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Methamidophos Facts

EPA 738-F-02-008
August 2002

EPA has assessed the risks of methamidophos and reached an Interim Reregistration Eligibility Decision (IRED) for this organophosphate (OP) pesticide. Although current uses may pose unreasonable adverse effects to human health and the environment, these effects can be mitigated by the measures identified in the Methamidophos IRED. Provided that these risk mitigation measures are adopted, methamidophos' individual, aggregate risks will be within acceptable levels, and the pesticide will be eligible for reregistration once EPA has considered the cumulative risks of the OPs.

Used to control insects on potatoes, cotton, and tomatoes, methamidophos residues in food do not pose risk concerns. Screening level modeling estimates indicate that drinking water from surface water sources may pose risk concerns. However, actual drinking water exposures and risks are likely to be lower than predicted by these estimates. EPA will require confirmatory surface water monitoring data to confirm its current interim conclusion that drinking water risks are not of concern and do not require mitigation. Methamidophos has no residential uses, so children and others should not be significantly exposed to this pesticide around the home. EPA assumes that methamidophos will fit into its own "risk cup;" it will not pose significant dietary or aggregate risk concerns. Methamidophos poses risks of concern to workers who mix, load, and apply the pesticide to agricultural sites, and to workers who re-enter treated agricultural areas. Birds, mammals, and freshwater invertebrates also encounter risks of concern. With mitigation measures, these worker and ecological risks will be below levels of concern for reregistration.

EPA's next step under the Food Quality Protection Act (FQPA) is to consider the cumulative effects of the OP pesticides, which share a common mechanism of toxicity. The interim decision on methamidophos will not be final until OP cumulative risks have been considered. The OP cumulative assessment may result in further risk mitigation measures for methamidophos.

EPA is reviewing the OP pesticides to determine whether they meet current health and safety standards. Older OPs require decisions about their eligibility for reregistration under FIFRA. OPs with food, drinking water, residential, and any other non-occupational exposures must be reassessed to make sure they meet the new FFDCA safety standard, brought about by FQPA.

The methamidophos interim decision was made through the OP pilot public participation process, which has increased transparency and maximized stakeholder involvement in EPA's development of risk assessments and risk management decisions. EPA worked extensively with affected parties to reach the decisions presented in this interim decision document.


Health Effects


Risk Mitigation

The following mitigation measures are required for methamidophos to address drinking water, worker, and ecological risks of concern.

Next Steps

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