The U.S. Environmental Protection Agency (EPA) has released an updated draft human health risk assessment (HH DRA) for malathion, a widely used organophosphate pesticide. This revision amends the 2016 assessments for dietary, occupational, and residential exposures with new information and methodologies, concluding that malathion poses no human health risks when used as directed.
Background on Malathion Use
Malathion serves a critical role in agriculture and public health, targeting pests on a variety of plants and controlling mosquito populations. With mosquito-borne diseases such as West Nile and Zika virus posing serious health threats, exacerbated by climate change, malathion's effectiveness in mosquito control is vital for preventing disease in the U.S., especially in densely populated and high-risk areas.
Key Findings of the Updated HH DRA
The comprehensive assessment focused on malathion and its metabolite malaoxon, which can inhibit the acetylcholinesterase enzyme, affecting the nervous system in insects and potentially in mammals at certain exposure levels. Notably, the updated HH DRA utilized modern scientific techniques, including a physiologically based pharmacokinetic-pharmacodynamic (PBPK) model, to provide a refined human toxicity estimation across different age groups and exposure routes. This approach, alongside updated dietary and exposure data, supports the finding of no significant human health risks.
Innovations in Risk Assessment
The updated assessment incorporates advanced methodologies:
- Physiologically Based Pharmacokinetic-Pharmacodynamic (PBPK) Modeling: Offers a realistic estimate of human toxicity from exposure.
- Updated Food Quality Protection Act Safety Factor (FQPA SF): Reduced based on a weight of evidence analysis of developmental neurotoxicity potential, indicating a more precise approach to risk management.
- Comprehensive Exposure Data: Includes the latest information on dietary, residential, and non-occupational bystander exposures.
Importance of Weight of Evidence Analysis
A key component of the updated assessment was the weight of evidence (WOE) analysis, especially in determining the FQPA safety factor. By evaluating all relevant evidence, including epidemiological and animal toxicity studies, the EPA was able to refine its safety margins, demonstrating the agency's commitment to evidence-based assessments.
Next Steps and Public Engagement
The EPA is in the process of finalizing the human health and ecological risk assessments for malathion, with decisions expected later this year. Public comments will be solicited on both the HH DRA and the ecological DRA as part of the proposed final decision (PFD) process. This comprehensive review, including endangered species and endocrine disruptor considerations, aims to ensure malathion's safe use and regulatory compliance.
