### 2 of 70 

## TABLE OF CONTENTS

1. EXECUTIVE SUMMARY .................................................................................................... 4

1.1. Introduction .................................................................................................................. .... 4

1.1.1. Toxicity ...................................................................................................................... ... 4

1.1.2. Exposure ...................................................................................................................... . 5

1.2. Results Summary.............................................................................................................. 6

2. PROBLEM FORMULATION ............................................................................................... 7

2.1. Approach ...................................................................................................................... .... 7

2.1.1. Air Dispersion Modeling .............................................................................................. 8

2.1.1.1. Prior Consideration of Availa ble Air Dispersion Models......................................... 8

2.1.1.2. PERFUM Modeling Approach ................................................................................. 9

2.2. Stressors of Concern....................................................................................................... 10

2.2.1. Use Characterization................................................................................................... 12

2.2.1.1. Agricultural Use ...................................................................................................... 12

2.2.1.1.1. Application Rate Information .............................................................................. 14

2.2.1.1.2. Acres Treated Information .................................................................................. 14

2.2.1.2. Non-Agricultural Use.............................................................................................. 15

2.3. Hazard Characterization ................................................................................................. 15

2.3.1. Mode of Action and Adverse Outcomes .................................................................... 15

2.3.2. Human Incidents: Summary of Respiratory Effects ................................................... 18

2.3.3. Dose Response and Endpoint Selection ..................................................................... 21

2.3.3.1. Acute Inhalation Exposure ...................................................................................... 21

2.3.3.2. Acute Toxicity Adjustment Factor for Chlorpyrifos-oxon ..................................... 22

2.4. Exposure Characterization ............................................................................................. 23

2.4.1. Field Volatility Data ................................................................................................... 23

2.4.1.1. Alfalfa (MRID 48883201) 7 

### ..................................................................................... 24

2.4.1.1.1. Study Summary ................................................................................................... 24

2.4.1.1.2. Flux Rates ............................................................................................................ 24

2.4.1.2. Potato (MRID 48998801) 11 

### ..................................................................................... 26

2.4.1.2.1. Study Summary ................................................................................................... 26

2.4.1.2.2. Flux Rates ............................................................................................................ 27

2.4.2. Conclusions and Modeling Inputs .............................................................................. 27

3. RISK ASSESMENT ............................................................................................................. 31

3.1. Buffer Distributions........................................................................................................ 31

3.1.1. Alfalfa ....................................................................................................................... .. 31

3.1.1.1. Chlorpyrifos (Parent Only) ..................................................................................... 31

3.1.1.2. Total Toxic Chlorpyrifos Residues ......................................................................... 35

3.1.2. Potato ........................................................................................................................ .. 37

3.1.2.1. Chlorpyrifos (Parent Only) ..................................................................................... 37

3.2. Buffer Durations ............................................................................................................. 37

3.2.1. Alfalfa ....................................................................................................................... .. 37

3.2.1.1. Chlorpyrifos (Parent Only) ..................................................................................... 37

3.3. Risk Estimations ............................................................................................................. 39

4. ISSUES FOR CONSIDERATION ....................................................................................... 47

4.1. Air Monitoring Data ....................................................................................................... 47

4.2. Uncertainties ................................................................................................................. .. 47

### 3 of 70 4.2.1. Hazard Assessment ..................................................................................................... 47

4.2.2. Application Rate Scaling ............................................................................................ 49

4.2.3. Crop to Crop Variation (Flux and Dispersion) ........................................................... 49

4.2.4. Formulation ................................................................................................................ 51

4.2.5. Application Method .................................................................................................... 53

4.2.6. Weather ....................................................................................................................... 54

4.2.7. Degradation in Air ...................................................................................................... 54

5. CONCLUSIONS................................................................................................................... 55

APPENDIX A: LIST OF ABBREVIATIONS AND ACRONYMS

APPENDIX B: CHLORPYRIFOS USAGE DATA

APPENDIX C: FLUX CALCULATIONS

APPENDIX D: CURRENT CHLORPYRIFOS BUFFER RESTRICTIONS

ATTACHMENT 1: CHLORPYRIFOS MASTER USE SUMMARY DOCUMENT

ATTACHMENT 2: PERFUM MODELING FILES

### 4 of 70 1. EXECUTIVE SUMMARY

1.1. Introduction

This assessment supplements the June 2011 Chlorpyrifos Preliminary Human Health Risk Assessment for Registration Review (HHRA) 1 

### and the recent spra y drift assessment 2 

### by evaluating the potential risk to bystanders, from exposure to vapor phase chlorpyrifos and chlorpyrifos-oxon emitted from treated fields fo llowing the applicati on of chlorpyrifos. For the purposes of this analys is bystanders are thos e who live and/or work in proximity to treated fields, including children. Pesticides emitted from treated fields can travel to non-target areas which, depending on concentr ations, could present a risk of concern. Bystander exposure from chlorpyrifos and chlorpyrifos-oxon emitte d from treated fields depends on two main factors: 1) the rate at which these chemicals are emitted (described as the off-gassing, emission or flux) off treated surfaces such as crops and 2) how those vapors disper se in the air over and

around the treated field.

This assessment employs approaches EPA has used previously to assess inhalation exposures to fumigant pesticides 3,4 

### and is consistent with the recomme ndations of the December 2009 Federal Insecticide, Fungicide, a nd Rodenticide Act Scientific Advisory Panel (SAP) 5 

### meeting on the

scientific issues associated with field volatili zation of conventional (sem i-volatile) pesticides.

1.1.1. Toxicity

This evaluation of bystander risk from chlorpyr ifos volatilization focu ses only on the inhalation route of exposure. This volatili zation assessment is based on an acute inhalation toxicity study 6


### using aerosolized chlorpyrifos which measur ed lung, plasma, red blood cell (RBC), and brain

1 Drew, D.; Britton, W.; Soderber, D.; Negrón-Encarnación, I.; Christensen, C.; Lowit, A.; Irwin, W.; Doherty, J.;

Smegal, D. U.S. EPA Office of Chemical Safety and Pollution Preven tion, Chlorpyrifos: Preliminary HumanHealth Risk Assessment for Registration Review, June 30, 2011 PC Code 059101 DP Barcode: 388070; EPAHQ-OPP-2008-0850-0025

2 Dawson, J.; Bohaty, R.; Mallampalli, N. U.S. EPA Office of Chemical Safety and Pollution Prevention,

Chlorpyrifos—Evaluation of the Potential Risks from Sp ray Drift and the Impact of Potential Risk Reduction

Measures

, June 20, 2012 PC Code 059101, DP Barcode 399483 and 399485; EPA-HQ-OPP-2008-0850-0105

3 U.S. EPA 2004d. FIFRA Science Advisory Panel Meeting Minutes - Fumigant Bystander Exposure Model

Review: Probabilistic Exposure and Risk Model for Fumi gants (PERFUM) Using Iodomethane as a Case Study. Available at http://www.epa.gov/scipoly/sap/meetings/20 04/august1/august2425minutes.pdf, also refer to the following for additional informa tion http://www.epa.gov/oppsrrd1/reregistration/soil_fumigants/

4 The assessments can be found in the dockets for each fumi gant. Four of which are pr ovided here chloropicrin -

EPA-HQ-OPP-2007-0350; dazomet - EPA-HQ-OPP-2005-0128; metam sodium/potassium - EPA-HQ-OPP-2005- 0125; and methyl bromide - EPA-HQ-OPP-2005-0123

5 U.S. EPA 2009. FIFRA Science Advisory Panel Meeting Minutes - Scientific Issues Associated with Field

Volatilization of Conventional Pesticides. Available at http://www.epa.gov/scipoly/sap/meetings/ 2009/december/120309m eetingminutes.pdf

6 EPA MRID 48139303: Acute Inhalation Exposure of Adult Crl:CD(SD) rates to particulate chlorpyrifos

aerosols: Kinetics of Concentration-Dependent Cholinesterase (CHE) Inhibition in Red Blood Cells, Plasma, Brain and Lung ; Authors: J. A. Hotchkiss, S. M. Krieger, K. A. Brzak, and D. L. Rick; Sponsor: Dow AgroSciences LLC, 9330 Zionsville Road Indianapolis, IN 46268-1054

### 5 of 70 cholinesterase (ChE) inhibition. Risk estimates were calculated for both lung and RBC ChE inhibition based on a 6-hour expos ure duration and used quantitativ ely to estimate risk. The point of departures (PODs) for lung and RBC were calculated using the EPA’s Reference concentration method for calculating human equi valent concentrations (HECs), which accounts for physiological differences between animals and humans.

1.1.2. Exposure

Dow AgroSciences (DAS) recently submitted a field volatility study 7 

### as part of the data call-in requirements for the registration review of chlorpyrifos. This study measured both vapor phase chlorpyrifos and chlorpyrifos-oxon, a transfor mation product, in air samples following an application of a low VOC (volatile organi c compounds or volatile organic chemicals)

formulation 8,9,10 

### of chlorpyrifos to alfalfa. Approximate ly 30% of the applied chlorpyrifos was emitted from the treated field in the first 24 hours (28% considering chlorpyrifos only; 30% considering chlorpyrifos and chlorpyrifos-oxon co mbined). The flux profile for chlorpyrifos is similar to those generally observed for fumigants in that there is a peak emission shortly after application during the warmer part of the day. The study measured chlorpyrifos for a period of 72 hours following application.

This assessment also incorporates a field vol atility study published in the open literature; conducted with application of a non-low VOC formulation of chlorpyrifos to potatoes. 11 

### Since the raw data for this study could not be obtai ned, the flux rates coul d not be independently verified by EPA and, thus, evaluatio n of experimental details and a ssociated data quality review of this study is not as rigorous as that associated with the al falfa study. The open literature study only measured parent chlorpyrifos and did not measure concentrations of chlorpyrifos-oxon. The results from this study are presented in this assess ment to provide another line of evidence of the potential volatility of chlorpyrifos, as demonstrat ed in the registrant submitted study, and to help describe the potential variability in chlorpyrifos flux rates du e to different study conditions ( e.g. ,

7 EPA MRID 48883201: Direct Flux Measurement of Chlorpyrifos and Chlorpyrifos-Oxon Emissions Following

Applications of Lorsban Advanced Insecticide to Alfalfa ; Authors: Aaron Rotondaro and Patrick Havens; Sponsor: Dow AgroSciences LLC, 9330 Zionsville Road Indianapolis, IN 46268-1054, 2012

. 8 California's Department of Pesticide Regulation (Cal DPR) defines a low VOC pesticide formulation when the

total emission potential (see footnote 9 ) is 25% or less (see footnote 10 ). The emission rate corresponds to total VOC emissions and not specially one component of the formulation ( i.e. , the active ingredient). EPA does not currently define low VOC pesticide formulations.

9 Emission potential is based on Thermogravimetric Analysis; Oros, D., Spurlock, F. California Department of

Pesticide Regulation, ESTIMATING PESTICID E PRODUCT VOLATILE ORGANIC COMPOUND OZONE

REACTIVITY. PART 1: SPECIATING TGA -BASED VOLATILE ORGANIC COMPUND EMISSIONS USING CONFIDENTIAL STATEMENTS OF FORMULA, January 27, 2011 http://www.cdpr.ca.gov/docs/emon/pubs/eha preps/analysis_memos/2286_segawa.pdf

10 Proposed regulation can be found at: http://www .cdpr.ca.gov/docs/legbills/rulepkgs/12-001/text.pdf

11 EPA MRID 48998801: Volatilization of the Pesticides Chlorpyrifos and Fenpropimorph from a Potato Crop ;

Authors: Minze Leistra, Johan H. Smelt, J. Hilbrand Weststrate, Frederik VanDenBerg, and Rene Aalderink; Sponsor: This work was carried out within the framework of the EU APECOP project Effective Approaches for Assessing the Predicted Environmental Concentrations of Pesticides (QLK4-CT-1999-01338) and of Research Program 416, Pesticides and the Environment, of the Du tch Ministry of Agriculture, Nature and Food Quality; Citation: Leistra, M; Smelt, J. H.; Weststrate, J. H.; Van Den Berg, F; Aalderink, R. Environ. Sci. Technol. 2006

, 40 , 96-102.

### 6 of 70 crop canopy, formulation, and weather). While the ab solute flux for chlorpyrifos observed in this study is higher than the al falfa study the flux profiles 12 

### are similar in both studies.

The two field volatility studies suggest that volat ilization of chlorpyrifos and/or chlorpyrifosoxon from treated crops is a pathway of dissipa tion in the environment that may result in bystander exposure to vapor phase chlorpyrifos and chlorpyr ifos-oxon. These studies were

conducted at rates much lower than the current maximum single broadcast application; however, based on usage data, the rates used in these studi es are consistent with typical average single application rates. In order to evaluate pot ential risks under varied conditions, offsite concentrations of chlorpyrif os and total toxic chlorpyrif os residues (chlorpyrifos and chlorpyrifos-oxon) were estimated using PERFUM and the flux rates derived from the two field volatility studies. This approach is consistent with what has been done for fumigant pesticides 4



### and with the recommendations of the 2004 3 

### and 2009 5 

### SAP reviews.

1.2. Results Summary

Volatilization as a pathway of exposure was exam ined to quantify the pot ential risk estimates associated with bystander exposure to vapor phase chlorpyrifos and chlorpyrifos-oxon near a treated field. This was done by comparing peak 6 hour chlorpyrifos and to tal toxic chlorpyrifos vapor [chlorpyrifos and chlorpyr ifos-oxon (expressed in chlorpyr ifos toxicity equivalents)]

concentrations estimated at various distances aw ay from a treated field with endpoints based on lung and RBC ChE inhibition. The resu lts indicate that offsite concentrations may exceed the target concentration established for lung ChE i nhibition for many currently registered uses at distances away from the field edge. Concentrat ions are not expected to exceed the RBC ChE inhibition target concentration unde r all the conditions th at were evaluated in this assessment.

Depending on which percentile of exposure and the field size considered, buffers zones 13



### estimated to ensure concentrati ons of chlorpyrifos (only) are at or below the lung ChE target concentration range from 0 to greater than 4000 ft away from the perimeter of a treated field. Higher application rates and/or large field sizes lead to highe r exposure and, therefore, large buffers. The spray drift buffers for prot ection of bystanders in sensitive sites 14 

### currently required on chlorpyrifos labels range from 0 to 100 feet depending on the application method. Consideration of vapor phase chlo rpyrifos-oxon in addition to chlo rpyrifos (only) increases the

estimated buffer distances needed to ensure air co ncentrations are below the target concentration than those presented for chlorpyrifos only.

In addition to estimating buffer distances based on the peak air concentrations, a buffer duration analysis was completed by examining air concentra tions over several days. This analysis is based

12 A flux profile is the emissions from a treated field over a defined period of time ( i.e. , an hourly time series of flux estimates during a period of measurement following application).

13 In the context of presenting modeling results the term "buffer zone" does not refer to any regulatory decision

pertaining to risk mitigation for chlorpyrifos. It refers to the distances determined base d on a target concentration defined by the HEC adjusted by the uncertainty factor.

14 Buffers are around sensitive sites (a circle drawn aroun d the sensitive site with a radius equal to the buffer

distance) and do not correspond to buffers around a given fi eld (a circle drawn around a treated field with a radius equal to the buffer distance).

### 7 of 70 on whole field buffers as compared to maxi mum buffers. Depending on which percentile of exposure and the field size evaluated, the estimat ed buffers may need to remain for several hours. For example, buffers would need to be in place for at least 12 hours for l pound of active ingredient per acre (lb a.i./A) ap plications and for at least 36 hour s for 6 lb a.i./A applications when considering the 95% percen tile exposure co ncentration.

2. PROBLEM FORMULATION

Problem formulation provides a strategic framewor k in the risk assessment. In this case, it describes the history of EPA’s air modeling appro ach and strategy used in this assessment to estimate potential risk due to volatilization of chlorpyrifos and its oxon following application in an agricultural setti ng. In addition, to identifying the chlorp yrifos application variables for the assessment, the problem formulation also outlin es relevant physical-chemical properties, transformation products, usage data, hazard e ndpoints and exposure data needed for the

assessment.

2.1. Approach

Pesticide volatilization can potentially impact those who are in proximity to treated fields following application events, as depicted in Figure 1 . The example in Figure 1 is an exposure pattern that is reasonably expected to occur with an emission event, given that farmers, residents ( e.g. , homeowners, renters, visitors, etc.) and the general public may freque nt areas adjacent to treated fields. To assess the potential risk from this exposure pathway, a residential/bystander assessment based on exposure to vapor phase residue s at various distances away from a treated

field was conducted. In order to ev aluate the volatiliza tion potential and associated risks, an approach based on dispersion modeling coupled w ith techniques used to evaluate inhalation exposure was utilized. In this case, disper sion modeling was completed for a variety of application scenarios including different field sizes, application ra tes, and metrological

conditions.

Figure 1. Conceptual Model of the Exposure Pathway Associated with Volatilization

### 8 of 70 2.1.1. Air Dispersion Modeling

2.1.1.1. Prior Consideration of Available Air Dispersion Models

Air dispersion modeling uses mathematical formulas to characterize how atmospheric processes will disperse a pollutant emitted by a source. For the fumigants, the EPA used dispersion models

to estimate the downwind concentration emitted from an area source such as a treated field consistent with the EPA’s air model development and implementation methods. 15 

### The EPA considered three air dispersion models for use in the soil fumigant risk assessments 16 

### . These

models consisted of two “G aussian Plume” models (ISCST3 model and AERMOD) and one “Gaussian Puff” model (CALPUFF) . All three of these models are currently listed or have previously been listed in A ppendix W of 40 CFR Part 51 (Gui deline on Air Quality Models) which contains the EPA’s guidance on the general regulatory applicability of various air quality dispersion models. 17 

### EPA selected the ISCST3 model, which in 2004 was the agency’s recommended regulatory air model, for use in the fumigant assessments. 16



### After a modeling approach based on the use of ISCS T3 was selected, a series of preliminary risk assessments were completed using ISCST3. 18 

### The findings indicated significant risk mitigation measures might be needed ( e.g. , large buffer distances) but there was the potential for refinements to refine risk estimates. The key refi nement was incorporating actual weather data as a basis for predicting risks instea d of using constant atmospheric conditions. In essence, this

refinement allowed for distributional considerat ion of changing weather conditions rather than the ISCST3 deterministic approach to weathe r which was based on wind speed, direction and atmospheric stability being constant.

The regulated community developed three mode ls that incorporated actual weather data: Probabilistic Exposure and Risk model for Fumigants (PERFUM) 19 

### , the Fumigant Emissions Modeling System (FEMS) 20 

### , and the Soil Fumigant Exposure Assessment System (SOFEA) 21



### , were submitted to the EPA by the regulated commun ity. All of these models are essentially preand post-processors for ISCST3 (and CALPUFF in the case of FEMS) that incorporate the ability to complete distributional and/or proba bilistic analyses. Each of these models was reviewed by the 2004 SAP. 3 

### The SAP concluded that each of the three models could provide scientifically defensible estimates of the bys tander exposures and risk s associated with soil fumigation practices and also s uggested modifications and additio nal data that could further refine risk estimates (for specifics see the final SAP report 3 

### ). Many of the SAP’s recommended

modifications have been made to these models since that time. After the SAP reviews, the EPA

15 See http://www.epa.gov/scr am001/ for more details.

16 See http://www.epa.gov/oppsrrd1/rere gistration/soil_fumigants/soil-fum-reg-backgrnd.html for more details

17 http://www.epa.gov/ttn/scram/guidance/guide/appw_05.pdf

18 There was a regulatory precedent for using ISCST3 as it had previously been used by EPA for air permitting, as

well as to define buffer zones fo r methyl bromide in California.

19 Reiss, R. and Griffin, J. 2006. Us er’s Guide for the Probabilistic Exposure and Risk Model for FUMigants

(PERFUM), Version 2. Arysta LifeScience North America Corporation. Cary, North Carolina.

20 Fumigant Exposure Modeling System (FEMS), Background Document: Fumigant Emissions Modeling System,

Sullivan, Hlinka, and Holdsworth, July, 2004

21 SOil Fumigant Exposure Assessment System (SOFEA), SOFEA (User's and Programmer's Guide), van

Wesenbeeck and Cryer, Copyright 2004

### 9 of 70 selected PERFUM as the probabilistic air mode l for use in the fumigant assessments. Other modeling analyses, using systems such as FE MS, SOFEA, AERMOD or CALPUFF, would also

be considered should these models be devel oped and submitted to the EPA for consideration,

since these models are also considered appropriate for regulatory purposes.

The 2009 SAP 5 

### discussed in limited fashion, as it was not part of their offici al charge, that the current dispersion models (mentioned above) have not been validat ed for non-fumigant pesticides. The EPA acknowledges that use of di spersion models was briefly discussed at the

2009 SAP 5 

### but no significant discussions were held on this particular issu e. The SAP concluded that the concept of coupling a fate and transport model, to predict the flux of a chemical, with a dispersion model, to estimate air concentrations at different dist ances from the field is a sound approach.

In order for a model to be included as an EPA recommended air model (part of Appendix W), the model must go through an extensive peer re view and testing proce ss. This peer review process ensures that models are acceptable to be used for a variety of sources like point sources ( e.g. , a stack on a building) and area sources ( e.g. , a treated field), as well as for a variety of pollutants ( i.e. , volatile organic compounds, semi-volatile organic compounds, and particulate matter). While this testing proce ss did not explicitly consider pesticides, except for one case where a fumigant was released from a field ( i.e. , the Prairie Grass Study 22 

### ), it included semivolatile organic compounds. Most pesticides fall under this classifi cation given physicalchemical characteristics such as vapor pressure . Based on the EPA’s model peer review process and the use of air dispersion modeling for the fumi gants risk assessments over the last ten years, the use of dispersion modeling for semi-volatile pest icides is considered a valid and scientifically defensible methodology.

