Changes in survival, swimming behavior, and stress biomarker expression in Crassostrea virginica larvae in response to exposure to drugs of abuse.

The continuous discharge and prevalence of psychoactive drugs in surface waters raises concerns about potential risks to ecosystems and public health. However, there is limited information on the ecotoxicity of these compounds in marine environments and aquaculture. In this study, we investigated the physiological and molecular effects of three commonly detected psychoactive drugs - benzoylecgonine, fentanyl, and ketamine - on Crassostrea virginica oyster larvae. For the physiological assessment, three-day-old larvae were exposed to drugs at environmentally relevant concentrations (100 ng/L and 1000 ng/L) in saltwater over two weeks, and survival and swimming behavior were monitored. For the molecular analysis, larvae were exposed to drugs (1000 ng/L) for 12 h, and changes in expression of four biomarker genes (mapk14, hsp70, sod1, and gst) were measured at different time points. After two weeks, survival declined in all treatments and doses, with benzoylecgonine causing the greatest reduction (62-76 % lower than control). Larvae exposed to ketamine showed significantly decreased swimming speeds. Notable shifts in swimming behaviors were also observed: motion changed from predominantly rectilinear (control) to circular (fentanyl) or motionless (benzoylecgonine and ketamine). Larvae exposed to benzoylecgonine showed the highest significant gene overexpression, particularly for sod1 (6.8 fold change after 4 h) and hsp70 (2.4 fold change after 2 h). These findings address a critical gap in our understanding of the toxicity of drugs of abuse in marine ecosystems, an area much less studied than freshwater environments. Overall, our results suggest that residual drug discharges may adversely affect oyster larvae and highlight the need for ecological risk assessments of these emerging contaminants in marine settings.