The physiological responses to titanium dioxide nanoparticles exposure in pearl oysters (Pinctada fucata martensii).

ABSTRACT

To evaluate the physiological responses to titanium dioxide nanoparticles exposure in pearl oysters (Pinctada fucata martensii), pearl oysters were exposed for 14 days to different levels (0.05, 0.5, and 5 mg/L) of nano-TiO2 suspensions, while a control group did not undergo any nano-TiO2 treatment. And then recovery experiments were performed for 7 days without nano-TiO2 exposure. At days 1, 3, 7, 14, 17, and 21, hepatopancreatic tissue samples were collected and used to examine the activities of protease, amylase, lipase, catalase (CAT), glutathione peroxidase (GPx), superoxide dismutase (SOD), lysozyme (LYS), alkaline phosphatase (AKP), and acid phosphatase (ACP). The microstructure of the nacreous layer in shell was also analyzed by scanning electron microscopy. Results showed that pearl oysters exposed to 5 mg/L of TiO2 nanoparticles had significantly lower protease, amylase, and lipase activities and significantly higher CAT, SOD, GPx, LYS, ACP, and AKP activities than control pearl oysters did even after 7-day recovery (P-values <0.05). Pearl oysters exposed to 0.5 mg/L or 0.05 mg/L of TiO2 nanoparticles had lower protease, amylase, and lipase activities and higher CAT, SOD, GPx, LYS, ACP, and AKP activities than control pearl oysters did during the exposure period. After 7-day recovery, no significant differences in protease, lipase, SOD, GPx, CAT, ACP, AKP, or LYS activities were observed between pearl oysters exposed to 0.05 mg/L of TiO2 nanoparticles and control pearl oysters (P-values >0.05). In the period from day 7 to day 14, indistinct and irregular nacreous layer crystal structure in shell was observed. This study demonstrates that TiO2 nanoparticles exposure influences the levels of digestion, immune function, oxidative stress, and biomineralization in pearl oysters, which can be partially and weakly alleviated by short-term recovery. These findings contribute to understanding the mechanisms of action of TiO2 nanoparticles in bivalves. However, studies should evaluate whether a longer recovery period can restore to their normal levels in the future.