2.1.1.2. PERFUM Modeling Approach

Before a PERFUM analysis can be performed, h azard and exposure inputs need to be defined. The hazard inputs used in this assess ment are discussed in detail in Section 2.3 . Exposure inputs in the form of a flux profile [the flux or rate of pesticide emissions from the treated fields per unit area per unit time (μg/m 2 

### /sec)] was determined from two di fferent field volatility studies

discussed further in Section 2.4 . Numerous factors can influence flux rates, such as the application rate, th e treated surface ( e.g. , foliage or soil), field structure ( e.g. , canopy type and shape), application practices, and atmospheric conditions such as temperature and humidity. A discussion of these factors is provided in Section 4 . In the end, PERFUM compares a target

concentration derived from the HEC and the uncertainty factor 23 

### to off field air concentrations estimated based on flux rates surrounding a treat ed field in order to estimate buffer zones 13 

### , if

needed.

22 United States Air Force. 1958. Proj ect Prairie Grass, A Field Program in Diffusion, Volume I. Geophysics

Research Directorate, Air Force Cambridge research Center, Air Research and Development Command Geophysical Research Papers No. 59, Document Number AD152572, July 1958

23 The uncertainty factor is this case is a value developed to account for uncertainty associ ated with animal to human extrapolation of toxicity data, as well the potentia l sensitivity difference between humans within a given population ( e.g. , sensitivity subpopulations ). See Section 2.3 for information on how the target concentration

used in this assessment was derived.

### 10 of 70 Buffer zones 13 

### and risk estimates are presented in Section 3 below for several different potential application scenarios (e.g., different meteorological conditions, field sizes, and application rates) for an array of percentiles of exposure for w hole field and maximum buffers. A summary of the results is provided in Section 4. Note: PERFUM does not produ ce buffer zones greater than 4724 ft (1440 m), thus, buffer zones for cases where th e 4724 ft (1440 m) limit is reached may be very large. These cases are indicated with a “>4724 ft”.

2.2. Stressors of Concern

Chlorpyrifos ( O,O -diethyl o-(3,5,6-trichloro-2-pyridyl phosphorothioate; CAS 2921-88-2) is a broad spectrum organophosphate (OP) insecticide. It is widely used in agriculture and has been measured in various air monitoring programs. Chemical identification and select physical chemical properties of chlo rpyrifos are provided in Table 1

.

Table 1. Chemical Identification and Select Physical-Chemical Properties of Chlorpyrifos and Chlorpyrifos-oxon

Parameter Chlorpyrifos Chlorpyrifos-oxon

Chemical Name O,O -diethyl O-(3,5,6-trichloro-2-pyridyl phosphorothioate O

, O -diethyl O-3,5,6-trichloropyridin-2-yl phosphate

Chemical

Abstracts Service (CAS) Registry

Number 2921-88-2 5598-15-2

Empirical

Formula C 20 H 17 F 5 N 2 O 2 C 9 H 11 Cl 3 NO 4 P

USEPA Pesticide Code (PC #) 059101 --

Smiles Notation S=P(OC1=NC(=C(C=C1Cl)Cl)Cl)(OCC)OCC O=P(Oc1nc(c(cc1Cl)Cl)Cl)(OCC)OCC Molecular Weight 350.57 g/mol 334.52 g/mol Vapor Pressure (25 °C) 1.87x10 -5 torr 6.65x10 -6 torr a

Water Solubility (20 °C) 1.4 mg/L 26.0 mg/L a

Henry’s Law

Constant 6.2 x 10 -6 atm - m 3 /mol 5.5 x 10 -9 atm - m 3 /mol a

Log K

ow 4.7 2.89 mg/L a
Saturated Vapor

Concentration (25 °C) 489 μg/m 3 b
353 μg/m 3 c 120 μg/m 3 d

a. EPI Suite estimated value.

b. See footnote 24

c. Calculated: n/V=P/RT; P=1.87x10 -5 torr x (1 atm/760 torr) =2.46x10 -8 atm @ 25 °C; R= 0.0821 L atm/ mol K; T=

25 °C= 298 K; 2.46 x10 -8 atm/ (0.0821 L atm/ mol K*298 K) = 1.0 x 10 -9 mol/L x (350.57 g/mol) x 10 6 μg/g = 0.353 μg/L* 1L/10 -3 m 3 ) = 353 μg/m 3

d. Calculated: n/V=P/RT; P=6.65x10 -6 torr x (1 atm/760 torr) =2.46x10 -8 atm @ 25 °C; R= 0.0821 L atm/ mol K; T=

25 °C= 298 K; 2.46 x10 -8 atm/ (0.0821 L atm/ mol K*298 K) = 3.6 x10 -10 mol/L x (334.52 g/mol) x 10 6 μg/g = 0.120 μg/L* 1L/10 -3 m 3 ) = 120 μg/m 3

24 Reported by Dow AgroScien ces on December 11, 2012 in a presentation (Bartels, M., Cleveland, C., Hotchkiss, J., Juberg, D. Perspectives on Risk Assessment Elements for Chlorpyrifos) to EPA.

### 11 of 70 Based on available environmental fate data submitted to EPA, chlorpyrifos is expected to undergo several chemical transformations in the environment as shown in Figure 2

.

O P O N Cl Cl

Cl S

O O P O N Cl Cl

Cl O

O

HO N Cl Cl

Cl Chlorpyrifos Chlorpyrifos-oxon

3,5,6-trichloro-2-pyridinol (TCP) H 3 CO N Cl Cl

Cl

3,5,6-trichloro-2-methoxypyridine (TMP) 

### Figure 2. Environmental Transformation of Chlorpyrifos

Chlorpyrifos-oxon, a transformation product, is considered as a residue of concern which has greater potency for cholinesterase inhibition than chlorpyrifos. Th ere are also air monitoring data that include both chlorpyrifos and chlorpyrifos-oxon detections supporting the potential exposure

to both chemicals as a result of emission from a treated field and subseq uent transport offsite. 25 

### It

is unclear if the concentrations observed in the majority of air m onitoring studies reported in the open literature are due to spray or vapor phase drift of chlorpyrifos and chlorpyrifos-oxon; however, the alfalfa field volatility study discussed in detail below indicate that it is likely that both vapor phase chlorpyrifos and chlorpyr ifos-oxon vapors are present simultaneously downwind of a treated field. Therefore, in addi tion, to exposure to ch lorpyrifos itself the potential exposure to both chlorpyrifos and chlor pyrifos-oxon at the same time is also explored

in this assessment.

In a recently submitted air photolysis study 26 

### chlorpyrifos was reported to undergo indirect and direct photolysis [t 1/2 

### = 2 h (indirect) and 6 h (direct)]. Th ese results have not been verified by EPA as the raw data submitted to the EPA are not adequate; however, the results obtained for indirect photolysis are consistent with the Estimation Program Interface (EPI) Suite 27



### estimations. 28 

### EPI Suite is commonly used by EPA to estimate physical-chemical parameters when data are unavailable. This study conf irms the formation of chlorpyrifos-oxon via photolysis. Chlorpyrifos-oxon wa s reported to undergo indir ect and direct photolysis [t 1/2 

### = 11 h (indirect) and 6 h (direct)]. The EPI Suite estimated indirect photolysis was about half 29 

### that

25 Glotfelty, D. E.; Majewski, M. S.; Se lber, J. N. Distribution of Several Organophosphorus Insecticides and Their

Oxygen Analogues in a Foggy Atmosphere . Environ. Sci. Technol.

, 1990

, 24 (3) , 353-357.

26 EPA MRID 48789701: Gas-Phase Photolysis and Photo-oxidation of Chlorpyrifos and Chlorpyrifos oxon ;

Authors: Amalia Munoz; Sponsor: Dow AgroSciences European Development Centre, 3 Milton Park, Abington, Oxon, OX14 4RN

27 http://www.epa.gov/opptintr/exposure/pubs/episuite.htm ; The version used in this assessment is 4.00.

28 t 1/2 = 3 h (indirect)

29 t 1/2 = 7 h (indirect)

### 12 of 70 calculated by the study authors. The physical-c hemical properties of chlorpyrifos-oxon are provided in Table 1

.

2.2.1. Use Characterization

There are several different types of chlorpyrifos formulations currently registered including: liquid, dry flowable, microencapsulated, and granul ar products. Registered use sites include food crops such as fruit and nut trees, many types of fruits and vegetables, and grain crops; and nonfood crops such as forage, golf course turf, industrial sites, greenhous e and nursery production, sod farms, and wood products. This section includes a summary of chlorpyrifos use, including: an evaluation of yearly chlorpyrif os percent crop treated (PCT), application rate information, and total acreage treated annually for all agri cultural crops treated with chlorpyrifos.

A complete list of chlorpyrifos use site s and application rate s are provided in ATTACHMENT

1 . Broadcast application rates currently permitted on chlorpyrifos labels range from 0.5 to 6 lb

a.i./A.

2.2.1.1. Agricultural Use

Based on private market research data 30 

### , approximately 8 million pounds of chlorpyrifos are used annually in agriculture. To tal chlorpyrifos usage by crop varies widely with the average PCT in the survey of years 2006-2010, unles s otherwise noted –as low as 1% for several crops and as high as 62 % (for apples). The fi ve crops with the highest PCT ar e apples (62%), broccoli (53%), walnuts (46%), onions (45%), and cauliflower (41%) as shown in Table 2 . These five crops account for approximately thirteen percent of th e total pounds of chlorpyr ifos applied each year. Crops that have low total chlorpyrifos usage (EPA defined this as less than 20,000 pounds used, on average) but show relatively la rge area treated (EPA defined th is as greater than 25% PCT) include: strawberries, aspa ragus, and cauliflower.

Table 2. Typical Use Data for Chlorpyrifos (all formulations combined; national level data)

Crop Average

Percent

Crop

Treated

(PCT) Average

Pounds Applied per

Year Average Single Application

Rate Upperbound Rate (Lbs. a.i./A-single app.)

Soybeans 6 1,800,000 0.41 0.5 (90%), 0.75 (95%)

Corn 1 1,000,000 0.9 1.25 (84%), 1.5 (97%)

Oranges 24 630,000 2.5 5.75 (81%), 6.0 (100%)

Alfalfa 3 450,000 0.56 0.75 (79%), 1.0 (100%)

Almonds 24 440,000 1.86 2.0 (97%)

Wheat, Winter 2 400,000 0.42 0.5 (93%)

Apples 62 390,000 1.5 1.75 (52%), 2.0 (99.9%)

Walnuts 46 350,000 1.85 2.0 (99%)

30 GfK Kynetec Database

### 13 of 70 Pecans 28 260,000 0.9 1.25 (91%)

Peanuts 7 160,000 1.72 2.0 (97%)

Sugar Beets 11 130,000 0.8 1.5 (88%)

Wheat, Spring 2 120,000 0.32 0.25 (65%), 0.5 (99%)

Cotton 2 100,000 0.3 0.75 (77%), 1.0 (100%)

Sweet Corn 11 100,000 0.96 1.25 (83%), 1.5 (94%)

Broccoli 53 100,000 1.36 2.0 (78%), 2.25 (100%)

Lemons 39 96,000 3.5 5.0 (88%)

Tobacco 13 90,000 1.96 3.0 (90%)

Cherries 37 84,000 1.5 2.0 (99.6%)

Sunflowers 6 66,000 0.46 0.5 (88%), 0.75 (94%)

Onions 45 65,000 0.9 3 1.0 (70%), 1.25 (99.8%) 3

Wine Grapes c 5 60,000 1.96 2.42

Peaches b 26 56,000 1.34 2 1.75 (69%), 2.0 (98%)2

Grapefruit 22 48,000 2.1 2.75 (90%)

Table Grapes c 13 27,000 1.88 2.43

Plums/Prunes 11 24,000 1.73 2.0 (100%)

Pears 17 20,000 1.85 2.0 (100%)

Cauliflower 41 17,000 1.09 1.25 (89%), 1.5 (97%)

Asparagus 39 16,000 0.99 1.0 (95%)

Strawberries 28 15,000 0.97 1.0 (99%)

Dry Beans/Peas a 1 13,000 0.48 0.5 (95%)

Cabbage 14 12,000 1.16 1.25 (86%), 1.5 (92%)

Sorghum (Milo) a 0.4 11,000 0.42 0.5 (80%), 0.75 (95%)

Hazelnuts a 10 4,800 1.27 1.5 (77%), 2.0 (100%)

Beans a 1 1,800 0.77 0.75 (84%), 1.0 (100%)

Peppers a 2 1,800 0.81 0.75 (77%), 1.0 (94%)

Pumpkins a 1 1,700 0.93 1.25 (100%)

Peas a 1 1,400 0.98 1.0 (98%)

Squash a 1 820 1.11 1.25 (88%), 1.5 (91%)

Cucumbers a 1 550 0.76 1.0 (100%)

Source: Proprietary Data 2006-2010. Table is sorted to show crops with highest to lowest total chlorpyrifos applied per year

a. Data are not robust (total sample size of <50 across 5 years and this crop not surveyed in USDA NASS)

b. Peaches: Higher values were reported in NASS. For a conservative value, EPA recommends: Rate: 1.6 lb a.i./A, Number of Applications: 1.4; 90th percentile rate: 2.6 lb a.i./A (USDA NASS 2009)

c. Updated Typical Use Data for Chlorpyrifos Used on Grapes in California (Average 2006 and 2009); Source: USDA NASS (2006, 2009) Agricu ltural Chemical Usage Fruit Summary

### 14 of 70 Chlorpyrifos use is highest on corn and soybean in terms of average poun ds total chlorpyrifos applied per year, accounting for approximately thirty-nine percent of the total pounds of chlorpyrifos applied each year . Corn use is over 1,000,000 pounds per year while soybean use is nearly 2,000,000 pounds per year for the period survey ed. Chlorpyrifos use on orchard and trellis crops is about thirty-three percent of the total chlorpyrif os use per year.

2.2.1.1.1. Application Rate Information

Table 2 also provides use information such as the application rate (avera ge single application rates and upper-bound single applica tion rates) for national-level total chlorpyrifos use (all formulations and all application methods) on us e sites where information was available from

2006-2010. 31 

### Seventeen crops (out of a total of 38 crops surveyed) show average application rates that are greater than 1 lb a.i./A. These crops are appl es, almonds, broccoli, cabbage, cauliflower, cherries, grapefruit, hazelnuts, lemons, oranges, peaches, peanuts, pears, plums/prunes, squash, tobacco, and walnuts. The majority of growers surveyed reported use of single application rates of 2 lb a.i./A or less. For many of the crops included in Table 2 the upper-bound single application rate is equal to the maximum singl e application ra te currently permitted on the label.

Additional analysis of the data by formulation type is presented in APPENDIX B

.

2.2.1.1.2. Acres Treated Information

Data on the size of fields trea ted per application of chlorpyr ifos helps define current use practices. However, with the exception of th e detailed pesticide use recording database maintained by the California Department of Pes ticide Regulation (CDPR), EPA is not aware of data sources that would provide th is kind of information for chlor pyrifos (or any other pesticide). Results of EPA’s analysis of rele vant CDPR data are presented in APPENDIX B ( Table B2 ). These data describe chlorpyrifos usage in Califor nia, and may not reliably apply to other parts of the United States as different pest pressures a nd crop production practices are likely altering the relative use of chlorpyrifos. Additional discussion of the scope of these data is included in

APPENDIX B

.

Using the CDPR data, EPA determined that the ar ea treated per application per day varies widely across use sites. In general, it appears that gr ound-based treatments covered larger acres treated per application per day than aerial treatments at the 90 th 

### percentile range. While the factors contributing to this result were not investig ated, EPA speculates such factors as cost of application, efficacy, and accessibility of applic ation equipment may influence the use of ground over aerial application methods. Although maximum area treated in some crops ( e.g. , walnuts, almonds, asparagus, grapes, alfalfa) can be seve ral hundred acres, these are often single data points ( i.e. , only one grower/applicator was reporting this amount treated). The 50th and 90th percentile columns depicted in Table B2 are probably more descriptive for typical use than the

31 Stebbins, K. U.S. EPA Office of Chemical Safe ty and Pollution Prevention, Chlorpyrifos: Additional Typical Use

Data for Chlorpyrifos, January 11, 2012 PC Code 059101

### 15 of 70 maximum reported number of acres treated per da y. The percentile columns show the amount of acres treated per application per day at or below which 50 or 90 percent of applicator reports

occur in the CDPR database (within each cr op/product/application method grouping).

2.2.1.2. Non-Agricultural Use

Chlorpyrifos is used in settings that are not considered an ag ricultural use pe r se including agricultural farm premises, nurseries and plantations ( e.g ., ornamental, non-bearing fruit tree, and Christmas tree), golf cour se turf, recreational areas, righ ts-of-way, and utility areas. However, usage data in these areas are not surv eyed by the proprietary market databases that EPA uses to gather pesticide use information. In addition, use information for these sites is not collected by the CDPR in a form that allows re liable interpretation for risk assessment purposes. Therefore, EPA has no verifiable description of application rates or area treated in these uses. This remains an uncertainty.

2.3. Hazard Characterization

2.3.1. Mode of Action and Adverse Outcomes

Chlorpyrifos, like other OPs, binds to and phosphorylates the enzyme, acetylcholinesterase (AChE), in both the central (bra in) and peripheral ner vous systems leading to accumulation of acetylcholine and, ultimately, to clinical signs of toxicity. For OPs, AC hE inhibition is most often the most sensitive dose response data for use in assessing human health risk. For chlorpyrifos, the EPA concluded in the 2011 pr eliminary HHRA, that ChE inhibition was the most sensitive dose response data for use in deri ving a POD for all durations, routes of exposure, and lifestages.

EPA typically uses data on AChE inhibition data, the in itiating event in the mode of action, for endpoint selection in human health risk assessm ent since protecting agai nst inhibition of AChE thereby protects against potential acu te neurotoxicity. EPA’s ChE policy 32 

### describes the manner

in which ChE data are used in human health ri sk assessment. Typically, experimental laboratory studies measure brain (central) and blood (plasm a and red blood cell) ChE. Blood measures do not represent the target tissue, per se , but are instead used as surr ogate measures for peripheral nervous tissue in studies with laboratory an imals when peripheral data are missing or for potential peripheral and/or centr al toxicity in humans. In addition, RBC measures represent AChE, whereas plasma measures are approxi mately 50% butyryl-ChE (BuChE). Thus, RBC AChE data may provide a better representation of the inhibition in target tissues than plasma

ChE data.

There are many experimental t oxicology studies which measure RBC and plasma ChEs. In general, measurements of AChE or ChE inhibition in peripheral tissues ( e.g. , liver, diaphragm, heart, lung, etc.) are rare. Data for chlorpyrifos are unique in th at measures of some peripheral tissue are available in some experimental toxici ty studies. For example, heart ChE was measured

32 USEPA (2000) Office of Pesticide Programs, US Environmental Protection Agency, Washington DC 20460.

August 18, 2000 Office of Pesticide Programs Science Polic y of The Use of Data on Cholinesterase Inhibition for Risk Assessments of Organophosphorous and Carbamate Pesticides.

### 16 of 70 in the chlorpyrifos develo pmental neurotoxicity study 33,34 

### , an associated companion study, in

addition to an acute oral study by Dittenber. 35 

### Liver ChE was measured by Lassiter 36 

### , Hunter 37



### , and Moser and Padilla 38 

### . Padilla 39 

### (measured diaphragm ChE) and Marable 40 

### (measured diaphragm, left atrium, and quadriceps ChE ) evaluated chronic exposure in adult animals where blood, brain and peripheral tissue ChE inhibition were at steady- state. Lung ChE was measured in the special acute inhalation st udy being used to assess the risk from volatilization. Other data on lung ChE come from oral studies. Specifically, in an oral study by Carr 41 

### heart, lung, and skeletal muscle ChE were evaluated in post-na tal pups dosed using a uni que design that included every other day dosing and differe nt durations and doses across different aged pups. Given the unique design of the Carr study, it is difficult to assess sensitivity of different tissues. Richard

and Chambers 42 

### evaluated lung ChE in rat fetuses fo llowing oral exposure to the dams and showed that lung ChE was similar at the lowest dose on PND1 to brain and RBC AChE but lung ChE was more inhibited in PND1 pups than brain and RBC AChE at the higher doses (ChE inhibition was not measured in dams).

With respect to clinical signs of neurotoxicity, in experimental toxicity st udies with chlorpyrifos acute, oral toxicity can be associ ated with signs typical of cho linergic overstimulation, such as hypothermia, salivation, lacrimati on, diarrhea, incoordi nation, tremors, and fasciculations. In addition, altered motor function was one of the more sensitive endpoints evaluated in these

studies. 43,38,44,45

33 EPA MRID 44648101 : Effects of Chlorpyrifos Administered Via Gavage to CD Rats During Gestation and

Lactation on Plasma, Erythrocyte, Heart and Brain Cholin esterase and Analytical Determination of Chlorpyrifos

and Metabolites. Authors: Mattsson J. L., Maurissen J. P., Spencer , P. J., Brzak K. A., Zablotny C.L.; Sponsor: The Dow Chemical Co. for Dow Ag roSciences, August 31, 1998.

