Transfer and efflux of cadmium and silver in marine snails and fish fed pre-exposed mussel prey

Subcellular metal distribution may play an important role in the bioaccumulation and trophic transfer of metals in marine food chains. In the present study, we preexposed the green mussel Perna viridis to Ag and Cd and quantified their trophic transfer efficiencies to two predators (whelks [Thais clavigera] and fish [Terapon jarbua]). For the mussels, more Ag was distributed in the metal-rich granule (MRG) fraction following Ag exposure, and more Cd was distributed in the metallothionein-like protein following Cd exposure. In addition, Cd was mainly bound with the proteins having a molecular size of approximately 20 kDa. After being fed with metal-exposed mussels, the assimilation efficiencies of Ag decreased significantly (from 77 to 29-60\% in whelks and from 9 to 2\% in fish) with an increasing percentage of Ag deposited in the MRG fraction of the prey. In contrast, the assimilation efficiencies of Cd remained comparable (81-85\% in whelks and 6-8\% in fish), because its partitioning in the soluble fraction of different treatments of the prey was similar. The efflux of Ag and Cd in the two predators was comparable after feeding on preexposed mussel prey. Our results imply that the subcellular distribution of metals in prey may affect the dietary assimilation of metals in predators, but such influence is clearly metal-specific. The present study may lead to a better understanding of metal trophic transfer in different marine food chains