Chemical speciation and bioavailability of copper in the Huron River ecosyste

The Huron River provides water for drinking, agriculture, and industrial infrastructure for approximately 445,000 inhabitants of southeastern Michigan. The river receives heavy loadings of trace metals, including copper. Although copper is an essential element for all living forms, at high concentrations it does become toxic. Given the importance of the Huron River and the impact that industries have on its water quality, there is a major need for conducting a thorough assessment of the processes in which copper is involved in this system An important objective of this study was to examine the copper chemical speciation and bioavailability in the Huron River ecosystem with a view to assessing the effects of copper complexation on its toxicity.;Dissolved and particulate copper levels were determined in Huron River waters in the spring and the fall. The concentrations found were above known toxic thresholds for sensitive organisms in lotic environments. In general, surface runoff seems to be a major factor in determining the copper distribution along the Huron River.;The complexation of copper was determined by anodic stripping voltammetry. Two types of voltammograms were obtained, which were attributed to the differences in organic material excreted by phytoplankton after a season of high biological productivity. The average fraction of complexed-to-total copper was estimated to be 99.0 +/- 0.8% in Huron River and Ford Lake samples. These results suggest that the strong complexation in the Huron River ecosystem can reduce the risk of copper toxicity to aquatic organisms. However, when 1 mug/L of copper was added to the samples, adverse effects were observed in the phytoplankton, suggesting some buffering of the labile copper at the critical safe dose.;The results from this study were used to evaluate the effects of the four major factors that determine the speciation of copper in the Huron River, namely, industrial inputs of organic pollutants, seasonal variations in the flow rate, excretion of complexing ligands by the phytoplankton, and photochemistry.