Metal subcellular partitioning of aquatic organisms reflects the physiological or biochemical changes during metal accumulation process. Different metal partitioning in organisms can manifest the sublethal metal toxicity and metal tolerance due to partitioning of metals to sensitive or detoxification fraction. Metal bioavailability to the next trophic level can also be understood by using the metal partitioning due to different bioavailability of different metal fractions. Thereby, understanding the subcellular metal distribution in the prey provides important information on different aspects of metal bioaccumulation in aquatic organisms....[ Read more ]

Metal subcellular partitioning of aquatic organisms reflects the physiological or biochemical changes during metal accumulation process. Different metal partitioning in organisms can manifest the sublethal metal toxicity and metal tolerance due to partitioning of metals to sensitive or detoxification fraction. Metal bioavailability to the next trophic level can also be understood by using the metal partitioning due to different bioavailability of different metal fractions. Thereby, understanding the subcellular metal distribution in the prey provides important information on different aspects of metal bioaccumulation in aquatic organisms.

This study designed a series of experiments to examine the influences of the changes of internal metal partitioning of trace metals (mainly Ag, Cd and Zn) in the prey on the trophic transfer and toxicity of metals to the predatory gastropods, Thais clavigera and marine fish, Terapon jarbua. Biomagnification of metals in the field environment was also quantified by using stable nitrogen isotopes.

Trace metal assimilation efficiencies (AE) of the predators were found to be dependent on the subcellular metal distribution in the prey. In addition to metals bound to the soluble fraction of the prey, metals in the insoluble and metal rich granules (MRG) fraction were also found to be bioavailable to the predatory gastropods. Generally, with more metals bound to the soluble fraction of the prey, the AEs of metals increased. No significant change was observed in the metal efflux rate constant of the predators after they were fed with prey with different subcellular metal distribution. Our study demonstrated the subcellular metal distribution in the prey influenced the trophic transfer of metals by altering the metals AE but not the efflux rate of the predators.

Apart from the influences on trophic transfer of metals, subcellular metal distribution of prey also affected the dietary toxicity to the predators. Our study demonstrated low toxicity of dietary metals to the predatory gastropod. Metallothionein (MT), a metal binding protein, was found to be the most sensitive biomarkers for dietary Cd exposure. With elevated Cd concentration in the prey, correlation was found between the Cd deposited in the tropically available metal (TAM) fraction of the prey and Cd in the metal sensitive fraction (MSF) of the predatory gastropod. Correlation was also found between the potentially available metal (PAM) of the prey and the Cd-MT isoform induction, indicating that the effects of dietary metals can be predicted by the subcellular metal distribution of the prey, and subcellular metal distribution was a potential biomarker for metal toxicity. Combined Cd and Zn exposure was also performed to examine the protective effect of Zn against Cd toxicity in the predatory gastropod. The results suggested pre-exposure to a metal-enriched diet did not significantly affect the uptake of Cd or Zn from the diet and no protective effect was observed.

This study also investigated the biomagnification of metals along different marine food chains in the field by using the stable isotope techniques. Our results showed that biomagnification of metals were dependent not only on the biodynamics of the organisms but also on the food web structure. Information presented in this study is important to understand the mechanisms of metal trophic transfer and dietary toxicity to the aquatic organisms.