Measuring bioavailable copper using anodic stripping voltammetry

Since speciation can affect bioavailability and toxicity of copper in aquatic systems, accurate predictions of effects of bioavailable forms require detection and/or measurement of these forms. To develop an approach for measurement of bioavailable copper, a copper sulfate solution (CuSO4·3Cu(OH)2·H2O) was used in 10‐d aqueous and sediment toxicity tests with Hyalella azteca Saussure. These tests encompassed ranges of pH (6.5 to 8.1), alkalinity (10 to 70 mg/L as CaCO3), hardness (10 to 70 mg/L as CaCO3), and conductivity (30 to 300 μmho/cm). Changes in copper speciation were measured using atomic absorption spectroscopy (AA) for dissolved copper and differential pulse anodic stripping voltammetry (DPASV) for labile copper, and concentrations were evaluated relative to amphipod survival. Ten‐day LC50s based on AA‐measured aqueous copper concentrations ranged from 42 to 142 μg Cu/L, and LC50s based on DPASV‐measured copper concentrations ranged from 17.4 to 24.8 μg Cu/L. In 10‐d tests using copper‐amended sediments with diverse characteristics and AA‐measured copper concentrations spanning an order of magnitude, total copper concentrations were not predictive of sediment toxicity, but H. azteca survival was explained by DPASV measurements that varied by ≤4%. In order to make defensible estimates of the potential risk of metals in sediments or water, it is essential to identify the fraction of total metal that is bioavailable. In these experiments, DPASV was useful for measuring bioavailable copper in aqueous and sediment tests with H. azteca.