unreasonable adverse effects. As part of registration review, the chlorpyrifos preliminary Human 

Health Risk Assessment (HHRA) was released for public comment in July 2011.2

 In the 

preliminary HHRA, risks to bystanders from spray drift and exposure from volatilization were 

identified as concerns. The public comment period closed in October 2011. As the Agency 

works to finalize its HHRA, it has further refined its analysis regarding spray drift from various 

chlorpyrifos application scenarios in order to have a broader understanding of the potential risks. 

That assessment, Evaluation of the Potential Risks from Spray Drift and the Impact of Potential 

Risk Reduction Measures3, is being released in conjunction with this decision document. 

In addition, in 2007, the Natural Resources Defense Council (NRDC) and Pesticide 

Action Network North America (PANNA) jointly petitioned the Agency to revoke all tolerances 

and cancel all registrations for chlorpyrifos.4 One of the issues identified in the Petition deals 

with inhalation routes of exposure from spray drift and volatilization. This more refined spray 

drift assessment and subsequent mitigation measures will inform the Agency’s response to the 

spray drift portion of petitioners’ inhalation claim. The Agency’s volatilization assessment 

continues to be refined in the context of the final HHRA. 

This more refined spray drift analysis resulted in a better estimate of potential exposures 

and risks to bystanders, particularly children, around treated fields. While the analysis showed 

there were health risks due to spray drift, the analysis also indicated that the risks could be 

mitigated by requiring buffer distances and specific application methods. Specifically, by linking 

droplet size with application rates and application methods in order to dictate appropriate buffer 

distances. Table 1 indicates the various buffer distances that will be required when using certain 

application rates, nozzle droplet type, and application method. 

Table 1: Buffer Distances from 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 801 10 10 

>2 - 3 medium 1001 10 10 

>3 - 4 medium or coarse NA2 25 10 

>4 medium or coarse NA 50 10 1

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

NA is not allowed. 

 

2

 Available at http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2008-0850-0025. 3

 Dawson J, Britton W, Bohaty R, Mallampalli N, Grube A. U.S. EPA (2012). Chlorpyrifos, PC Code 059101, DP 

Barcode 399483 and 399485; Evaluation of the Potential Risks From Spray Drift and the Impact of Potential Risk 

Reduction Measures. Available at http://www.regulations.gov/#!docketDetail;D=EPA-HQ-OPP-2008-0850. 4

 Petition of Natural Resources Defense Council and Pesticide Action Network North America to Revoke All 

Tolerances and Cancel All Registrations for the Pesticide Chlorpyrifos (September 12, 2007) at 1. (hereinafter 

Petition). Available at http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2007-1005-0005.