A study in Peru has highlighted the association between pesticides and cancer risk by considering the real-world exposure of the population to a mixture of substances. A study in Peru has highlighted the association between pesticides and cancer risk by considering the real-world exposure of the population to a mixture of substances.
There is a strong correlation between exposure to agricultural pesticides present in the environment and the risk of developing cancer. This is revealed by a new scientific study published in Nature Health. Researchers from the Ird, the Institut Pasteur, the University of Toulouse in France, and the National Institute of Neoplastic Diseases (Inen) in Peru have combined environmental data, the Peruvian national cancer registry and biological analyses using an innovative and integrated approach that accounts for the complexity of real-world population exposures to pesticides.
These chemical substances are widely present in food, water and the environment, often in the form of complex mixtures. Until now, however, most studies have focused on isolated substances and experimental models that differ considerably from real exposure conditions, making it difficult to accurately assess their effects on human health.
The study was conducted in Peru, a country characterised 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, and pesticide contamination levels in the population are a cause for concern.
The researchers' approach considered 31 chemical substances used in agriculture, none of which is classified as carcinogenic to humans by the World Health Organization. "We first modelled the dispersal 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 the areas with the highest exposure risk," explains Jorge Honles, a PhD researcher in epidemiology at the University of Toulouse.
By cross-referencing this map with the geographical data of over 150,000 patients diagnosed with a disease between 2007 and 2020, the researchers were able to identify areas where people are more likely both to be exposed to environmental pesticides and to be affected by certain types of cancer. In these areas, the risk of developing cancer was, on average, 150 per cent higher than in less exposed zones. The data highlight greater pesticide exposure in certain groups, particularly indigenous and farming communities. On average, these populations are simultaneously exposed to 12 different pesticides detected at high concentrations.
"This is the first time we have been able to link, on a national scale, pesticide exposure to biological changes that suggest an increased cancer risk," explains Stéphane Bertani, a molecular biology researcher at the Ird. The study demonstrates, in fact, that certain tumours, despite affecting different organs, share common biological vulnerabilities linked to their cellular origin, which can be weakened by pesticide exposure. In particular, the liver is a key organ in the metabolism of chemical substances and is considered a sentinel site for environmental exposure. Molecular analyses conducted at the Institut Pasteur show that pesticides alter the processes that help maintain cellular function and identity. These biological changes appear before the development of cancer, suggesting early, cumulative and silent effects, and could render tissues more vulnerable to other risk factors, such as infections, inflammation or environmental stress.
The findings call into question conventional toxicological approaches, which are based on the assessment of isolated substances and the definition of thresholds considered safe. They underscore the importance of considering pesticide mixtures, environmental exposure and real socio-ecological contexts. The study also suggests that extreme weather events, such as El Niño, can exacerbate exposure by altering pesticide use and their dispersal in the environment. Climate and environmental change, unsustainable land management and social inequalities can combine to influence the health of the population, particularly the most vulnerable, such as indigenous communities and farmers in Peru. The researchers call for a review of risk assessment and prevention policies within a broader debate on global health and planetary boundaries.