast, Groundboom, High volume 

Spray (dilute), Low Volume Ground 

(concentrate) Sprayer 

2.5 (24c) Trunk Drench, Hand Held Sprayer 

2.0 Soil Broadcast, Chemigation Orchard 

Floors, Fertilizer Treatment; Mechanical 

Mixer 

1.0 Soil Ground Orchard Floors

Soil Ground, Chemigation Orchard Floors, 

Fertilizer Treatment, Trunk Drench, Soil 

Broadcast, Directed Spray, Granule 

Applicator, Mechanical Mixer, Power 
45 of 60 

Sprayer, Backpack Mist

Citrus orchard floors 1.0 Soil Ground orchard floors

Soil Ground, chemigation orchard floors

Clover (Grown for Seed) 2.0 (24c) Soil Ground (preplant), Broadcast Foliar 

Ground (postplant) 

Corn (Field, Grown for Seed 

and Sweet)

3.0 Soil Incorporation (preplant)

2.0 Soil In-Furrow, T-Banding, Granule 

Applicator (at plant; post plant) 

1.5 Aerial, Broadcast, Chemigation 

(postemergence) 

1.0 Foliar Aerial (postplant); 

Soil Band/In-Furrow Ground (preplant, atplant, preemergence); Broadcast, 

Chemigation 

Field, sweet 0.06 lb/lb seed (24c) Commercial seed treatment 

Field, sweet 0.5 Foliar Ground, Aerial, Chemigation 

(preplant, at plant, postemergence) (24c)

Cotton 2.0 (24c) Aerial, Broadcast, Power Sprayer 

Cotton 1.0 Aerial, Foliar, Broadcast, Chemigation, 

Groundboom

Cotton 012 lb/lb seed Commercial Seed Treatment 

Cranberry 1.5 Aerial, Chemigation, Groundboom, 

Broadcast Sprayer

Fig (CA only) 2.0 Soil Incorporation (dormant)

Ginseng 2.0 Soil Broadcast (preplant incorporation, 

postemergence) 

Grapes 2.0 Soil Surface, Broadcast Ground Spray 

(dormant, delayed dormant) (24c, East of 

Continental Divide) postharvest (24c)

1.0 Soil Drench (prebloom), Soil Broadcast, 

Ground, Hand-Held Sprayer (base, vine, 

Soil) (24c)

Legume Vegetables (Succulent 

or Dried, Except for Soybeans)

1.0 Soil Incorporation, T-Band, Ground 

(preplant, at-plant)

Mint (Peppermint and 

Spearmint)

2.0 Chemigation, Groundboom

Onion (Dry Bulb) 1.0 Groundboom, Tractor Drawn Spreader, 

Handgun

Peanut 2.0 Soil Ground (at-plant)

Foliar Ground (postplant, band rescue)

Soil Ground (preplant)

Peppers 1.0 Broadcast, Foliar, Groundboom (24c)

Pineapple (Non-bearing) 2.0 Broadcast, Foliar Ground (postplant) (24c)

Radish 3.0 Soil Ground Spreader or Splitter (at-plant 

in-furrow)

Radish (Grown for Seed) 1.0 Foliar Ground (24c)

Rutabaga 8.8 Soil T-Band (at plant) 

2.0 Soil T-Band, Incorporation (preplant; atplant)
46 of 60 

Sorghum 3.0 Soil Band, Incorporation (at plant) 

1.0 Aerial, Chemigation, Groundboom, Soil TBand, Incorporation, Broadcast (at plant, 

postemergence, Foliar)

0.0024 lb/lb seed Commercial Seed Treatment

Soybean 2.0 Soil T-Band, Incorporate, Ground (at-plant, 

postplant)

1.0 Aerial, Broadcast, Foliar Groundboom, 

Chemigation (preemergence, at-plant, 

postemergence) 

Strawberry 2.0 Groundboom, Soil Incorporation, Broadcast 

(preplant spring, Foliar)

1.0 Broadcast, Directed Spray (Foliar), Soil 

Incorporation (preplant); Foliar Ground 

(postharvest)

Sugarbeet 2.0 Soil Incorporation, Band, (preplant, at plant, 

postplant) 

1.0 Aerial, Chemigation, Groundboom, 

Broadcast, Soil Band, Incorporation, (atplant, preplant, postemergence) 

0.5 Soil band, Incorporation (preplant, at plant)

Sugarbeet (Grown for Seed) 2.0 Soil incorporation, (preplant, at-plant) 