34 Mattsson, J. L., Mauri ssen, J. P., Nolan, R. J., and Brzak, K. A. La ck of differential sensitivity to cholinesterase

inhibition in fetuses and neonates compared to dams treated perinatally with chlorpyrifos. Toxicol Sci, 2000

, 53

, 438-46.

35 EPA MRID 44273901 : Chlorpyrifos: Evaluation of Single Oral Doses on Cholinesterase and Neurotoxic

Esterase Inhibition in F344 Rats. Author: Dittenber, D. A., Sponsor: Dow Chemical Co. Study No. 960036. March 13, 1997.

36 Lassiter T. L., Padilla S., Mortensen, S.R., Chanda, S. M., Moser, V.C., Barone, S . Gestational Exposure to

Chlorpyrifos: Apparent Protection of the Fetus? Toxicol. Applied Pharmacol. 1998a, 152 , 56-65

37 Hunter, D. L., Lassiter, T. L., and Padilla, S. Gestati onal Exposure to Chlorpyrifos: Comparative Distribution of

Trichloropyridinol in the Fetus and Dam. Toxicol Applied Pharmacol. 1999

, 158 , 16-23.

38 Moser, V. C., Padilla, S. Age- and Gender-related Differ ences in the Time Course of Behavioral and Biochemical

Effects Produced by Oral Chlorpyrifos in Rats. Toxicol Applied Pharmacol. 1998

, 149, 107-19.

39 Padilla, S., Marshall, R. S., Hunter, D. L., Oxendine, S., Moser, V. C., Southerland, S. B., Mailman, R. B.

Neurochemical Effects of Chronic Dietary and Repeated High-level Acute Exposure to Chlorpyrifos in Rats.

Toxicol Sci. 2005

, 88 , 161-71.

40 Marable, B.R., Maurissen, J. P., Ma ttsson, J. L., Billington, R. Differentia l Sensitivity of Blood, Peripheral, and

Central Cholinesterases in Beagle Dogs Fo llowing Dietary Exposure to Chlorpyrifos. Regul. Toxicol. Pharmacol.

2007

, 47

, 240-8.

41 Carr, R. L., Chambers, H. W., Guarisco, J. A., Richardson, J. R., Tang, J., Chambers, J. E. Effects of Repeated

Oral Postnatal Exposure to Chlorpyrifos on Open-field Behavior in Juvenile Rats. Toxicol. Sci

. 2001

, 59 , 260-7.

42 Richardson, J., Chambers, J. Effect s of Repeated Oral Postnatal Exposure to Chlorpyrifos on Cholinergic

Neurochemistry in Developing Rats. Toxicol. Sci. 2003

, 84 , 352-59.

43 Mattsson, J. L., Wilmer, J. W., Shankar, M. R., Berdas co, N. M., Crissman,J. W., Maurissen, J.P., and Bond, D.

M. Single-dose and 13-week Repeated -dose Neurotoxicity Screening Studies of Chlorpyrifos Insecticide. Food

Chem. Toxicol. 1996

, 34 , 393-405.

### 17 of 70 With respect to the respirator y tract, although there are three chlorpyrifos inhalation studies, none measured apical outcomes relevant to pulm onary function. As such there are no data in experimental animals evaluating the potential effects of lung ChE inhibition on pulmonary function following inhalation chlorpyrifos exposure. Trach eobronchial glands receive parasympathetic innervation; AChE inhibitors can stimulate secre tion of tracheobronchial fluid, in addition, to bronchorestriction and stimulation of chemoreceptors in the carotid and aortic

bodies. 46



### Volatile nerve agents are highly potent OP chemi cals that inhibit AChE, as do the OP pesticides. In humans, OP nerve agents cause paralysis of respiratory muscles ( e.g. , diaphragm, abdominal, thoracic), airway secretions , edema and bronchoconstriction 47 

### . Experimental toxicology studies with laboratory animals exposed to OP war agen ts are consistent with these effects on the peripheral nervous system. For example, inhala tion exposure to OP war agents in baboons induces cardiac arrhythmias, apnea, hypoxia, and respirat ory disturbances. 48 

### There are some experimental studies in laborat ory animals where lung, bronchoal veolar lavage fluid and/or diaphragm ChE has been measured following exposure to war agents ( e.g. , VX, sarin, soman). 47,49,50,51



### EPA acknowledges that information on war agents needs to be interprete d with caution in the context of the toxicological pr ofile for chlorpyrifos. Although, there are rat three inhalation

studies 6,52,53 

### available with chlorpyrifos; none of these chlorpyrifos studies specially evaluated effects relevant to pulmonary function. Thus , the relationship between measures of ChE inhibition in the lung and pulm onary effects is not known. Th e war agent studies aid in

44 Nostrandt, A. C., Padilla, S., Moser, V. C. The Relationship of Oral Chlorpyrifos Effects on Behavior,

Cholinesterase Inhibition, and Mus carinic Receptor Density in Rat. Pharmacal. Biochem. Behav. 1997

, 58 , 15-23.

45 Moser, V. C., Chanda, S.M., Mortensen, S.R., Padilla, S. Age- and Gender-Related Differences in Sensitivity to

Chlorpyrifos in the Rat Reflect Developmental Profiles of Esterase Activities. Toxicol. Sci. 1998

, 46 , 211-222.

46 Taylor, P. Cholinergic Agonists in Goodman and Gillman’s The Pharmacological Basis of Therapeutics

. 1985

Seventh Edition.

47 Graham, J.R., Wright, B.S., Rezk, P. E., Gordon, R. K., Sc iuto, A. M., Nambiar, M. P. Butyrylcholinesterase in

Guinea Pig Lung Lavage: A Novel Biomarker to Assess Lung Injury Following Inhalation Exposure to Nerve Agent VX. Inhal Toxicol.

, 2006

, 18 , 493-500.

48 Anzueto, A., deLemos, R.A., Seidenfeld, J., Moore, G., Hamil, H., Johnson, D., Jenkinson, S.G.,1990. Acute

inhalation toxicity of soman and sarin in baboons. Fundam. Appl. Toxicol. 14, 676–687.

49 Che, M.M., Song, J., Oguntayo, S., Doctor, B.P., Re zk, P., Perkins, M.W., Sciuto, A.M., Nambiar, M.P.

Treatment with Endotracheal Therap eutics After Sarin Microinstillation Inhalation Exposure Increases Blood Cholinesterase Levels in Guinea Pigs. Toxicol. Mech. Methods. 2012

, 22 , 250-9.

50 Perkins, M.W., Pierre, Z., Rezk, P., Song, J., Oguntayo, S., Sciuto, A. M., Doctor, B. P., Nambiar, M. P. Acute

Changes in Pulmonary Function Following Microinstillation Inhalation Exposure to Soman in Nonatropenized Guinea Pigs. Int. J. Toxicol. 2011

, 30 , 348-57.

51 Perkins, M.W., Pierre, Z., Rezk, P., Sabnekar, P., Kabra, K., Chanda, S., Oguntayo, S., Sciuto, A.M., Doctor, B.

P., Nambiar, M. P. Acute Respiratory Toxicity Follo wing Inhalation Exposure to Soman in Guinea Pigs. Toxicol. Appl. Pharmacol. 2010

, 245 , 171-8.

52 EPA MRID 40013901 and 40166501 : Chlorpyrifos: 13-Week Nose-only Vapor Inhalation Exposure Study in Fischer 344 Rats Laboratory Project Id: HET K-044793-077 . Authors: Corley, R.; Landry, T.; Calhoun, L. et al.; Sponsor: Dow Chemical USA 1986

53 EPA MRID 40908401 : A Thirteen Week Nose-Only Inhalation Toxi city Study of Chlorpyrifos Technical (Pyrinex) in the Rat: Project No. 88-8058. Authors: Newton, P.; Prepared by Bio/dynamics, Inc.; 1988

### 18 of 70 considering the human relevance and toxicological adversity asso ciated with changes in lung ChE and potential cholinergic eff ects on the respiratory system. Th e qualitative findings of the war agent studies provide a starti ng point for evaluating human inci dent reports for the kinds of potential respiratory effects whic h may result from exposure to high levels of chlorpyrifos.

2.3.2. Human Incidents: Summary of Respiratory Effects

EPA considers human incident data in order to assist in better defini ng and characterizing the risk of pesticides/pesticide products. It is importa nt to recognize, however, that reports of adverse health effects allegedly due to a specific pesticide exposure are la rgely self-reported and therefore, generally speaking, neither exposure to a pesticide nor reported symptoms (nor the connection between the two) is va lidated. Therefore, only rarely can causation be determined or definitively identified based on incident data. However, incident information can provide important feedback to the EPA regarding the na ture, circumstances, frequency, and severity of pesticide exposure events. Human in cident data, considered jointly with the human health risk assessment, can assist the Agency in determini ng the risk pesticides/pes ticide products may or may not pose and can help characterize that risk in a qualitative manner.

Following the chlorpyrifos incident report summarized in the 2011 HHRA, chlorpyrifos incidents from the OPP Incident Data System (ID S), the National Pesticide Information Center (NPIC), National Institute for Occupational Sa fety and Health’s (NIOSH) Sentinel Event Notification System for Occupati onal Risk (SENSOR-Pesticides), and the California Pesticide Illness Surveillance Program (CA PISP) were further reviewed for an association with respiratory effects (such as wheezing, chest ti ghtening, and difficulty breathing). Respiratory

effects are consistent with what is seen in an imal studies exposed to chlorpyrifos by inhalation. The incidents reviewed involved only the single ac tive ingredient chlorpyrifos because incidents involving only one pesticide are considered to pr ovide more certain information on the suspected substance that may be causing adverse effects. EPA’ s review of chlorpyrifos incidents showed an association between chlorpyrifos incidents and respiratory e ffects across all the databases

reviewed. These incidents occurred due to both agriculture related use of chlorpyrifos and nonagriculture related use of chlorpyr ifos. To focus the scope of the review in a manner relevant to

this volatilization assessment and to be consistent with the curre nt use pattern, EPA focused the

review on incidents associat ed with drift, including vol atilization, occu rring post 2002.

In general, it should be noted that it is difficult to distinguish between in cidents associated with

drift and those associated with volatilization be cause information may be limited on the timing of exposure relative to the application event in eac h of the incident databases. In SENSOR, for example, drift is defined as “...the movement of pesticides away from the treatment site. The pesticide spray, mist, fumes, or odor are carried fr om the target site by air.” As such, there is no

clear distinction between cases e xposed from volatilization versus spray drift when analyzing the SENSOR-Pesticides data. This is generally true of the other incident databases as well.

Incidents associated with chlorpyrifos from each of OPP’s four databases are described below in

additional detail:

### 19 of 70 OPP’s Main Incident Data System: For OPP’s Main Incident Data System (IDS), from January 1, 2002 to February 1, 2011, there were 141 incident s in which chlorpyrifos was the only active ingredient in the suspected substance. 54 

### Of these 141 incidents, 52 (37%) incidents reported respiratory effects including—but not limited to—dyspnea, throat i rritation, irritated breathing, difficulty breathing, coughing/chok ing, and nasal congestion. Th ese incidents were mostly categorized as HCs (Human Moderate s); however, there was one fatality 55 

### and 4 incidents classified as major severity. Due to the limited and varying exposure scenario details available, it is not possible to dis tinguish between incidents occurring due to drift and those occurring due

to volatilization.

National Pesticide Information Center: From 2002 to 2010, National Pesticide Information Center (NPIC) reported 88 cases in which chlor pyrifos was the only active ingredient in the suspected substance. 56 

### Of these 88 cases involving chlo rpyrifos, 20 (23%) had respiratory symptoms such as difficulty breathing, coughi ng, runny nose, and tightness in chest. Ten incidents occurred due to drift exposure; howev er, only 4 of these drif t incidents reported respiratory effects.

California Pesticide Illness Surveillance Program : For California Pesticide Illness Surveillance Program ( CA PISP) from 2002 to 2009, there were 100 cases in which chlorpyrifos was the only active ingredient in the suspected substance. 57 

### Of these 100 cases, 56 (56%) reported respiratory effects, su ch as shortness of breath, di fficulty breathing, coughing, chest tightness, throat irritation, respir atory discomfort. Sixty one of the chlorpyrifos incidents are

associated with drift or volatili zation. Of these 61 incidents associ ated with drift or volatilization, 39 (45%) reported respiratory effects. While the av ailable data are insufficient to directly link respiratory effects to chlorpyrif os volatilization exposure, this may be because bystanders are less likely to associate respiratory symptoms with volatilization than they are, for example, with an obvious spray drift incident. A specific drift example involves an incident that occurred in 2007 in Tulare County, California. Twenty six vineyard workers repor ted effects from the drift/volatilization from a chlorpyrifos applicatio n to almonds in an adjacent field. Twelve of these workers reported respirator y effects. These respiratory e ffects include difficulty breathing, shortness of breath, cough, so re throat, chest tightness.

NIOSH Sentinel Event Notification Syst em for Occupational Risk-Pesticides: For NIOSH SENSOR-Pesticides from 2002 to 2009, th ere were 204 cases in which chlorpyrifos was the only active ingredient in the suspected substance. 58 

### Specifically:

54 There were 106 additional incident reported to IDS for chlorpyrifos that involved multiple chemicals.

55 The death incident is described in the database as follows, “ A 58 year old male was reportedly exposed to a ULV product five to six times. Each time he was taken to the emergency room with difficulty breathing and an upset stomach. He was diagnosed with and treated for COPD. Th e last time he was exposed to the ULV product, he fell while taking a shower after the exposure. He was subsequently hospitalized and died about 10 days later. He also suffered from peeling skin.”

56 There were 90 additional incidents reported to NPIC for chlorpyrifos that involved multiple chemicals.

57 There were 133 additional incidents reported to CA PI SP for chlorpyrifos that involved multiple chemicals.

58 SENSOR-Pesticides 2002-2009 has a total of 409 cases involving Chlorpyrifos. Of these, 204 cases involve a

single Active Ingredient (pc code=059101). For the purpos es of this analysis, only the 204 cases involving a single AI will be included.

### 20 of 70  Of the 204 cases, 91 cases (45%) reported one or more respiratory symptoms.

 Of the 91 cases with respiratory symptoms, 77 were low in severity, 11 were moderate in severity and 3 were high in severity.

 Of the 91 cases with respiratory symptoms , the most commonly reported respiratory effect was upper respiratory pain (n=44), followed by cough (n=27) and dyspnea/shortness of breath (n=26).

 42 of the 204 cases (21%) were attributab le to drift, including volatilization 59 

### and of these 42 drift cases, 20 (49%) reported one or more respiratory symptoms.

 There are 20 cases in SENSOR-Pesticides that are both attributable to drift and have a respiratory symptom. Six of these 20 cases involved bystander exposures to drift; 13 were work-related (exposure while conducting field work or applyi ng pesticide), and one

involved a residentia l application.

 

### Of the 42 chlorpyrifos drif t cases, 12 cases (29%) involve d a cited violation. These 12

cases all stem from one event in New Mexi co (event ID # NM00001) where a certified applicator was cited for a drift event that resu lted in these 12 case reports. Further, of the 42 chlorpyrifos drift cases, 20 cases ha ve label use information, of which 19 cases did not

follow the label and one case did follow the la bel. Twelve of the 19 cases that did not

follow the label were in fact the same cas es from New Mexico (event ID # NM00001).

SENSOR-Pesticides collects inform ation on the activity that was performed at the time of the exposure. Of the 91 cases that involved a respirator y effect: 24 cases were applying the pesticide, 37 cases were conducting routine work activity (includes field residue), and 15 cases were conducting routine i ndoor living activities 60 

### (other activities were unknown or included a small

number of cases and ar e not included here).

In summary, 45% of the chlorpyrifos cases reported in SENSOR-Pesticides from 2002-2009 had respiratory symptoms. It is impor tant to note that in SENSOR-Pes ticides, respiratory effects are the most commonly reported symptom with 45% of all cases in the database reporting a respiratory symptom.

Conclusion

EPA’s review of chlorpyrifos incidents fr om IDS, NPIC, PISP, and SENSOR-Pesticides

databases show numerous instances in which respiratory effects were seen following both occupational and residential chlorp yrifos exposures. While the avai lable data are insufficient to directly link respiratory effects to chlorpyrifos volatilization e xposure, the data suggest that

59 The SENSOR-Pesticides program defines drift as “...the m ovement of pesticides away from the treatment site.

The pesticide spray, mist, fumes, or odor are carried from the target site by air.” There is no clear distinction between cases exposed from volatilization versus spray drift when analyzing the SENSOR-Pesticides data.

60 Residential uses of chlorpyrifos are no longer allowed.

### 21 of 70 inhalation exposure to some forms of chlorpyrifos (vapor or aerosol) may result in respiratory health effects. The reported respiratory symptoms appear to be consis tent with cholinergic stimulation of the respiratory tract. Specifical ly, symptoms commonly re ported include difficulty breathing, nasal congestion coughing, and chest ti ghtening which are qualit atively consistent with the anticipated cholinergic effects reported by Taylor 46 

### and by studies of OP war agents.

2.3.3. Dose Response and Endpoint Selection

2.3.3.1. Acute Inhalation Exposure

As discussed in detail in the 2011 preliminary HHRA, the agency did a thorough review of the

scientific literature and determined that Ch E inhibition provides the most robust dose response data for deriving PODs. Moreover, EPA determin ed that route-specific studies were most

relevant to avoid uncertainties associated with route to route extrapol ation. The evaluation of residential bystander risk from chlorpyrifos vol atilization is focused onl y on the inhalation route of exposure, and for short durations.

For chlorpyrifos, there is a special acute inhalation toxicity study 6 

### available that can be used in

the assessment of volatil ization risk. In the special acute inhalation study, female rats were exposed by nose only to atmospheric concentrations of up to 53.9 mg/m 3 

### of particulate chlorpyrifos for 6 hours and allowed an addi tional 72 hours to recover. The mass median aerodynamic diameter (MMAD)/geometric standard deviations for these exposure levels were determined to be 1.93/1.58, 1.86/1.61, 1.79/1.59 a nd 1.9/1.51 microns, respectively. Plasma, RBC, brain, and lung ChE were measured.

The EPA uses the Reference concentration (RfC ) methodology in extrapolating animal PODs to human equivalent concentrations (for details of the RfC calculations, see the 2011 HHRA). In the 2011 risk assessment, the POD was an HEC calculated based on 24 hour exposure duration which was appropriate for evaluating ambient air e xposure. In this volatilization assessment, a 6 hour exposure duration was selected for the purpose of assessing residential bystander risk from

volatilization to avoid th e need for an exposure duration adjustment and to better match the offfield volatility data (samples we re collected every six hours in th e alfalfa field volatility study;

see Section 3.4 ).

Consistent and significant l ung and plasma ChE inhibition were noted at the lowest concentration tested of 3.7 mg/m 3 

### , which is a lowest-observed- adverse-effect-level (LOAEL).

RBC and brain ChE inhibition were noted at ≥ 12.9 mg/m 3 

### and 53.9 mg/m 3 

### , respectively, indicating less sensitiv ity than lung and plasma ChE i nhibition following acute inhalation exposures. A no-observed-adverse-effect-level (NOAEL) was not established. A benchmark dose (BMD) analysis was attempted with the lung ChE data but did not provide high confidence results (for details, see 2011 HHRA). A 6-hour HEC was calculated to be 2.5 mg/m 3 

### based on the LOAEL of 3.7 mg/m 3



### .

For the RBC ChE data, a benchmark response (BMR ) level of 10% was used to calculate a benchmark response level of 10% ( 

### BMDL 10 

### ). The BMD 10 

### is the estimated dose where ChE is inhibited by 10% compared to background. The BMDL 10 

### is the lower confidence bound on the

### 22 of 70 BMD 10 

### . Extensive analyses conducted as a part of the OP cumulative risk assessment 61 

### have

demonstrated that 10% is a level that can be re liably measured in the majority of rat toxicity studies, and is generally at or near the limit of sensitivity for discerning a statistically significant decrease in ChE activity. BMD analysis of the RBC ChE data resulted in a BMDL 10 

### = 4.3 mg/m 3 

### . Using the RfC methodology, a 6-hour HE C was calculated to be 15 mg/m 3



### .

The inhalation endpoints and PODs used for this analysis are summarized in Table 3

.

Table 3. Toxicological Concentrations, Huma n Equivalent Concentrations, Endpoints and Points of Departure for the Chlorpyrifos Residential Bystander Assessment from

Volatilization

Exposure Scenario Point of Departure (mg/kg/day) Study and Toxicological

Effects

Acute Inhalation (Lung) Inhalation LOAEL = 3.7 mg/m 3

HEC = 2.5 mg/m 3

UFA = 3x UFH = 10x UFDB = 10x (LOAEL to NOAEL extrapolation

Residential LOC for MOE = 300 Lung ChE Inhibition Special 6 hour acute inhalation study (MRID 48139303). (Aerosol) - 47% lung ChE inhibition (LOAEL = 3.7 mg/m 3

, NOAEL not established)

Acute Inhalation (RBC) BMDL 10 = 4.3 mg/m 3

HEC = 15 mg/m 3

UFA = 3x UFH = 10x

Residential LOC for MOE = 30 RBC ChE Inhibition

Special 6 hour acute inhalation study (MRID 48139303). (Aerosol) - 10 % lung ChE inhibition (BMDL 10 = 4.3 mg/m 3 ) lowest observe affect level (LOAEL); no observe affect level (NOAEL); human equivalent concentration (HEC); uncertainty factor for animal to human extrapolation (UF A ); uncertainty factor for w ith human variability to account for sensitivity subpopulations (UF H ); uncertainty factor database (UF DB ); level of concern (LOC); margin or exposure (MOE); cholinesterase (ChE); red blood cell (RBC); benchmark response level of 10% (BMDL 10 )



### 2.3.3.2. Acute Toxicity Adjustment Factor for Chlorpyrifos-oxon

There is potential for bysta nder inhalation exposure to vo latilized chlorpyrifos-oxon, a transformation product of chlorpyrifos. EPA devel oped a toxicity adjustment factor (TAF) to estimate the potency of chlor pyrifos-oxon relative to chlorpyrifos. An acute study evaluating ChE inhibition from inhalation exposure to the o xon is not available. As such, EPA must use the

oral studies as a reas onable approximation.

