Do fungicides known as “succinate dehydrogenase inhibitors” (or SDHI) present uncontrollable health and environmental risks? For three years, a heated controversy has opposed a group of researchers from the academic world, who warn about the risks posed by these pesticides, and the health authorities for whom this warning is not sufficiently substantiated. This dispute has prompted an intensification of research on these substances. As evidenced by the work just published in the journal Chemosphere, showing in an animal model the toxicity to brain development of one of the most popular SDHIs, bixafen, marketed by Bayer. This result is all the more striking given that the concentrations tested by the researchers are relatively low and, above all, that the neurotoxic properties of this pesticide were not evaluated by the health authorities before its authorization, there is a little less a decade.
Led by biologist Nadia Soussi-Yanicostas (CNRS), researcher at the NeuroDiderot laboratory (Robert-Debré hospital, Inserm, University of Paris), the authors used an animal model that has become the star of laboratories in recent years: the zebrafish (Danio rerio). They exposed embryos of this small vertebrate to low concentrations of bixafen and analyzed the effects of this treatment on the development of their central nervous system (brain and spinal cord). “The zebrafish are an excellent model for anticipating what can happen in humans, because a large part of the building mechanisms of the nervous system have been well preserved during evolution”, explains Mme Soussi-Yanicostas. The researchers used transgenic embryos with fluorescent neurons to be able to observe in vivo, by microscopy, the effect of the treatment on the development of the brain and spinal cord.
Two exposure doses were tested. “We used a high concentration, which kills about 30% of individuals, and a low concentration, which causes no directly visible effect on the external appearance of the animals”, explains the researcher. Result: at the first exposure dose (0.2 mg / l) as at the second (0.083 mg / l), the researchers observed a reduction in the size of the brain and an abnormal development of the motor neurons, those which make it possible to connect the central nervous system to the muscles. With a more marked effect at higher doses as well as when the exposure time increases. “We then sought to compare these observations with the ability of the fish to move: their movements were analyzed by an automated system which makes it possible to quantify the differences in their ability to move., says Mme Soussi-Yanicostas. The locomotor defects that we have thus measured on animals are consistent with our observations. “ Each experiment, carried out on several specimens, was repeated several times, she says.
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