23
Jan
Chronic Low-Dose Exposure to Insecticide Chlorpyrifos Reduces Wild Fish Lifespan by Accelerating Aging
(Beyond Pesticides, January 23, 2026) A fish called a lake skygazer (Culter dabryi) shows accelerated aging when exposed to chronic low doses of the insecticide chlorpyrifos, according to a powerful study by researchers from several Chinese institutions, as well as Carleton University in Canada and the University of Notre Dame in Indiana. The study, in Science, finds that chronic low-dose exposures resulting in the accumulation of sublethal effects over time cause deterioration of molecular, cellular, and organ functions that reduce lifespan and fertility.
In the study, the fish showed reduced survival in a “dose- and physiological age-dependent manner,†while acute high doses did not have these effects, the authors write. Because the mechanisms researchers focused on are conserved throughout vertebrates, “even low doses of pesticide may pose long-term risks to longevity†in thousands of species, including humans.
The regulation of pesticides is based on laboratory animals’ exposure to acute high doses of a chemical–generally measured as the dose that kills half the test animals within 96 hours of exposure. Thus, the assumption that guides the calibration of “safe†or allowable levels of exposure is that lower doses, even if chronic, pose no threat. The current study unambiguously refutes that assumption, which must be retired from regulatory policies.
The study focuses on 24,388 wild fish collected from three Chinese lakes between 2020 and 2023. One lake had little or no pesticide exposure. The other two lakes had received pesticides from regional agriculture. The researchers compared the pesticide burdens in the fish from each lake by assaying concentrations of 93 pesticides in the fishes’ livers. Nineteen pesticides were detected in the fish. The researchers calculated a “toxic unit†representing the relative cumulative exposure of fish in each lake. The total units were higher in the pesticide-receiving lakes than in the more pristine lake. The higher the toxic units attributed to a lake, the fewer fish aged three years and older were found.
To determine whether chronic low-dose pesticide exposure caused the dearth of fish older than three years, the researchers examined lipofuscin deposition in the liver and relative telomere length, two measures of physiological aging. Lipofuscin accumulates in aging cells, including heart cells and neurons. Telomeres protect the ends of chromosomes from DNA degradation, and every time a cell divides, its telomeres get a little shorter. At a critical point, the cell stops dividing, becoming a “zombie†that contributes to the hallmarks of aging, such as chronic inflammation and degrading tissue function.
The fish in the two pesticide-laden lakes had two to three times as much lipofuscin as the fish from the pristine lake. Telomeres were longest in the year-old fish from all three lakes, but in two- and three-year-old fish, the longest telomeres were in the fish from the pristine lake. The two lakes with the highest toxic units had shorter telomeres in fish of the same ages, suggesting sublethal pesticide exposures were prematurely aging the fish. These results are consistent with previous laboratory and field studies on pesticides’ influence on telomere lengths. Significantly, the negative association between telomeres and pesticide exposure was strongest in younger fish, which the researchers speculate is because the most sensitive fish do not survive beyond a year.
Of the 19 pesticides found in the fish, chlorpyrifos is the standout bad actor. It was the only pesticide negatively correlated with telomere length in fish aged one to three years. It was also negatively associated with the number of three-year-old fish—the more chlorpyrifos in the lake, the fewer three-year-old fish. In fact, the toxic units in the two pesticide-affected lakes were 70% chlorpyrifos. “[C]hlorpyrifos was the top candidate for causing the observed accelerated senescence of C. dabryi in the wild,†the authors write.
As a companion to their field study, the researchers exposed two- and three-year-old fish from the pristine lake and one of the pesticide-exposed lakes to either zero or one of two concentrations of chlorpyrifos for four months. This meant that exposure was independent of their ages or lake sources. As would be normally expected, the older fish were physiologically older—they had more lipofuscin and shorter telomeres—than the younger fish. But in addition, fish from the pesticide-exposed lake were physiologically older than those from the pristine lake, even if they were the same age in years.
All the fish in the study experienced shortened telomeres and increased lipofuscin from the chronic chlorpyrifos exposure, and there were decreases in survival proportional to their ages, exposure doses, and source population. But the fish from the pristine lake did not suffer higher mortality regardless of their age, possibly because they had longer telomeres than the other fish to begin with. The older fish from the pesticide-drenched lake had higher mortality at the two chlorpyrifos levels compared to the younger fish from that lake. The authors believe the telomere shortening is likely the main mechanism driving fish mortality from chronic chlorpyrifos exposure.
The authors also tested to see whether acute high-dose exposures they might have missed could have caused shortened telomeres and higher mortality among physiologically older fish. They exposed two- and three-year-old fish from the two polluted lakes to five acute doses of chlorpyrifos. But the acute exposures caused higher fish mortality regardless of the source population or physiological age, yet did not significantly change the relative telomere lengths or lipofuscin levels in any of the fish. Further, the level at which half the fish died was comparable across populations and ages—they just died directly and quickly from chlorpyrifos’s acute toxicity—showing that missing acute exposures were unlikely to be the source of the effects seen in fish exposed over longer periods to lower doses.
