EPA Publishes Updated Risk Assessments for Chemical Acephate

Released on August 30, 2023

Today, the U.S. Environmental Protection Agency (EPA) released a revised human health draft risk assessment (HH DRA) and refined drinking water assessment (DWA) for acephate, an organophosphate pesticide (OP) that is registered for both agricultural and non-agricultural uses. The acephate HH DRA includes an assessment of methamidophos, which is also an OP compound that is formed when acephate is metabolized. The revised HH DRA showed significant dietary risks of concern from drinking water for registered uses of acephate, including non-agricultural uses. EPA also identified dietary risks of concern when only the two highest agricultural usage sites (measured by pounds sold), cotton and soybean, are considered.

The revised HH DRA includes additional information on dietary risk, as well as risk identified for occupational handlers and post-application scenarios, non-occupational bystanders, and residential exposures. The revised HH DRA reflects numerous updates since the previous risk assessment, including reevaluation of the Food Quality Protection Act safety factor (FQPA SF), which is intended to provide an additional 10X margin of safety to account for any additional risk to pregnant women and children, but which can be reduced or removed if a scientific determination is made that no such additional risk exists.

The document entitled Approach for Evaluating Developmental Neurotoxicity Potential for the Organophosphate Pesticides outlines EPA’s decision to evaluate the developmental neurotoxicity (DNT) potential of OPs to pregnant women and children on a chemical-by-chemical basis using high quality, chemical-specific data from three primary lines of evidence – epidemiological studies, animal toxicity studies, and a battery of in vitro assays. These data are then used to evaluate DNT potential using a weight of evidence (WOE) approach, which is a process that integrates all relevant evidence to support decision-making that allows for consideration of strengths and limitations of each line of evidence.

Applying the principles described in the document referenced above to acephate, EPA updated the FQPA SF determination to include the WOE analysis for DNT potential to pregnant women and children using chemical-specific data for acephate and methamidophos. This WOE analysis can be found in the document entitled Evaluation of the Developmental Neurotoxicity Potential of Acephate/Methamidophos to Inform the FQPA Safety Factor.

Taking the WOE evaluation for DNT potential into account, although acephate and methamidophos are known neurotoxicants (i.e., chemicals that disrupt normal activity of the nervous system), there is little to no evidence that acephate or methamidophos are developmental neurotoxicants (i.e., chemicals that impact the normal development of the nervous system during pregnancy or childhood). Therefore, there is no additional risk when exposures of acephate or methamidophos occur to pregnant women or children. Changes in acetylcholinesterase (which causes a neurotoxic effect, not a developmental neurotoxic effect) continues to be the most sensitive and health-protective endpoint for the acephate human health risk assessment. As a result, EPA concluded there is reliable chemical-specific data to support reducing the acephate FQPA factor to 1x.

The Agency is still assessing the benefits and alternatives of acephate through the ongoing registration review process. These assessments, as well as the revised HH DRA and refined DWA, will inform the acephate proposed interim decision (PID), which is expected to be completed sometime next year. With the availability of these documents, the Agency will be reaching out to acephate registrants to discuss the human health risks identified in the revised HH DRA and the ecological risks that were previously identified in the March 2017 ecological risk assessment. Earlier this year, the Agency received information from the Department of Agriculture on the importance and benefits for the use of acephate on crops and non-agricultural applications. A public comment period will be open following the publication of the PID, and stakeholders may also comment on the revised HH DRA and refined DWA at that time.

Acephate is one of 18 OPs currently in registration review, with many scheduled to have interim decisions between 2024-2026. For more information on the registration review of acephate, including the HH DRA, DWA, and supporting documents, please visit the acephate docket on regulations.gov under Docket ID EPA-HQ-OPP-2008-0915.