In order to determine a TAF for chlorpyrifos -oxon, BMD modeling of av ailable oxon data for acute oral dosing studies was conducted as part of the preliminary risk assessment. 1 

### The complete BMD analysis is described in the 2011 preliminary HHRA; only summary information is provided here.

61 U.S. Environmental Protection Agency. Revised Orga nophosphorous Pesticide Cumulative Risk Assessment; June 10, 2002. Available at: http://www.ep a.gov/pesticides/cumulative/rra-op/.

### 23 of 70 There is a high quality comparative ChE study fo r the oxon and parent, chlorpyrifos using the oral route of exposure. 62 

### The comparative ChE study evaluates effects of brain and blood ChE in juvenile and adult rats following acute exposures and following 11 repeat ed exposures. Only the results of the acute study are re levant for the acute TAF and thus only the results of the acute study are discussed here. The most sensitive endpoint from the acute comparative ChE study is RBC ChE inhibition for both chlorpyr ifos and chlorpyrifos-oxon.

When deriving PODs, the agency uses the BMDL, not the BMD, since the BMDL accounts for variability of the data. When making comparis ons among chemicals, the BMD provides the more appropriate point of comparison across studies . In the case of this assessment, the BMD 10 

### provides the basis for determini ng the relative toxicity of the chlorpyrifos oxon compared to chlorpyrifos. A toxicity factor for chlorpyrifos-oxon was calcula ted by dividing the chlorpyrifos

BMD 10 

### for the endpoint associated with the most se nsitive compartment fro m the most sensitive sex for the duration of interest by the corresponding BMD 10 

### for the oxon. Acute (all populations) toxicity factors of 8.8 (males) and 11.9 (females ) were calculated from BMD analysis of inhibition of male and female pup RBC ChE (acu te phase of the comparative ChE study). The toxicity factors may be used in assessments wh ere exposures to chlorpyrifos and chlorpyrifosoxon are to be combined ( i.e. , when exposure to both chemi cals is expected to occur simultaneously).

2.4. Exposure Characterization

2.4.1. Field Volatility Data

EPA reviewed and incorporated the results from two field volatility studi es (applied to alfalfa and potato) conducted with chlorpyrifos. While chlo rpyrifos is not currently registered for use on potatoes in the United States, potatoes are though t to be reasonable representative, for the purposes of extrapolation of fiel d volatility data, of ot her field crops treated with chlorpyrifos and the results of potato field volatility st udy provide useful inform ation on the potential volatility of chlorpyrifos under field conditions. As previously mentioned, the majority of chlorpyrifos is applied to field crops (67% of the total chlorpyrifos a pplied per year) including alfalfa (6% of the total chlorpyrifos applied per year).

These studies were conducted at rates much lower than the cu rrent maximum single broadcast application rate; however, based on usage data the ra tes used in these studie s are consistent with typical average single application rates for thes e crops. These two studies are summarized in the sections below and were used to estimate flux rates ( i.e. , rate of volatilizati on) off treated crops. Additional study details are provided in the da ta evaluation record (DER) for each of the respective studies. 7,11

62 Marty and Andrus 2010, MRID No.: 48139301 TXR No. 0055409

### 24 of 70 2.4.1.1. Alfalfa (MRID 48883201) 7



### 2.4.1.1.1. Study Summary

The concentration of chlorpyrifos, chlor pyrifos-oxon, and 3,5-6 tric loropyridinol (TCP) 63 

### in air were measured following applicati on of Lorsban Advanced Insecticide 64 

### (EPA Reg. No. 62719- 591; a liquid, low VOC formulation containing 3.66 lb/gal chlorpyrif os as the active ingredient), to a 7.59 acre alfalfa field (a crop height of 10 inches) via ground broadcast application at an application rate of 0.877 lb a.i./A. The study was conducted in Los Baños, California. The application was made on Septembe r 9, 2011, between 9:10 – 10:40 am.

Air sampling was conducted for three days during and after the application. Air samples were collected from eight off-field monitoring stati ons placed uniformly around each field (30 m from the edge of the treated area) during the first sampling period, which included the application event. The sampling height of the off-field mon itors was 1.5 m. After the application, an on-site profile monitoring station was set up in the cent er of the field to measure concentrations at heights of 0.15, 0.33, 0.55, 0.90, and 1.5 m. The on-field air samples were taken at approximately 6 hour intervals from time 0 (aft er the application) through 24 hours and at 12

hour intervals from time 24 to 72 hours. The 12 hour samples coincided approximately with

sunrise and sunset and were centered at 07:00 and 19:00 hours when possible. On-site meteorological conditions were monito red continuously at the site.

Flux rates for chlorpyrifos and total toxic ch lorpyrifos residues (TTCR; chlorpyrifos and chlorpyrifos-oxon) in μg/m 2 

### -s were calculated using the Indire ct Flux Method (IFM) for the first period when the application was in progress (S ampling Period 1) and both the Integrated Horizontal Flux (IHF) method and the Aer odynamic (AD) method for the other sampling periods. A brief description of these methods is provided 

### in APPENDIX C . Approximately 28% (chlorpyrifos) and 30% (TTCR) of the applied active ingredient was observed to volatilize within the first 24 hours. For dispersion modeling and subsequent buffer calculations, TTCR is defined in terms of toxic parent equivalents—the sum of the chlorpyrifos c oncentration and the oxon concentration that has been corrected to parent equivalents using a toxic ity adjustment factor (TAF; discussed in detail in Section 2.3 ) of 12. 65



### This study is classified as acceptable and is used quantitatively in this assessment.

2.4.1.1.2. Flux Rates

EPA calculated flux rates for chlorpyrifos (parent only) and TTCR (chlorpyrifos and chlorpyrifos-oxon) in μg/m 2 

### -s for the first period ( e.g. , during application) (Sampling Period 1) employing the IFM. Flux rates for the subsequent sampling periods (thru day 3) were calculated using both the IHF method and the AD flux method. Flux rates were calculated accounting for field fortifications (FF) as well as stor age stability and are reported in the DER. Table 4 contains the flux rates for chlorpyrifos (parent only) calculated using both methods (AD and IHF)

63 TCP is not considered as a residue of concern.

64 Marketed as a low VOC chlorpyrifos formulation.

65 Email from Wade Britton (OPP/HED) to Roche lle Bohaty (OPP/EFED) September 10, 2012.

### 25 of 70 incorporating data for both FF and storage stability for all sa mpling periods and based on the application rate of 0.877 lb a.i./A used in the study.

Table 4. Estimated Flux Rates for Chlorpyrif os Using AD and IHF Methods for the Alfalfa Study

Period Sample Start

Times Sample End

Times Duration (hh:mm) Hours Post Application at Sample

Collection AD

Method IHF

Method*

Estimated

Flux FF (μg/m 2 -s) Estimated

Flux FF (μg/m 2 -s)

2 9/9/2011 10:45 9/9/2011 13:00 2.25 2.25 0.824 0.591

3 9/9/2011 13:00 9/9/2011 19:00 6.00 8.25 0.260 0.759

4 9/9/2011 19:00 9/10/2011 1:00 6.00 14.25 0.038 0.171

5 9/10/2011 1:00 9/10/2011 7:00 6.00 20.25 0.026 0.054

6 9/10/2011 7:00 9/10/2011 19:00 12.00 32.25 0.081 0.167

7 9/10/2011 19:00 9/11/2011 7:00 12.00 42.25 0.012 0.021

8 9/11/2011 7:00 9/11/2011 19:00 12.00 54.25 0.020 0.033

9 9/11/2011 19:00 9/12/2011 7:00 12.00 66.25 0.007 0.006

10 9/12/2011 7:00 9/12/2011 19:00 12.00 78.25 0.018 0.012

11 9/12/2011 19:00 9/13/2011 7:00 12.00 90.25 0.002 0.005 Field Fortification (FF) *Flux profile used in assessment for quantitative assessment ( i.e. , used in PERFUM modeling). Data provided in this table are based on the appli cation rate used in the study (0.877 lb a.i./A).



### The results for chlorpyrifos (parent only) for the AD method compared we ll against the values calculated by the study authors; however, the resu lts for the IHF method we re higher than those calculated by the study author. A review of the st udy author’s calculations indicated that the IHF analysis was truncated at 150 cm, which resulted in lower flux rate estimates. The IHF method provided slightly more conservati ve flux profiles; therefore, the flux rates from this method were used in the PERFUM analyses.

EPA examined the flux rate values for oxon only; however, attempts at conducting a regression analysis generated poor fitting results. The study authors also completed this analysis and their

results are consistent with EPA’ s analysis. It is unclear if th e chlorpyrifos-oxon concentrations are a result of chlorpyrifos-oxon flux off the field or from transformation of chlorpyrifos in the

air or on the tube. 66 

### In any case, it suggests the potential for exposure to chlorpyrifos oxon. In

order to account for the formation and potential increased toxicity from exposure to chlorpyrifosoxon, EPA used a total toxic residue approach wh ich combines chlorpyrifos and chlorpyrifosoxon residues. Initial attempts at conducting a re gression analysis for the TTCR generated poor fitting results. In general, the oxon concentrations did not follow a decreasing trend with height as did the chlorpyrifos c oncentrations, resulting in poor fitting results. In an effort to use the available data, a conversion factor was develope d for each sampling period, which took the total mass of oxon for all four air samplers and divided this total by the total mass of chlorpyrifos for

66 The study authors conducted an additional analysis and developed a correction factor to adjust the chlorpyrifosoxon concentrations to account for chlorpyrifos-oxon formation on the sample tubes during the study.

### 26 of 70 all four air samplers. The mass of chlorpyrif os at each height was then multiplied by this conversion factor to estimate the mass of oxon at the same height.

Table 5 contains the TTCR flux profile developed for all sampling pe riods for the alfalfa study.

Table 5. Estimated Flux Rates for Total Toxi c Chlorpyrifos Residues (Chlorpyrifos and Chlorpyrifos-oxon) Using AD and IH F Methods for the Alfalfa Study

Sampling

Period Sample Start

Times Sample End

Times Duration (hh:mm) Hours Post Application at Sample

Collection AD

Method IHF

Method*

Estimate

d Flux

FF (μg/m 2

- s) Estimated

Flux FF (μg/m 2 -s)

2 9/9/2011 10:45 9/9/2011 13:00 2.25 2.25 0.83 0.59

3 9/9/2011 13:00 9/9/2011 19:00 6.00 8.25 0.27 0.78

4 9/9/2011 19:00 9/10/2011 1:00 6.00 14.25 0.038 0.17

5 9/10/2011 1:00 9/10/2011 7:00 6.00 20.25 0.026 0.051

6 9/10/2011 7:00 9/10/2011 19:00 12.00 32.25 0.088 0.18

7 9/10/2011 19:00 9/11/2011 7:00 12.00 42.25 0.012 0.024

8 9/11/2011 7:00 9/11/2011 19:00 12.00 54.25 0.021 0.033

9 9/11/2011 19:00 9/12/2011 7:00 12.00 66.25 0.007 0.006

10 9/12/2011 7:00 9/12/2011 19:00 12.00 78.25 0.020 0.013

11 9/12/2011 19:00 9/13/2011 7:00 12.00 90.25 0.002 0.004 Field Fortification (FF) *Flux profile used in assessment Data provided in this table are based on the appli cation rate used in the study (0.877 lb a.i./A). Flux profile is based on mass only and does not take into account the difference in toxicity between chlorpyrifos and chlorpyrifos-oxon.



### 2.4.1.2. Potato (MRID 48998801) 11



### 2.4.1.2.1. Study Summary

The rate of volatilizatio n of chlorpyrifos only was measured following a 0.61 lb a.i./A ground broadcast application of Dursba n EC, an emulsifiable concen tration, non-low VOC formulation containing 4.0 lb a.i./gal chlorpyr ifos as the active ingredient [the currently marketed equivalent is Dursban 4E (EPA Reg. No.62719-220)], to a pot ato field (crop height of 22 inches). This study did not measure chlorpyrifos-oxon con centrations. The study was conducted in the Netherlands on June 25, 2002, with the a pplication beginning at 11:30 am.

Air concentration samples were collected begi nning at 12:35 pm and ending the following day at 1:37 pm. Samples were collected at 1.0, 1.6, and 1.9 m above the top of ri dges on the soil surface at the center of a potato field. Wind speed and temp erature data were collect ed at various heights using equipment positioned at the center of the field during the sample collection period.

Flux rates for chlorpyrifos in μg/m 2 

### -s were calculated using the AD method. Approximately 71% of the applied chlorpyrifos was estimated to volatilize within 24 hours following application assuming continuous flux. Sampling did not occur at night; therefore, in order to develop a 24

### 27 of 70 hour flux profile. EPA developed a flux rate for the missing sampling periods by averaging the flux rate prior to and after the time period when sample collection did not occur.

This study is classified as supplemental and is used for characteriza tion purposes in this

assessment.

2.4.1.2.2. Flux Rates

EPA developed a flux profile (shown in Table 6 ) for chlorpyrifos in mg/m 2 

### -hr using the flux rates calculated by the study au thors using the AD method fo r the first 24 hours following application of chlorpyrifos at 0.61 lb a.i. /A to potatoes. During the overnight hours (approximately 21:00 to 10:00) samp le collection did not occur. In order to develop a 24 hour flux profile, the average flux rate for the samp ling period immediately before and immediately after the overnight hours (Periods 4 and 5 in Table 6 ) were averaged and assumed to represent the flux that occurred during the overnight period. The raw data for this study have not been

made available to EPA so the flux rates could not be independently verified by EPA. However, the results from this study are pr esented here to provide another li ne of evidence to characterize the observations in the registrant submitted study to help describe the potential variability in flux rates due to difference in study conditions ( e.g. , crop canopy, formulation, and weather).

Table 6. Estimated Flux Rates for Chlorpyrifos AD Method For the Potato Study

Sampling

Period Sample Start

Times Sample End

Times Duration (hh:mm) AD Method

Estimated Flux (μg/m 2 -s)

1 6/25/2002 12:35 6/25/2002 13:56 1:21 1.87

2 6/25/2002 14:01 6/25/2002 15:34 1:33 2.17

3 6/25/2002 15:42 6/25/2002 17:26 1:44 0.82

4 6/25/2002 19:20 6/25/2002 20:44 1:24 0.17

5 6/26/2002 09:54 6/26/2002 11:32 1:38 0.16

6 6/26/2002 11:42 6/26/2002 13:37 1:55 0.08

Data provided in this table are based on the app lication rate used in the study 0.61 lb a.i./A.



### 2.4.2. Conclusions and Modeling Inputs

In general, the flux trends estimated by EPA a nd those by the study author for the alfalfa study are consistent. In addition, although the magnitudes of the peak flux rate are different, the results of the potato study are consiste nt with the alfalfa study ( Figure 3 ).

### 28 of 70 a) b)

Figure 3. 24 Hour Flux Profile Generated Ba sed on the Two Available Field Volatility Studies for Chlorpyrifos (Parent Only); a) the flux rate compared to hours post application and b) the flux rate compared to the time of day. NOTE: Flux profiles are scaled up from the actual application rates of 0.877 lb a.i./A (alfalfa) and 0.61 lb a.i./A (potato) to 6 lb a.i./A (current the highest single maximum broadcast application rate registered).



### The difference in the peak flux values estimated between the two studies may be the result of several different factors including: the product formulation used, the crop treated (alfalfa compared to potato), environmental conditions (tem perature, humidity, etc.), differences in plant foliage and canopy structure, or a combination of these and ot her factors. In addition, the difference in the peak values obtained may also be the result of the difference in sample collection periods which could have led to an av eraging out of the peak flux based on the longer sampling period used in the alfalfa st udy as compared to the potato study. Figure 3 shows the flux profile for both studies for the first 24 hours following chlorpyrifos ap plication based on the

calculated flux rates.

The flux profile for chlorpyrifos is similar to thos e observed for fumigants in that there is a peak emission shortly after application ( Figure 3a ) and during the warmer part of the day ( Figure

3b ). The peak is followed by a much lower emi ssion rate that generally decreases over time. While the potato study does not extend beyond 24 hour s post application, the alfalfa study shows a general decrease in emission ra tes over the next two days. Ho wever, a secondary “peak” flux was observed on day two of the alfalfa field vol atility study. This observed increase in the flux rate following the overnight hours is likel y due to an increase in temperature.

For PERFUM modeling the flux rates from the fi eld volatility studies we re adjusted to an application rate of 6 lb a.i./A (currently, the highest single ma ximum broadcast application rate registered). In the past, flux rates and subs equent modeling were completed by scaling down results for studies conducted at higher applicatio n rates; however, in this case, the available studies were conducted at applicat ion rates [0.877 lb a.i./A (alf alfa); 0.61 lb a.i./A (potato)] which is below the maximum labeled single broadcast application rate (6 lb a.i./A for citrus). The single application rate used in the alfalfa study is lower than the currently labeled maximum single application rate for alfalfa (1 lb a.i./A).

### 29 of 70 The flux profiles used in PERFUM model runs are presented in Table 7 (alfalfa) and Table 8 (potato). To account for the increased toxicity of the oxon (alfalfa study) co mpared to the parent chlorpyrifos, the observed oxon concentration was adjusted by a TAF of 12 to generate an exposure concentration in units of parent equivalent toxicity 67 

### . The adjusted concentration value ([oxon]*TAF) was added to chlorp yrifos (parent only) concentr ation to develop a TTCR flux profile for PERFUM analyses (shown in Table 7 ).

Table 7. Flux Profile Used in PERFUM Anal ysis Generated from the Alfalfa Study

Hour of the Day Chlorpyrifos (only) a μg/m 2 /sec Total Toxic Chlorpyrifos Residues a,b
μg (parent toxicity equivalent units)/m 2 /sec

Day 1 Day 2 Day 3 Day 1 Day 2 Day 3

1 1.17 0.14 0.04 1.35 0.32 0.05

2 0.37 0.14 0.04 0.44 0.32 0.05

3 0.37 0.14 0.04 0.44 0.32 0.05

4 0.37 0.14 0.04 0.44 0.32 0.05

5 0.37 0.14 0.04 0.44 0.32 0.05

6 0.37 0.14 0.04 0.44 0.32 0.05

7 0.37 0.14 0.04 0.44 0.32 0.05

8 1.14 0.23 0.04 2.63 0.39 0.26

9 1.14 0.23 0.23 2.63 0.39 0.26

10 1.50 1.14 0.23 3.14 2.63 0.39

11 1.50 1.14 0.23 3.14 2.63 0.39

12 4.04 1.14 0.23 5.41 2.63 0.39

13 4.04 1.14 0.23 5.41 2.63 0.39

14 5.19 1.14 0.23 8.68 2.63 0.39

15 5.19 1.14 0.23 8.68 2.63 0.39

16 5.19 1.14 0.23 8.68 2.63 0.39

17 5.19 1.14 0.23 8.68 2.63 0.39

18 5.19 1.14 0.23 8.68 2.63 0.39

19 5.19 1.14 0.23 8.68 2.63 0.39

20 1.17 0.14 0.04 1.35 0.32 0.05

21 1.17 0.14 0.04 1.35 0.32 0.05

21 1.17 0.14 0.04 1.35 0.32 0.05

22 1.17 0.14 0.04 1.35 0.32 0.05

23 1.17 0.14 0.04 1.35 0.32 0.05

24 1.17 0.14 0.04 1.35 0.32 0.05

67 Parent equivalent toxicity is not representative of the mass balance.

### 30 of 70 Hour of the Day Chlorpyrifos (only) a μg/m 2 /sec Total Toxic Chlorpyrifos Residues a,b
μg (parent toxicity equivalent units)/m 2 /sec

Day 1 Day 2 Day 3 Day 1 Day 2 Day 3

a. Flux profile has been scaled up from an application rate of 0.877 lb a.i./A to 6 lb a.i./A (current

maximum single broadcast application rate) and are based on the flux profile that considers FF samples.

b. To account for the increased toxicity of the oxon compared to the parent chlorpyrifos, the

observed oxon concentration was adjusted by a toxicity adjustment factor (TAF) of 12 to generate an exposure concentration in units of parent equivalent toxicity 67 . The adjusted concentration value ([oxon]*TAF) was added to chlorpyrifos (parent only) concentration to develop a TTCR flux profile. These values do not directly correlate to 12x the values presented

in Table 5

.



### Table 8. Flux Profile Used in PERFUM An alysis Generated from the Potato Study

Hour Chlorpyrifos (only) a μg/m 2 /sec

Day 1

1 1.58

2 1.58

3 1.58

4 1.58

5 1.58

6 1.58

7 1.58

8 1.58

9 1.58

10 1.58

11 1.58

12 1.58

13 18.67

14 18.67

15 21.67

16 21.67

17 8.22

18 8.22

19 8.22

20 1.68

21 1.68

21 1.58

22 1.58

23 1.58

24 1.58

### 31 of 70 Hour Chlorpyrifos (only) a μg/m 2 /sec

Day 1

a. Flux profile has been scaled up from

an application rate of 0.61 lb a.i./A to 6 lb a.i./A (current maximum single broadcast application rate).



