New study links pesticide exposure to cancer risk

By combining environmental data, a nationwide cancer registry, and biological analyses, researchers from the IRD, the Institut Pasteur, the University of Toulouse, and the National Institute of Neoplastic Diseases (INEN) in Peru have shed new light on the role of pesticide exposure in the development of certain cancers. The results have been published in Nature Health. 

Pesticides are widely present in food, water, and the environment, often in the form of complex mixtures. Until now, it has been difficult to accurately assess their effects on human health, as most studies focus on isolated substances and experimental models that are far removed from real-world exposure conditions. This new study adopts an innovative, integrative approach that accounts for the complexity of real-world exposures experienced by populations. 

Peru is characterized by intensive agriculture in certain regions, a wide variety of climates and ecosystems, and significant social and territorial inequalities. Cancer has become a public health priority there, and levels of pesticide contamination in the population are cause for concern. The data highlight increased exposure to pesticides among certain groups, particularly Indigenous and peasant communities. On average, these populations are simultaneously exposed to 12 different pesticides detected at high concentrations. 

The study relies on modeling that maps the areas of the country most exposed to pesticide-related environmental pollution. Applied across the entire country, this approach incorporates 31 chemicals used in agriculture—none of which are classified as known human carcinogens by the World Health Organization (WHO)—and models how they spread in the environment. “We first modeled the dispersion of pesticides in the environment over a six-year period, from 2014 to 2019, which allowed us to create a high-resolution map and identify areas with the highest risk of exposure,” explains Jorge Honles, PhD in epidemiology at the University of Toulouse. 

By cross-referencing this mapping with geodata from more than 150,000 patients diagnosed between 2007 and 2020, the researchers were able to identify areas where people are both more likely to be exposed to pesticides in the environment and more likely to be affected by certain cancers. In these areas, the risk of developing cancer was, on average, 150% higher. “This is the first time we have been able to link pesticide exposure, on a national scale, to biological changes suggesting an increased risk of cancer,” explains Stéphane Bertani, a researcher in molecular biology at the French National Research Institute for Sustainable Development (IRD), at the PHARMA-DEV laboratory (IRD/University of Toulouse). 

The study shows that certain tumors, although they affect different organs, share common biological vulnerabilities linked to their cellular origin that can be weakened by pesticide exposure. Notably, the liver is a key organ in the metabolism of chemicals and is considered a sentinel site for environmental exposure. Molecular analyses conducted at the Institut Pasteur by the team led by Pascal Pineau show that pesticides disrupt processes that help maintain cell function and cellular identity. These biological changes appear before cancer develops, suggesting early, cumulative, and silent effects. They could make tissues more vulnerable to other risk factors, such as infections, inflammation, or environmental stressors. 

The results challenge conventional toxicological approaches, which are based on the evaluation of isolated substances and the establishment of thresholds considered safe. They highlight the importance of considering pesticide mixtures, environmental exposure, and real-world socio-ecological contexts. The study also suggests that extreme weather events, such as El Niño, can exacerbate exposure by altering pesticide use and their dispersion in the environment. It calls for a reassessment of risk evaluation and prevention policies. 

Beyond Peru, this study is part of a broader discussion on global health and planetary boundaries. It illustrates how environmental changes, unsustainable land management, extreme weather events, and social inequalities can combine to affect population health, particularly the most vulnerable, such as Indigenous and peasant communities in Peru. 

The researchers plan to continue their work to better understand the identified biological mechanisms and strengthen prevention tools to support more equitable and effective public health policies. 

Source: Institut Pasteur 

01.04.2026

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