Mine tailings piles and abandoned mine soils are often contaminated by a suite of toxic metals which were wasted in the mining process. Traditional toxicity testing of such areas has been conducted using Toxicity Characteristic Leachate Procedure (TCLP) or traditional toxicity tests using organisms such as the earthworm Eisenia foetida. The TCLP is essentially a total acid digestion, which measures total metals present rather than metals that are bioavailable, and E. foetida tests take between 48 hours to two weeks, rely on a limited number of organisms per test concentration, and require culturing. Enzymatic bioassays provide an easier, less costly, and more time-effective toxicity screening procedure for Mining Impacted Soils (MIS) such as mine tailings and abandoned mine soil leachates. This study evaluated the commercially available enzymatic toxicity assay, MetPLATE™. The MetPLATE™ assay uses a modified strain of the Escherichia coli bacteria as the test organism. When the E. coli bacteria are not stressed, they produce the enzyme ?-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. Variations in water chemistry parameters affect the bioavailability of metals present in MIS and MIS leachates, an thus their inhibition on MetPLATE™ E. coli, by altering the concentration, competition, and complexation. Increased concentration caused an increase in toxicity. An increase in competitive cations, such as those of hardness (Ca2+, Mg2+, and Na+), caused a decrease in inhibition. Elevated inorganic complexes, such as alkalinity (HCO3-, CO32-), and organic complexes, such as natural organic matter, also provided protective effects to the E. coli in the MetPLATE™ assay. Additionally, the MetPLATE™ assay requires a very short testing period (~2 hours), contains 100,000+ organisms per sample concentration, and eliminates the need for a culture.