Metallothionein-like proteins turnover, Cd and Zn biokinetics in the dietary Cd-exposed scallop Chlamys nobilis

In this study, we tested whether metallothionein-like proteins (MTLPs) affected the biokinetics of Cd and Zn in the scallops Chlamys nobilis following dietary Cd exposure. The scallops were fed Cd-contaminated diatoms for 8 or 40 days, and then the tissue Cd concentrations, MTLP turnover and their standing stocks, Cd and Zn kinetics were monitored. After 8 days of dietary Cd exposure (at 98 or 196 μg Cd g−1), their Cd levels were increased by 7.4-12.5 times, newly synthesized MLTPs by 1.7-2.1 times, and their MLTP stocks doubled. However, after 40 days of dietary Cd exposure (at 58 or 115 μg Cd g−1), MTLP synthesis and MTLP stocks did not change despite the fact that Cd bioaccumulation increased by 2.7-4.2 times. MTLPs played little role in the overall Cd and Zn uptake from either food or water, since enhanced MTLP induction did not improve the sequestration of newly incoming Cd or Zn. As MTLP-metal complexes degraded, the released Cd was immediately sequestered by newly synthesized MTLPs while most Zn was depurated. This may explain why scallops eliminated Cd more slowly than Zn. Induced proteins were shown to play a minor role in the detoxification of dietary Cd in C. nobilis, but the species can modify its Cd assimilation to reduce the impact of high dietary Cd levels. MTLPs are probably unsuitable as biomarkers for environmental monitoring involving C. nobilis.