Relating the Speciation of Cd, Cu, and Pb in Two Connecticut Rivers with Their Uptake in Algae

Abstract

Metal complexation characteristics (conditional stability constants and available ligand concentration) were measured with differential pulse anodic stripping voltammetry (DPASV) for the trace metals cadmium, copper, and lead in two Connecticut rivers. These parameters permit calculation of the free ion concentration [M2+ (H2O)n] for each metal. Parallel experiments in waters from the same rivers were conducted to measure metal uptake in a representative freshwater diatom (Stephanodiscus hantzschii) and chlorophyte (Chlorella vulgaris). For copper the results of the uptake experiments are consistent with calculated speciation based on the measured DOM complexation characteristics, supporting the belief that voltammetry can provide valid information about metal bioavailability. Although uptake of lead did not closely follow speciation predictions, an inverse relationship between uptake and the concentration of available ligands in each river existed, similar to that of copper.