Enantioselective toxicity of 3,4-methylenedioxypyrovalerone in Daphnia magna: Assessment of morphophysiological, behavioural, biochemical and reproductive responses

The enantioselective toxicity of 3,4-methylenedioxypyrovalerone (MDPV) remains unexplored in freshwater organisms. This study investigated the effects of MDPV racemate and its enantiomers in Daphnia magna using two approaches: (i) an 8-day sub-chronic assay focused on early development stages; and (ii) the standard 21-day reproduction assay. The sub-chronic assay tested two environmental concentrations (0.10 and 1.0 μg L^-1), for both racemate or individual enantiomers, and a higher sublethal concentration of 10 μg L^-1 for the racemate. Survival, morphophysiological, behavioural, reproductive, and biochemical responses were evaluated. The reproduction assay tested concentrations from 0.10 to 1.79 μg L^-1, and evaluated survival, body size, and reproductive effects. Sub-chronic exposure to 10 μg L^-1 (R,S)-MDPV decreased survival. MDPV racemate and its enantiomers changed morphophysiological parameters, except for body growth. In juveniles, the heart area increased with 0.10 μg L^-1 of (R)-MDPV whereas the heart size decreased with 0.10 and 1.0 μg L^-1 of (S)-MDPV. Enantioselective effects were observed in swimming behaviour: (S)-MDPV increased speed and (R)-MDPV increased active time. No effects were observed in biochemical (except in reactive oxygen species for (S)-MDPV) and early reproductive parameters. The reproduction assay revealed enhanced growth in all MDPV forms (except at 0.56 μg L^-1). A nonsignificant reduction in survival to the higher concentrations of (R)-MDPV was accompanied by reduced reproductive output (at 1.00 and 1.79 μg L^-1) and intrinsic rate of population increase (at 1.79 μg L^-1). Our findings suggest that, in general, (S)-MDPV triggers more severe sub-chronic effects, whereas (R)-MDPV is associated with harmful effects for longer time exposure.