New insights into car tire rubber particle toxicity: chemical composition and ecotoxicity assessment of leachate on gamete quality of the Mediterranean mussel Mytilus galloprovincialis

Thousands of tire rubber particles (TPs) enter the marine environment every year, contributing to microplastic pollution. The toxicity of TPs can be related to the particles themselves or chemical additives, which can leach into seawater and potentially affect marine organisms. The current study presents new insights into TPs' impact on marine organisms' reproductive processes. The leachates of end-of-life TPs and their adverse effects on gamete quality were evaluated by analysing the chemical compositions of seawater leachates and several gamete physiological parameters, taking the mussel Mytilus galloprovincialis as a model. Chemical analyses revealed the leaching of different metals, among which zinc showed the highest level (∼3 mg/L). Organic compounds such as antioxidants, vulcanising and protective agents were annotated in leachates and correlated with the observed harmful effects on the reproductive process. The exposure of oocytes and spermatozoa to TP leachates negatively affects the gamete quality by increasing the mitochondrial activity in both gamete types and decreasing the motility of spermatozoa, which may impair the reproductive success of mussels. Since reproductive success is a key factor in species survival, this study highlights the urgent need to extend the presented research to other marine organisms.