Population-dependent stress response of bivalve mollusc Unio tumidus to ibuprofen, microplastic and their mixture

Abstract Even though bivalve molluscs are recognized as bioindicators of freshwater quality, their responses to multiple stressors are unpredictable. This study aims to elucidate the inter-population peculiarities of the effect in the sub-chronic environmentally relevant exposure to novel contaminants. The specimens of Unio tumidus from pristine (Pr) and contaminated (Ct) areas were treated with ibuprofen (IBU, 0.8 µg L− 1), microplastic (MP, 1.0 mg L− 1, size 0.1–0.5 mm), or their combination (Mix) for 14 days. Untreated mussels (PrC- and CtC-groups) served as controls. The PrC-group had higher levels of antioxidants Mn-SOD, Cu,Zn-SOD, catalase, and cholinesterase (AChE) as well as lesser levels of oxidative lesions (TBARS and protein carbonyls) in digestive gland than the CtC-group, confirming different quality of life in two populations. However, lysosomal stability was similar in all studied groups. IBU induced antioxidant and AChE responses and lysosomal integrity in the Ct-group, only. MP caused the up-regulation of Mn-SOD and TBARS, and the suppression of Cu,Zn-SOD solely in the Pr-group. Discriminant analyses indicated lesser differences between Pr-groups, demonstrating their resistance across all treatments compared to Ct-groups. Most remarkable response was revealed in the CtIBU-group, and the alleviation of individual effects was established in combined exposures. The qualification of stress-neutral and stress-positive populations were proposed for Pr- and Ct-populations correspondingly. Inter-population peculiarities must be taken into consideration when environmental impact of MP and pharmaceuticals is evaluated.