1 Note to Docket # EPA

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- 2008

- 0850

Publication Date: February 6, 2013

Chlorpyrifos Volatility Assessment: Guide to Commenters

The purpose of this note is to announce that the Environmental Protection Agency ( EPA ) is opening the public comment period for the Chlorpyrifos Preliminary Evaluation of the Potential Risks from Volatilization. The public is invited to comment on EPA’s volatilization assessment. EPA will carefully consider all comments, as well as any add itional information or data provided in a timely manner, prior to issuing a final assessment. The chlorpyrifos volatilization assessment can be found at www.regulations.gov , in docket EPA

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- 0850. The publ ic comment period is 30 days from the date of the Federal Register Notice announcing the availability of the volatilization assessment

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The chlorpyrifos volatility assessment evaluates the potential exposure to vapor phase chlorpyrifos and chlorpyrifos

- ox on emitted from treated fields. Two different field volatility studies suggest that volatilization of chlorpyrifos and/or chlorpyrifos

- oxon from treated crops is a route of dissipation 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, bystander exposures were examined to quantify the potential risks associated with vapor phase chlorpyrifos and chlorpyrifos

- oxon near a treated field.

As part of this draft risk assessment, EPA has also determined a n acceptable concentration for exposure to volatilized residues of chlorpyrifos and chlorpyrifos

- oxon based on an acute inhalation toxicity study conducted with aerosolized chlorpyrifos. Using that study EPA determined that humans should not experience any adverse effects from exposures that are less than 8.3 μg/m 3

. This level is the target concentration. EPA has concerns about potential risks for bystanders when the estimated concentration for bystanders is above the target concentration.

The approaches used to evaluate the volatilization of chlorpyrifos and chlorpyrifos

- oxon and the associated risks resulting from exposure to the volatilized residues are consistent with the methodology used in assessme nts conducted in the past for fumigant pesticides. As discussed in the Preliminary Evaluation of the Potential Risks from Volatilization, w hile there are a number of uncertainties and assumptions associated with this assessment, available data indicate tha t bystander exposure to vapor phase chlorpyrifos and chlorpyrifos

- oxon is possible, and can occur at concentrations that may cause adverse effects

. Generally, application rates greater than 1 lb a.i./A in large field s results in concentrations of concern a t significant distances offsite.

If the final assessment estimates risks similar to those presented in this preliminary evaluation

, EPA anticipates that it may be necessary to take actions to reduce bystander risks. There are several risk assessment inputs and assumptions that if fu r ther refined could reduce exposure that would result in lower risk estimates. Although no final decisions regarding risk mitigation have been made, o ne of the possible risk mitigation measures could be to require buffer zo nes between application sites and areas where bystanders might be present. Additional information explaining how buffer zones c ould be designed appears after the list of questions on which EPA is seeking2 comment. During this public comment period, stakehol ders are specifically asked to provide information and data on the following questions that will assist EPA in co mpleting a refined
assessment.

Questions regarding assessing volatility 1. What crop related factors (e.g., canopy height, leaf area index, leaf type, crop density, surface roughness) should be considered when measuring pesticide flux rates and interpreting (e.g., scaling flux rates or modifying flux rates from one crop to another) the results? What are the potential impacts of such factors? 2. What f ield conditions (e.g., degree of foliage, lea f type and shape, crop canopy, etc.) should be considered when measuring pesticide flux rates and interpreting the results? 3. What are the best methods for conducting a flux study so that it can be used to represe nt a broad spectrum of agricultural uses? Are approaches available for extrapolating flux results from one crop to another crop or from one region to another? 4. The correlation of pesticide application parameters (i.e., application rate) to the flux rate is assumed to be linear (i.e., as the application rate increases, the flux rate increases directly). What data are available to suggest otherwise or are there other application parameters that should be considered? If data are available , what are those parame ters? When i s it appropriate to scale the flux rate up or down based on application rates? 5. What other assumptions and uncertainties or sources of variability should be considered when measuring pesticide flux rates, interpreting flux data, and extrapolatin g results (e.g., stable meteorological conditions/calm wind)?

