USING COMMERICALLY AVAILABLE ENZYME BIOASSAYS TO RAPIDLY SCREEN AND MONITOR METAL-CONTAMINATED SITES

Former sites of mining activities, such as tunnels, waste-rock dumps, and tailings piles, often affect the surrounding soil, sediment, water, and biota. The release, through weathering, of toxic metals (Cu, Zn, Cd, etc.) can have a major environmental impact. The degree of the environmental impact depends on both the leachability of the metals and their bioavailability, the former controlled by the soild phases with which the metals are associated and the latter by aqueous chemical speciation.

Indicator organisms, such as Ceriodaphnia dubia, Daphnia Magna, other invertebrates, and fish, have traditionally been used to assess toxicity of chemicals in the aquatic environment. These bioassays are generally time-consuming, expensive, and require culturing of live organisms. Microbioassays are being established as less costly alternatives for screening purposes. Two microbioassays were selected for this particular study. MetPLATE® and Toxichromotest® are two commercially available microbioassays that are based on the selective inhibition of the activity of β-galactosidase enzyme in a mutant Escherichia coli strain. Since the hydrolase enzyme is specific for heavy metals, these assays are described as being sensitive to heavy metal toxicity.

In this study we combine a simple water field leach procedure with the enzyme bioassays to develop a rapid screening tool for asessing the toxicity potential of mine-waste rock piles. These easily releasable metals were determined by ICP-AES analysis. Application of the enzyme bioassays to the leachate provided a measure of the bioavailable fraction. In order to evaluate the enzyme-based methods, they were compared to 48-hour Ceriodaphnia dubia tests in a study of a mining impacted area. Initial results suggest that MetPLATE® provides a sensitive screening tool for determining the environmental impact of mining activities.

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