Uptake, depuration, and behavioural effects of oxazepam on activity and foraging in a tropical snail (Melanoides tuberculata)

Pharmaceuticals are increasingly being detected in surface waters around the globe, giving rise to concerns that they may alter the physiology and behaviour of aquatic organisms exposed in the wild. Invertebrates represent important components of many ecosystems and bear a high potential for transmitting pharmaceutical contaminants to higher trophic levels. Here, we present a laboratory study in which we exposed a freshwater tropical snail, Melanoides tuberculata, to a serial dilution of the benzodiazepine oxazepam ranging from 50 ng/L to 5 mg/L. We tested for subsequent behavioural effects, including locomotor activity and foraging propensity, at two diurnal time points (day and night), and across three days. We found that the snails displayed a high level of behavioural tolerance to all treatments of oxazepam except at the highest exposure, where locomotor and foraging activity declined. We also detected a weak non-monotonic response curve suggestive of behavioural disinhibition at moderate exposure levels. Regardless of treatment, the snails were also less active after three days of exposure and more active during nighttime observations. We measured the uptake of oxazepam in tissues across treatments, showing that it bioconcentrated at up to 29 times the water exposure level (BCF range: 7 - 29). Finally, we characterized the uptake/depuration pharmacokinetics of oxazepam in snail tissues across time, which revealed that the snails reach a steady state equilibrium in < 8 hours of exposure and depurate at a similar rate. Overall, our study suggests that snails such as M. tuberculata, due to their behavioural resilience and high bioconcentration potential, could act as vectors for pharmaceutical transfer throughout the food web in pharmaceutical-polluted habitats (e.g., wastewater outfalls).