Toxicological impacts of microplastics: the effect on the levels of cellular thiols in Mytilus galloprovincialis.

Over the last decade, the biological impact of microplastics (MPs) in marine environments has become a serious global concern. Beyond their biological complexity, it is believed that many lethal and sub-lethal effects related to MPs toxicity are triggered by oxidative stress and subsequently activated pathways. Thus, for marine organisms, having efficient mechanisms to fight the accumulation of oxidizing agents becomes indispensable to counteract the effects of MPs. To date, our knowledge on the physiological effects of MPs and the response of the antioxidant system in benthic species is still limited. The purpose of this study was to investigate the effects of short-term exposure on the levels of two fundamental non-protein antioxidants, Glutathione (GSH) and Ovothiol (OSH), in different tissues of Mytilus galloprovincialis. Our results show that the metabolism of OSH and GSH in mussels is clearly affected by acute MPs exposure, and that the antioxidant response differs based on sex and reproductive stage. Indeed, while in the reproductive season the overall levels of GSH and OSH in different tissues significantly increase with respect to the control condition, the antioxidant response of the organisms, especially males, in the spent stage often exhibits a biphasic U-shaped dose-response effect. This study represents a pivotal investigation on the effects of MPs exposure on the pools of two fundamental cellular antioxidants, with potential eco-diagnostic implications to forecast the stress status after exposure to MPs, and highlights the possibility that the effects of these contaminants may vary over time based on the physiological condition of the animals.