(24c)Aerial, Chemigation, Groundboom

Sunflower 2.0 Soil Ground (at-plant)

Soil Ground (preplant)Aerial, Groundboom

1.5 Foliar Ground, Aerial Broadcast 

(postemergence)

Sweet Potato 2.0 Soil preplant incorporation

Tobacco 2.0 Soil preplant incorporation

Almonds 4.0 Chemigation, Soil Broadcast, Foliar, Mound 

Treatment

3.0 lb/100 gal Trunk Drench, Foliar 

2.0 Foliar Ground, Aerial, Broadcast, Ground, 

High Volume Dilute and Low Volume 

Concentrate Sprays (dormant/delayed 

dormant)

Almond orchard floor 4.0 Soil Ground orchard floor, Soil Broadcast, 

chemigation, individual Mound Treatment

Filbert 2.0 Foliar Ground, Aerial, Broadcast, Ground, 

High Volume Dilute and Low Volume 

Concentrate Sprays (dormant/delayed 

dormant)

Pecan 4.0 Chemigation, Soil Broadcast, Foliar

2.0 Foliar Ground, Aerial, Broadcast, Ground, 

High Volume Dilute and Low Volume 

Concentrate Sprays (dormant/delayed 

dormant)
47 of 60 

1.0 Foliar Ground, Aerial, Broadcast, Ground, 

High Volume Dilute and Low Volume 

Concentrate Spray (dormant/delayed 

dormant) 

Pecan orchard floor 2.0 Soil Ground, chemigation orchard floors

Walnut 4.0 Chemigation, Soil Broadcast, Foliar

2.0 Foliar Ground, Aerial, Broadcast, Ground, 

High Volume Dilute and Low Volume 

Concentrate Sprays (dormant/delayed 

dormant)

1.0 Foliar Ground, Aerial, Broadcast, Ground, 

High Volume Dilute and Low Volume 

Concentrate Sprays

Apple 3.0 Ground High Volume Dilute Spray 

(dormant, delayed dormant)

2.0 Ground High Volume Dilute & Low 

Volume Concentrate Spray 

(dormant/delayed dormant), Broadcast

1.5 lb/100 gal Trunk Spray Low Volume Handgun, 

Shielded Spray equipment 

Cherry-sour 1.5 Foliar Ground, Aerial

Cherry 2.0 Foliar Ground, Aerial (dormant, delayed 

dormant)

3 lb/100 gal Ground trunk Spray (Foliar, postharvest)

Nectarine, Peach 2.0 Ground High Volume Dilute & Low 

Volume Concentrate Spray, 

(dormant/delayed dormant) 

 3 lb/100 gal Ground trunk Spray or preplant dip

Pear 3.0 Ground High Volume Dilute Spray 

(dormant, delayed dormant)

2.0 Ground airblast speed Sprayer 

(postharvest); Ground High Volume Dilute 

& Low Volume Concentrate Spray ( 

dormant/delayed dormant)

Plum/prune 3.0 Ground High Volume Dilute & Low 

Volume Concentrate Spray (dormant, 

delayed dormant)

3 lb/100 gal Trunk Drench, Foliar 

Pumpkin 0.0625 lb/lb seed (24c) Commercial Seed Treatment, preplant 

Triticale 0.0024 lb/lb seed Commercial Seed Treatment 

Turnip 2.25-2.4 Soil Ground spreader or splitter ; Broadcast, 

Directed Spray, Soil band, Incorporation, 

(preplant, at-plant, postplant)

1.4 oz/1000 ft row Soil Ground (preplant, at-plant, postplant)

Wheat 4.0 (24c) Soil Incorporation, Foliar 

1.0 Aerial, Broadcast, chemigation 

0.5 Aerial, Chemigation, Groundboom, 

Broadcast, Foliar
48 of 60 

0.0024 Commercial seed treatment

 

Table A2: Summary of Chlorpyrifos Non-Agricultural Uses 

Crop or Target

Maximum (Single) 

Application Rate

(lb ai/A)

Application Equipment

Ants (Fire Ant Mound, 

Carpenter)

0.080 (lb ai/gallon) Backpack Sprayer, Handgun, Low Pressure 

Handwand

Cattle Ear Tags 0.0066 (lb ai/ ear tag) Pliers (spring, summer)

Christmas Trees (Nurseries and 

Plantations, Stumps) 

