For decades, regulators viewed chlorpyrifos — a pesticide widely used in the U.S. and around the world — primarily as a neurotoxin that disrupts signaling in the brain and nervous system.
But as the U.S. Environmental Protection Agency (EPA) reconsiders whether to continue to allow its use on foods like apples and soybeans, a new review indicates other insidious harms.
Published in April in the International Journal of Molecular Sciences, the review synthesizes findings from nearly 300 studies worldwide published up to this year. These include laboratory experiments, animal studies, epidemiological research, regulatory documents and risk assessments.
Growing evidence suggests chlorpyrifos may damage the brain, hormones, liver, gut microbiome, muscles, reproductive organs and bones. Studies also link the pesticide to DNA damage and lasting changes in gene activity that may increase the risk of chronic disease.
Together, the findings portray chlorpyrifos as what the reviewers call a “multi-system toxicant” that poses a more significant threat to public health than previously understood.
It suggests the pesticide acts on the body in ways far beyond disrupted nerve signaling or obvious poisoning. Pregnancy and early childhood are especially sensitive periods for chemical exposure.
“What has genuinely evolved over time is our understanding that chlorpyrifos causes harm in ways that go beyond its effects on the nervous system including damage to DNA, changes in how genes are switched on or off, interference with hormones, and disruption of the healthy bacteria that live in the gut,” said Dana Boyd Barr, Ph.D., a professor at Emory University’s Rollins School of Public Health and past president of the International Society of Exposure Science.
The authors warn that current regulatory systems may not fully capture the complexity of chlorpyrifos’ dangers to the body. Many occur at levels too low to be detected by current safety testing, which looks for the disruption of an enzyme involved in nerve cell communication.
The review links chlorpyrifos exposure to:
- Biological changes associated with inflammation, chronic disease and cancer.
- Brain and nervous system damage, including lower IQ and developmental harms in children, neurodegenerative disease, and disrupted cell growth, survival and communication.
- DNA damage and altered gene regulation that hinders normal cell repair and changes how genes are switched on and off during development (epigenetics).
- Hormone disruption involving thyroid, estrogen and testosterone pathways.
- Liver injury, gut bacteria disruption and metabolic dysfunction are linked to obesity and Type 2 diabetes.
- Reproductive, muscular and skeletal harm, including reduced sperm quality and bone loss.
Industry pushback despite reported harms
The review comes as the EPA reassesses whether the pesticide’s remaining uses meet the statutory standard of “no unreasonable adverse effects.” The action follows years of official stalling, prior bans, policy reversals and legal challenges.
Meanwhile, agrichemical companies are lobbying federal and state lawmakers to shield pesticide manufacturers, including Bayer and its subsidiary Monsanto, from some lawsuits involving Roundup weedkiller. The suits allege their products cause non-Hodgkin lymphoma, among other cancers.
In February 2020, Corteva Agriscience — then the world’s largest producer of chlorpyrifos — announced it would stop production, citing declining demand.
But existing stocks continued to be used. The chemical remains approved for several major crops in the U.S., including apples, strawberries, soybeans, citrus, wheat and peaches.
Hellbound and Down 