The transfer of metals in marine food chains: A review
重金属在海洋食物链中的传递

There are now increasing interests in the food chain transfer of metal contaminants in different marine food chains. The importance of metal dietary uptake in aquatic animals has been highlighted in many recent studies using both empirical experimental and modeling approaches. The application of bioenergetic-based kinetic model has played an important role in the delineation of the exposure of metal contaminants in the animals. This review summarizes the recent progress in this field, particularly on the measurements of a few important metal physiological parameters (e.g., assimilation efficiency from ingested food sources-AE, efflux rate constant during physiological turnover period) in several representative marine animals, including copepods, bivalves, gastropods and fish. Differences of these metal physiological parameters in different groups of marine animals are discussed. The potential trophic transfer factor (or biomagnification potential) of metals along marine food chains can be predicted based on a simple kinetic equation by incorporating metal AE, metal efflux rate and ingestion activity of the animals. With such approach, it is possible to dissect the complicate metal-food chain interaction in marine ecosystems. The transfer of a few metals (e.g., Cd, Hg, Zn) may be related to the trophic levels in the food chain, whereas for other metals, such trends are less obvious. At each trophic level, the potential biomagnification of metals is influenced either by metal AE only, or by metal efflux only, or by both assimilation and efflux. In the classical marine planktonic food chain (phytoplankton to copepods to fish), copepods can very efficiently remove the metals by their efflux systems, leading to a low metal concentration in the animals. The inter-species difference in metal AE is relatively small and metal AE is controlled by both metal distribution in the phytoplankton cytoplasm and metal gut passage across the copepod's gut. Typically particle reactive metals are less assimilated by the copepods as compared with those less particle reactive metals. In contrast, the metal assimilation efficiency in fish is generally low, resulting in a low trophic transfer factor of metals in the fish. The metal AEs show less variation among different functional groups of fish. Consequently, the potential biodiminution of metals in the planktonic food chain is caused by the efficient efflux in zooplankton and the low assimilation in fish. Metals showing exception to this general trend are the methylmercury and Se. Radiocesium also has the potential of being biomagnified in the marine fish as a result of its very high AE. In the marine benthic food chains, metals are efficiently assimilated and retained in the bivalves, resulting in high trophic transfer. There is a large inter-species difference in metal AEs among different species of bivalves, reflecting the complexity of metal handling strategies in marine bivalves. In the benthic top predators such