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Revised Human Health Risk Assessment on Chlorpyrifos

In November 2016, we revised our human health risk assessment and drinking water exposure assessment for chlorpyrifos. The revised analysis shows risks from dietary exposure (i.e., residues of chlorpyrifos on food crops) and drinking water. Currently, chlorpyrifos remains registered as it undergoes registration review. As part of the ongoing registration review, we will continue to review the science addressing neurodevelopmental effects and complete our assessment by October 1, 2022.

View the 2016 revised human health risk assessment and the refined drinking water assessment. These analyses were available for a 60-day comment period in docket EPA-HQ-OPP-2015-0653 at www.regulations.gov.

 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. 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 exposure from currently registered uses, including water exposure from non-food uses, continues to exceed safe levels, even taking into account more refined drinking water exposure. This assessment also shows risks to workers who mix, load and apply chlorpyrifos pesticide products.

2. What are EPA's next steps?

In March 2017, EPA denied a petition asking us to revoke all pesticide tolerances (maximum residue levels in food) for chlorpyrifos and cancel all chlorpyrifos registrations. We will continue to review the science addressing neurodevelopmental effects of chlorpyrifos as part of the ongoing registration review and complete our assessment by the statutory deadline of October 1, 2022. Read the Federal Register notice announcing our response to the petition.

As part of the ongoing registration review for chlorpyrifos, EPA is also assessing the potential ecological risks from chlorpyrifos.  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 of a PBPK/PD model in assessing a chemical’s risks, including one meeting 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, 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 EPA assessed risks, please see  revised risk assessment.

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. 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 consulting with the U.S. Fish and Wildlife Services and the National Marine Fisheries Services to evaluate potential impacts on endangered species. 

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