US EPA releases proposed protections for pesticide malathion

The U.S. Environmental Protection Agency (EPA) is releasing the Proposed Interim Registration Review Decision (PID) for the pesticide malathion. The PID proposes mitigation measures to reduce potential ecological risks. The malathion PID—as well as the revised Human Health Draft Risk Assessment and Ecological Draft Risk Assessment released earlier this year—will be open for public comment for 60 days. 

Background 

Malathion is an organophosphate (OP) pesticide registered for controlling pests on fruit, vegetables, landscaping plants, and shrubs. Malathion is an important pesticide tool for local mosquito control districts who use it to manage adult mosquito populations, including those that vector disease. Mosquito-borne diseases, such as West Nile virus, Zika virus, chikungunya virus, Dengue, yellow fever, and St. Louis Encephalitis, pose a significant risk to people in the United States. Climate change also increases the risk of human exposure to mosquito-borne diseases, as studies show that warmer temperatures can expand the range and breeding season of mosquitos, as well as accelerate mosquito development, biting rates, and the incubation of the disease within a mosquito. Using pesticides like malathion to control mosquitos is important to maintaining public health, particularly in densely populated, overburdened communities. 

Growers benefit from malathion use on fruit and vegetable crops due to the short pre-harvest intervals—the time-period required between when an application can be made and harvesting. Malathion is effective in controlling insect pests that can harm a harvest, such as fruit flies in cherries and blueberries, and dried fruit beetles in figs. Malathion is also the primary component of some federal and state insect pest management programs including the U.S. Department of Agriculture’s Cotton Boll Weevil Eradication Program and Fruit Fly (Medfly) Control Program, Mormon cricket and grasshoppers in rangeland, beet leafhopper within the Beet Curly Top Virus Control Program in California, and invasive Tephritid fruit flies in quarantine areas nationwide.  

Risk Assessment 

Under the Endangered Species Act (ESA), EPA is responsible for ensuring that its actions—including pesticide registration actions—do not jeopardize listed species or destroy or adversely modify their critical habitats. In 2017, EPA released a biological evaluation for malathion under the ESA that found that malathion is likely to adversely affect listed species and their critical habitats. As a result of these findings, EPA entered into required consultation with the National Marine Fisheries Service and the U.S. Fish and Wildlife Service (collectively, the ″Services″). The Services developed biological opinions that required mitigation measures for malathion to protect these species and habitats. EPA implemented these measures on all malathion labels in August 2023. In April 2024, the Bulletins Live! Two website with maps showing geographically specific limitation areas for malathion use became available to the public.  

In March 2024, EPA released an ecological draft risk assessment under the Federal Insecticide, Fungicide, and Rodenticide Act that assessed risks to non-listed species in order to determine whether mitigations were needed. This draft risk assessment found potential risks of concern to fish, aquatic invertebrates, birds, mammals, terrestrial amphibians, aquatic and terrestrial plants, and terrestrial invertebrates. The draft assessment also accounted for the mitigations required by the biological opinions.   

Also, in March 2024, EPA released an updated draft human health risk assessment (HH DRA), amending the 2016 malathion dietary, residential, aggregate, and occupational risk assessments using updated information and risk assessment methodologies. Given concerns that have previously been raised about OPs and their association with developmental neurotoxicity (DNT), in conducting the HH DRA, EPA paid particular attention to whether malathion had the potential to cause DNT. EPA evaluated multiple lines of evidence, including epidemiological studies (investigation of human populations for patterns and causes of health outcomes), animal toxicity studies performed with laboratory animals, and a battery of in vitro assays (testing of cells from the nervous system) and found potential DNT effects only occur at concentrations approximately 6 to 4,800 times higher than the level of the pesticide that causes neurotoxicity (shown by changes in acetylcholinesterase enzyme levels, which was the most sensitive effect). Therefore, protecting people from neurotoxicity will also protect them from DNT. The updated draft HH DRA found no human health risks of concern for malathion when used according to label instructions. 

Proposed Interim Decision 

EPA did not find potential human health risks of concern when malathion is used in accordance with its current label, but did identify potential ecological risks of concern, even after considering the measures that EPA has adopted to protect listed species and their habitats. The PID is proposing mandatory spray drift language for boomless ground applications (e.g., one or two nozzles spraying laterally from an all-terrain vehicle) and updated advisory spray drift language for all spray applications. Pesticide spray drift is the movement of pesticide dust or droplets through the air at the time of application or soon after, to any site other than the area intended. Additionally, the Agency is proposing a 96-hour water holding time before releasing floodwaters after the treatment of rice. Holding water used to flood rice fields allows for pesticide residues to dissipate before being released into the environment.   

The Agency will be accepting public comments for 60 days on the malathion PID and the DRAs that were released in March. The PID, DRAs, and supporting documents can be found in the public docket at www.regulations.gov (Docket ID: EPA-HQ-OPP-2009-0317). 

Read the Proposed Interim Decision