Do polystyrene microplastics affect juvenile brown trout (Salmo trutta f. fario) and modulate effects of the pesticide methiocarb?

Abstract

Background During the last decade, there has been rising interest of the scientific community and the public in the environmental risk related to the abundance of microplastics in aquatic environments. Besides potential effects of the particles themselves, also their interaction with organic micropollutants is of particular concern. Up to now, however, scientific knowledge in this context is scarce and insufficient for a reliable risk assessment. This is especially true for data on microplastics in freshwater ecosystems.Results Against the background of this shortage, we investigated possible adverse effects of polystyrene particles (10 4 particles/L) and the pesticide methiocarb (1 mg/L) both alone as well as in combination in juvenile brown trout ( Salmo trutta f. fario ) after a 96 h laboratory exposure. PS beads (density 1.05 g/mL) were cryogenically milled and fractionated resulting in irregular shaped particles (<50 µm). Besides body weight of the animals, biomarkers for proteotoxicity (stress protein family Hsp70), oxidative stress (superoxide dismutase, lipid peroxidation) and neurotoxicity (acetylcholinesterase, carboxylesterases) were analysed. As an indicator of overall health histopathological effects were studied in liver and gills of exposed fish. Polystyrene particles alone did not influence any of the investigated biomarkers. In contrast, the exposure to methiocarb led to a significant reduction of the activity of acetylcholinesterase and the two carboxylesterases. Moreover, the tissue integrity of liver and gills was impaired by the pesticide. Body weight, the oxidative stress and the stress protein levels were not influenced by methiocarb. Effects caused by the mixture of polystyrene microplastics and methiocarb were the same as those caused by methiocarb alone.Conclusions Overall, methiocarb led to strong effects in juvenile brown trout. In contrast, polystyrene microplastics in the tested concentration did not negatively affect the health of juvenile brown trout and did not modulate the toxicity of methiocarb in this fish species.