Thermal discharge influences the bioaccumulation and bioavailability of metals in oysters: Implications of ocean warming.

Human-induced temperature changes influence coastal regions, both via thermal pollution and ocean warming, which exerts profound effects on the chemistry of metals and the physiology of organisms. However, it remains unknown whether the increased temperature of discharged water or ocean warming, as a result of climate change, lead to an increase of human health risks associated with the consumption of sea foods. In this study, the influence of temperature on metal accumulation by oysters was studied in individuals collected from a coastal area affected by the thermal water discharge of the Houshi Power Plant, China. The bioaccumulation factor (BAF) and oral bioavailability (OBA) of metals in oysters was determined. Elevated temperatures led to an increase in BAF for Cu, Zn, Hg, and Cd (p < 0.05), but no change was observed for As and Pb (p > 0.05). The OBA for Cd, As, and Pb correlated positively to elevated temperatures (p < 0.05). However, for Cu and Zn, OBA was negatively correlated with increasing temperature (p < 0.05). As, Pb, and Cd in the trophically available metal (defined as a sum of heat-stable proteins, heat-denaturable proteins, and organelles) was significantly elevated at the highest temperature seawater site (site A) compared to the lowest seawater site (site B). Thus, the irregular variation of OBA for each metal may be the result of variations in the subcellular distribution of metals and the protein quality influenced by the increased temperature. Moreover, the increased temperature and increased the hazard quotient values of As and Cd (p < 0.05 for As, n = 6, p < 0.05 for Cd, n = 6), which provided an indication of the potential risks of the consumption of oysters or other seafood to future warming under climate change scenarios.

Regulated effects of Prorocentrum donghaiense Lu exudate on nickel bioavailability when cultured with different nitrogen sources.

Exudates by marine phytoplankton and metals coexist in the seawater, but little is known about their interaction. In this study, cultures of Prorocentrum donghaiense Lu were grown in urea and ammonium, and then exposed to different Ni ion levels in order to study the effects of Ni ions on algal growth. The regulatory mechanisms of P. donghaiense Lu for coping with different Ni ion levels was investigating by characterizing dissolved organic carbon (DOC), carbohydrate and protein content released per cell, hydropathy properties (hydrophilic and hydrophobic fractions) and thiol compounds (cysteine-like or glutathione-like). Lower levels of Ni ions (pNi>10.0) significantly promoted the growth of P. donghaiense Lu when incubated in urea; however, the same was not true for P. donghaiense Lu cultivated in ammonium. An increased presence of hydrophobic fractions and thiol compounds (cysteine-like or glutathione-like compounds) induced by low Ni ions (pNi>10.0) in urea cultures suggest that the activation of cellular mechanisms in response to insufficient Ni ion stress enhances Ni bioavailability. Furthermore, the abundance of carbohydrates and proteins released by cells when exposed to higher Ni ions levels (from pNi = 10.0 to pNi = 8.0) both in urea and ammonium cultures suggests that algal cells may utilize exudate to complex Ni cations and reduce their toxicity. Therefore, it can be speculated that phytoplankton can produce large amounts of specific exudate, which may accelerate the metal bioavailability (insufficient levels) and reduce metal toxicity (excess levels) to maintain an equilibrium with metals in the environment.