Neonicotinoids: effects on human health that are worrying, but uncertain due to lack of large-scale studies

The Duplomb law, adopted on July 8 in Parliament , immediately and conditionally reintroduces acetamiprid, an insecticide from the neonicotinoid family harmful to bees - banned since 2018 in France but authorized in Europe until 2033, a measure demanded by beet and hazelnut producers.

A petition launched by a student to oppose this reintroduction collected a record 1.3 million signatures on the National Assembly website on Monday morning.

What concerns?

In terms of human health, neonicotinoids pose a classic problem concerning pesticides: can these substances, designed to kill insects, also harm us through their mechanisms of action?

The specificity of neonicotinoids is that they target the nervous system. They therefore primarily raise questions about their neurological effects, particularly their potential role in neurodevelopmental disorders in children and adolescents.

But researchers have also looked at other risks: to what extent do neonicotinoids affect our hormones, as endocrine disruptors? Are they associated with a higher risk of cancer?

What do we know?

The current consensus, as expressed in the scientific literature and various health authorities, is largely one of uncertainty, sometimes accompanied by calls for the precautionary principle.

"Major uncertainties" remain regarding the neurodevelopmental effects of acetamiprid, the European Health Agency (EFSA) summarized in March 2024. "New evidence" is needed to "adequately assess the risks and hazards" of acetamiprid, the agency insisted, calling for the time being to significantly lower the thresholds at which this pesticide is considered potentially dangerous.

"Neonicotinoids are pesticides whose effects on humans have been little studied," explains Sylvie Bortoli, a toxicologist at Inserm. "The literature remains quite sparse compared to other flagship pesticides such as DDT or glyphosate."

A body of research has nevertheless existed for several years. It essentially combines "in vitro" work, which describes what happens when a cell is exposed to neonicotinoids in the laboratory, with studies on animals, generally mice. The first type of study (called mechanistic) has notably shown the harmful effects of neonicotinoids on neurons. The second category has highlighted their action in neurological disorders, but also in other pathologies. A study, published in 2022 in the journal Environment International, demonstrated the ability of acetamiprid to cause breast cancer in mice.

While these studies support the idea that neonicotinoids pose potential risks, they do not allow us to definitively conclude that they actually play a role in human pathologies, at least at the level at which these products are used in real life.

Researchers agree on the need for more epidemiological studies. Such studies assess the frequency of certain disorders within a group of people based on their greater or lesser exposure to a given factor, in this case neonicotinoids.

"There is a critical need for large-scale epidemiological studies to clarify the potential health effects of neonicotinoid exposure," summarized a 2022 knowledge review in the journal Environment International.

These studies would provide important insights into whether toxicity, measured in the laboratory or on animals, actually translates into health problems in the population. And, if so, they would allow for a better assessment of the risk according to the type of exposure: among farmers, among people living near farms, among consumers of food treated with neonicotinoids, etc.