Mercury is notorious for its bioaccumulation in the organisms and biomagnification along the food web. However, research on the effects of mercury to phytoplankton, at the bottom of aquatic food chain, is inadequate. Therefore, the present study investigated toxicity, detoxification, toxicity prediction and pre-exposure effects of inorganic mercury and methylmercury in marine phytoplankton. We found that: (1) MeHg had no influence on the electron transport chain, but it inhibited population growth by reducing the rate of algal cells division. In contrast, Hg(II) could inhibit the electron transport chain, reduce the cell viability and then population growth. (2) Phytoplankton could synthesize phytochelatins (PCs) to cope with mercury stress. Both synthesis and degradation/export...[ Read more ]

Mercury is notorious for its bioaccumulation in the organisms and biomagnification along the food web. However, research on the effects of mercury to phytoplankton, at the bottom of aquatic food chain, is inadequate. Therefore, the present study investigated toxicity, detoxification, toxicity prediction and pre-exposure effects of inorganic mercury and methylmercury in marine phytoplankton. We found that: (1) MeHg had no influence on the electron transport chain, but it inhibited population growth by reducing the rate of algal cells division. In contrast, Hg(II) could inhibit the electron transport chain, reduce the cell viability and then population growth. (2) Phytoplankton could synthesize phytochelatins (PCs) to cope with mercury stress. Both synthesis and degradation/export of PCs showed rapid response to mercury exposure. And the ability of MeHg to induce PCs was much lower than that of Hg(II). (3) Both subcellular fraction and speciation of mercury could explain and predict the interspecies differences in mercury sensitivity. For MeHg, the species-related sensitivity could be interpreted by organelles, metal-rich granule (MRG), or metal sensitive fraction (MSF) based MeHg. While For Hg(II), heat-stable protein (HSP) or biologically detoxified metal (BDM) may be the best predictor of the growth inhibition. And the Hg(II) tolerance also increased with the ability of phytoplankton to biotransform Hg(II) to PCs-Hg complex and metacinnabar (β-HgS). (4) A unchanged tolerance to Hg(II) while an enhanced tolerance to MeHg were observed in the multi-generation exposed algal cells, which may be resulted from the changes in cellular mercury accumulation and their detoxification ability. Overall, our studies demonstrated the toxicity and detoxification mechanisms of Hg(II) and MeHg in marine phytoplankton, which are significant in understanding the changes in mercury trophic transfer and community composition.