### 3. RISK ASSESMENT

Chlorpyrifos can be used under a variety of agricultural and en vironmental conditions. In order to understand the impact such varied conditions can have on exposure (and subsequent risk assessments), analyses were completed using PERFUM to examine the impact of varied application rates, field sizes, and meteorological data (see bullets below). These are the same parameters which have been used as the basi s for other similar analyses completed for soil fumigants by EPA. For brevity onl y a subset of these analyses are presented in the sections below. Example PERFUM output files are provided in ATTACHMENT 2

. The results of this analysis are presented in the sections below. Note: the PERFUM analyses do not provide insight into the potential impact of t opography, field layout crop ca nopy, and formulation, on air

concentrations. These variables are further discussed in Section 4

.

 Application rates: 6, 5, 4, 3, 2.3, 2, 1, 0.5, and 0.1 lb a.i./A

 Field size: 1, 5, 10, 20, 40, 60, 80, 100, and 120 acres

 Meteorological data: Bakersfield, Californi a; Bradenton, Florida; Flint, Michigan; Tallahassee, Florida; Ventura, Ca lifornia; and Yakima, Washington

3.1. Buffer Distributions

3.1.1. Alfalfa

3.1.1.1.Chlorpyrifos (Parent Only)

Table 9 presents the PERFUM results based on lung ChE inhibition and the flux profile derived from the alfalfa study. The results are provided for chlorpyrifos (parent only) at an application rate of 1 lb a.i./A. An application ra te of 1 lb a.i./A as presented in Table 9 is close to the actual application rate made in the alfalfa study (0.877 lb a.i./A) and many applications for various crops ( e.g. , alfalfa, asparagus, bean, sweet corn, cott on, onions, peas, soybean, strawberries, and wheat) are made at approximately 1 lb a.i./A or less. The results from three of the six meteorological datasets ( i.e. , Ventura, California, Bradenton, Fl orida, and Flint, Michigan) used in model simulations are presented as these three meteorological datasets are thought to reasonably represent the range of environm ental conditions across the United States.

### 32 of 70 Table 9. Comparison of Results For Chlo rpyrifos (parent only) PERFUM Buffer Distributions Based On Alfalfa Study a, b

Percentiles Meteorological Station Location Ventura, CA Bradenton, FL Flint, MI

Max

Buffer c

(ft) Whole

Field

Buffer d

(ft) Max

Buffer c

(ft) Whole

Field

Buffer d

(ft) Max

Buffer c

(ft) Whole

Field

Buffer d

(ft) 10 A, 1 lb a.i/A

50 16 - 33 - - -

75 16 - 148 - 16 -

90 66 16 262 33 16 -

95 148 16 377 98 49 16

99 377 82 607 246 148 16 20 A, 1 lb a.i/A

50 16 - 98 - - -

75 33 - 246 16 16 -

90 164 16 427 82 66 16

95 262 16 607 164 131 16

99 623 180 1001 394 279 82 60 A, 1 lb a.i/A

50 16 - 262 - 16 -

75 148 16 558 16 82 -

90 410 33 935 213 230 16

95 623 131 1312 377 344 66

99 1345 443 2100 804 640 262 120 A, 1 lb a.i/A

50 82 - 443 - 16 -

75 279 16 902 66 180 -

90 689 98 1542 361 410 49

95 1050 230 2165 591 607 148

99 2215 722 3510 1263 1198 459

a. Lung: 6 h HEC 2,500 μg/m 3 , UF=300, target concentration 8.3 μg/m 3

b. Registrant study conducted on alfalfa using Lorsban Advanced

c. Max buffers are the largest buffer estimated fro m any given direction away from the field.

d. Whole field buffers are estimated based on an array of results for the entire perimeter of a

field.



### The results presented in Table 9 show how buffer distances (whole field 68 

### and maximum 69


### buffers) change in relation to field size, percen tile of exposure, and meteorological conditions.

Buffer distances are calculated based on the di stance at which the target concentration [ i.e.

, toxicity point of departure (HEC for lung ChE i nhibition) divided by the uncertainty factor] of 8.3 μg/m 3 

### is reached. Depending on the percentile of exposure and the field size considered, the

maximum buffers needed to be at or below the ta rget concentration range from 0 to greater than 3500 ft. Spray drift buffers to prot ect bystanders in sensitive sites 70 

### required on chlorpyrifos

68 Whole field buffers are estimated based on an arra y of results for the entire perimeter of a field.

69 Max buffers are the largest buff er estimated from any given direction away from the field.

70 Buffers are around sensitive sites (a circle drawn around the sensitive site an d do not correspond to buffers around

a given field (a circle dr awn around a treated field).

### 33 of 70 labels range from 0-100 feet depending on the ap plication method. The buffers currently required on all chlorpyrifos labels are summarized in APPENDIX D

.

Considering an application scenario similar to that reported in the alfalfa study—1 lb a.i./A (actual: 0.877 lb a.i./A) chlorpyrif os application made to a 10 A (actual: 7.59 A) alfalfa field in Ventura, California (actual: Los Baños, California) 

### —a 16 foot whole field buffer and a 148 foot maximum buffer were estimated by PERFUM to ensu re that 95% of the time bystanders offsite would not be exposed to concentrations higher than the target concen tration. If, however, a similar application where to occur in an ar ea with meteorological conditions similar to Bradenton, Florida 71 

### PERFUM estimates that a 98 foot whole field buffer and a 377 foot

maximum buffer are needed to ensure that 95% of the time bystanders are not exposed to air concentrations higher than the target concentrati on. When considering a larger treatment area, for example, a 120 A alfalfa field similar to the study site. 72 

### PERFUM estimates that a 230 foot

whole field buffer and a 1050 foot maximum buffer are needed to ensure that 95% of the time bystanders are not exposed to air concentratio ns higher than the ta rget concentration.

Although not presented in detail in this assessment, similar analys es using a target concentration of 497 μg/m 3 

### derived based on the RBC ChE inhibition e ndpoint, indicate that currently labeled buffers ( APPENDIX D) would result in bystander exposure to offsite co ncentrations that are less than the target concentration. The target concentration based on the RBC ChE inhibition endpoint is approximately equal to the saturated vapor concentration (489 μg/m 3 

### ) of chlorpyrifos. Error! Bookmark not defined. This suggests that in the environment, due to mixing and dispersion, chlorpyrifos vapor concen trations are not likely to occur near the RBC ChE inhibition target concentrati on except under extreme conditions ( e.g. , inversion).

Table 10 presents the buffer distributions for a range of applications rates. Again, these results are based on the lung ChE inhi bition endpoint and the alfalfa flux profile. Model run results reported in Table 10 are for chlorpyrifos (only) using the Bradenton, Florida meteorological data. Generally this meteorological dataset result s in the largest estimated buffers of all six meteorological stations. Examination of the bu ffer distributions resul ting from the PERFUM runs for all the meteorological datasets s how results similar to those presented in Table 10 . This analysis indicates that higher application rates le ad to larger estimated buffers as expected. For example, when considering a same chlorpyrifos a pplication scenario to th at presented above for alfalfa in Bradenton, Florida 71 

### , but using a higher application rate ( i.e. , turf at 4 lb a.i./A—the current maximum single application rate) the es timated buffer is approximately seven times higher. For chlorpyrifos (only) , a 673 foot whole field buffer and a 2215 foot maximum buffer

would be needed to ensure that 95% of the time the air concentration that bystanders are exposed is not higher than the lung ChE inhibition target concentration.

71 1 lb a.i./A (actual: 0.877 lb a.i./A) chlorpyrifos appli cation made to a 10 A (actual: 7.59 A) alfalfa field in

Bradenton, Florida (actual: Los Baños, California)

72 1 lb a.i./A (actual: 0.877 lb a.i./A) chlorpyrifos app lication made to a 120 A (actual: 7.59 A) alfalfa field in

Ventura, California (actual: Los Baños, California)34 of 70Table 10. Comparison of Results For Chlorpyrifos (parent only) PERFUM Buffer Distributions Based On Different ApplicationRatesa,bPercentilesBradenton, FL0.5 lb a.i./A1 lb a.i./A2 lb a.i./A4 lb a.i./A6 lb a.i./AMaxBufferc(ft)WholeFieldBufferd(ft)MaxBufferc(ft)WholeFieldBufferd(ft)MaxBufferc(ft)WholeFieldBufferd(ft)MaxBufferc(ft)WholeFieldBufferd(ft)MaxBufferc(ft)WholeFieldBufferd(ft)10 A50 - - 33 - 328 - 886 - 1394 -75 16 - 148 - 541 33 1280 148 1969 23090 16 - 262 33 820 213 1804 459 2674 64095 16 16 377 98 1033 328 2215 673 3248 96899 131 16 607 246 1476 623 2871 1230 4347 177220 A50 - - 98 3 525 - 1362 - 2133 1675 16 - 246 16 837 98 1969 246 3018 34490 16 - 427 82 1296 328 2822 689 4298 93595 98 16 607 164 1624 509 3510 1017 >4724 142799 262 66 1001 394 2264 935 >4724 1870 >4724 264160 A50 16 - 262 - 1066 - 2740 16 4511 6675 33 - 558 16 1722 213 4183 492 >4724 68990 180 16 935 213 2674 640 >4724 1296 >4724 172295 279 33 1312 377 3461 984 >4724 1936 >4724 272399 640 213 2100 804 >4724 1821 >4724 3707 >4724 3120 A50 16 - 443 - 1706 16 4511 66 >4724 13175 115 - 902 66 2789 344 >4724 755 >4724 101790 328 16 1542 361 4446 984 >4724 1919 >4724 257595 509 98 2165 591 >4724 1493 >4724 2936 >4724 418399 1099 361 3510 1263 >4724 2838 >4724 >4724 >4724 >4724a.Registrant study conducted on alfalfa using Lorsban Advancedb.Lung: 6 h HEC 2,500 μg/m3, UF=300, target concentration 8.3 μg/m3c.Max buffers are the largest buffer estimated from any given direction away from the field.d.Whole field buffers are estimated based on an array of results for the entire perimeter of a fielde.Note: PERFUM does not produce buffer zones greater than 4724 ft (1440 m), thus, buffer zones for cases where the 4724 ft (1440m) limit isreached may be very large. These casesare indicated with a “>4724 ft ”.

### 35 of 70 3.1.1.2. Total Toxic Chlorpyrifos Residues

To account for the potential exposure to both ch lorpyrifos and chlorpyrifos-oxon simultaneously,

PERFUM was also used to estimate buffer dist ances based on exposure to TTCR. This technique incorporates a toxicity adjustme nt factor that accounts for the potential difference in toxicity between the two chemicals (discussed in Section 2.3 ). Table 11 presents the PERFUM results, again based on the toxicity e ndpoint derived from lung ChE i nhibition and the flux profile derived from the alfalfa study, for both chlor pyrifos (parent only) and TTCR [in parent equivalents ( i.e. , chlorpyrifos + chlo rpyrifos-oxon*TAF)].

Table 11. Comparison of Results For Chlo rpyrifos (parent only) and Total Toxic Chlorpyrifos Residues PE RFUM Buffer Distributions a

Percentiles Bradenton, FL Chlorpyrifos (parent only) TTCR (Chlorpyrifos + Oxon*TAF)

Alfalfa b Potato c Alfalfa b

Max

Buffer d

(ft) Whole

Field

Buffer e

(ft) Max

Buffer d

(ft) Whole

Field

Buffer e

(ft) Max

Buffer d

(ft) Whole

Field

Buffer e

(ft) 10 A , 1 lb a.i/A

50 33 - 394 - 213 -

75 148 - 558 82 394 16

90 262 33 738 262 623 148

95 377 98 902 377 804 246

99 607 246 1280 623 1165 492 20 A, 1 lb a.i/A

50 98 - 607 - 361 -

75 246 16 837 148 623 49

90 427 82 1132 394 984 246

95 607 164 1362 558 1263 377

99 1001 394 1919 919 1821 755 60 A, 1 lb a.i/A

50 262 - 1132 16 738 -

75 558 16 1624 295 1296 148

90 935 213 2198 738 2034 492

95 1312 377 2690 1033 2641 771

99 2100 804 3904 1722 3953 1460 120 A, 1 lb a.i/A

50 443 - 1690 33 1181 -

75 902 66 2510 459 2067 246

90 1542 361 3494 1083 3379 755

95 2165 591 4364 1526 4380 1165

99 3510 1263 >4724 2625 >4724 2264

a. Lung: 6 h HEC 2,500 μg/m 3 , UF=300, target concentration 8.3 μg/m 3

b. Registrant study conducted on alfalfa using Lorsban Advanced

c. Open literature study conducted on potato using Dursban

d. Max buffers are the largest buffer estimated fro m any given direction away from the field.

e. Whole field buffers are estimated based on an array of results for the entire perimeter of a

field

### 36 of 70 Based on exposure to the total to xic residues (expressed in pare nt equivalents), the modeling results indicate that larger buffers are necessary to ensure air concentrations that bystanders could be exposed to are lower than the target concentration estimated, compared to those estimated for chlorpyrifos (parent only). When considering chlorpyrifos (parent only) in the application scenario (10A, 1 lb a.i./A ) presented above for Bradenton, Florida 71 

### a 98 foot whole

field buffer and a 377 foot maximum buffer are needed for the 95 th 

### % percentile of exposure. However, when the concentrations of chlorpyr ifos (parent only) and chlorpyrifos-oxon are combined and accounted for, the increased toxici ty of chlorpyrifos-oxon are taken into account, the buffer estimates are larger—246 feet (whole field buffer) and 804 feet (maximum buffer) for

the 95 th 

### percentile of exposure.

While the flux profiles are derived from concentr ations measured on the field of application, PERFUM modeling does not account for the poten tial transformation of chlorpyrifos and chlorpyrifos-oxon as these chemicals move offsit e (flux study sampling o ccurs on the application site). Potential transformation pathways in ai r for chlorpyrifos and chlorpyrifos-oxon include direct and indirect air photolysis . To evaluate the impact of ai r photolysis on chlorpyrifos air concentrations, EPA ran simulations fo r a 20 acre square field using AERMOD 73 

### with and

without the half-life te rm of 7200 seconds, or 2 hours (based on indirect photolysis), in the control pathway. All othe r input parameters ( e.g. , field size, meteorological conditions, receptor locations, etc) remained the same for both si mulations. In both cases, the maximum 1-hour chlorpyrifos concentration occurred at the same receptor location (n ear the edge of the corner of the field) and meteorological conditions. The chlorpyrifos air concentration incorporating air photolysis was approximately 7% lower than the air concentration, which did not account for air photolysis. Therefore, the concentration of chlorpyr ifos is not expected to markedly change and little impact on the estimated buffer distances fo r chlorpyrifos (parent only) generated using PERFUM and a 6-hour endpoint is expecte d, if air photolysis is considered.

This analysis reinforces the hypothesis that chlor pyrifos can be converted to chlorpyrifos-oxon in

the air via direct and indirect photolysis, and demonstrates that even at low concentrations ( ≤ 7%) formation of chlorpyrifos-oxon can have an appreciable impact on the estimated buffers distances for TTCR due to the expected increased toxicity (12x) of ch lorpyrifos-oxon compared to chlorpyrifos. The formation of chlorpyrifos-oxon in the air over a treated field is expected to be captured in the flux profile for TTCR derived from the alfalfa study.

73 AERMOD is a steady-state plume model that incorpor ates air dispersion based on planetary boundary layer turbulence structure and scaling conc epts, including treatment of both surface and elevated sources, and both simple and complex terrain. Developed by the American Meteorological Society/Environmental Protection Agency Regulatory Model Improvement Committee (AERMIC), AERMOD became EPA’s preferred air dispersion model in 2005, replacing the Industrial Source Complex (ISC) model. AERMOD uses a simple runstream setup file, which contains information on the selected modeling options, as well as source location and parameter data, receptor locations, meteorological data file specifications, and output options. Unlike ISC, AERMOD requires two types of meteorological data f iles that are provided by the AERMET meteorological preprocessor program. One file consists of surface scalar parameters, and th e other file consists of vertical profiles of meteorological data.

### 37 of 70 3.1.2. Potato

3.1.2.1.Chlorpyrifos (Parent Only)

In addition to the buffer distribution analysis considering chlorpyrifos (parent only) and TTCR based on the alfalfa study, Table 11 also includes buffer distributi ons based on the flux profile for chlorpyrifos (parent only) derived from th e potato study. This table shows that both whole and maximum field buffers calculated using PE RFUM are larger based on the potato flux study as compared to the alfalfa study. For example, in the application scenario presented above for alfalfa in Bradenton, Florida, 71 

### PERFUM estimates that based on the potato flux profile for chlorpyrifos (parent only) a 98 foot whole field buffer and a 377 f oot maximum buffer are

needed to ensure that 95% of the time the conc entration bystanders may be exposed to is less than the target concen tration based on the alfalfa study. For the potato stud y the estimated buffers are 377 ft (whole field buffer) and 902 ft (max imum buffer) related to the same scenario.

The difference in the flux profile and the results of the dispersion modeling (buffer size) between the two studies may be the result of different experimental conditions between the two studies including: the crop treated (alfalfa compared to potato), meteorological conditions (temperature, humidity, etc.), the product formulation us ed (low VOC compared to a non-low VOC formulation), or a combination of these and other factors. In addition, some of the variation in the estimated buffer distances may be an artifact of the study design give n the differences in sample collection periods [6 h (alfalfa) versus 1.5 h (potato)]. This could have led to an averaging out of the peak flux due to the longe r sampling periods used in the alfalfa study as compared to the potato study. The aforem entioned issues are further discussed Section 3.5

.

3.2. Buffer Durations

This assessment is based on peak offsite expos ure concentrations estimated using PERFUM modeling based on flux profiles derived from two av ailable field volatility studies. An analysis on the potential duration that a bu ffer would need to be in pla ce to ensure bystanders are not exposed to chlorpyrifos and chlorpyrifos- oxon concentrations highe r than the target concentration is presented below. The shape of flux profiles was an im portant consideration included in the soil fumigant asse ssments conducted in the past ( e.g. , how long significant emissions occur after application).

3.2.1. Alfalfa

3.2.1.1.Chlorpyrifos (Parent Only)

Based on the six hour exposure duration, six ho ur toxicity endpoint for lung, and the 95 th


### percentile exposure, a 50 foot buffer would need to be in place for at least 12 hours for a 10A

field treated at 1 lb a.i./A. A 300 foot buffer woul d need to be in place for 18 hours for the same size field treated at 6 lb a.i/A, in order to ensure that bystanders are not exposed to concentrations of chlorpyrifos (parent only) higher than the ta rget concentration. A graphical

### 38 of 70 depiction of this anal ysis is provided in Figure 4 . The same analysis was conducted for 20, 60,

and 120 acre field sizes. Results for 1 lb a.i./A and 6 lb a.i./A are presented for all the field sizes

assessed in terms of risk estimations in Section 4 . The results indicate the peak concentration of chlorpyrifos (parent only) estimated offsite occu rs on the day of applicat ion; however, on the day following application, there is an increase in the estimated fl ux concentrations likely due to an increase in temperature following the overnight hours. For some application scenarios, concentrations exceed the target concentrati on on the second day even when concentrations observed for the 6 hours sampling period prior to th is secondary peak conc entrations are lower than the target concen tration. For some scenarios large buffers ( e.g. , 300 ft) may need to be inplace for a shorter duration ( e.g. , 12 hr) than a smaller buffer ( e.g. , 200 ft; 18hr); however,

since the buffer duration for the smaller buffe r may be longer, the longer duration may be considered for the larger buffers.

Figure 4. Buffer Duration Analysis for Va rious Buffer Distances for a 10 Acre Field Considering Chlorpyrifos (parent only) usin g Bradenton, Florida Meteorological Data; Registrant conducted field vola tility study on alfalfa using Lors ban Advanced; Lung: 6 h HEC

### 39 of 70 2,500 μg/m 3 

### , UF=300 ( i.e. , MOE =300), target concentration 8.3 μg/m 3 

### ; a. actual distance: 230 ft (70 m)

3.3. Risk Estimations

The risk estimates associated with bystande r inhalation of vapor pha se chlorpyrifos and chlorpyrifos-oxon (specific to the alfalfa appl ication scenario) were calculated based on estimated air concentrations (based on an averag e concentration around the entire field similar to the whole field buffer concept) at various buffer di stances away from a chlorpyrifos treated field for a range of percentiles of exposure and appl ication rates. This provides an additional, conceptual approach of evaluating the potential for bystander risks. The re sults for chlorpyrifos (parent only) are presented in Table 12 . The toxicological endpoint used in this analysis is lung ChE inhibition (6 h HEC 2,500 μg/m3). The total applicable uncertainty factor is 300, so a margin of exposure (MOE) < 300, with cells hi ghlighted in red, woul d be of concern.