1.0 Foliar Ground nurseries & plantations

Foliar Ground plantations; Broadcast, 

Aerial (Helicopter)

3 lb/100 gal Stump treatment, Drench

Golf Course Turf 4.0 Spot treatment 

1.0 Belly Grinder, Low Pressure Handwand, 

Push Type Spreader, Tractor Drawn 

Spreader, Turfgun; Soil Broadcast, Mound 

Treatment, 

Grass Seed (Perennial Crops) 1.0 Foliar, Ground, Aerial

Greenhouse and Nursery 

Production (Bedding Plants, 

Containerized Ornamentals, Cut 

Flowers, Flowering Hanging 

Baskets, Pine Seedling 

Transplant, Potted Flowers, 

Ornamentals, Trees and Shrubs)

4.0 Soil Ground (preplant) field grown nursery 

stock

3.0 High Volume Dilute Spray, Ground 

(dormant, delayed dormant) 

1.0 High Volume Dilute Spray, Ground 

(dormant, delayed dormant), Low 

Volume Concentrate Spray, trunk 

Drench, stump treatment, Foliar, 

preplant incorporation, Broadcast 

(Power Sprayer, Hand Held), 

1.0 Submerge Soil (containerized (potted) or 

balled & burlapped nursery stock)

Mosquitocide (Outdoor 

Residential, Recreational, or 

Other Non-Cropland Areas)

0.010 Wide Area Aerial and Ground

Non-crop Areas (Commercial 

Indoor/Outdoor Industrial Sites, 

Commercial Livestock Holding 

and Housing, Dumpsters/ Trash 

Areas, Food Processing Plants, 

Grown for Seed, Industrial 

Plant Site Perimeter 

Treatments, Manufacturing 

Sites, Power Utilities, Railroad 

Box Cars, Railroad Equipment, 

Road Medians, Ship Holds, Sod 

Farms, Telecommunications, 

1.0 Aerial (ultra Low Volume), Belly Grinder, 

Groundboom, Push Type Spreader, Tractor 

Drawn Spreader, Soil Broadcast, 

band,treatment, Mound Treatment 

0.11 (lb ai/gallon) Backpack Sprayer

0.080 (lb ai/gallon) Handgun, Low Pressure Handwand, Paint 

Brush/Roller

0.044 (lb ai/1,000 sq ft) Shaker Container

0.018 (lb ai/1,000 sq ft) Open Pour Bag 
49 of 60 

Warehouse Sites)

Ornamentals (Cut Flowers, 

Industrial Buildings/Plant Sites 

Perimeter Treatments and Road 

Medians, Evergreens, Field 

Grown Nursery Stock, Flowers, 

Greenhouses, Non-bearing Fruit 

Trees Shrubs, Nurseries, Trees, 

Vines, Woody) 

6.0 Belly Grinder, Push Type Spreader, Tractor 

Drawn Spreader, Broadcast, preharvest

4.0 Groundboom, Preplant Incorporation

3.0 High Volume Dilute Ground Sprayer 

(dormant, delayed dormant)

2.0 Broadcast, Hand Held Sprayer, Power 

Sprayer 

0.16 (lb ai/gallon) Backpack Sprayer, Handgun, High Pressure 

Handwand, Low Pressure Handwand

0.020 (lb ai/gallon) Drench/Dip

Poultry Litter 3.0 Bedding/Litter Treatment; Sprayer 

Roach Control Bait Stations 0.00026 (lb ai/bait 

station)

Hand

Sewer Manhole Walls 0.30 lb/manhole Airlee Spray Equipment Delivered thru a 6 

ft. Spray Wand 

Trees (Cottonwood and Poplar 

Trees Grown for Pulp, Conifer, 

Deciduous, Grown in Nurseries 

and Greenhouses) 

2.0 Foliar Ground, Aerial, (dormant/delayed 

dormant) (24c)

Turfgrass (Sod or Seed) 4.0 Soil surface, Spot Treatment, 

1.0 Tractor Drawn Spreader, Soil Broadcast 

treatment, Sprayer

Wood Products (Fence Posts, 

Industrial Sites, Landscape 

Timbers, Logs, Manufacturing, 

Pallets, Processed Wood, Right 

of Way, Railroad Ties, Utility 

Poles, Wooden Containers) 

16.65 lb/10,000 sq. ft. Belly Grinder, Push Type Spreader, wood 

Surface Treatment, Brush, Sprayer

 
50 of 60 

Appendix B - Lorsban 75WP Label Excerpt 

Spray Drift Management

Do not allow spray to drift from the application site and contact people, structures people occupy 

at any time and the associated property, parks and recreation areas, non-target crops, aquatic and 

wetland sites, woodlands, pastures, rangelands, or animals. 

