Developmental effect of parental or direct chronic exposure to environmental concentration of glyphosate on the larvae of rainbow trout, Oncorhynchus mykiss.

The environmental safety profile of glyphosate, the most commonly used herbicide worldwide, is still a subject of debate and little is known about the generational toxicity of this active substance (AS) and the associated commercial formulations called "glyphosate-based herbicides" (GBHs). This study investigated the impact of parental and direct exposure to 1μgL of glyphosate using the AS alone or one of two GBH formulations (i.e. Roundup Innovert® and Viaglif Jardin®) in the early developmental stages of rainbow trout. Three different modes of exposure on the F1 generation were studied: (1) intergenerational (i.e. fish only exposed through their parents); (2) direct (i.e. fish exposed only directly) and (3) multigenerational (i.e. fish both exposed intergenerationally and directly). The impact of chemical treatments on embryo-larval development (survival, biometry and malformations), swimming behaviour, biochemical markers of oxidative stress equilibrium (TBARS and catalase), acetylcholine esterase (AChE) and energy metabolism (citrate synthase, CS; cytochrome-c oxidase, CCO; lactate dehydrogenase, LDH; glucose-6-phosphate dehydrogenase, G6PDH) was explored. Chemical exposure did not affect the survival of F1 embryos or malformation rates. Direct exposure to the AS induced some biometric changes, such as reduction in head size (with a 10% decrease in head length), independently of co-formulants. Intergenerational exposure to the AS or the Roundup GBH increased swimming activity of the larvae, with increase of between 78 and 102% in travel speeds. Viaglif co-formulants appear to have counteracted this behavioural change. The minor changes detected in the assayed biochemical markers suggested that observed effects were not due to oxidative damage, AChE inhibition or alterations to energy metabolism. Nonetheless, multi- and intergenerational exposure to Roundup increased CS:CCO and LDH:CS ratios by 46% and 9%, respectively, with a potential modification of the aerobic-to-anaerobic energy production balance. These biochemical effects were not correlated with those observed on individual level of biological organization. Therefore, further studies on generational toxicity of glyphosate and its co-formulants are needed to identify the other mechanisms of glyphosate toxicity at the cellular level.