The buffer duration analysis presented in Section 3.2 is presented in terms of risk estimations for

all field sizes assessed for 1 lb a.i./A and 6 lb a.i./A in Table 13 . These results are for chlorpyrifos (parent only), are specific to the al falfa application scenario and are based on whole

field buffers. This buffer duration an alysis indicates that buffers need to be in place for at least 12 hours for l lb a.i./A applica tion and for at least 36 hours for 6 lb a.i./A application when considering the 95% percentile e xposure concentration. This anal ysis is based on estimated air concentrations (based on an av erage concentration around the enti re field similar to the whole field buffer concept) at various buffer distances away from a chlorpyrifos treated field.40 of 70Table 12. MOEs Comparison for Chlorpyrifos (parent only) Based on Various PERFUM Buffersa,bBradenton, FLScenario50 ft (15 m)c100 ft (30 m)c200 ft (61 m)c300 ft (91 m)cApplicationRate (lb a.i./A)PercentileFieldSize (A)[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE0.55010 0 15000 0 -- 0 -- 0 --20 0 7500 0 15000 0 -- 0 --60 1 3000 1 5000 0 -- 0 --120 1 2143 1 3000 0 7500 0 150007510 2 1250 2 1667 1 3750 1 500020 3 938 2 1250 1 2143 1 300060 4 652 3 789 2 1250 2 1500120 5 556 4 652 3 938 2 10719010 4 652 3 789 3 1250 2 150020 5 517 4 612 3 938 2 115460 6 390 6 455 4 612 4 714120 8 333 7 375 5 484 5 5569510 5 500 4 600 3 938 2 107120 6 405 5 484 4 682 3 78960 8 313 7 353 5 469 5 536120 926892947 375 6 4179910 14174220092888 33320 12211112348 300 7 34160 11221102428 313 7 341120 1318812205102549278150100-0-0--0--2013750075000--0--6021500125000--0--12021071215001375007500751046253833118751250020546946252107121500608326639546253750120927883265469553690108326639546253750201025983065469457760131951122783067357120151671318810242927895101025083005469553641 of 70Bradenton, FLScenario50 ft (15 m)c100 ft (30 m)c200 ft (61 m)c300 ft (91 m)cApplicationRate (lb a.i./A)PercentileFieldSize (A)[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE20122031024273416395601615614176112349268120191341714713188122089910298725100171441516720241062111717150151706023110211211615615170120279424103201271813925010 1 3750 0 -- 0 -- 0 --20 1 1875 1 3750 0 -- 0 --60 3 750 2 1250 0 -- 0 --120 5 536 3 750 1 1875 1 37507510 8 313 6 417 3 938 2 125020 112348 313 5 536 3 75060 15163131978 313 7 375120 18139151631123492689010 15163131978 313 7 37520 191291615311234928860 2697221141615314179120 3083279421121181399510 201251715011234926820 2510121121151701319760 327828882111719134120 376734742794241049910 98725100171441516720 35723182231102012560 4555416032782985120 534749513964366945010118750--0--0--203938118750--0--60737546250--0--120926873753938118757510161561220854694625202111716156926873756031822599161561318842 of 70Bradenton, FLScenario50 ft (15 m)c100 ft (30 m)c200 ft (61 m)c300 ft (91 m)cApplicationRate (lb a.i./A)PercentileFieldSize (A)[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE120366931822111719134901031822599161561318820396533772111717144605149445733772889120604253474160366995104063337521117191342049514160298525996064395744435937671207533683753474852991057445050357230832069366141455540636091288330643959431201072397267932723565010 2 1250 0 -- 0 -- 0 --20 4 625 2 1250 0 -- 0 --60 102506 417 0 -- 0 --120 14179102504 625 2 12507510 24104181398 313 6 41720 327824104141791025060 465438662410420125120 54464654327828899010 46543866241042012520 584349513278269660 7732663849514260120 90288031624054469510 604250503278288920 743462404457386660 9626852964395645120 1122210225803172359910 862978335248455620 1042492276837604260 136181242096268828120 21811204121701515816a.Registrant study conducted on alfalfa using Lorsban Advanced43 of 70Bradenton, FLScenario50 ft (15 m)c100 ft (30 m)c200 ft (61 m)c300 ft (91 m)cApplicationRate (lb a.i./A)PercentileFieldSize (A)[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOEb.Lung: 6 h HEC 2,500 μg/m3, UF=300 (i.e., MOE =300), target concentration 8.3 μg/m3c.50 ft (15 m)creported for Ring; 100 ft (30 m) reported for Ring 6; 200 ft (61 m) reported for Ring 8 [actual distance: 230 ft (70 m]; 300 ft(91 m) reported for Ring10Table 13. Buffer Duration Comparison for Chlorpyrifos (parent only) Based on Various PERFUM Buffersa,b,cBradenton, FLScenario50 ft (15 m)d100 ft (30 m)d200 ft (61 m)d300 ft (91 m)dApplicationRate (lb a.i./A)FieldSize(A)Hours Posttreatment[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE1106 4 577 3 750 2 1250 2 150012 102508 300 5 469 5 53618 4 682 3 750 2 1071 2 125024 2 1500 1 1875 1 2500 1 375030 1 1875 1 2500 1 3750 0 750036 3 938 2 1250 1 1875 1 250042 0 7500 0 7500 0 7500 0 750048 0 7500 0 7500 0 7500 0 750054 0 7500 0 7500 0 -- 0 --60 0 7500 0 7500 0 7500 0 --66 0 -- 0 -- 0 -- 0 --72 0 -- 0 -- 0 -- 0 --206 5 500 4 625 3 938 2 107112 12203102427 341 6 39518 5 536 4 577 3 833 3 93824 2 1250 2 1500 1 2500 1 250030 2 1500 1 1875 1 3750 1 375036 3 833 3 938 2 1250 2 150042 1 3750 1 3750 0 7500 0 750048 1 3750 0 7500 0 7500 0 750054 0 7500 0 7500 0 -- 0 --60 0 7500 0 7500 0 7500 0 750066 0 -- 0 -- 0 -- 0 --72 0 -- 0 -- 0 -- 0 --44 of 70Bradenton, FLScenario50 ft (15 m)d100 ft (30 m)d200 ft (61 m)d300 ft (91 m)dApplicationRate (lb a.i./A)FieldSize(A)Hours Posttreatment[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE606 6 395 5 469 4 682 3 75012 161561417611234926818 6 395 6 417 5 536 4 57724 3 938 2 1071 2 1500 2 150030 2 1250 2 1500 1 2500 1 250036 4 625 4 682 3 938 2 107142 1 2500 1 2500 1 3750 1 375048 1 3750 1 3750 0 7500 0 750054 0 7500 0 7500 0 7500 0 750060 1 3750 1 3750 0 7500 0 750066 0 7500 0 7500 0 -- 0 --72 0 -- 0 -- 0 -- 0 --1206 7 341 6 395 5 536 4 62512 19134171471318812 20818 8 326 7 341 6 417 6 44124 3 833 3 938 2 1250 2 125030 2 1071 2 1250 1 1875 1 187536 5 500 4 577 3 750 3 83342 1 2500 1 2500 1 2500 1 375048 1 2500 1 3750 1 3750 1 375054 0 7500 0 7500 0 7500 0 750060 1 3750 1 3750 1 3750 0 750066 0 7500 0 7500 0 7500 0 750072 0 -- 0 -- 0 -- 0 --6106 269620125122081025012 604250503278288918 2211420125141791220824 102508 313 6 417 4 62530 8 313 6 417 4 625 2 125036 16156122088 313 6 41742 2 1250 2 1250 2 1250 2 125048 2 1250 2 1250 2 1250 2 125054 2 1250 2 1250 0 -- 0 --45 of 70Bradenton, FLScenario50 ft (15 m)d100 ft (30 m)d200 ft (61 m)d300 ft (91 m)dApplicationRate (lb a.i./A)FieldSize(A)Hours Posttreatment[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE60 2 1250 2 1250 2 1250 0 --66 0 -- 0 -- 0 -- 0 --72 0 -- 0 -- 0 -- 0 --206 308324104161561417912 743462404457386618 28892696181391615624 12208102506 417 6 41730 102508 313 4 625 4 62536 1813916156122081025042 4 625 4 625 2 1250 2 125048 4 625 2 1250 2 1250 2 125054 2 1250 2 1250 0 -- 0 --60 2 1250 2 1250 2 1250 2 125066 0 -- 0 -- 0 -- 0 --72 0 -- 0 -- 0 -- 0 --606 38663278221142012512 962685296439564518 386636692889269624 1615614179102501025030 12208102506 417 6 41736 2410422114161561417942 6 417 6 417 4 625 4 62548 4 625 4 625 2 1250 2 125054 2 1250 2 1250 2 1250 2 125060 4 625 4 625 2 1250 2 125066 2 1250 2 1250 0 -- 0 --72 2 1250 2 1250 0 -- 0 --1206 4457386628892410412 11222102258031723518 465444573669347424 1813916156122081220830 141791220883138 31336 30832696201251813946 of 70Bradenton, FLScenario50 ft (15 m)d100 ft (30 m)d200 ft (61 m)d300 ft (91 m)dApplicationRate (lb a.i./A)FieldSize(A)Hours Posttreatment[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE[Conc.(μg/m3)]MOE42 6 417 6 417 6 417 4 62548 6 417 4 625 4 625 4 62554 2 1250 2 1250 2 1250 2 125060 4 625 4 625 4 625 2 125066 2 1250 2 1250 2 1250 2 125072 2 1250 2 1250 2 1250 2 1250a.Registrant study conducted on alfalfa using Lorsban Advancedb.Lung: 6 h HEC 2,500 μg/m3, UF=300 (i.e.,MOE =300), target concentration 8.3 μg/m3c.For brevity, the results are presentedfor the 95% percentile of exposure.d.50 ft (15 m)creported for Ring; 100 ft (30 m) reported for Ring 6; 200 ft (61 m) reported for Ring 8 [actual distance: 230 ft (70 m]; 300 ft(91 m) reported for Ring10

### 47 of 70 4. ISSUES FOR CONSIDERATION

4.1. Air Monitoring Data

There are 15 available chlorpyrifos air monito ring studies which were summarized in the preliminary HHRA. 1 

### These include two application site studies done in Tulare and Lompoc Counties, California by the Calif ornia Air Resources Board (CAR B), and 13 ambient air studies in which the particular source of chlorpyrifos wi thin the impacted areas was not identified. These

ambient air studies were conducted in the Nort h Central and Yakima Valleys of Washington by the University of Washington Department of Envi ronmental and Occupational Health Sciences. The remaining11 studies were conducted by Pesticide Action Network North America (PANNA), two in Cowiche and Tieton, Wash ington, and nine in Lindsay, California.

The risk associated with air concentrations measur ed in these studies was assessed as part of the 2011 preliminary HHRA which also provides more detail concerning the conduct of the studies. 1


### Risks of some degree were identif ied in both the ambient and app lication site monitoring data. Risks associated with ambient monitoring do not dir ectly relate to the type of analysis presented herein because the monitoring data may represent multiple chlorpyrifos applications but the data suggest chlorpyrifos is found in air samples which may be the result of volatilization off a treated field. The risks identified for application sites monitoring studies are directly related to this analysis and are consistent with the findings of this assessment. These data coupled with the alfalfa and potato flux studies furt her indicate that chlorpyrifos vol atilize from treated crops after applications at levels which could lead to bystander exposure at le vels of concern.

4.2. Uncertainties

4.2.1. Hazard Assessment

The special, acute inhalation study evaluated measures of the centr al (brain) and peripheral

nervous system (e.g ., pulmonary tissues) and the blood measur es. This study also includes time course data to establish the time to peak effect and time to recovery for ChE inhibition in each tissue. As noted in EPA’s ChE policy, measures of peripheral nervous tis sue are preferred over surrogate measures; specifically, use of lung ChE alleviates the unc ertainties associated with use of surrogate tissue ( i.e. , RBC AChE) which are not innervated. Measurements of lung ChE provide a direct measure relevant to the route of interest and thus protecting against lung ChE should thereby protect against chol inergic effects in the respirat ory system. Because there are no measures of pulmonary function in the acute i nhalation study, the relations hip between measures of lung ChE inhibition and respiratory effects is not known. Thus, there is uncertainty associated with relating the degree of lung ChE inhibition with adverse apical outcomes ( e.g. , pulmonary function). However, human inci dent reporting is consistent w ith the anticipated respiratory effects associated with cholinergic stimulation. The incident reported in the databases suggest difficulty breathing, nasal congestion, coughing, and chest tightening which are qualitatively consistent with the anticipated ch olinergic effects reported by Taylor 46 

### and by studies of OP war

agents. 48,49,50,51 

### While the available human incident da ta are insufficient to directly link respiratory effects to chlorpyrif os volatilization exposur e, this information qualitatively supports

### 48 of 70 the lung ChE effects reported in the acute inhalation study in rats as being relevant for human

health risk assessment.

In addition to the lung ChE POD, the EPA is also estimating volatilizat ion risk using the RBC ChE endpoint. Despite the uncertainties associated with surrogate measures, the EPA is taking this approach because 1) the agency has signifi cant experience with the blood endpoints in risk assessment and thus provides a historical compar ison point(s); 2) the RBC AChE inhibition data can be used as a surrogate for other peripheral tissues ( e.g. , digestive tract, heart) for which such inhalation data are not available; 3) PODs for other routes ( i.e. , dermal, oral) are being derived from RBC AChE data; and 4) the acute TAF is derived from RBC AChE data.

There are areas of uncertainty a ssociated with the hazard charact erization/identification in the volatilization assessment such as the toxicity adju stment factor derived from oral data and the nature of the exposure (aerosol) in the acute inhalation study used to assess volatilization exposure (vapor). The tissue dos imetry appears to be different between oral and inhalation exposure. With oral exposure, the liver primarily metabolizes chlor pyrifos prior to circulation to the remainder of the body. In contrast, from i nhalation exposure, chlor pyrifos enters the blood stream directly. Given the diffe rent patterns of tissue dosimetry between oral and inhalation, there is uncertainty in the extent to which the or al toxicity adjustment f actor is predictive of inhalation exposure. Nonetheless, the comparative ChE oral study is the best available source of dose response data comparing th e parent and its transformati on product and thus provides a source of data to develop a toxicity adjustment factor. If additional inhalation data for chlorpyrifos-oxon become available in the future , the EPA will, if appr opriate, reconsider the adjustment factor.

The special acute inhalation st udy involves aerosolized chlorpyr ifos with relatively small particles (MMAD/geometric standard deviations:1.93/1.58, 1.86/1.61, 1.79/1.59 and 1.9/1.51 microns). There are two subchr onic inhalation studies which i nvolved exposure to vapor phase chlorpyrifos. Toxicity studies based on vapor ex posure are believed to be more relevant for assessing risks of volatilizati on exposure. The vapor studies sh owed no biologically relevant findings up to 287 μg/m 3 

### (albeit, lung ChE, the most sensitive endpoint from the aerosol study was not measured). In contrast, the aerosol st udy shows close to 50% lung ChE inhibition at the lowest concentration of 3.7 mg/m 3 

### (370 μg/m 3 

### ). Given the high quality design and conduct of the aerosol study, that the particle size was < 2 microns, and that the aerosol study involves acute exposure which is more relevant to volatilizat ion, EPA has chosen to use the special acute inhalation study for deriving a POD fo r this volatilization assessment.

In the preliminary HHRA, the EPA determined that for acute oral exposures, RBC AChE data from post-natal day 11 (PND11) represented the 

### most sensitive life stage. With respect to this assessment, the special acute inhalation study invo lved testing of only adult female rats. As such, there is some uncertainty as to whether or not juvenile rats may be more sensitive than adults to inhalation exposure of chlorpyrifos. It is noteworthy that t 

### he degree of sensitivity noted in the oral CCA study for PND11 rats comp ared to adult rats is only 2-fold. There are two literature studies which evaluated lung ChE in fe tuses exposed to chlorpyrifos during gestation 39 

### or rat pups directly dosed postnally but neither provides useful information about the relative sensitivity between post-natal pups and adults with respect to lung ChE inhibition. 41 

### Given the small (2-fold)

### 49 of 70 difference in sensitivity between PND11 and adult rats in the CCA study, the lack of inhalation data in rats pups does not contribute large uncertainty to this volatility assessment. 

### Despite the noted uncertainties related to aerosoli zed chlorpyrifos vs. vapor chlorpyrifos and the lack of inhalation data in pos t-natal pups, given the robust study design and conduct of the special acute inhalation study, EPA has confidence in the hazard assessm ent for chlorpyrifos presented in this assessment.

4.2.2. Application Rate Scaling

The flux studies available for consideration in th is assessment were conducted using application rates [0.877 lb a.i/A (alfalfa) and 0.61 lb a.i./A (potato)] and are much lower than the maximum single broadcast application rate of 6 lb a.i./A for citrus currently permitted on chlorpyrifos products. In addition to citrus, several other uses also have maximum single application rates higher than those used in the ava ilable flux studies including: mint (2.0 lb a.i./A), turf (4.0 lb a.i./A) and alfalfa (1 lb a.i./A).

In past assessments ( e.g. , conducted for the soil fumigants), maximum application rates were used in the flux studies and, for mitigation pu rposes, EPA assumed that there was a linear correlation between pesticide applic ation rate and the flux rate ( i.e. , as the application rate decreased, the flux rate should decrease directly ). This assumption was justified, as one would not expect less material to leave the field on a per unit basis if the application rate were lowered. There is also regulatory precedent for this type of approach in human health risk assessment ( e.g. , scaling of dislodgeable foliar re sidue data to calculate Restrict ed Entry Intervals). There is some additional uncertainty, however , with scaling up based on the a pplication rate; it is unclear

as to how the diffusion of the material into the air would be impacted by adding more material to the foliar surface or by increasing th e layer of active ingredient on the foliar surface. Thus, the magnitude of the resulting buffers could be highe r than expected based on the current approach ( i.e. , a linear scale up based on the application rate).

4.2.3. Crop to Crop Variation (Flux and Dispersion)

The difference in flux rates and subsequent dispersion of vapor pha se chlorpyrifos and chlorpyrifos-oxon residues from different cr ops is unknown. There are several crop related factors including canopy shape and height, l eaf area index, leaf t ype, crop density, surface roughness length, and possibly others factors that may influence the flux rate of a given pesticide on a particular treated crop and the dispersion of the pesticide in and around the treated area. Therefore, the extrapolation of the flux rates measured in both the alfalfa and potato field volatility studies to other cr ops is an uncertainty.

There is some uncertainty in using PERFUM for dispersion modeling of se mi-volatile pesticides applied to elevated crops such as orchards and tr ellis crops. At this ti me, EPA has not evaluated if this uncertainty is due to the flux estimates not being representative of emissions from these types of crops, or is a result of insufficien t model parameterization. The use of PERFUM to model dispersion associated with an application to crops wa s an issue discussed by the 2009

SAP 5 

### as there are no validated methods available to explore this uncertainty and very limited monitoring data are available to do a compar ison. As a follow-up to the 2009 SAP, and in

### 50 of 70 addition to searching the open scientific liter ature, EPA has engaged government, academic, and

industrial scientists eith er directly or at various scient ific conferences to gain a better understanding of the various crop related factor s and how such factors may impact pesticide volatilization from vegetativ e surfaces. To date, EPA is not awar e of research that addresses this area of uncertainty.

Nevertheless, for the particular scenarios us ed in this assessmen t a validation study was conducted that closely resembles the scenario cons idered in this assess ment for chlorpyrifos treated field crops with strongly supports the approach used in this analysis. This study is referred to as the Prairie Grass study 22 

### that was used to support the ground level release algorithms in the ISCST model is the underlying PERFUM engine. This study was conducted on an uncultivated field covered with natural prairi e grasses using a volatile pesticide with field

conditions similar to the available flux studies conducted on alfalfa and potato.

To provide some characterization of the PERFUM model for an elevated source, EPA looked at monitoring data (offsite concentrations) collected following a chlorpyrifos citrus application and compared the measured concentrations to the m odel estimated results, based on the flux derived from the alfalfa flux study. The measured and es timated concentrations are in good agreement as far as magnitude [30 μg/m 3 

### (peak observed); 20-40 μg/m 3 

### (peak estimated)]. An explanation of this analysis is provided below.

In June of 1996, the CARB conducted an air monitoring study around a 60-acre orange orchard that had been treated with chlorpyrifos at a rate of 6 lb a.i./A. The maximum 6-hour measured air concentration for chlorpyrif os was approximately 28 μg/m 3 

### measured 57 feet from the edge of the field. In order to characterize the magnit ude of air concentration around an orchard ( i.e. , to see if the levels from the model were approxima tely the same as those observed in the CARB monitoring study), EPA used PERFUM and th e flux rates from the alfalfa study. EPA ran PERFUM in the greenhouse mode to simulate an elevated source. The source had an area of 60 acres and a release height of 4 m. The flux profile was the same one developed from the alfalfa study for chlorpyrifos (parent only), scaled for a 6 lb a.i./A app lication rate. Ventura, California meteorological data for June 1995-1999 were us ed. The maximum 6-hour concentration 60 feet from the edge of the field was 24 ug/m 3 

### . Although PERFUM has yet to be validated for semivolatile emissions from an orchard and chlorpyrifos flux data are not availa ble for an orchard, the modeling simulations are in reasona ble agreement with the 28 μg/m 3 

### observed in the CARB study.

EPA is aware of one literature article 74 

### that describes a method for ad justing flux rates to develop an estimated flux profile for orchard crops taking into account the leaf surface area and orchard tree density. Using the method reported in the lite rature article, flux rate s would be much higher and as a result, EPA expects that the buffer z ones would need to be even larger than the estimated buffers reported in this assessmen t to ensure bystanders are not exposed to concentrations higher than the target concentr ation. It is important to note that the method

74 Woodrow, J. E.; Seiber, J. N. Corre lation Techniques for Estimating Pestic ide Volatilization Flux and Downwind

Concentrations, Environ. Sci. Technol

. 1997

, 31 , 523-529.

