Why One Group is Suing the Government Over Malathion, a Dangerous Pesticide

Malathion, a commonly used pesticide for both agricultural use and home gardening, has had a long and widely disputed history. First approved for use in 1956, it increased in popularity during the 1980s due to its efficacy against the Mediterranean fruit fly. Malathion has worked its way into products many US consumers wouldn’t take a second glance at, such as mosquito spray or lice shampoo. 

However, over the years, it’s become clear that malathion isn’t always safe for use, and, even if no humans are negatively impacted by it on a case-by-case basis, it’s much more likely to negatively impact unintended critters or plants, some of which might be endangered. Malathion remains on the market in the US (the United Kingdom withdrew malathion for sale in 2002 due to safety concerns), but some organizations are pushing back, citing the pesticide’s murky history and evidence that malathion isn’t as safe as you might want to believe.

On September 9, 2024, the Center for Biological Diversity, an organization dedicated to protecting endangered species from human impact, sued the U.S. Fish and Wildlife Service (USFWS) for “failing to adequately protect more than 1,500 species of wildlife and plants from the insecticide malathion—in violation of the Endangered Species Act.” This came after years of back-and-forth on malathion’s safety. 

In 2017, scientists within the USFWS found that a single exposure to malathion “could be catastrophic” and that repeated use of the insecticide could eliminate entire populations of endangered species in particular areas. However, their findings went nowhere after that scientific determination was reversed by then-Secretary of the Interior David Bernhardt, which delayed the finalization of the biological opinion by five years. 

Fast forward to 2022, and the USFWS changed its tone: This time, it finalized its biological opinion on malathion and concluded that the pesticide does not pose an extinction risk to a single protected species of wildlife or plant in the United States. There’s very little to explain why such a drastic difference in findings would occur over such a short timespan. 

Lori Ann Burd, environmental health director for the Center for Biological Diversity (CBD), says that, despite the shift from the USFWS, the CBD remains steadfast that malathion is harmful. “Malathion belongs to an old class of pesticides called organophosphates. Organophosphates are potent neurotoxins associated with a suite of risks to human health, including death,” says Burd. “Farmworkers suffer disproportionate exposure to pesticides, including malathion. But others can also suffer substantial exposures, including people who spray malathion for landscaping, golf courses and mosquito control; people who live in areas where malathion is frequently used for mosquito control, and workers in factories where malathion is produced.” 

A glance back in time through malathion incident reports finds concerning stories from the 1980s and ’90s. In California, malathion was the third most common cause of pesticide-related illness from 1981 to 1985, especially among applicators exposed during indoor application, usually due to inhalation of fumes. Malathion is second on the list of active ingredients thought to be responsible for the largest number of acute occupational pesticide-related illnesses, using 1999 data. One incident report recounts the time a young girl ran across a lawn five hours after the application of malathion; she was left with blisters on her feet for months afterwards. Another incident from 1995 finds that a worker installing a door was exposed to malathion sprayed by the property owner; he was hospitalized for days with dysarthria, nausea, and vomiting. 

In fairness, malathion is generally safe enough for humans—usually. Malathion is of low toxicity to humans, but absorption or ingestion into the human body metabolizes malathion into malaoxon, which is substantially more dangerous. Symptoms of malaoxon toxicity can onset within minutes to hours after exposure, and can result in minor concerns such as allergic reactions or skin rashes to nervous system impacts, seizures, loss of consciousness, and even death. Even low levels of exposure can lead to these effects.  The National Institute for Occupational Safety and Health (NIOSH) recommends that workers not be exposed to more than 10 mg/m³ of malathion for a 10-hour workday, 40 hours per workweek. NIOSH also recommends that a level of 250 mg/m³ of malathion in the air be considered as immediately dangerous to life and health.

How can one stay protected from potential malathion toxicity? It’s important to use protective equipment when applying malathion, including gloves, rubber boots, a mask covering the nose and mouth, and eyewear. Even when wearing gloves, it’s important to thoroughly wash your hands afterwards. Windows should stay closed to prevent vapors from entering your house. Similarly, remember that anything you spray has the potential to cause harm; remove pet bowls, children’s toys, or anything else that might unknowingly harbor malathion. However, it’s important to consider others when choosing your pesticide; if you are unable to limit the exposure of others, such as neighborhood kids or dogwalkers, you may want to reconsider using a pesticide believed by many, and evidenced by many incident reports, to cause serious harm.

Malathion is, like most other insecticides, indiscriminate in who it kills; that means that endangered species that come in contact with it are likely to die. These species include the Karner blue butterfly, rusty-patched bumble bee, Indiana bat, northern long-eared bat, American burying beetle, lesser prairie-chicken, and many plant species. Bat species may actually be at an increased risk, as they may feed on mosquitoes sprayed with malathion before they succumb. Similarly, feral cats, or outdoor cats and dogs, might interact with objects sprayed by malathion, or eat insects or small animals that are contaminated. 

The government’s reply to the lawsuit is due by the end of January, and the incoming Trump administration could be a factor in how it proceeds. “The election could certainly lead to changes in how the government chooses to defend itself in the case, but we still feel confident in the strength of our claims,” says Burd. 

“The Fish and Wildlife Service submitted to the pesticide industry’s demands and hung more than 1,500 endangered species out to dry by failing to rein in malathion use in their habitats,” said Burd in a release regarding the CBD lawsuit. “Today, these animals and plants continue to be harmed by one of the worst neurotoxic pesticides on the market, which can be sprayed in the last few homes of some of our most imperiled species. That includes nearly every endangered butterfly, beetle and dragonfly we have. We just can’t let this go on.” 

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