Questions regarding assessing hazard characterization/identification 6. Please provide comment on the interpretation of the special acute inhalation study 1 for use in the human health risk assessment. As part of your comments, consider the findings related to cholinesterase (ChE) inhibition in lung, plasma, red blood cells, and brain. Specific to lung ChE, please provide information relevant to interpreting ChE inhibition in the lung and its relationship to adverse effects on pulmonary function

. 7. Please provide comment on the strengths and limitations associated with use of an inhalation study conducted with aerosolized chlorpyrifos to assess the toxicity of chlorpyrifos i n the vapor phase.

Questions regarding additional information on chlorpyrifos use 8. Please provide information regarding application rates and acres treated per application per day (i.e. field size treated per day), specific to your growing region and pest spectrum 9. What application methods do you most frequently/typically use? 10. What formulation types do you most frequently use? 11. What is the application timing (date of first application and application intervals) by crop

– national, state, and county?

a. When duri ng the growing season do chlorpyrifos applications predominately occur in tree and vine crops?

1 MRID 48139303, available at http://www.epa.gov/opp00001/chem_search/cleared_reviews/csr_PC

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- 11_a.pdf

.3 After reviewing comments received during the public comment period, EPA may issue a revised volatilization assessment, explain any changes from the preliminary volatilization assessment, respond to comments, and evaluate the need for any regulatory action

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Useful Information

A. What is a Buffer Zone ?

B uffer zone s are areas around a treated field that are established to manag e the risks from acute inhalation exposu re to bystanders. A buffer zone is the distance between the application site (i.e., edge of field) and the bystanders that allows airborne residues to disperse before reaching the bystanders. The greater the distance (i.e. buffer zone) , the greater the p otential for residues to disperse, thus decreasing the likelihood that air concentrations where bystanders are located will cause acute adverse effects. EPA’s goal is to determine distances, or buffer zones, which will adequately protect bystanders from ac ute exposures

. The distance or size of the buffer zones would be based on factors such as application rates and field size . Air monitoring data, incident reports, and air dispersion modeling based on these factors can be used to help determine appropriate buffer zone distances.

B. What is a Buffer Zone Period?

Buffer zones, if required, would begin at the start of a chlorpyrifos application and remain i n effect for a specified period of time after the application is complete . The durat ion of the buffer zone requirement would depend upon when off

- site emissions have declined to a point where bys tanders are no longer at risk. This duration is known as the buffer zone period.

C. What Type of Buffer Zone Might Be Required?

If buffer zones are required, due to the length of time that the vapor phase of chlorpyrifos exceeds the target concentration, the buffer zone s would likely need to remain in place for some period of time (e.g. 6, 12, 24, etc hours) after application. A buffer zone for so me set period of time would allow for the dispersion of chlorpyrifos vapor such that the likelihood of bystanders experiencing acute adverse effects diminishes because it would allow the vapor concentration to drop below the target concentration

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EPA als o believes that if buffer zones are required, the buffers would likely need to encompass the entire field . That is, whatever buffer distance is determined appropriate to manage the risks of acute inhalation exposure to bystanders, w ould be the distance fro m the edge of the application area around the entire perimeter of the field equally in all directions

. This approach is consistent with the approach used and presented in the recent fumigant risk assessments. 2 Buffers around the entire perimeter would likely be necessary because due to the length of time a buffer zone may need to be maintained (e.g. hours not just at the time of application) makes it difficult to determine when a person may utilize the area surrounding the application site . In

2 The assessments can be found in the dockets for each fumigant. Four of which are provided here chloropicrin

- EPA

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- 2007

- 0350 ; dazomet

- EPA

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- 2005

- 0128 ; metam sodium/potassium

- EPA

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- OPP

- 2005

- 0125 ; and methyl bromide

- EPA

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- OPP

- 2005

- 0123

.4 addition, the variability of meteorological conditions makes it hard to predict where peak concentrations will occur around the application site, thus necessitating the need for buffers around the entire perimeter

. EPA’s decision regarding the appropriate buffer di stance is informed by the “Whole Field Buffer” and “Maximum Buffer” distributions. 3 The “Whole Field B uffer ” is estimated based on an array of results for the entire perimeter of a field. The “ Max imum B uffer ” is the largest buffer estimated from any given direction away from the field.

3 For more information regarding “Whole Field Buffer” and “Maximum Buffer” see one of the fumigant risk assessments such as the “Chloropicrin: Third Revision of the HED Human Health Risk Assessment” available at http://www.regulations.gov/#!documentDetail;D=EPA

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- 2007

- 0350

- 0398 . The discussion begins on page 38.