Limited effects of chronic exposure to field-realistic concentrations of carbamazepine on Deleatidium spp. mayfly nymphs

Pharmaceuticals are a class of emerging organic contaminants found in freshwaters. Potential chronic effects of many legacy drugs (those developed pre-2006) on freshwater biota were not investigated thoroughly before their market release. Carbamazepine, a drug used to treat epilepsy and certain types of neuropathic pain, is a legacy contaminant commonly detected in surface freshwaters worldwide, yet its potential impacts on aquatic invertebrates are largely unknown. Our study investigated the chronic effects (21-d exposure) of environmentally relevant concentrations of carbamazepine (measured values: 0.12, 1.88, 3.31, 4.77, 6.44, 7.96 and 9.81 µg/L), using nymphs of Deleatidium spp. (a native New Zealand mayfly) as model species in a static-renewal laboratory experiment. The experimental design included three controls: negative, solvent, and positive (the neonicotinoid insecticide imidacloprid, measured concentration: 2.05 μg/L). Endpoints measured to assess chronic effects were mayfly nymph survival, moulting propensity, emergence, impairment, immobility, feeding, and swimming. Carbamazepine weakly stimulated mayfly feeding activity, a possible adaptive response to mildly stressful conditions. No other adverse effects were detected. By contrast, toxicity from imidacloprid occurred as expected based on previous related research, with mayfly mortality, impairment and immobility all being significantly higher in imidacloprid treatments. Our findings suggest that carbamazepine may not be toxic to Deleatidium larvae at field-realistic concentrations applied for 21 d and based on the endpoints measured. Due to the high specificity of pharmaceutical drugs to certain molecular targets, the mayfly Deleatidium might be less suitable for evaluating carbamazepine toxicity than some vertebrate models, thus further research on other pollution-sensitive model taxa is warranted.