Avoiding spray drift at the application site is the responsibility of the applicator. The interaction 

of many equipment and weather-related factors determine the potential for spray drift. The 

applicator is responsible for considering all of these factors when making the decision to apply 

this product. 

Observe the following precautions when spraying Lorsban 75WG adjacent to permanent bodies 

of water such as rivers, natural ponds, lakes, streams, reservoirs, marshes, estuaries, and 

commercial fish ponds. 

The following treatment setbacks or buffer zones must be utilized for applications around the 

above-listed aquatic areas with the following application equipment: 

Application Method Required Setback 

(Buffer Zone) (feet) 

ground boom 25 

chemigation 25 

orchard airblast 50 

aerial (fixed wing or helicopter) 150 

Making applications when wind is blowing away from sensitive areas is the most effective way 

to reduce the potential for adverse effects. 

The following spray drift best management practices are recommended to avoid off-target drift 

movement from applications. 

Aerial Application 

• The boom width must not exceed 75% of the wingspan or 90% of the rotor blade. 

• Nozzles must always point backward, parallel with the air stream, and never be pointed 

downward more than 45 degrees. 

• Nozzles must produce a medium or coarser droplet size (255 to 340 microns volume 

median diameter) per ASABE Standard 572 under application conditions. Airspeed, 

pressure, and nozzle angle can all effect droplet size. See manufacturer's catalog or 

USDA/NAAA Applicator's Guide for spray size quality ratings. 

• Applications must not be made at a height greater than 10 feet above the top of the 

target plants unless a greater height is required for aircraft safety. Making applications at 

the lowest height that is safe reduces exposure of droplets to evaporation and wind. 
51 of 60 

• Use upwind swath displacement and apply only when wind speed is 3 to 10 mph as 

measured by an anemometer. Do not apply product when wind speed exceeds 10 mph. 

• If application includes a no-spray zone, do not release spray at a height greater than 10 

feet above the ground or crop canopy. 

Where states have more stringent regulations, they must be observed. 

The applicator should be familiar with and take into account the information covered in the 

Aerial Drift Reduction Advisory. 

Aerial Drift Reduction Advisory 

This section is advisory in nature and does not supercede the mandatory label 

requirements. 

Information on Droplet Size: The most effective way to reduce drift potential is to apply large 

droplets. The best drift management strategy is to apply the largest droplets that provide 

sufficient coverage and control. Applying larger droplets reduces drift potential, but will not 

prevent adverse effects from drift if applications are made improperly, or under unfavorable 

environmental conditions (see Wind, Temperature and Humidity, and Temperature Inversions). 

Controlling Droplet Size: 

• Volume - Use high flow rate nozzles to apply the highest practical spray volume. 

Nozzles with higher rated flows produce larger droplets. 

• Pressure - Do not exceed the nozzle manufacturer's recommended pressures. For many 

nozzle types, lower pressure produces larger droplets. When higher flow rates are needed, 

use higher flow rate nozzles instead of increasing pressure. 

• Number of nozzles - Use the minimum number of nozzles that provide uniform 

coverage. 

• Nozzle orientation - Orienting nozzles so that the spray is released parallel to the 

airstream produces larger droplets than other orientations and is the recommended 

practice. Significant deflection from horizontal will reduce droplet size and increase drift 

potential. 

• Nozzle type - Use a nozzle type that is designed for the intended application. With most 

nozzle types, narrower spray angles produce larger droplets. Consider using low-drift 

nozzles. Solid stream nozzles oriented straight back produce the largest droplets and the 

lowest drift. 

Boom Length: For some use patterns, reducing the effective boom length to less than 3/4 of the 

wingspan or rotor length may further reduce drift without reducing swath width. 

Application Height: Applications should not be made at a height greater than 10 feet above the 

top of the target plants unless a greater height is required for aircraft safety. Making applications 

at the lowest height that is safe reduces exposure of droplets to evaporation and wind. 

