TiO2 Nanoparticles in the Marine Environment: Enhancing Bioconcentration, While Limiting Biotransformation of Arsenic in the Mussel Perna viridis.

The increasing use of nanoscale TiO2 particles (nTiO2) and their subsequent leakage into aquatic environments poses a threat to the ecosystem. One major concern is that nTiO2 may alter the environmental behaviors of arsenic (As) and disrupt the equilibrium of As accumulation and speciation in organisms. In this study, we investigated the effects of nTiO2 on the bioaccumulation and biotransformation of As(V) in the mussel Perna viridis. Exposure to nTiO2 significantly increased As accumulation in mussels. Our As speciation analysis demonstrated that nTiO2 treatment increased the proportion of inorganic As and reduced that of organic As, displaying inhibitory effects on the methylation and detoxification of inorganic As in mussels. Analysis of enzyme systems related to As metabolism in mussels demonstrated that nTiO2 might limit the methylation of inorganic As by suppressing the GST activity and GSH content. The strong adsorption capacity and weak desorption rate of As by nTiO2, which could result in the disruption of As distribution and decrease of the amount of As involved in biotransformation, might serve as another mechanism to the limition on As methylation in mussels. Moreover, exposure to nTiO2 disturbed the osmotic adjustment system in mussels by reducing arsenobetaine and Na+-K+-ATPase activity, resulting in enhanced toxicity of As after coexposure. The findings indicate, for the first time, that nTiO2 can block the transformation and detoxification of As in mussels, which would increase the risk of As to marine animals and even humans via the food chain, and may disrupt the biogeochemical cycle of As in natural environments.