Evidences of metabolic alterations and cellular damage in mussels after short pulses of Ti contamination.

Mytilus galloprovincialis mussels were exposed to seawater contaminated with Ti. Initial concentrations were 4.1, 32, and 66 μg L-1 that declined during the first 24 h of the experiments, and after 48 h values were <2 μg L-1. Experiments were run in triplicate, under constant salinity and temperature. Mussels were fed every two days, and water renewed every seven days and Ti concentrations re-stabilized. During the first 28 days of experimental period, mussels were exposed to four short pulses of contamination, followed by few days of low Ti concentration between weekly contamination renewals. Then mussels were exposed to additional 14-day exposure to Ti uncontaminated seawater. Only residual Ti concentrations were measured in mussels' whole soft tissue after the four pulses of Ti contamination, indicating low Ti accumulation by the organisms. Nevertheless, the biomarkers related to mussels' metabolic capacity (electron transport system activity, ETS), oxidative damage (lipid peroxidation, LPO and reduced glutathione content, GSH), and defense mechanisms (antioxidant and biotransformation enzymes) evidenced the impact of Ti during the 28 days of experimental period. The biomarkers that better indicated the recovery of mussels' biochemical performance were the ETS, LPO, GSH, and the antioxidant enzyme glutathione peroxidase (GPx). LPO was the prime indicator among the analyzed biochemical responses. Organisms appear to hold coping mechanisms to lower the damage induced by Ti, and to recover, albeit the 14 days period of exposure to uncontaminated seawater following the four Ti pulses were not enough for full recovery, as evidenced by results on LPO levels and GSH concentrations. Despite the low solubility of Ti in seawater, the toxicity of this element to a model marine organism was demonstrated.