Acclimation alters glyphosate temperature-dependent toxicity: Implications for risk assessment under climate change

The evaluation of temperature-dependent chemical toxicity (TDCT) is imperative for future risk assessments of pesticides under global climate change scenarios. Few TDCT studies have so far considered the ability of organisms to acclimate to altered temperatures prior to pesticide exposure, although this may change their thermal tolerance range and hence their susceptibility to pesticide stress. The objective of this study was to evaluate the effect of temperature acclimation on the sensitivity of the cladoceran Ceriodaphnia silvestrii to Glyphosate. We used the shift in sensitivity of the organisms to Glyphosate when exposed to short term temperature changes as a proxy for the effect of the developmental acclimation on sensitivity. We observed that acclimation to higher temperatures reduces the sensitivity to Glyphosate when organisms are exposed to this pesticide in lower temperatures. Therefore, acclimation to high temperatures offers some protective effect against Glyphosate toxicity. We argue that pesticide risk assessments based on tests conducted at one standard temperature should be considered with care. Realistic risk assessments considering climate change scenarios should assess the mode of which organisms are exposed to temperature, therefore taking into consideration the potential effect of temperature acclimation on the sensitivity of a species to a toxicant.