Copper and zinc content of periphyton from two rivers as a function of dissolved metal concentration

Measuring the metal content of periphyton is a means of evaluating the state of metal contamination in the environment with respect to levels of metals and their bioavailability. The aim of this study was to identify relationships between the dissolved metal concentrations and the total or intracellular metal concentrations in the periphyton from two rivers. Metal levels at non-contaminated sites were comparable in both rivers (0.07-0.71 mumol Cu g(-1) dw and 0.22-4.36 mumol Zn g(-1) dw). The metal content of periphyton from three sites of the Birs River was generally reflective of the dissolved Cu and Zn concentrations in the water. In contrast, metal content in periphyton from two sites of the Thur River did not reflect the dissolved metal concentrations in the water, probably due to speciation effects. Nonexchangeable (intracellular) metal determined after washing of periphyton samples with EDTA was variable and unpredictable when considering total metal content only. The different relationships in the two rivers between the metal contents in periphyton and the dissolved concentrations indicate the influence of speciation on adsorption and bioavailability. Results are discussed in respect to the significance of metal content as a tool for evaluating metal bioavailability.