AbstractA firefly luciferase bioluminescent assay of bacterial adenosine triphosphate (ATP) was used to measure the toxic effects of metal ions on six bacterial genera isolated from two geographically different marsh treatment systems. The toxicity of eleven different metals, as well as metal mixtures, was monitored using the agar plate test and the resazurin reduction test in addition to measurement of intracellular ATP. All the organisms surveyed tended to be sensitive to much lower concentrations of metals when the metals were present in mixtures. Isolates from a marsh system constructed on normal soil exhibited lower metal resistance patterns than organisms isolated from a marsh built on mine tailings. The intracellular ATP assay appeared to be the most sensitive method of determining the viability of bacterial cells following metal treatment.