LAUSR

Amphetamine (AMP) is a chiral psychoactive substance which exhibits enantioselectivity in its pharmacological properties. AMP has been detected in wastewaters and surface waters and can occur as enantiomeric mixtures, but little is known about its environmental risk and potential enantioselective toxicity to aquatic organisms. This study aimed to target enantioselectivity in AMP toxicity on the freshwater invertebrate Daphnia magna. Daphnids were sub-chronically exposed to the racemate (rac-AMP: 0.1, 1.0, and 10 µg/L) and pure enantiomers, (R)-AMP and (S)-AMP (0.1, and 1.0 µg/L), for 8 days. Morphophysiological, swimming behaviour, reproductive and biochemical variables were evaluated during critical life-stages (juveniles vs adults). Some responses were context-dependent and often enantioselective varying between racemate and enantiomers and across the life stage of the organisms. Overall, rac-AMP stimulated D. magna growth, decreased heart rate and area, affected behaviour, and stimulated reproduction. The effect of enantiomers was totally or partially concordant to rac-AMP, except for swimming behaviour and reproduction. Enantioselectivity was observed for body size and number of eggs per daphnia, and heart rate (steeper decrease caused by (R)-AMP at day 3). Changes in biochemical parameters were also observed: AMP caused a significant decrease in catalase activity as racemate or pure enantiomers, whereas a decrease in acetylcholinesterase activity was found only for rac-AMP. Evidence on oxidative stress was contradictory, although both enantiomers caused a significant decrease in reactive oxygen species (unlike rac-AMP). Overall, these results show that AMP can interfere in an enantioselective way with aquatic organisms at low concentrations (e.g., 0.1 µg/L), demonstrating the relevance of this kind of studies for an accurate environmental risk assessment regarding medium- to long-term exposure to this psychoactive drug.