Hemocyte responses of the thick shell mussel Mytilus coruscus exposed to nano-TiO2 and seawater acidification

Abstract

With increasing production from nanotechnology industries, nanomaterials are inevitably released into the aquatic environment, thereby posing a potential risk to aquatic organisms. Thus, concerns have been raised on the potential ecotoxicological effect of nanoparticle. Furthermore, the ecotoxicological consequences caused by the interaction of nanoparticles with other environmental stresses, such as seawater acidification on marine animals, have not been evaluated. In particular, whether acidification enhances the susceptibility to nanoparticles in bivalves needs to be evaluated. In the present study, we investigated the combined effects of low pH and nanoscale titanium dioxide (nano-TiO2) on some immune parameters of hemocytes in the mussel Mytilus coruscus by flow cytometry under six combinations of two pH values (7.3 and 8.1) and three nano-TiO2 concentrations (0, 2.5, and 10mgL−1) for 14 d. Afterward, the mussels were shifted to normal conditions without nano-TiO2 at pH 8.1 for 7 d further to test their recovery from the multiple stresses. Total hemocyte count (THC), phagocytosis (Pha), esterase (Est), and lysosomal content (Lyso) decreased under low pH and high nano-TiO2 concentration conditions, whereas hemocyte mortality (HM) and reactive oxygen species (ROS) increased with nano-TiO2 concentrations under low pH conditions. The interactive effects between pH and nano-TiO2 were observed at the latter part of the exposure experiment (7 and 14 d) in most hemocyte parameters. Nano-TiO2 influenced the immune functions of mussel more severely than low pH. Slight recovery from the combined stresses was observed for HM, THC, Pha, and Lyso, but significant carry-over effects of nano-TiO2 and low pH were still observed. This study demonstrated that both low pH and high concentration of nano-TiO2 had negative effects on mussels, and these effects still acted for some time even though the mussels were already out of such stressors.