Long-term exposure to a common pesticide speeds up aging in fish, study finds
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Chronic exposure to small amounts of a pesticide approved for almost a dozen US crops speeds up aging in fish and cuts their lives short, adding to concerns about the chemical’s human health risks, according to a new study.
The insecticide chlorpyrifos has been linked to brain damage and brain development issues in children, and a recent study found that people exposed to the chemical for years in California farm communities were more than twice as likely to develop Parkinson’s disease than residents not exposed to it.
Previous research has demonstrated that chlorpyrifos is toxic to fish even at very low doses. The chemical is also known to be toxic to pigeons, ducks, bees and other wildlife, and an assessment by the US Environmental Protection Agency (EPA) previously found that the insecticide was harming 97% of protected species. In March, a federal judge ordered the US Fish and Wildlife Service to reduce harms to endangered species from chlorpyrifos, along with four other pesticides.
The new study is “the latest in a long line of scientific literature regarding this organophosphate insecticide that exemplifies the deficient regulatory processes currently in place that fail to provide adequate health and safety protections for all,” said Sara Grantham, a scientist with the group Beyond Pesticides who was not involved in the study.
“Chlorpyrifos is just one of over a thousand pesticide active ingredients that pose risks to not only aquatic organisms, but all wildlife, the environment and human health,” she added.
In the new study, published Jan. 15 in the journal Science, scientists detected chlorpyrifos and 18 other pesticides in the tissues of over 24,000 Lake skygazer fish in China. They found that fish contaminated with higher pesticide levels had shorter protective caps at the ends of their chromosomes, called “telomeres” – as telomeres shorten, DNA breaks down and cells age faster. Further tests revealed that only the insecticide chlorpyrifos was linked to shorter telomeres in the fish from two contaminated lakes.
Next, the researchers exposed fish from one of the contaminated lakes, as well as fish from a lake that was not contaminated, to 10 nanograms per liter (ng/liter) or 50 ng/liter of chlorpyrifos for four months, finding the exposure increased signs of cellular aging in the fish, with greater effects seen when the fish were exposed to higher doses. Chlorpyrifos exposure also lowered the survival of fish from the contaminated lake but did not impact survival of those from the cleaner one – possibly because those fish had longer telomeres to begin with, the researchers speculated.
“Chronic low-dose exposure to these chemicals may pose similar aging-related risks in humans, potentially contributing to age-associated diseases,” the authors write. “Although acute lethal (hours to days) and chronic sublethal (days to months) toxicities have traditionally guided chemical safety regulations, our results highlight the need for a greater consideration of chronic lethal effects of chemicals in regulatory decision-making.”
Over 25 years ago, federal regulators and manufacturers reached an agreement to phase out most uses of chlorpyrifos, but farmers in certain states are still allowed to use it on apples, cherries, peaches, wheat and other crops. Health and environmental groups successfully pushed the US Environmental Protection Agency to ban the pesticide from food crops in 2021, but the ban was partially overturned two years later.
Some US states have banned chlorpyrifos or restricted its use, including Hawaii, California, Maine, Maryland, New York and Oregon. The European Union banned the pesticide in 2020, although a 2023 investigation revealed that European companies have continued exporting the harmful chemicals to countries in the Global South with weaker regulations.
In May 2025, a meeting of the Stockholm Convention on Persistent Organic Pollutants in Geneva, Switzerland agreed to a global ban on chlorpyrifos, with exemptions for 22 uses of the pesticide.
Jayakumar Chelaton, chair of the Pesticide Action Network (PAN) International, said in a statement that the exemptions were designed to protect corporate profits, “thus weakening science-based decision-making.”
“We failed to protect the future for our children,” said Chelaton. “We urge countries that care for people to stop all uses…without any exemptions.”
Featured image: Jennifer Chen/Unsplash +
