EU concerns on potential neonicotinoid pesticide effects on brain development - Printable Version
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EU concerns on potential neonicotinoid pesticide effects on brain development - mtwalsh01 - 12-19-2013
The European Food Safety Authority (EFSA) has proposed that guidance levels for exposure to two members of the neonicotinoid class of pesticide, namely imidacloprid (IMI) and acetamiprid (ACE), be reduced. They have based this proposal on studies that indicate these pesticides may have greater than previously thought effects on developing mammalian brains and nervous systems. These pesticides are used worldwide to protect crops from pest insects and domestic animals from fleas and have become the most prominent class of insecticides in the world. Their popularity has grown as they are perceived as being less harmful to human health and to the environment than older pesticides. However, the European Union (EU) had already introduced a two year moratorium on the use of these pesticides on crops attractive to bees amid growing evidence that their increasingly widespread use was harmful to bees.
The concerns on possible detrimental effects on the developing human nervous systems have arisen from the results of studies on, for example, neonatal rat cerebellar neurons. The neonicotinoids are agonists of nicotinic acetylcholine receptors (nAChRs). They were considered to be have selective binding affinity for insect nAChRs, hence their toxicity to insects. However, a growing body of evidence suggested that they could also have greater than previously thought stimulatory effects on mammalian nAChRs. Studies on neonatal rat cerebellar neurons showed that both ACE and IMI induced significant excitatory Ca2+ influxes at concentrations greater than 1 µM in small neurons in cerebellar cultures expressing mRNA of the α3, α4, and α7 nAChR subunits. These effects were significantly inhibited by nAChR inhibitors. In other studies, young rodents exposed to IMI experienced effects including brain shrinkage, weight loss and reduced movement. Exposure in utero to IMI resulted in decreased sensorimotor performance in neonatal rats while IMI has also been shown to stimulate human α4β2 nAChR subtypes.
The EFSA has acknowledged that the available evidence is limited but maintains that the concerns raised are sufficient to suggest that the current guidelines "may not be protective enough to protect against developmental neurotoxicity and should be reduced". The chemical companies concerned are now being invited to comment on the research findings prior to a possible amendment of the reference values by March 2014. Other experts suggest that the EFSA is precautionary. For example Prof Alan Boobis of Imperial College London has pointed out that “the conclusions of EFSA do not suggest that exposure of humans to these compounds at the levels that occur normally in food or in the environment is a cause for concern."
Kimura-Kuroda, J., Komuta, Y., Hayashi, M. and Kawano, H., 2012. Nicotine-Like Effects of the Neonicotinoid Insecticides Acetamiprid and Imidacloprid on Cerebellar Neurons from Neonatal Rats. PLoS ONE 7(2): e32432. doi:10.1371/journal.pone.0032432.