Swath Adjustment: When applications are made with a crosswind, the swath will be displaced 

downwind. Therefore, on the up and downwind edges of the field, the applicator should 
52 of 60 

compensate for this displacement by adjusting the path of the aircraft upwind. Swath adjustment 

distance should increase, with increasing drift potential (higher wind, smaller drops, etc.). 

Wind: Drift potential is lowest between wind speeds of 2 to 10 mph. However, many factors, 

including droplet size and equipment type, determine drift potential at any given speed. 

Application should be avoided below 2 mph due to variable wind direction and 'high inversion 

potential. Note: Local terrain can influence wind patterns. Every applicator should be familiar 

with local wind patterns and how they affect spray drift. 

Temperature and Humidity: When making applications in low relative humidity, set up 

equipment to produce larger droplets to compensate for evaporation. Droplet evaporation is most 

severe when conditions are both hot and dry. 

Temperature Inversions: Applications should not occur during a temperature inversion because 

drift potential is high. Temperature inversions restrict vertical air mixing, which causes small 

suspended droplets to remain in a concentrated cloud. This cloud can move in unpredictable 

directions due to the light variable winds common during inversions. Temperature inversions are 

characterized by increasing temperatures with altitude and are common on nights with limited 

cloud cover and light to no wind. They begin to form as the sun sets and often continue into the 

morning. Their presence can be indicated by ground fog; however, if fog is not present, 

inversions can also be identified by the movement of smoke from a ground source or an aircraft 

smoke generator. Smoke that layers and moves laterally in a concentrated cloud (under low wind 

conditions) indicates an inversion, while smoke that moves upward and rapidly dissipates 

indicates good vertical air mixing. 

Sensitive Areas: The pesticide should only be applied when the potential for drift to adjacent 

sensitive areas (e.g., residential areas, bodies of water, known habitat for threatened or 

endangered species, nontarget crops) is minimal (e.g., when wind is blowing away from the 

sensitive areas). 

Ground Boom Application 

The following mandatory spray drift best management practices are required to reduce the 

likelihood of off-target drift movement from ground applications. 

• Choose only nozzles and pressures that produce a medium or coarse droplet size (255 to 

400 microns volume median diameter), per ASABE Standard 572. See manufacturer's 

catalog or USDA/NAAA Applicator's Guide for spray size quality ratings. 

• Apply with nozzle height no more than 4 feet above the ground or crop canopy. 

• Do not apply product when wind speed exceeds 10 mph as measured by an 

anemometer. 

Orchard Airblast Application 

The following mandatory spray drift best management practices are required to reduce the 

likelihood of off-target drift movement from airblast applications. 

• Nozzles must be directed so spray is not projected above the canopies. 
53 of 60 

• Apply only when wind speed is 3 to 10 mph at the application site as measured by an 

anemometer outside of the orchard/vineyard on the upwind side. 

• Outward pointing nozzles must be shut off when turning corners at row ends. 

The applicator should take into account the following best management practices to reduce offsite spray drift. This section is advisory and does not supersede mandatory label requirements. 

• Number of nozzles, nozzle orientation and spray volume, air speed and wind direction are key 

factors in adjusting airblast spray delivery to match the height and density of the crop canopy. 

Airblast equipment should be adjusted to provide uniform coverage while minimizing the 

amount of spray movement over-the-top or completely through the crop canopy. 

• High air volumes deliver spray more efficiently than air at high speed. Reducing 

forward travel speed decreases the air speed necessary to deliver the spray to the top of 

the crop canopy. 

• Use air guides along with the number and orientation of spray nozzles to achieve the 

desired spray coverage and directional control. 

• The following steps should be taken to minimize drift and the amount of non-target spray: 

• Orient nozzles and adjust air speed/volume/direction to force the spray through the crop 

canopy but not allow drift past the canopy. 

• Shut off spray delivery when passing gaps in crop canopy within rows. 

• Spray the outside rows of orchards from outside in, directing the spray into the orchard 

and shutting off nozzles on the side of the sprayer away from the orchard. 

• When treating smaller trees, vines or bushes, shut off top nozzles to minimize over-the-top 

spray movement. 
54 of 60 

Appendix C- Summary of Use Information

Chlorpyrifos usage data on all crops were compiled from a private marketing research database. 

For the years 2006-2010, the following information was queried at the crop level: pounds of 

active ingredient (a.i.) applied, total area treated (includes multiple applications to the same 

field), base area treated (the area treated at least once), crop area grown, percent of crop treated, 

average a.i. single application rate, the average number of applications per year (row crops only). 

