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Controversial pesticides linked to human neurotoxicity

Europe should slash the acceptable human exposure limits on two neonicotinoids — a class of insecticide previously linked to bee declines — says a key European Union safety agency.

In a report released today, the European Food Safety Agency (EFSA), based in Parma, Italy, says that recent research suggests that acetamiprid and imidacloprid “may affect the developing human nervous system”.

The European Commission — which requested that the EFSA look at a potential link to human health in the first place — now has to decide what action to take on the basis of the agency’s recommendation.

Neonicotinoid chemicals have been a controversial subject this year, after the EFSA in January linked imidacloprid and two other ‘neo-nics’ to declines in bee health. Debate over the chemicals’ role in declines in insect pollinators that had been on-going in the scientific literature jumped into the mainstream (see ‘Europe debates risk to bees’).

That January assessment relating to bee health was of three neonicotinoids deemed a priority: thiamethoxam, clothianidin and imidacloprid. Assessment of the impact on bees of two other compounds — acetamiprid and thiacloprid — is currently on hold while that work continues.

But the EFSA is also looking at the impact of neonicotinoids on humans. These chemicals work as agonists of insect nicotinic acetylcholine receptors, but their effect on mammals has been unclear. The EFSA explicitly cites a paper from last year by a Tokyo-based team as shaping its thinking.

That paper, published in PLoS ONE by Junko Kimura-Kuroda of the Toyko Metropolitan Institute of Medical Science, and colleagues, found that both acetamiprid and imidacloprid triggered similar effects in cultures of rat neurons as are seen with nicotine. The authors point out that as nicotine may disrupt brain development in humans, so neonicotinoids “may adversely affect human health, especially the developing brain”.

After reviewing this and other evidence, the EFSA recommends that various acceptable exposure levels to these two chemicals be substantially lowered. Although it notes that the evidence available “has limitations” and recommending further research, the agency says that all neonicotinoids should now be assessed for their potential developmental neurotoxicity.


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