Revised Human Health Risk Assessment on Chlorpyrifos

We have revised our human health risk assessment and drinking water exposure assessment for chlorpyrifos that supported our October 2015 proposal to revoke all food residue tolerances for chlorpyrifos. The revised analysis shows risks from dietary exposure (i.e. residues of chlorpyrifos on food crops) and drinking water.

View a prepublication version of the newly available analyses (PDF)(13pp, 81, About PDF). These analyses will be available for a 60-day comment period upon publication in the Federal Register in docket EPA-HQ-OPP-2015-0653 at www.regulations.gov. We are specifically soliciting comments on all new analyses and information as well as reopening comment on any other aspect of the proposal or the underlying support documents that were previously available for comment.

Learn more about the revised risk assessment on chlorpyrifos:

  1. What does EPA's revised human health risk assessment show?
  2. What are EPA's next steps?
  3. How did EPA assess risks?
  4. Did EPA take into account the 10X safety factor specified under the Food Quality Protection Act to protect children?
  5. Who is at risk for chlorpyrifos exposure?
  6. Can chlorpyrifos affect wildlife?

1. What does EPA’s revised human health risk assessment show?

This assessment shows dietary and drinking water risks for the current uses of chlorpyrifos. Based on current labeled uses, the revised analysis indicates that expected residues of chlorpyrifos on food crops exceed the safety standard under the Federal Food, Drug, and Cosmetic Act (FFDCA). In addition, the majority of estimated drinking water exposures from currently registered uses, including water exposures from non-food uses, continue to exceed safe levels even taking into account more refined drinking water exposures. This assessment also shows risks to workers who mix, load and apply chlorpyrifos pesticide products.

2. What are EPA's next steps?

EPA’s revised analyses do not result in a change to the EPA’s proposal to revoke all tolerances that was issued on October 30, 2015. Learn about the proposal and read the Federal Register Notice

EPA will consider all comments received during the 60-day public comment period on the new analyses, as well as other supporting documents, before issuing a final tolerance decision by March 31, 2017.  Worker risks will be addressed after this time, through the chlorpyrifos registration review decision. View the prepublication version of the newly available analyses (PDF)(13 pp, 81 K, About PDF)

As part of the ongoing registration review for chlorpyrifos, EPA is also assessing the ecological risks from chlorpyrifos in conjunction with the agency’s Endangered Species Protection Program.  We issued the draft biological evaluation for public comment in 2016. In January 2017, we completed the biological evaluation and initiated formal consultation with the Fish and Wildlife Service and National Marine Fisheries Service.  View the final biological evaluation for chlorpyrifos.

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3. How did EPA assess risks?

This was one of the first risk assessments to employ a physiologically-based pharmacokinetic and pharmacodynamic (PBPK/PD) model. This is a mathematical model that enhances our ability to assess risk by allowing us to consider variations in a chemical’s effects on a person based on such variables as age and genetics and allows us to predict how the same dose may affect various members of a large population differently. EPA has held several meetings of the FIFRA Scientific Advisory Panel to get independent advice on the relevance and usefulness that a PBPK/PD model can provide in assessing a chemical’s risks and one specifically on PBPK/PD and chlorpyrifos.

The 2014 revised human health risk assessment used dose-response data on acetylcholinesterase inhibition (AChI) in laboratory animals to derive a point of departure. However, the EPA believes that evidence from epidemiology studies indicates effects may occur at lower exposures than indicated by the toxicology database. The 2016 revised human health risk assessment uses neurodevelopmental effects as the critical effect, taking into account recommendations from the 2016 chlorpyrifos SAP on deriving a point of departure for risk assessment. For additional details on how the EPA assessed risks, please see the prepublication version of the notice of availability and revised risk assessment (PDF).(13 pp, 81 K, About PDF)

4. Did EPA take into account the 10x safety factor specified under the Food Quality Protection Act to protect children?

Yes, EPA did retain the 10x factor for this risk assessment. 

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5. Who is at risk for chlorpyrifos exposure?

We are concerned that safe levels of chlorpyrifos in the diet may be exceeded based on current chlorpyrifos uses. We are also concerned about workers who mix, load and apply chlorpyrifos to agricultural and other non-residential sites and workers re-entering treated areas after application.

EPA issued a proposal on October 30, 2015, to revoke all chlorpyrifos tolerances. Learn about the proposal and read the Federal Register notice.

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6. Can chlorpyrifos affect wildlife?

Yes, and EPA has taken actions to help protect wildlife from chlorpyrifos exposure. For example, many of the reported incidents of wildlife mortality associated with chlorpyrifos use were related to residential lawn and termite uses and use on golf courses. The residential uses have been eliminated, termiticide uses have been restricted, and the application rate on golf courses has been reduced. Additionally, no-spray buffers around surface water bodies, as well as rate reductions for agricultural uses further reduced the environmental burden of chlorpyrifos.

The agency is currently assessing the ecological risks for chlorpyrifos in conjunction with the agency’s Endangered Species Protection Program.

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