As the authors state, “prolonged low-dose exposure can have lethal consequences over time.†In the U.S., acceptable continuous chlorpyrifos exposure in freshwater is 41 nanograms per liter (ng/l). In the European Union, the acceptable concentration is 0.46 ng/l—nearly 100 times lower. The researchers find harmful effects at their lowest exposure level of 10 ng/l, and that level is exceeded in more than 90% of surveys in 15 countries of chlorpyrifos concentrations in surface waters. Clearly, regulators must take note and act.
In aquatic vertebrates, “the loss of older individuals affects reproductive dynamics, genetic diversity, and ecosystem stability,†the authors write. Of course, these same processes operate in terrestrial vertebrates, including humans. Because vertebrates have longer life spans than invertebrates, they have more time to bioaccumulate toxic chemicals, meaning their age-related cellular processes will be accelerated. The authors also note that research in humans has found links between exposure to synthetic chemicals and telomere degradation.
This study demonstrates that chlorpyrifos is the single most toxic pesticide of the 19 found in the fish livers. Beyond Pesticides has detailed its numerous and deep toxic effects on humans and other life forms. See Beyond Pesticides’ Sara Grantham’s analysis of the current study and its implications in The New Lede’s coverage of the study.
EPA has a history of failure regarding chlorpyrifos. After years of mounting evidence of harm, the agency finally planned to ban it from agriculture in 2017, but the first Trump administration slammed the brakes on the action. In 2021, the Ninth Circuit Court of Appeals ordered EPA to ban chlorpyrifos based on evidence presented in litigation by farmworker groups and environmental organizations. This milestone was then reversed by the Eighth Circuit in favor of growers and CropLife International. See Beyond Pesticides’ coverage here.
Currently, the Trump EPA is considering a rule proposed by the Biden administration to allow chlorpyrifos on 11 crops, including asparagus, cotton, and sugar beet,s while banning it for most other crops. The allowed crops represent about 55% of total chlorpyrifos agricultural use between 2014 and 2018, according to EPA. In other words, the new rule, if enacted, will still allow, at the very least, more than half the total use of chlorpyrifos, which was estimated in 2024 to be about 30 million pounds.
Allowing continued usage of any kind is unacceptable to environmental and health groups. In March 2025, Beyond Pesticides submitted a letter to EPA stating that, “Eliminating all chlorpyrifos uses represents the best practice to protect children, waterways, and wildlife from this toxic pesticide. Given the serious risks involved, we urge EPA to revoke all tolerances of chlorpyrifos, including the 11 remaining products…that are among the most extensively grown and used in the world.†In May 2025, the Conference of the Parties for the Stockholm Convention on Persistent Organic Pollutants voted to place chlorpyrifos on its list of pollutants to be eliminated, except for a small number of exemptions.
EPA claimed it would issue an updated Human Health Risk Assessment (HHRA) in 2025, but is now promising it for 2026, along with a revised Proposed Interim Decision (PID). According to an EPA summary of the most current assessment, which is from 2016, “expected residues of chlorpyrifos on food crops exceed the safety standard under the Federal Food, Drug, and Cosmetic Act (FFDCA). In addition, the majority of estimated drinking water exposure from currently registered uses, including water exposure from non-food uses, continues to exceed safe levels.â€
The fish study provides more damning evidence that chlorpyrifos must be banned altogether. Environmental and health groups are pressuring EPA to do the right thing. Chlorpyrifos is currently in the regulatory limbo of registration review, but should the next steps be issued as promised, the HHRA and PID will provide an opportunity for the public and environmental advocates to convey the urgency of eliminating chlorpyrifos to EPA and the current administration. In the meantime, support organic agriculture at every opportunity.
You can continue to stay apprised of the most pressing developments on various issues and campaigns by signing up for Weekly News Update and Action of the Week—including a call to tell your governor to adopt policies that support organic land management and ecological balance.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Sources:
Chronic low-dose exposure to chlorpyrifos reduces life span in a wild fish by accelerating aging
Huang et al.
Science, January 15, 2026
https://www.science.org/doi/10.1126/science.ady4727
Long-term exposure to a common pesticide speeds up aging in fish, study finds
Shannon Kelleher
The New Lede, January 15, 2026
https://www.thenewlede.org/2026/01/long-term-exposure-to-a-common-pesticide-speeds-up-aging-in-fish-study-finds/
Celebrated 2021 Ag Ban of Deadly Pesticide, Chlorpyrifos, Reversed by Court Despite Decades of Review and Litigation
Beyond Pesticides, November 14, 2023
https://beyondpesticides.org/dailynewsblog/2023/11/2021-ag-ban-of-deadly-pesticide-chlorpyrifos-reversed-by-court-despite-decades-of-review-and-litigation/
Commentary: Are Children, Agricultural Workers, and the Food Supply Safe with EPA’s Chlorpyrifos Decision?
Beyond Pesticides, August 19, 2021
https://beyondpesticides.org/dailynewsblog/2021/08/commentary-are-children-agricultural-workers-and-the-food-supply-safe-with-the-chlorpyrifos-decision/
Long-term pesticide exposure accelerates aging and shortens lifespan in fish
Deanna Csomo Ferrell
Notre Dame News, January 15, 2026
https://news.nd.edu/news/long-term-pesticide-exposure-accelerates-aging-and-shortens-lifespan-in-fish/
Fish and Other Aquatics
https://www.beyondpesticides.org/programs/wildlife/fish