### 51 of 70 described in this article has not been validated and it is uncertain if this is a suitable method for scaling flux profiles to account for volatili zation of pesticides from orchard canopies.

In summary, there is uncertainty related to the emissions of pesticides applied to orchard and trellis crops. This includes the methods that can be used for quantify emissions from treated orchard and trellis crops. Also, there are ongoing discussions in th e scientific community on the driving factors for emission from treated crops ( e.g. , alfalfa) and how these factors may affect flux rates for other crops such as orchard and trellis crops. The disparate findings between the two analysis (CARB monitoring comparison and the leaf area i ndex scale up method) attempted by EPA also underscore this uncertainty. Given thes e considerations, at this time EPA believes it is appropriate to acknowledge the uncertainties an d note that these factors should be considered when developing a risk management st rategy for orchard and trellis crops.

4.2.4. Formulation

Two formulations of chlorpyrifos were used to generate the available emissions data (Lorsban Advance and Dursban EC). There are marked di fferences in the emission rates for each. This could be based on a variety of factors as discusse d above such as field conditions, crop, weather, formulation, etc. It is unclear how the volatility of chlorpyrifos may differ between formulations ( i.e. , between one low VOC formulation and anot her or a low VOC formulation, and a non-low VOC formulation) as the low VOC designation is solely based on a reduction in the total amount of mass loss from a given formula tion including components such as solvents, and is not specific to the active ingredient. Explorat ion of the potential formulati on effect on volatility following application was done using CDPR’s online VOC Emissions Calculator. 75 

### This tool was developed based on Thermogravimetric analysis (T GA) data submitted to the State of California. TGA allows for the comparison of one formulation to another by comparing the amount of total material that can be displaced as a result of heating. Examination of several different formulations suggests that non-low VOC formulations may result in volatilization that is twice as high as low-VOC formulations on a total mass basis (see Figure 5 ). These results are for total

mass—that is the total amount of volatility organic chemicals—and is not necessarily reflective of one component of the formulation ( i.e. , the active ingredient). In general, the low VOC formulations developed for chlorpyrifos repla ce volatile solvents with water to reduce the volatility of the overall formulation. In the case of the Lorsban Advanced formulation, it is unclear if the change in formulation reduces the volatility of chlorpyrifos or simply reduces the

amount of total VOC emitted.

75 http://apps.cdpr.ca.gov/vo c-calculator/start.cfm; accessed September 19, 2012

### 52 of 70 Figure 5. Volatility Comparison for Various Chlorpyrifos Formulated Products

Chlorpyrifos emissions presented in Figure 5 were calculated based on the percentage included in the product formulation and may not reflect ac tual emissions concentrations. In addition, this analysis was based on an applica tion rate of 1 gallon formulated product/acre applied to a 20 acre

field. Since the studies used in the deve lopment of the VOC Emissions Calculator 75 

### are not chemical specific ( i.e. , the studies did not specially measur e the amount of chlorpyrifos emitted),

the formulation effect on the volatilizati on rate of chlorpyr ifos is unclear.

A report 76 

### recently submitted by Dow AgroSciences to EPA indicates that under laboratory conditions the volatility of chlorpyrifos does not vary between liquid formulations except when the active ingredient is encap sulated. This study was done by applying aqueous dilutions of various chlorpyrifos formulations to an inert sand surface. The samples were stored in an uncapped vial in a 54 °C (129 °F) oven. At select ed time points, chlorpyrifos was extracted from the sand samples and quantified. Figure 6 shows the results from this study in terms of remaining chlorpyrifos—that is the amount of ch lorpyrifos that was extracted from the sand.

76 EPA MRID 49005301 : Lab Volatility Study of selected Chlorpyrifos Products ; Author: Dennis Wujek Study

Sponsor: Dow AgroSciences LLC, 9330 Zionsville Road Indianapolis, IN 46268-1054

### 53 of 70 Figure 6. Laboratory Volatility Comparison for Various Chlorpyrifos Formulations

Encapsulation (pyrinex), as expected, was show n to reduce the volatility of chlorpyrifos. However, this study did not specif ically measure the amount of chlo rpyrifos that volatilized, just the amount remaining in the sand, assuming volati lization was the only pathway of dissipation. It is also unclear how the conditions in this study can be extrapolated to environmental conditions [ e.g. , cooler temperatures, higher or lower humidit y, surface properties (crop surfaces)] and used quantitatively for risk estimation.

Formulations that include the enca psulation of chlorpyrifos either in a microcapsule or within a granular (as long as the microcapsu le is not allowed to rest in an application solution where the active ingredient can diffuse into solution or gra nular is not dissolved pr ior to application) are likely to result in lower concentrations of ch lorpyrifos and chlorpyrifos-oxon off field as chlorpyrifos would be expected to be released sl owly over time. At this time, EPA does not have any data to conduct an assessm ent on volatilization of chlorpyr ifos and chlorpyrifos-oxon following the application of microencapsulated or granular form ulations. In order to address this uncertainty, additional studies would be necessary to evaluate flux rates following applications of microencapsulated and granul ar chlorpyrifos formulations.

4.2.5. Application Method

Different applications methods may result in diff erent surface coverage of chlorpyrifos on crops, and may impact volatilization of chlorpyrif os and chlorpyrifos- oxon from treated crops. Additional data would be needed that explores the surface coverage of chlorpyrifos using different application methods a nd the subsequent volatilization.

Applications made directly to soil surfaces will likely result in reduced chlorpyrifos volatilization, as chlorpyrif os is expected to sorb to soil surf aces. Furthermore, incorporation of

### 54 of 70 liquid formulations of chlorpyrifos should also reduce volatility; however, the magnitude of the

reduction is unknown. To address this uncertaint y, a flux study conducted on a bare-soil plot could be completed with and without soil incorporation.

4.2.6. Weather

In addition to temperature, environmental factor s such as wind speed, air turbulence, humidity, and rainfall may influence the amount of chlo rpyrifos and chlorpyrifos-oxon observed in air samples. While the temperature throughout the alfalfa flux study may have been high, higher humidity may increase the amount of chlorpyr ifos and chlorpyrifos-oxon observed in air samples. It is uncertain how the results obtaine d from the alfalfa flux study conducted in the San Joaquin Valley of California, compare to the resu lts that may be obtained for other sites in the United States. The same uncertainty can be said for extrapolation of the potato study conducted in the Netherlands to represent areas within th e United States. While the weather was slightly different (lower average temper ature and higher winds reported in the potato study as compared to the alfalfa study) in both of these studies , the studies were conduc ted during the typical growing reason and, therefore, reasonably represen t the potential volatili zation of chlorpyrifos and chlorpyrifos-oxon under t hose specific conditions.

To address this uncertainty, when limited studies were available for fumi gant risk assessments, PERFUM modeling was conducted using all six of th e available meteorologi cal stations and the largest buffers calculated for all the scenarios were reported for risk assessment purposes. In addition, for some soil fumigants, this uncerta inty was addressed by submission of additional field volatility data. For chlorpyr ifos, additional studies permit an empirical evaluation of flux rate variability under different environmental co nditions in different regions of the country.

4.2.7. Degradation in Air

In an air photolysis study 77 

### , chlorpyrifos was observed to convert to chlorpyrifos-oxon. PERFUM modeling results presented in this assessment do not account for the potential for degradation to occur during dispersion as the m odeling results are based on flux profiles derived

from air concentrations measured on the field of applications. Based on a tier I analysis using AERMOD, the rate of direct and indirect photolysis for chlorpyrifos is not likely to impact the buffers estimated for chlorpyrifos (parent only). Conve rsion of chlorpyrifos to chlorpyrifos-oxon may result in the need for larger buffers due to the increased toxicity of chlorpyrifos-oxon; however, EPA’s current methods for dispersion modeling of pesticides do not permit the

consideration of the rate of fo rmation and decline of transfor mation products. Nevertheless, the total toxic residue approach uti lized in this assessment is t hought to reasonably capture the potential exposure to both chlorpyrifos and chlorpyrifos-oxon simultaneously.

77 EPA MRID 48789701: Gas-phase Photolysis and Photo-oxidation of Chlorpyrifos and Chlorpyrifos-oxon ;

Authors: Amalia Munoz; Sponsor: Dow AgroSciences, European Development Centre, 3 Milton Park, Abingdon, Oxon, OX144RN

### 55 of 70 5. CONCLUSIONS

In summary, two different field volatility stud ies suggest that volatili zation of chlorpyrifos and/or chlorpyrifos-oxon from tr eated crops is a pathway of dissi pation in the environment that may result in bystander exposure to vapor phase chlorpyrifos and chlorpyrifos-oxon. Based on these two studies as well as monitoring data bys tander exposures were examined to quantify the potential risks associated with vapor phase ch lorpyrifos and chlorpyr ifos-oxon near a treated

field.

The approaches used to evalua te the volatilization of chlorpyrifos and chlorpyrifos-oxon and

associated risks are consistent with assessments conducted in the past for fumigant pesticides and have been vetted through a public peer review process. 3,5 

### While there are a number of uncertainties associated with this assessment, as discussed in the previous section, available data indicate that bystander exposure to vapor phase chlorpyrifos and chlorpyrifos-oxon is possible, and can occur at concentrations higher than th e concentration of concer n established in this assessment for lung. Generally application rates gr eater than 1 lb a.i./A and large field sizes results in concentrations that are higher than th e target concentration at distances ranging from 0 to greater than 4724 feet dependi ng on the percentile of exposure. The uncertainties which have

been identified should also be considered in the interpretation of this assessment and any subsequent regulatory actions based on its findings.

Further refinements may require additional research that could be focused on eliminating or reducing the uncertainties associated with this an alysis and its findings. The design of any such research should be discussed with the Agency. Given the current available information and the state of the science concerning vo latilization of pesticides, this preliminary risk assessment

indicates risks of concern are ex ceeded for bystanders. While the ri sk to bystanders in terms of the distance from treated fields over time, the in formation currently evaluated indicates that the risks are likely offsite regardless of how the stated uncertainties are interpreted.

### 56 of 70 

## APPENDIX A

LIST OF ABBREVIATI ONS AND ACRONYMS

AChE acetylcholinesterase AD Aerodynamic

AERMIC American Meteorological Society/Environm ental Protection Agency Regulatory Model Improvement Committee

BMD benchmark dose

BMDL 10 benchmark response level of 10% BMR benchmark response BuChE butyryl-ChE

CA PISP California Pesticide Illness Surveillance Program

CARB California Air Resources Board

CAS Chemical Abstract Service CDPR California Department of Pesticide Regulation

ChE cholinesterase DAS Dow AgroSciences

DER data evaluation record

EC emulsifiable concentration EPA Environmental Protection Agency FEMS Fumigant Emissions Modeling System

FF field fortifications HECs/HEC Human Equivalent Concentrations/ Human Equivalent Concentration HHRA Chlorpyrifos Preliminary Human Health Risk Assessment for Registration Review IDS OPP Incident Data System

IFM Indirect Flux Method IHF Integrated Horizontal Flux ISC Industrial Source Complex ISCST3 Industrial Source Complex-short term lb a.i./A Pound active ingredient per acre

LOAEL lowest-observed- adverse-effect-level

LOC level of concern MMAD Mass Median Aerodynamic Diameter MOE margin or exposure NIOSH National Institute for Occupational Safety and Health

NOAEL no-observed-adverse-effect-level

NPIC National Pesticide Information Center OP organophosphate OPP Office of Pesticide Programs

PANNA Pesticide Action Network North America PCT chlorpyrifos percent crop treated PERFUM Probabilistic Exposure and Risk model for Fumigants PODs/POD point of departures/ point of departure

RBC red blood cell SAP Federal Insecticide, Fungicide, and Ro denticide Act Scientific Advisory Panel

SENSOR-Pesticides NIOSH’s Sentinel Event Notification System for Occupational Risk SOFEA Soil Fumigant Exposure Assessment System TAF toxicity adjustment factor TCP 3,5-6 tricloropyridinol TTCR total toxic chlorpyrifos residues UF uncertainty factor

### 57 of 70 UF A uncertainty factor for animal to human extrapolation

UF DB uncertainty factor database

UF H uncertainty factor for with human variability to account for sensitivity subpopulations VOC volatile organic compounds or volatile organic chemicals

### 58 of 70 

## APPENDIX B

CHLORPYRIFOS USE BY FORMULATION

The discussion below, along with the data presented, is excerpted from a supporting memorandum developed by OPP’s Biological and Economic Analysis Division (BEAD). This

paper 78 

### will also be included in the chlorpyrifos docket.

Chlorpyrifos Application Rate Information

Table B.1. presents chlorpyrifos application rates with information for low VOC formulations broken out separately from other formulations . The low VOC products id entified in the usage data presented are Lorsban AdvancedTM and Chlo rpyrifos 4E AGTM. For about one-half of the

non-low VOC formulations the number of obser vations was large enough that the rate information should be quite reliable. However, for most of the low VOC formulations the

number of observations was much lower. The average and 90th percen tile single application

rates for the non-low VOC and low VOC formulati ons are generally quite close. Although not noted in the tables, for some crops and formul ations the 90th percentil e was equal to the 100th percentile (maximum).

Table B.1. Chlorpyrifos Single Applicatio n Rate Data for Low VOC and Non-low VOC

Formulations a

Crop Formulation Application Rate (lb a.i./A)
Average

Single Application

Rate (Non-low

VOC

Products b 

### ) 90th

Percentile

Single Application

(Non-low

VOC Products) Average Single Application (Low VOC

Products c ) 90th percentile

Single Application (Low VOC Products) Ratio d of Low

VOC to Nonlow VOC

Products Applications

Oranges Liquid 2.6 6 2.3 5.7 0.28

Lemons Liquid 3.4 5 3.4 5.7 0.28

Grapes, Table Liquid 2.9 4 1.6 2.2 0.14

Grapefruit Liquid 2.1 3 1.6 2.4 0.37

Broccoli Liquid 1.5 2.3 1.9 2.2 0.28

Broccoli Granular 1.5 2.1 . . .

Cabbage Granular 1.2 2.1 . . .

Almonds Liquid 1.9 2 1.8 2 0.22

Apples Liquid 1.6 2 1.4 2 0.12

Cherries Liquid 1.8 2 1.7 2 0.11

Grapes, Raisin Liquid 2 2 1.6 2.2 0.18

Grapes, Wine Liquid 2 2 1.8 1.9 0.38

78 Mallampalli, N. A. Grube, and J. Becker. “Information on Application Ra tes and Acres Treated per Application per Day for Selected Chlorpyrifos Formul ations”. USEPA/OCSPP/OPP/BEAD memorandum.

### 59 of 70 Peaches Liquid 1.3 2 2.1 3 0.04

Peanuts Granular 1.8 2 . .

Pears Liquid 1.8 2 2 2 0.09

Plums/Prunes Liquid 1.9 2 1.4 2 0.1

Sugar Beets Granular 1.3 2 . .

Tobacco Liquid 1.9 2 2 2 0.01

Walnuts Liquid 1.9 2 1.8 2 0.15

Apples Dry Flowable 1 1.6 . . .

Apples Wettable 1 1.5 . . .

Hazelnuts Liquid 1.1 1.5 1.9 1.9 0.07

Cauliflower Granular 1.2 1.4 . . .

Corn Granular 1.1 1.4 . . .

Sweet Corn Granular 1.2 1.4 . . .

Cherries Dry Flowable 0.9 1.2 . . .

Onions Granular 0.9 1.1 . . .

Pumpkins Granular 0.7 1.1 . . .

Alfalfa Liquid 0.5 1 0.6 0.9 0.03

Asparagus Liquid 0.9 1 0.9 1 0.26

Beans, Green Liquid 0.9 1 0.9 1 1.21

Broccoli Dry Flowable 0.9 1 . .

Broccoli Wettable 1 1 . .

Cabbage Liquid 1 1 1.6 2.2 0.27

Cauliflower Dry Flowable 1 1 . . .

Cauliflower Liquid 1 1 1.1 1.9 0.17

Corn Liquid 0.6 1 0.4 0.5 0.09

Cotton Liquid 0.7 1 0.9 1 0.13

Onions Liquid 0.9 1 0.9 1 0.13

Oranges Granular 0.8 1 . . .

Pecans Liquid 0.9 1 0.9 1 0.08

Pumpkins Liquid 0.9 1 . .

Squash Liquid 0.8 1 1 1 0.05

Strawberries Liquid 1 1 0.9 1 0.1

Sugar Beets Liquid 0.5 1 0.5 0.6 0.09

Sweet Corn Liquid 0.9 1 0.9 1 0.22

Soybeans Dry Flowable 0.4 0.7 . . .

Sorghum Liquid 0.4 0.6 . . .

Dry Beans/Peas Liquid 0.5 0.5 0.8 1 0.17

Soybeans Liquid 0.4 0.5 0.3 0.5 0.07

Sunflowers Liquid 0.4 0.5 0.5 0.6 0.05

Wheat, Spring Liquid 0.3 0.5 0.3 0.5 0.23

Wheat, Winter Liquid 0.4 0.5 0.3 0.5 0.03

### 60 of 70 a. The table is arranged to show data for the 90 t h p ercentile application rate for non-low VOC products in descending order.
b. Examples include: Lorsban 75WG (EPA Reg. No. 62719-301), Lorsban 4E (EPA Reg. No. 62719-220)

c. Examples include: Lorsban AdvancedTM (EPA Reg. No. 62719-591), Chlorpyrifos 4E AGTM (EPA Reg. No. 19713-520); The “Ratio” column provides a comparison of the number of applications of “low VOC” products compared to the number of applications of “traditional” products.

Crops and formulations with very low numbers of observations (less than a total of 10 observations over the five year period)
are not included.

“.” Entr y indicates no data for use of an y low VOC p roduct. Note that low VOC products are all liquid formulations.



### The ratio of the number of low VOC product ap plications to the num ber of traditional chlorpyrifos product applications in each crop were calculated wh en data were available. The number of applications of each type of product was summed acro ss the five year period before the ratios were computed. A ratio of one means equal numbers of grower observations for both formulation types; a ratio of less than one i ndicates higher use of non-low VOC formulations, while a ratio greater than one indi cates higher use of low VOC products.

Scope and Data Limitations

For many crops and formulations, there were a limited number or reported users over the survey period, which leads to uncertainty with how repr esentative the usage data are for the respective crop/formulation combinations. For chlorpyrifos used on only a small percentage of a crop, the sampling procedure may lead to no use being reported, simply because none of the users happened to be among those surveyed.

Crop/formulation combinations with very low nu mbers of observations (less than a total of 10 observations over the five year period) were excl uded. Crops where data on some (but not all) formulations were excluded due to low sample size include: alfalfa, almonds, apples, apricots, asparagus, green beans, cabbage cantaloupes, cauliflower, celery, cherries, corn, cotton, grapefruit, lemons, lettuce, onions, oranges, peaches, peanuts, green peas, pecans, peppers, pistachios, potatoes, sorghum, soybeans, squas h, strawberries, sunflowe rs, sweet corn, tobacco, tomatoes, and walnuts.

There are also some labeled crops for which pestic ide use data are not available in the pesticide usage database, and these crops are, therefore, not included in this analys is. These crops include Brussels sprouts, collards, cranberries, figs, ka le, kohlrabi, kumquats, limes , nectarines, radishes, rutabagas, sweet potatoes, tangelo s, tangerines, and turnips.

Based on private pesticide marketing survey da ta, over the five year period from 2007 to 2011 twenty nine different chlorpyrif os formulated products were used on agricultural sites. For individual crop/year combinations , anywhere from one to eight di fferent products were reported as having been used. Liquid formulations accoun ted for about 90% of total national use. One Lorsban 4ETM, accounted for more than one-half (approximately 4,000,000 pounds) of all chlorpyrifos use on agricultural crops. Lorsban pr oducts also accounted for most granular use of chlorpyrifos. Application rates for chlorpyrifos varied signifi cantly among crops. Rates for the citrus crops and grapes were higher than for any other crops. Field crops tended to have the lowest average application and 90t h percentile application rates.

### 61 of 70 According to the available usage data, two “low VOC” products show substantial use in the agricultural crops surv eyed. These products are Lorsban AdvancedTM (approximately 400,000 pounds of chlorpyrifos applied across all crops) and Chlorpyr ifos 4E AGTM (approximately 200,000 pounds of chlorpyrifos applied across all cr ops). Together, these products accounted for about 10% of the liquid formulation pounds of chlo rpyrifos applied and a bout 9% of the total pounds of chlorpyrifos applied nationally, as de scribed in the proprie tary database.

For most crops, the low VOC formulations account fo r a relatively small percentage of the liquid chlorpyrifos applications. This would be exp ected since the low VOC formulations account for about ten percent of all liqui d chlorpyrifos formulations when measured in pounds of chlorpyrifos applied. The exception is green beans, where more than half the applications were

with the low VOC formulations. A bout 30% of the applications to wine grapes, broccoli, lemons and grapefruit were made with the low VOC formulations.

Chlorpyrifos Area Treated per Application per Day Information

Data and Scope

Since 1990 California has required the full reporting of annual agricu ltural pesticide use. Under this program, all agri cultural pesticide use is reported monthly to county agricultural commissioners, who in turn, report the data to the CDPR. These data are accessible from CDPR’s website and provide the most detailed information available on the use of agricultural pesticides in California. No other state has comparable information on pesticide use.

