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According to a new study published in Occupational & Environmental Medicine, workplace exposure to pesticides is associated with a 60% to 70% increased risk of amyotrophic lateral sclerosis (ALS), a progressive and often rapidly fatal neurodegenerative disease.
Study details and key findings
ALS is the most common form of motor neuron disease, a neurodegenerative condition that affects the ability to speak, eat, breathe, and swallow. It is a rare and often rapidly fatal disease, and there is currently no cure. On average, people with ALS survive only two to three years after diagnosis.
Most patients are diagnosed with ALS between the ages of 40 and 70. In over 90% of ALS patients, the disease occurs sporadically, which means that patients have no known family history or identified genetic cause behind the disease. The remaining 10% of patients either have a known genetic variant or family history of ALS.
Currently, it's not known what triggers either the sporadic or familial forms of the disease, but interaction between genes and the environment could play a role.
In a new study, researchers from Canada's Occupational Health and Safety Research Institute and the University of Montreal analyzed data from studies that estimated the risk of ALS after occupational pesticide exposure published between 1990 and 2025.
The researchers focused on eight primary case-control studies that included 1,734 ALS cases. Using statistical regression models, the researchers evaluated how sex, chemical classes, exposure intensity, and research methods affected ALS cases.
Overall, the researchers found that any workplace exposure to pesticides was associated with a 58% to 60% increase in ALS risk compared to no exposure. Low-level exposure was associated with a near-doubling of ALS risk while high-level exposure almost tripled the risk. Workers who did not use personal protective equipment also faced up to 40% higher risk compared to those who did.
There were slight differences in risks depending on the type of pesticides used. Herbicides were associated with a 71% increase in risk while fungicides had a 61% increased risk and insecticides had a 57% increased risk.
There were also differences in risk when it came to sex. Men who were exposed to pesticides were twice as likely to develop ALS compared to men who hadn't been exposed. However, there was no difference in risk for women who had been exposed to pesticides and those who had not. Notably, men are around 20% more likely to develop ALS than women.
Some jobs with potential occupational exposure to pesticides include farming and other agricultural jobs, landscaping, and pest control.
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Commentary
According to the researchers, the study's findings "add to the evidence that occupational exposure to pesticides may increase the risk of ALS and should encourage the implementation of interventions aimed at reducing exposure during occupational pesticide use."
However, they also highlighted the limitations of their study, including that only a few studies met the criteria for meta-analysis and that many of them did not account for other factors that could have contributed to ALS risk, such as past head trauma or drinking private well water.
"To strengthen the evidence on risk factors for ALS, primary studies particularly need methodological improvements on exposure assessment, on the selection of reference groups, and on adjustment for potential confounders, including analysis for interactions between risk factors," the researchers wrote.
Separately, Rachel Tan, an associate professor of neuroscience at the Brain and Mind Centre at the University of Sydney, said more research is needed to identify which chemicals could be directly linked to ALS.
"The overall evidence base is not entirely consistent, some studies are finding no clear association, some studies are finding that this association is more driven by men than women," Tan said. "Some of the most important questions that we will need to find out is what components of pesticides might increase the person's risk, whether longer exposure to pesticides increased that risk further."
(Tan, The Conversation, 8/5; Smith, Technology Networks, 8/5; Mestri, Medical Xpress, 8/4; Saunders, People, 8/5)
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