engleski

Cadmium accumulation and Cd-binding proteins in marine invertebrats - a radiotracer study

Marine invertebrates are known to accumulate high levels of heavy metals in their tissues and yet survive in polluted environments. Their tolerance of high tissue levels of the metal at least partly depends on the ability of these organisms to regulate the heavy metal cation concentration inside the cell and to accumulate excess metal in non-toxic forms. To assess the toxicity of a metal it is, in general, necessary to determine both the transfer of a metal from the medium to the organism and the effects. The objectives of this study were: - to clarify tissue-, species- and concentration-dependent accumulation of cadmium ; - to quantify the response to elevated Cd concentrations using metallothioneins Three concentrations of Cd in seawater (0.05, 2 and 50 &micro ; g Cd L-1) were used to expose the three species of organisms (blue mussel Mytilus edulis, the tunicate Ciona intestinalis and the sea star Asterias rubens) using radioactive Cd-109 as a tracer. Quantitative data were obtained by dissecting, weighing and subsequently measuring radioactivity in organs and tissues. Differences between each exposure and each tissue with regard to the amount of radioactivity and MT content were evaluated. An expected bioaccumulation of cadmium was observed, although with obvious interspecies, as well as inter-tissue, differences in Cd accumulation. The highest Cd accumulation was found in M. edulis, which filters large volumes of seawater for the purpose of respiration and feeding. No concentration-dependent differences in Cd body burden were found for the studied species and tissues. The highest concentration of MT of any organism or tissue was found in the digestive gland of M. edulis. Intestinal MT in sea squirt, C. intestinalis, increased in a dose-dependent fashion with increasing Cd exposure, although with a drop at the highest concentration. The most surprising finding was that even the lowest Cd exposure concentration (0.05 &micro ; ; ; g Cd L-1) caused MT induction in pyloric caeca of A. rubens, but there was no increase in MT at higher exposure levels.

blue mussel (Mytilus edulis); sea star (Asterias rubens); sea squirt (Ciona intestinalis); cadmium; metallothioneins

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