After testing the effect of chronic exposure to low doses of glyphosate, pure or mixed with co-formulants, scientists from the Fish Virology, Immunology and Ecotoxicology Unit at the Ploufragan-Plouzané-Niort laboratory from ANSES exposed five-month-old trout for four days to a concentration of 500 µg of glyphosate per liter of water. This concentration is 75 times lower than the median lethal dose (causing the death of half the population) established by the European Food Safety Authority (EFSA) for rainbow trout (38 mg/l). The experiments, carried out both with pure glyphosate and with two herbicide products containing glyphosate, did not induce any major physiological change in trout.
Exposure to glyphosate and then to a virus: a double challenge
Even if the trout do not seem to have undergone significant disturbances, it is possible that the effects of exposure to glyphosate and/or co-formulants represent a metabolic cost for the fish, which might handicap them to face a second environmental stress. After exposure to the chemicals, the researchers tested the trout’s ability to resist viral infection.
No significant difference in mortality was observed between chemically exposed and non-exposed groups, with virus-caused mortality rates ranging from 60% to 67%. The two stress factors combined nevertheless had effects on the activity of certain enzymes linked to energy metabolism. Thus, 96 hours following infection with the virus, the activity of the enzyme G6PDH, involved in the repair of damage due to oxidation, had for example increased by 65% for trout which had been exposed to pure glyphosate. and up to 138% for the group exposed to one of the herbicide products. Another enzyme, acetylcholinesterase, saw its activity increase by 62% following exposure to pure glyphosate and by 79% following exposure to one of the two herbicides, while remaining identical to that of the control group for the group exposed to the other product.
These results confirm the importance of considering environmental factors, such as infectious agents, in assessing the effects of chemicals on animals.
