A BACTERIAL BIOASSAY FOR THE ASSESSMENT OF COPPER BIOAVAILABILITY IN FRESH-WATERS

Copper-sensitive bacteria were isolated from a tropical river water sa mple and used to develop a simple, inexpensive bioassay for the determ ination of copper bioavailability in freshwaters. The 48-h bioassay, w hich has an EC50 for inorganic copper of 7.1 mu g/L, involved addition of copper-sensitive bacteria to filtered water samples amended with g rowth-stimulating nutrients and measurement of growth. Matrix-matched control solutions were prepared by adding the metal complexing agent E DTA to a portion of each sample tested. In order to optimize sensitivi ty of the bioassay, a nutrient medium was developed, which stimulated bacterial growth, but did not appreciably alter copper speciation of t he sample. This necessitated omission of many organic compounds common ly incorporated in growth media because of their ability to complex co pper. Performance of the bacterial bioassay was evaluated on freshwate r samples from tropical and temperate river systems. Bacterial 48-h EC 15 values ranged from 5.0 to 25.0 mu g Cu/L. and were much higher than the observed EC15 value of 2.8 mu g/L for inorganic copper in deioniz ed water (no organic matter present). A linear correlation (r = 0.93, p less than or equal to 0.005) was observed between the measured EC15 values and the copper complexation capacities of river water samples d etermined by anodic stripping voltammetry. This confirmed the role of natural organic matter in ameliorating copper toxicity. Results of thi s study provide further evidence that the bioavailability of copper in freshwaters is significantly reduced in the presence of natural organ ic matter. A generic protocol for development of metal-sensitive bacte rial bioassays was developed as part of the work. (C) 1998 by John Wil ey & Sons, Inc. Environ Toxicol Water Qual 13: 263-271, 1998.