Averages were calculated for each variable over the five years of data. To calculate the average 

number of applications per year for the specialty crops, the total area treated was divided by the 

base area treated. When possible, a comparison was made to the relevant data that were 

available from the USDA National Agricultural Statistics Service (NASS) pesticide use reports. 

For the following crops: beans, cucumbers, dry beans, hazelnuts, peas, peppers, plums/prunes, 

pumpkins, sorghum, and squash, the data are considered less robust because the values are based 

on a limited sample size (this is defined as a total sample size of <50 across 5 years), and the data 

could not be verified in NASS. While the low sample size may simply be a function of low use, 

sample size is also an indication of reliability and should be considered when using the data. 

In addition to estimating the average application rate for chlorpyrifos, a rate distribution was 

generated to estimate an upper bound application rate for each crop. The data were generated 

using the a.i. Rate Range database variable (set from 0-10 pounds applied per application and at a 

rate interval of 0.25 pounds a.i. applied per application) along with the total acres treated 

database variable. These variables are part of the search functions available in the software 

provided along with the proprietary market database. To calculate the upper bound rate, the total 

area treated reported at each rate interval was divided by the cumulative total area treated across 

all intervals. A running total was included to show the cumulative percentile at each rate 

increment and the rate associated with the 90th percent was reported as the upper bound rate. 

The upper bound rate in this analysis is the rate at which 90% (or as close to 90% as possible) of 

the acres treated with chlorpyrifos are treated at or below. The values obtained using this 

process, related to the overall use of chlorpyrifos, are provided in an accompanying spreadsheet 

to this document denoted as D399483-Appendix C. 

The key information, excerpted from a separate memorandum, which details how ground 

applications play a role in chlorpyrifos use (Grube, 2012) is included below for informational 

