Effects of environmentally relevant concentrations of diclofenac in Mytilus trossulus

The presence of pharmaceuticals in the marine environment is a growing problem of global importance. Al-though awareness of the significance of this issue is increasing, many questions related to the ecotoxicology of pharmaceuticals remain unclear. Diclofenac is one of the drugs most commonly detected in the marine environ-ment and its potential toxicity has been previously highlighted, thus its impact on organisms deserves a special attention. Therefore, in this study, a thorough analysis of the effects of diclofenac on a condition and tissue level of a model representative of marine invertebrates - Mytilus trossulus - was performed. During the 25-day experiment, divided into exposure and depuration phases, bivalves were exposed to two environmentally relevant drug concentrations of 4 and 40 mu g/L. The study showed that mussels absorb diclofenac in their tissues and the highest recorded concentration was 1.692 mu g/g dw on day 8. Moreover, the content of diclofenac metabolites (4-OH and 5-OH diclofenac) was also examined, but they were not detected either in water or in tissues. Al-though exposure to low diclofenac concentrations did not significantly affect the condition index of organisms, changes in numerous histopathological parameters were noted. Performed histological examination provided additional valuable information on the influence of drugs on the functioning of invertebrates. Nevertheless, applicability of histopathological techniques in ecotoxicology of drugs requires additional evaluation in future studies. (C) 2020 Elsevier B.V. All rights reserved.