Studies On The Bioaccumulation Of Heavy Metal In Marine Bivalves And The Influencing Factors

Marine bivalves have been employed extensively as biomonitors of coastal contamination largely because of their high bioaccumulation capacity and faithful responses to ambient bioavailable metal levels. The changes of environmental factors and physiological processes of organism play an important role in controlling the bioavailability of metal to marine bivalves. The bioaccumulation and transport pathway of heavy metal in green mussels Perna viridis were studied under different environmental conditions employed radiotracer techniques. The relative mechanisms of metal transport were also discussed.For the first time we coupled respirometric and radiotracer techniques to simultaneously measure the rates of oxygen and metal uptake in the green mussel under different environmental conditions. Under the progressive hypoxic conditions, the Cd and Se uptake decreased with an increasing degree of oxygen limitation. When the mussels were tested at constant hypoxic and anoxic conditions (0-10kPa) , Cd and Se uptake also decreased with decreasing PO2 Under anoxic conditions, Cd and Se uptake was 3.7 and 7.5 times lower than that under normoxia. There was a significant correlation between the 62 consumption rate and uptake rate of Cd and Se, respectively. With re-immersion of the mussels after aerial exposure, there was an apparent Q2 debt, and metal uptake was closely coupled with the Q2 debt repayment. Similarly, the quantified uptake rates of Cd and Zn were directly correlated with the O2 consumption rate in this experiment Although the O2uptake in mussels was enhanced by exposure to pentachlorophenl, an uncoupler of oxidative phosphorylation, the Cd uptake was significantly decreased due to the depression of ATP production. Both 62 consumption rate and Cd and Zn uptake rates were temperature-dependent and increased with increasing temperature. When the temperature oscillated from 15 to 30 , Zn uptake was further stimulated whereas Cd uptake was reduced as compared to the uptake measured at 30 癈 without oscillation. These experimental results suggested that Cd and Zn uptake was correlated with the energy metabolism, and may even be involved in an active transport, besides the facilitated transport. The mechanism of contrasting Cd and Zn accumulation induced by temperature oscillated sharply need to be further considered.The interaction of selenium (Se) and mercury (Hg) in marine invertebrates has been less well studied. In this study, we examined the influences of different species of Se (selenite, selenate, seleno-L-methionine) on the accumulation of inorganic Hg2 and methylmercury (MeHg) by the green mussels via the pathway of pre-exposure and concurrently exposure. The interaction of Se and Hg in marine invertebrates was further discussed. At the experimental concentrations tested (<500 u.g I/1), selenite and selenate did not significantly affect the accumulation of either mercury species by the green mussels. In contrast, selenomethionine significantly inhibited the uptake of MeHg and enhanced the uptake of Hgy the mussels, but it did not affect the assimilation from the ingested diatoms. We further examined the influence of tissue body burden of Se in the green mussels following pre-exposure to selenite and selenomethionine on the accumulation of Hg2 and MeHg from the dietary and aqueous phases. The results showed that tissue Se concentrations increased with increasing Se pre-exposure period. The accumulation of both mercury species in aqueous phase were significantly inhibited, whereas the dietary assimilation of MeHg were significantly enhanced at low concentration tissue Se. The influences on the aqueous uptake and dietary assimilation of both mercury species werealso variable at high concentration tissue Se. The study thus strongly highlights the specificity of the Se and Hg interaction in marine mussels for element species, concentration and exposure pathway.The study r esults c an provide us well understanding o f influences of heavy m etal contaminants on marine ecosystem and biologic resources, and...