A new scientific study,
published in Nature Health, reveals a strong link between exposure to agricultural pesticides present in the environment and the risk of cancer development.
By combining environmental data, national cancer registries, and biological analyses, researchers from the IRD, the Institut Pasteur, the University of Toulouse, and Peru's Instituto Nacional de Enfermedades Neoplásicas (INEN) have highlighted for the first time how exposure to pesticides can contribute to the development of certain cancers.
Pesticides are diffusely present in food, water, and natural environments, often in the form of mixtures. Until now, it has been difficult to precisely assess their effects on human health, as most studies focus on isolated substances and experimental models far removed from real-life exposure conditions. This new study adopts an innovative and integrative approach, capable of accounting for the complexity of exposures as experienced by populations.
Peru, a relevant field of study
The country is characterized by intensive agriculture in certain regions, a great diversity of climates and ecosystems, as well as significant social and territorial inequalities. Cancer has become a public health priority there, and levels of bodily contamination by pesticides are a concern.
The results highlight increased exposure of certain populations, particularly rural and indigenous communities, to pesticides. On average, they are exposed simultaneously to 12 different pesticides detected at high concentrations.
The study is based on modeling that allows mapping the areas of the territory most exposed to environmental pollution linked to pesticides. Applied to the entire country, this approach integrates 31 chemical substances used in agriculture—none of which are classified as proven carcinogens for humans by the World Health Organization (WHO)—and models their dispersion in the environment.
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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 very high-resolution map and identify areas with the highest risk of exposure," explains Jorge Honles, a doctor of epidemiology from the University of Toulouse.
By cross-referencing this map with data from over 150,000 patients diagnosed between 2007 and 2020, researchers were able to identify areas where populations are both more likely to be exposed to pesticides in the environment and more affected by certain cancers. In these territories, the risk of developing cancer was on average 150% higher.
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This is the first time we have been able to link, on a national scale, exposure to pesticides and biological disruptions suggesting an increased risk of cancer," explains Stéphane Bertani, a research director in molecular biology at the Institut de Recherche pour le Développement, within the PHARMA-DEV laboratory (IRD/University of Toulouse).
Early and silent biological effects
The study shows that certain tumors, although affecting different organs, share common biological vulnerabilities related to their cellular origin and can be weakened by exposure to pesticides. It is known, for example, that the liver is a key organ in the transformation of chemical substances and is considered a sentinel of environmental exposure. However, molecular analyses conducted by Pascal Pineau's group at the Institut Pasteur on Peruvian samples show that pesticides disrupt the mechanisms that maintain the identity and normal functioning of cells.
These biological alterations appear before the development of cancer, suggesting early, cumulative, and silent effects. They could make tissues more vulnerable to other factors, such as infections, inflammations, or environmental factors.
The findings challenge classical toxicological approaches, based on the assessment of isolated substances and the establishment of thresholds considered safe. They show the importance of taking into account pesticide mixtures, environmental exposure, and real socio-ecological contexts. The study also suggests that extreme climate events, such as El Niño, can worsen exposure by altering the use and dispersion of pesticides in the environment. It argues for a reassessment of risk assessment methods and prevention policies.
Beyond Peru, this study is part of a broader reflection on global health and planetary boundaries. It illustrates how environmental changes, unsustainable agricultural practices, extreme climate events, and social inequalities can combine to affect population health, particularly that of the most vulnerable, such as the rural and indigenous communities of Peru.
The researchers plan to continue their work to better understand the identified biological mechanisms and strengthen prevention tools, in order to support more just and effective public health policies.