Uptake and depuration of copper and zinc in relation to metal-binding protein in the polychaete Eurythoe complanata

Bioassays were conducted with the polychaete Eurythoe complanata to study the patterns of accumulation and depuration of copper and zinc in relation to the levels of metal-binding proteins during sublethal exposure. Acute toxicity tests indicated 96-hr LC(50) of 1.3 mg Cu+2.1(-1) and 139.6 mg Zn+2.1(-1), from which sublethal levels of 0.2 mg.1(-1) of copper or 10 mg.1(-1) of zinc were established for a 24-day exposure. At those sublethal levels, tissue (carcass) concentrations of copper and zinc in E. complanata reached maximal levels of 29.6 and 319 mu g.g(-1) dry mass, respectively, at the end of the exposure period, whereas unexposed worm levels (carcass) were estimated in 5.6 and 35.9 mu g.g(-1) dry mass of copper and zinc, respectively. After 22 days of depuration, tissue levels were reduced to a minimum of 13.7 and 108 mu g.g(-1) dry mass, respectively. Exposure to a mixture of metals resulted in lower tissue levels of copper and zinc as compared with those found for each individual metal analysis. During uptake and depuration phases, Sephadex G-75 chromatography revealed metallothionein-like proteins of molecular weights between 10 and 20 kDa with a higher affinity for zinc than for copper, as well as heavier metalloproteins (>60 kDa), displaying a higher affinity for copper. These data suggest different biochemical mechanisms underlying the control of zinc and copper metabolism through the activity of low- and high-molecular weight metal binding proteins.