Effect of Chelating Agents on the Accumulation of Cadmium by the Barnacle Semihlanus balanoides, and Complexation of Soluble Cd, Zn and Cu

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Abstract
The effect of the presence of the chelating agents humate, alginate [polysaccharide components of the cell walls of brown algae] and EDTA on the accumulation of dissolved Cd from seawater by the barnacle S. balanoides (L.) was investigated. Humate and alginate significantly reduced the accumulation of Cd after 7 days but any reduction in accumulation after 15 and 30 days was not significant. EDTA significantly reduced Cd accumulation throughout 30 day exposure. The amount of Cd accumulated by the barnacles is a function of the level of free Cd2+ ions available in solution. Soluble Cd, Zn and Cu in the barnacles are bound to high (> 30,000) MW proteins and to low MW compounds eluting at or below the lower limit of linear separation of the gel Sephadex G-50 (.apprx. 1500 MW). There was no evidence for the binding of Cd, Zn and Cu to metallothionein-like proteins. The external presence of dissolved Cd complexed with low MW metabolites extracted from barnacles, resulted in no change of Cd accumulation by barnacles, indicating that Cd uptake does not require the external binding of Cd ions with released metabolites before entry into the barnacle.