Data files for 2006 through 2010 were downloaded from CDPR’s website (CDPR, 2012). These data were then extracted and imported into a SA S dataset. Supplemental data on crop sites, county, chemical, product, and formulation were added to this dataset. An an alytical chlorpyrifos

dataset was created from this co mprehensive dataset by keeping only data records that met all of the following criteria: active ingredient is chlorp yrifos, record is not a CDPR identified error, area treated is in units of acres, record is an individual application (i.e., not a monthly summary), application was made to an ag ricultural site. Using these criteria, a total of 60,910 observations

are summarized in Table B.2 below.

There are some limitations that should be considered when interpreting these data. Caution should be used when extrapolating these results to areas outside of California, as different pest pressures, crop production practi ces, etc. in these areas will li kely alter the relative use of chlorpyrifos. BEAD also notes here that the da ta are shown as reporte d by individual county staff. Some counties sometimes enter crop type specifically, while others may use generic crop codes ( e.g. , the one for “grapes” instead of “grapes, wine”). Furthermore, CDPR does not have crop codes for some types of crops ( e.g. , there is no specific code for “table grapes”). These

limitations are reflected in the table below.

Table B.2. Acres Treated with Chlorpyrifos per Application per Day a, b

Crop c Application Product Sample Acres treated per application per day

### 62 of 70 Method d Applied e Size Minimum 50th

Percentile 90th

Percentile Maximum

Corn (human consumption) Air Liquid 7 13 30 160 160

Avocado Ground Liquid 10 1 6 158 300

Almonds Air Liquid 267 4 51 156 640
Grapes (wine) Ground Liquid 1117 0 32 146 595
Sorghum (Forage/Fodder) Air Liquid 13 36 70 140 160

Sorghum (Milo) Air Liquid 11 10 59 130 160
Sugarbeets Air Liquid 19 18 70 128 146

Almond Ground Liquid 1394 1 36 120 626
Grapes (wine) Air Liquid 3 14 27 116 116

Cotton Air Liquid 300 4 47 114 316
Asparagus Air Liquid 171 1 18 110 235
Wheat (unspecified type) Air Liquid 97 5 45 102 216

Lemons Air Liquid 15 5 28 100 100
Wheat (forage/fodder) Air Liquid 426 4 62 100 185

Alfalfa Air Liquid 11735 1 50 96 518

Alfalfa Other Liquid 33 2 40 95 101
Tomatoes (processing) Air Liquid 3 58 76 93 93

Walnuts Air Liquid 745 1 34 93 430
Sugarbeets Ground Liquid 2 59 76 92 92
Corn (forage/fodder) Air Liquid 1539 1 39 91 399
Corn (forage/fodder) Ground Liquid 582 1 38 85 308
Sorghum (Forage/Fodder) Ground Liquid 6 10 55 85 85

Strawberries Ground Liquid 558 1 28 84 220
Prunes (dried plums) Ground Liquid 40 2 34 82 120

Alfalfa Ground Liquid 1846 0 37 80 217
Corn (forage/fodder) Other Liquid 28 20 47 80 100
Figs Air Liquid 1 80 80 80 80

Sunflowers Air Liquid 35 2 25 78 170
Corn (grain) Air Liquid 2 38 57 77 77

Sunflowers Other Liquid 4 14 58 75 75
Wheat (forage/fodder) Ground Liquid 11 38 70 75 113

Cotton Ground Liquid 82 3 38 74 160
Grapes (unspecified type) Ground Liquid 237 1 25 73 322

Asparagus Ground Liquid 141 1 30 69 586

Walnuts Ground Liquid 3271 1 20 65 517
Citrus (unspecified type) Ground Liquid 32 2 7 60 240

Mint Ground Liquid 25 2 25 60 160
Beans (dried) Air Liquid 2 25 40 55 55

Lemons Ground Liquid 1402 0 14 54 145

### 63 of 70 Crop c Application

Method d Product Applied e Sample

Size Acres treated per application per day

Minimum 50th

Percentile 90th

Percentile Maximum

Almond Other Liquid 9 6 20 53 53

Tomatoes Air Liquid 2 38 46 53 53

Orchard floor (unspecified crop) Ground Liquid 1 46 46 46 46

Figs Ground Liquid 1 40 40 40 40

Oranges Ground Liquid 3152 0 15 40 240

Oranges Other Liquid 28 1 19 40 42

Pecans Ground Liquid 33 2 19 40 42

Grapes (wine) Other Liquid 14 4 14 39 41

Plums Ground Liquid 325 1 10 38 140

Sweet potatoes Ground Liquid 10 8 19 38 38

Beans (dried) Ground Liquid 27 5 19 37 43

Brussels sprouts Ground Liquid 363 1 12 35 52

Lemons Other Liquid 2 15 25 35 35

Turf/Sod Other Liquid 6 7 27 35 35

Oranges Air Liquid 3 9 10 33 33

Onions (dry) Ground Liquid 30 1 15 32 45

Peaches Air Liquid 3 8 10 30 30

Pomelo Ground Liquid 14 2 5 30 30

Walnuts Other Liquid 5 10 18 30 30

Turf/Sod Ground Liquid 23 5 17 27 60
Grapes (unspecified type) Other Liquid 2 10 18 25 25

Sudangrass Air Liquid 1 25 25 25 25

Tangelo Ground Liquid 87 1 10 25 80

Strawberries Air Liquid 1 24 24 24 24
Corn (human consumption) Ground Liquid 35 4 10 23 39

Tangerines Ground Liquid 166 1 10 23 73

Apples Ground Liquid 164 1 5 21 72

Peaches Ground Liquid 235 2 8 21 46
Beans (unspecified type) Ground Liquid 1 20 20 20 20

Broccoli Ground Liquid 3899 0 11 20 162

Nectarines Ground Liquid 181 1 9 20 47

Pears Ground Liquid 11 1 2 20 35

Turnips Ground Liquid 13 8 10 20 25

Broccoli Other Liquid 22 5 10 19 36

Sunflowers Ground Liquid 3 8 10 18 18

Cauliflower Ground Liquid 1125 1 10 16 36

Peas Ground Liquid 33 3 10 16 19

Beans (succulent) Ground Liquid 12 4 10 15 18

Cherries Ground Liquid 34 1 5 15 20

Tangerines Other Liquid 1 15 15 15 15

### 64 of 70 Crop c Application

Method d Product Applied e Sample

Size Acres treated per application per day

Minimum 50th

Percentile 90th

Percentile Maximum

Broccoli Air Liquid 6 5 7 14 14

Cabbage Ground Liquid 381 1 6 14 27

Cauliflower Air Liquid 1 13 13 13 13

Collards Ground Liquid 10 5 9 12 13

Grapefruit Other Liquid 1 12 12 12 12

Kale Ground Liquid 70 0 2 12 15

Pecans Air Liquid 2 11 11 11 11

Beans (succulent) Air Liquid 1 10 10 10 10

Grapefruit Ground Liquid 109 0 5 10 46

Lettuce (leaf) Ground Liquid 1 10 10 10 10

Limes Ground Liquid 3 1 2 6 6

Rappini Ground Liquid 103 1 5 6 9

Bok Choy (cabbage) Air Liquid 1 3 3 3 3

Bok Choy Ground Liquid 249 0 1 3 5
Cabbage, Chinese (Nappa) Ground Liquid 187 1 2 3 5

Kumquats Ground Liquid 1 2 2 2 2

Radishes Ground Liquid 191 1 1 2 3

Grapes (wine) Ground Low VOC 367 3 42 212 560

Sorghum (Milo) Air Low VOC 9 38 76 115 115

Prunes (dried plums) Ground Low VOC 8 7 25 114 114

Corn (forage/fodder) Ground Low VOC 33 2 50 110 230
Citrus (unspecified type) Ground Low VOC 14 1 10 102 150

Alfalfa Ground Low VOC 73 3 40 100 150

Lemons Air Low VOC 2 5 53 100 100

Alfalfa Air Low VOC 473 1 52 97 319

Almond Ground Low VOC 231 3 20 90 470

Corn (forage/fodder) Air Low VOC 210 3 38 84 262
Grapes (unspecified type) Ground Low VOC 68 3 40 80 301

Cotton Air Low VOC 6 10 30 76 76

Walnuts Air Low VOC 90 5 21 76 163

Walnuts Ground Low VOC 430 2 20 76 200

Wheat (forage/fodder) Air Low VOC 3 25 65 66 66

Strawberries Ground Low VOC 70 0 28 60 324

Almond Air Low VOC 2 8 31 54 54

Asparagus Air Low VOC 47 1 21 53 125

Asparagus Ground Low VOC 62 4 24 53 471

Sunflowers Air Low VOC 3 10 10 50 50

Turf/Sod Ground Low VOC 7 10 30 50 50

Lemons Ground Low VOC 229 1 10 45 126

Oranges Air Low VOC 2 10 28 45 45

### 65 of 70 Crop c Application

Method d Product Applied e Sample

Size Acres treated per application per day

Minimum 50th

Percentile 90th

Percentile Maximum

Apples Ground Low VOC 21 1 18 43 80

Brussels sprouts Ground Low VOC 42 2 8 40 52
Corn (human consumption) Ground Low VOC 5 2 8 40 40

Oranges Ground Low VOC 758 1 17 40 248

Tangerines Ground Low VOC 61 2 12 40 157

Peas Ground Low VOC 7 7 12 38 38

Cotton Ground Low VOC 1 36 36 36 36

Sweet potatoes Ground Low VOC 4 10 20 34 34

Almond Other Low VOC 1 32 32 32 32

Beans (succulent) Ground Low VOC 56 3 20 31 50

Tangelo Ground Low VOC 26 5 10 31 42

Peaches Ground Low VOC 16 2 10 24 40

Beans (dried) Ground Low VOC 16 10 14 21 25

Broccoli Other Low VOC 35 3 15 20 25
Grapes (unspecified type) Other Low VOC 1 20 20 20 20

Grapefruit Ground Low VOC 27 2 6 20 26

Onions (dry) Ground Low VOC 1 20 20 20 20

Pecans Ground Low VOC 8 12 19 20 20

Strawberries Air Low VOC 3 5 7 18 18

Broccoli Ground Low VOC 1061 0 10 17 29

Cauliflower Ground Low VOC 145 1 10 17 25

Plums Ground Low VOC 13 2 7 17 30

Pomelo Ground Low VOC 10 1 6 16 20

Broccoli Air Low VOC 3 12 12 13 13

Cauliflower Other Low VOC 2 5 8 11 11

Nectarines Ground Low VOC 9 2 5 11 11

Oranges Other Low VOC 2 10 10 10 10

Radishes Ground Low VOC 65 3 5 7 9

Cabbage Ground Low VOC 94 1 4 5 13

Sunflowers Ground Low VOC 1 5 5 5 5

Bok Choy Ground Low VOC 38 1 2 3 3
Cabbage, Chinese (Nappa) Ground Low VOC 12 1 1 2 2

Kale Ground Low VOC 6 1 2 2 2

Kale Other Low VOC 1 2 2 2 2
Citrus (unspecified type) Ground Granular 35 15 80 240 240

Corn (forage/fodder) Ground Granular 121 6 40 89 192

Walnuts Ground Granular 10 5 24 82 99

Lemons Ground Granular 16 1 5 80 85

Strawberries Ground Granular 7 4 14 71 71

Tangerines Ground Granular 24 1 14 69 88

### 66 of 70 Crop c Application

Method d Product Applied e Sample

Size Acres treated per application per day

Minimum 50th

Percentile 90th

Percentile Maximum

Sweet potatoes Ground Granular 93 4 19 60 104

Oranges Ground Granular 198 0 19 58 240

Tangerines Other Granular 1 48 48 48 48

Broccoli Other Granular 15 1 10 40 40

Cauliflower Other Granular 18 8 15 40 40
Corn (human consumption) Ground Granular 119 2 16 40 48

Onions (dry) Ground Granular 39 3 24 40 180

Cauliflower Air Granular 6 4 9 35 35

Broccoli Air Granular 119 1 11 28 45

Broccoli Ground Granular 9847 0 10 19 161

Cabbage Ground Granular 1012 1 8 19 53

Cauliflower Ground Granular 3542 0 10 16 276

Mustard Ground Granular 13 6 14 15 16

Brussels sprouts Ground Granular 412 1 8 14 44

Collards Ground Granular 27 3 9 14 16

Rappini Ground Granular 56 1 5 12 20

Grapefruit Ground Granular 38 0 3 10 23

Oranges Other Granular 1 10 10 10 10

Turf/Sod Ground Granular 1 10 10 10 10

Peas Ground Granular 3 6 7 9 9

Cabbage Other Granular 2 8 8 8 8

Lettuce (leaf) Ground Granular 3 3 4 8 8

Cabbage Air Granular 3 5 6 7 7

Canola (rapeseed) Ground Granular 4 4 6 7 7
Cabbage, Chinese (Nappa) Ground Granular 1471 0 4 6 15

Kale Ground Granular 137 0 1 4 10

Bok Choy Ground Granular 751 0 2 3 8

Alfalfa Ground Granular 1 2 2 2 2

Radishes Ground Granular 81 0 0 1 24

Turnips Ground Granular 85 0 0 1 2
a. Data are for use in the years 2006 through 2010. The table shows data grouped first by “product applied” and within these groups, sorted by the 90 th percentile application rate (in descending order--high to low].

b. “Product” is referred to as “form” in the CDPR database. c. Crop names are shown as reported in the CDPR database (see the “Data and Scope’ section above for further discussion).

d. “Other” application methods may include one or more of the following, as described by CDPR: chemigation, paints, dips, or other non-tractor ground-based methods.

e. “Liquid” products correspond to the “regular” – non-low VOC – products

### 67 of 70 

## APPENDIX C

FLUX CALCULATIONS

1. Flux determination using the Indirect Method (IM) :

The indirect method, commonly referred to as th e “back calculation” method, was the technique employed for estimating flux rates from fields during application. In the indirect method, air samples are collected at various locations outside the boundaries of a treated field. Meteorological conditions, including air temperature, wind speed, an d wind direction, are also collected for the duration of the sampling event. The dimensions and orientation of the treated field, the location of the samplers, and the meteorological informati on is used in combination with the ISCST3 dispersion model (Version 02035) and a unit flux rate of 0.001 μg/m2•s to estimate concentrations at the sampler locations. Since th ere is a linear relationship between flux and the concentration at a given location, the results from the ISC model runs are compared to those concentrations actually measured and a regressi on is performed, using the modeled values along the x-axis and the measured values along the y-ax is. If the linear regression does not result in a statistically significant relationship, the regression may be rerun forcing the intercept through the origin, or the ratio of averages between the monitored to modeled concentrations may be computed, removing the spatial relationship of th e concentrations. The indirect method flux back calculation procedure is described in detail in Johnson et al. , 1999.

2. Flux determination using the integrated horizontal flux (IHF) method:

The integrated horizontal flux method, also re ferred to as the “mass balance” method, was the technique employed for estimating flux rates from fi elds following application. In the integrated horizontal flux method, a mast is erected in th e middle of the treated field and concentration samples are typically collected at four or five di fferent heights, ranging from approximately 0.5 to 5 feet. Likewise, wind speed data are collected at a variety of heights. A log-linear regression is performed relating the natural logarithm of the sa mple height to the air concentration and wind speed following the log law relationships for the atmospheric boundary layer. These relationships are then incorporated into an equation to estim ate flux. The methods to estimate flux and related equations are presented in Majewski et al. , 1990. The equation for estimating flux using the integrated horizontal flux method is the following expression:



# 

 p Z

Z 

### dz u c

x P

0 

### 1

where P is the volatile flux in units of  g/m 2 ·s, 

### c is the average pesticide residue concentration in

units of  g/m 3 at height Z in units of meters, 

### u is the wind speed in units of m/s at height Z, x is the fetch of the air trajectory blowing across the field in units of meters, Z 0 is the aerodynamic surface roughness length in units of meters, Z p is the height of the plume top in units of meters, and dz is the depth of an incremental layer in units of meters. Following trapezoidal integration, the above equation is simplified as follows (Yates, 1996):



#     P Z

Z 

### dz D z Ln C B z Ln A

x P

0 

### ) ) ( * ( * ) ) ( * ( 1

### 68 of 70 where A is the slope of the wind speed regression lin e by ln(z), B is the intercept of the wind speed regression line by ln(z), C is the slope of the concentration regression by ln(z), D is the intercept of the concentration regression by ln(z), z is the height above ground level. Z p can be determined from the following equation:



##        



 C D Z P 

### 1

. 0 exp

The minimum fetch requirement of 20 meters for this method to be valid was satisfied at all times. The raw wind speed and wind direction data at varying heights were averaged for the concentration sampling durations. The wind direc tion values were used to calculate a fetch at every minute, which then was av eraged for the concentration sam pling periods. Finally, the period averaged wind speed values were used al ong with the natural logarithm of the height measurements to calculate regression co efficients (slope, intercept, and r 2 ) for each period. Period averaged meteorological parameters fo r each field and the meteorological regression coefficients are shown in Appendix B.

3. Flux determination using the Aerodynamic Method (AD) :

The aerodynamic method, also referred to as the “flux-gradient” method, was the technique employed for estimating flux rates from fields following application. In the aerodynamic method,

a mast is erected in the middle of the treated field and concentration samples are typically collected at four or five different heights, ra nging from 0.5 to 10 feet. Likewise, temperature and wind speed data are collected at a variety of he ights. A log-linear regression is performed relating the natural logarithm of the sample height to the concentration, temperature, and wind speed. These relationships are then incorporated into an equation to estimate flux. These methods to estimate flux and related equations are presented in Majewski et al. , 1990. The equation for estimating flux using the aerodynamic method is Thornthwaite-Holzman Equation which is shown in the following expression:

2

1 2 2



### ] [ln ) )( (

         



z z u c k P

p m



###  

where P is the flux in units of  g/m 2 ·s, k is the von Karman’s constant (dimensionless ~0.4), Δ 

### c is the vertical gradient pesticide residue concentration in air in units of  g/m 3 between heights z top and z bottom in units of meters, Δū is the vertical gradient wind speed in units of m/s between
heights z top and z bottom , and 

### 

m and 

### 

p are the momentum and vapor stability correction terms
respectively. Following the conditions expected in the neutrally stable internal boundary layer characterized by an absence of convective (buo yant) mixing but mechanical mixing due to wind shear and frictional drag, a log-linear regression is performed relating the natural logarithm of the sample height to the concentration, temperat ure, and wind speed. The adjusted values of the concentration, temperature, and wind speed from th is regression is incorporated into the equation above to arrive at the following equation, which is ultimate used to compute the flux.

2 2



### ln ) )( ( ) 42

. 0 (

          



bottom top

p m zbottom ztop zbottom ztop



### z z u u c c Flux

 

### 69 of 70 where 

### 

m and 

### 

p are internal boundary layer (IBL) stability correction terms determined
according to the following conditions based on the calculation of the Richardson number, R i :



### Equation x 3 

#   2 

### 16

. 273 2 ) )( )( 8

. 9 (

zbottom ztop zbottom ztop zbottom ztop bottom top

i



### u u T T T T z z R

     

   

           



where T ztop and T zbottom are the regressed temperatures at the top and bottom of the vertical profile

in units of °C.

if R i >0 (for Stagnant/Stable IBL) 

##   33

. 0 

### 16 1 i m 

### R    and 4

. 0 

### ) 34 1 ( 885

. 0 i p 

### R   

if R i <0 (for Convective/Unstable IBL) 

##   33

. 0 

### 16 1 



###   i m 

### R  and 4

. 0 

### ) 22 1 ( 885

. 0





###   i p 

### R 

The minimum fetch requirement that the fetch is 100 times the highest height of the air sampler

for this method to be valid was not satisfied at all times. The raw wind speed and temperature data at varying heights were averaged for th e concentration sampling durations. The period averaged wind speed and temperature values were used along with the natural logarithm of the height measurements to calculate regression coefficients (slope, intercept, and r 2 ) for each period. Meteorological parameters for each averaging peri od and the regression coefficients are shown in Appendix D. The aerodynamic method used to estimate flux and related equations are presented in Majewski et al. , 1990.

### 70 of 70 

## APPENDIX D

CURRENT CHLORPYRIFOS BU FFERS RESTRICTIONS

Table D.1. Chlorpyrifos Buffer Distances for Aquatic Sites

Application Method Required Buffer Zone (feet)

Groundboom 25 Chemigation 25

Airblast 50 Aerial (fixed wing or helicopter) 150



### Table D.2. Chlorpyrifos Human Health Spray Drift Buffer Zones for Sensitive Sites

Application rate (lb ai/A) Nozzle Droplet Type Required Setback (Buffer Zones) (feet)

Aerial Airblast Ground

>0.5 - 1 coarse or very coarse 10 10 10

>0.5 - 1 medium 25 10 10

>1 - 2 coarse or very coarse 50 10 10

>1 - 2 medium 80 10 10

>2 - 3 coarse or very coarse 80 a 10 10

>2 - 3 medium 100 a 10 10

>3 - 4 medium or coarse NA b 25 10

>4 medium or coarse NA 50 10

a. Aerial application of greater than 2 lb ai/A is only permitted for Asian Citrus Psylla control, up to 2.3 lb

ai/A.
b

. NA is not allowed.



### Table D.3. Granular Applications Chlorp yrifos Buffer Zones for Sensitive Sites

Application Rate (lb a.i./A) Required Setback (Buffer Zones) (feet)

Aerial Ground a

>0.5 - 1 25 10

>1 - 2 Not allowed 10

>2 - 3 Not allowed 10

>3 - 4 Not allowed 10

>4 Not allowed 10

a. The required buffer zones for ground application apply

to applications made via spreaders.