COMPARISON OF ENZYMATIC BIOASSAYS TO CONVENTIONAL AQUATIC TOXICITY TESTING IN A MINING INFLUENCED STREAM

Acid mine drainage (AMD) leaching from mill tailings into the North Fork of Clear Creek, located near Golden, CO, causes the river to be considered a mining influenced water (MIW). The AMD inflow produces metal toxicity to aquatic organisms in the river, the extent of which must be evaluated in order to determine what will be required to improve the river ecosystem health. Traditional aquatic toxicity tests are conducted by raising organisms such as Ceriodaphnia dubia, Daphnia magna, brown trout, and fathead minnows, and exposing them to potentially toxic water. Such tests can be expensive and time-consuming. Enzymatic bioassays may provide an easier, less costly, and more time-effective toxicity screening procedure for MIW.

This study evaluated three commercially-available enzymatic toxicity assays: MetPLATE^TM, Toxichromotest^®, and Super IQ^® test kits (Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government). The MetPLATE^TM and Toxichromotest^® assays use a modified strain of the Escherichia coli bacteria as the test organism. When the E. coli bacteria are not stressed, they produce the enzyme β-galactosidase, which cleaves a chromogenic substrate. Conversely, when the E. coli bacteria are stressed, they cleave lesser amounts of substrate or no substrate at all. The inhibition of the enzyme can be measured colorometrically with a 96-well spectrophotometer. The Super IQ^® test kit also determines the inhibition of the β-galactosidase enzyme, but uses D. magna and is measured fluorometrically. The various methods were performed on water samples collected in August, 2003; March, 2004; and May, 2004. The results were compared for cost, ease of use, time efficiency, reproducibility, and comparability to traditional metal aquatic toxicity testing. Of the three tests in this study, the MetPLATE^TM assay provided the best reproducibility, comparability to traditional testing, and showed the greatest sensitivity to copper and zinc.