Tyre rubber exposure causes oxidative stress and intracellular damage in the Baltic clam (Macoma balthica).

Car tyres are considered to release a substantial amount of particles to the environment. Due to the high emission volumes and the chemical risks associated with tyre rubber, there is an urgent need to quantify their ecotoxicological effects. The effects of exposure to particles derived from end-of-life tyres were investigated on the Baltic clam (Macoma balthica), which is one of the key invertebrate species living in the soft-bottom sediments of the northern Baltic Sea. Tyre rubber particles (10-188 µm) were added to the aquaria in an environmentally relevant concentration (1.08 g per kg dry sediment), and the clams had either direct or indirect contact to the particles for 5 and 29 days. The effects of exposure were studied by applying a battery of biomarkers and cell ultrastructure examination of clam tissues, and the concentrations of selected polycyclic aromatic hydrocarbons and trace metals originating from tyre rubber were quantified from the exposure water and clam tissues. The exposure did not affect the mortality of the clams but induced multiple sublethal responses, including an elevated glutathione S-transferase activity, a reduction in the activity of superoxide dismutase, and increased oxygen radical absorbance capacity during the prolonged exposure. Macromolecular damage was indicated by elevated cytogenetic damage and ultrastructural changes in mitochondria and lysosomes. The results demonstrate the potential of environmentally relevant concentrations of tyre rubber particles to disturb the health of marine biota and underline their importance as a yet understudied environmental contaminant.