Behavioural impacts of ionisable and neutral pharmaceuticals on marbled crayfish (Procambarus virginalis)

Ionisable environmental pollutants, including pharmaceutical residues, can be readily bioavailable, bioaccumulative, and potentially toxic for aquatic biota. Risks to organisms arise from continuous exposure, facilitated ion entry through cell membranes and various modes of action on cell receptors. In the present study, we examined behavioural changes in marbled crayfish Procambarus virginalis exposed to environmentally relevant concentrations (EC) and lowest observed effect concentrations (LOEC) of three selected pharmaceuticals. The anticonvulsant carbamazepine (neutral compound; EC = 11.6; LOEC = 116 µg/L), the anti-inflammatory diclofenac (ionisable weak acid; EC = 31; LOEC = 310 µg/L), and the antihistamine diphenhydramine (ionisable weak base; EC = 1.4; LOEC = 95 µg/L) were selected to investigate pharmaceutical-induced behavioural alterations in crayfish following a 96-hour exposure under laboratory conditions (water pH 7.6 and temperature 22 °C). The results showed that exposure to carbamazepine stimulated locomotor activity in crayfish, while no changes were observed in crayfish exposed to diclofenac or diphenhydramine. Specifically, crayfish exposed to EC of carbamazepine displayed an increased percentage of movement activity, nearly double the distance moved, and a higher walking speed compared to the solvent control. However, the exposure to the LOEC of carbamazepine resulted only in an increase in relative movement activity. This study demonstrates that the modes of action and physicochemical properties of pharmaceuticals may significantly influence how aquatic crustaceans respond to chemical stressors. Alterations in ecologically important behavioural traits may occur even at ECs of pharmaceuticals present in aquatic environments.