A major scientific advance that could change our understanding of the links between environment and health. A study published in Nature Health establishes, for the first time on the scale of an entire country, a solid association between exposure to pesticides, although considered non-carcinogenic, and increased risk of cancer. What’s called putting one’s foot in the dish?.
An old question, finally revisited differently
Pesticides are everywhere: in food, water, soil. However, despite decades of research, their exact role in the development of cancer remained difficult to demonstrate under real exposure conditions. At issue: limited evaluation methods, often focused on isolated substances, tested in the laboratory or on specific populations.
To overcome these limits, a team bringing together researchers from the IRD, the Pasteur Institute, the University of Toulouse and the Instituto Nacional de Enfermedades Neoplásicas (INEN) in Peru chose a radically different and much more revealing approach.
Peru, an open-air laboratory
The scientists carried out their work across Peru, a country particularly relevant for this type of study. Intensive agriculture in certain regions, great climatic diversity, strong social disparities: all factors which influence exposure to pesticides.
“The country is marked by intensive agriculture in certain regions, a great diversity of climates and ecosystems, as well as strong social and territorial inequalities”underline the authors.
In this context, certain populations, particularly rural and indigenous people, are simultaneously exposed to multiple chemical substances, sometimes up to a dozen different pesticides.
A methodology that changes everything
The originality of this study is based on an approach called “environmental exposure mapping” at very high resolution.
The researchers actually modeled the dispersion of 31 pesticides used in agriculture, over a period of six years (2014-2019), taking into account real conditions: agricultural use, climate, environment. Highlight: none of these substances is classified as a proven carcinogen by the World Health Organization (WHO).
These data were then cross-referenced with national cancer registers, covering more than 150,000 patients diagnosed between 2007 and 2020. Result: precise mapping of areas where environmental exposure and cancers coincide.
Where there are pesticides, there are more cancers
The study highlights a clear association between exposure to pesticides and the occurrence of cancer.
In the most exposed areas, the risk of developing cancer is on average 150% higher.
“This is the first time that we can link, on a national scale, exposure to pesticides and biological disturbances suggesting an increased risk of cancer,” underlines Stéphane Bertani, research director at IRD.
Another striking element: cancers affecting different organs seem to share common vulnerability mechanisms, linked to their cellular origin.
But beyond the statistics, the study also provides unprecedented biological insight. Analyzes carried out in particular by teams from the Pasteur Institute show that pesticides do not necessarily act as direct carcinogens. Rather, they insidiously disrupt the functioning of cells:
- Modification of gene expression;
- Alteration of cellular identity;
- Disruption of biological mechanisms.
These effects appear well before the development of cancer.
In short, they weaken tissues, making them more susceptible to other factors such as infections, inflammations or other environmental exposures.
Pesticide cocktails are also more dangerous
These results also challenge traditional approaches to the little-studied cocktail effect. Until now, assessments were based on the study of substances taken in isolation, with thresholds considered “safe”.
However, this study shows that:
- Pesticide mixtures can have cumulative effects;
- Chronic exposure at low doses can be decisive;
- The actual environmental context plays a key role.
In other words, substances deemed safe individually could become problematic in combination. Which happens relatively often in agriculture.
Another important lesson: exposure to pesticides could be amplified by extreme climatic events. Phenomena such as El Niño modify the conditions of use and dispersion of chemicals, potentially increasing population exposure levels.
What are the consequences for public health?
Beyond the Peruvian case, this study raises global issues. It highlights the combined impact of agricultural practices, climate change and social inequalities on human health. The most vulnerable populations — particularly rural and disadvantaged — appear to be the most exposed.
Researchers are now calling for a rethinking of prevention policies.
Their objective: to finally integrate the complexity of real exposures into the assessment of health risks. “This study shows the need to review our assessment methods and better take into account global environmental exposures they summarize.
By revealing a strong link between pesticides and cancer in real-life conditions, this study marks an important milestone. And implicitly poses an essential question: are our current models still adapted to effectively protect the health of populations in the face of modern environmental exposures?