Metal accumulation kinetics by the estuarine macroalga, Fucus ceranoides

• Accumulation of Cu, Cd and Pb by the estuarine macroalga, Fucus ceranoides, decreases along a salinity gradient.
• Accumulation of Cu and Pb proceeds via a reversible pseudo-first-order reaction.
• In contrast, accumulation of Cd proceeds via an irreversible first-order reaction.
• Differences in reaction mechanisms are attributed to differences in the ability of metals to be internalised.

The kinetics of Cu, Cd and Pb accumulation by the macroalga, Fucus ceranoides, was studied under simulated estuarine conditions. Accumulation of Cu and Pb proceeded via a pseudo-first-order reaction that was reversible, suggesting desorption or efflux of accumulated metal, with forward rate constants on the order of 0.1 h−1. For both metals, reaction reversibility increased and the equilibrium constant decreased with increasing salinity (from 1 to 33.5) and system response times were <10 h throughout. Accumulation of Cd proceeded via a first-order reaction that was irreversible, suggesting little desorption or efflux of metal, with rate constants that decreased with increasing salinity (from 0.023 to 0.015 h−1) and reaction half-lives ranging from approximately 30–50 h. Inorganic equilibrium speciation calculations suggest that interactions of Cu, Cd and Pb principally involve the respective free ions, but that additional ions (e.g. CdCl+) and biotic processes may also be significant.