purposes. 
55 of 60 

Table 1: Ground Applications of Chlorpyrifos to Agricultural Crops 2006-

2010 excluding Seed Treatments and Incorporated Applications

%of Total 

Applications Maximum Rate 

Observed 

Applied by %of Total Average Lbs for Ground Applications 

Ground Crop 

Acreage 

AI Year 

Applied by 

Average 

Application Rate 

(rounded up) When 90th 

percentile is 

 Treated by Ground for Ground lower it is shown in 

Crop Ground Applications parentheses 

Alfalfa 69 2 320,000 0.6 1.0 

Almonds 86 20 380,000 1.9 (2.0) 4.0 

Apples 95 59 370,000 1.5 (2.0) 2.8 

Asparagus 76 29 10,000 (1.0) 1.5 

Beans (Snap) 99 2,000 0.5 1.0 

Broccoli 100 53 100,000 1.4 (2.1) 2.3 

Cabbage 100 14 10,000 1.1 (1.5) 2.3 

Cauliflower 99 40 15,000 1.1 (1.5) 2.3 

Cherries 98 36 80,000 1.5 (2.0) 3.0 

Com 19 0 200,000 0.9 (1 .5) 3.0 

Cotton 32 150,000 0.8 1.0 

Dry 

BeanslPeas 37 0 5,000 0.5 (0.5) 0.8 

Grapefruit 98 22 50,000 1.9 3 

Grapes, 

Raisin 100 8 50,000 1.9 (2.0) 2.2 

Grapes, Table 100 51 140,000 2.7 4 

Grapes, Wine 100 9 120,000 2 (2.0) 4.0 

Hazelnuts 68 8 4,000 1.4 2 

Lemons 96 37 90,000 3.6 6 

Onions 100 45 70,000 0.9 (1.1) 2.8 

Oranges 93 22 600,000 2.6 6 

Peaches 95 26 50,000 1.3 (2.0) 3.0 

Peanuts 13 20,000 1.6 2 

Pears 97 17 20,000 1.8 2 

Peas (Fresh) 100 1,000 1 (1.0) 1.4 

Pecans 85 24 200,000 0.9 (1.0) 3.4 

Peppers 93 2 2,000 0.8 1.5 

PlumsIPrunes 100 11 25,000 1.8 2 

Potatoes 82 0 1,000 0.8 I 

Pumpkins 100 1 2,000 1 (1.1) 1.2 

Sorghum 47 0 6,000 0.5 0.8 

Soybeans 82 5 3,000,000 0.4 (0.8) 1.1 

Squash 99 2 800 (1.5) 2.0 

Strawberries 100 28 15,000 (1.0) 2.0 

Sugar Beets 38 4 40,000 0.7 (1 .0) 2.0 

Sunflowers 20 15,000 0.5 (0.5) 0.6 

Sweet Com 57 7 70,000 1.1 (2.0) 4.0 

Tobacco 83 11 80,000 2.1 (2.1) 5.0 

Walnuts 94 43 320,000 1.8 (2.0) 4.0 

Wheat, 

'Spring 56 70,000 0.3 (0.5) 1.0 

Wheat, 

Winter 69 2 290,000 0.4 (0.8) 1.0 
56 of 60 

Table 2. Incorporated Ground Applications of Chlorpyrifos 2006-2010 

 Maximum Rate 

Observed for 

% of Total Incorporated 

Applications % of Total Crop Average Lbs AI Averagc Applications (rounded 

Incorporated Acreage With Year Applied Application Rate up)When 90th 

percentile 

 Incorporated by Incorporated for Incorporated is lower it is shown in 

Crop Treatments Applications Applications parentheses 

Com 65 800,000 1.0 (1.4) 2.0 

Cotton 5 0 15,000 0.4 1.0 

Dry Beans/Peas 45 0 5,000 0.5 0.5 

Peanuts 85 6 140,000 1.7 2.0 

Potatoes 10 0 <500 1.1 1.5 

Sorghum 13 0 3,000 0.8 0.8 

Soybeans 0 40,000 0.6 1.2 

Sugar Beets 50 5 80,000 1.0 (1.0) 2.0 

Tobacco 17 2 13,000 1.6 (2.1) 5.0 

The applications reported in this table were those for which the application method clearly indicated incorporation. This level of 

detail 

about application method was not available for fruits and vegetables so some of the ground applications for those crops may have 

incorporated as well as some of the ground applications for field crops not listed here. Source: Private market research data, 2006-

2010. 
57 of 60 

Appendix D- Model Screenshots

 
58 of 60 

Appendix E - Results of Drift Modeling

Figure E.1. Tier II Spray Drift Analysis: Deposition Curves for a Fine to Medium Droplet 

Size Following Chlorpyrifos Application Using Several Different Aerial Application 

Configurations 

Figure E.2. Tier II Spray Drift Analysis: Deposition Curves for a Medium to Coarse 

Droplet Size Following Chlorpyrifos Application Using Several Different Aerial 

Application Configurations 

 

0

0.1

0.2

0.3

0.4

0.5

0.6

0 50 100 150 200 250 300

Fraction of Applied

Distance Downwind From Treated Fields (feet)

F2M, AT401, 10 mph, 37% SD 

F2M, WASP, 10 mph, 37% SD

F2M, AT401, 5 mph, 37% SD 

F2M, AT401, 10 mph, 100% SD

F2M, AT401, 5 mph, 100% SD

F2M, WASP, 5 mph, 100% SD 

0

0.1

0.2

0.3

0.4

0.5

0.6

0 50 100 150 200 250 300

Fraction of Applied

Distance Downwind From Treated Fields (feet)

M2C, AT401, 10 mph, 28% SD

M2C, WASP, 10 mph, 28% SD 

M2C, AT401, 5 mph, 28% SD

M2C, AT401, 10 mph, 100% SD 

M2C, AT401, 5 mph, 100% SD

M2C, WASP, 5 mph, 100% SD 
59 of 60 

Figure E.3. Tier II Spray Drift Analysis: Deposition Curves for a Coarse to Very Coarse 

Droplet Size Following Chlorpyrifos Application Using Several Different Aerial 

Application Configurations 

Detailed results and calculations are provided in an attached supplemental spreadsheet as 

Appendix E. 

0

0.1

0.2

0.3

0.4

0.5

0.6

0 50 100 150 200 250 300

Fraction of Applied

Distance Downwind From Treated Fields (feet)

C2VC, AT401, 10 mph, 21% SD

C2VC, WASP, 10 mph, 21% SD 

C2VC, AT401, 5 mph, 21% SD

C2VC, AT401, 10 mph, 100% SD 

C2VC, AT401, 5 mph, 100% SD 

C2VC, WASP, 5 mph, 100% SD 
60 of 60 

Appendix F- Inhalation Risk Calculations

This appendix is an accompanying spreadsheet to this document. 

 
61 of 61 

Appendix G- Risk Calculations From 

Deposited Residues on Lawns

This appendix is an accompanying spreadsheet to this document.