CO(2)-induced pH reduction increases physiological toxicity of nano-TiO(2) in the mussel Mytilus coruscus

The increasing usage of nanoparticles has caused their considerable release into the aquatic environment. Meanwhile, anthropogenic CO(2) emissions have caused a reduction of seawater pH. However, their combined effects on marine species have not been experimentally evaluated. This study estimated the physiological toxicity of nano-TiO(2) in the mussel Mytilus coruscus under high pCO(2) (2500–2600 μatm). We found that respiration rate (RR), food absorption efficiency (AE), clearance rate (CR), scope for growth (SFG) and O:N ratio were significantly reduced by nano-TiO(2), whereas faecal organic weight rate and ammonia excretion rate (ER) were increased under nano-TiO(2) conditions. High pCO(2) exerted lower effects on CR, RR, ER and O:N ratio than nano-TiO(2). Despite this, significant interactions of CO(2)-induced pH change and nano-TiO(2) were found in RR, ER and O:N ratio. PCA showed close relationships among most test parameters, i.e., RR, CR, AE, SFG and O:N ratio. The normal physiological responses were strongly correlated to a positive SFG with normal pH and no/low nano-TiO(2) conditions. Our results indicate that physiological functions of M. coruscus are more severely impaired by the combination of nano-TiO(2) and high pCO(2).