The effect of wastewater on the sensitivity of toxicity and genotoxicity assays for the detection of heavy metals was evaluated. Five microbiological toxicity tests were used to compare the toxicity of cadmium, copper, chromium, mercury, nickel, and zinc, both in deionized water solutions and in wastewater. The toxicity assays employed were: Microtox®, two tests of growth inhibition using Pseudomonas fluorescens, and two spectrophotometric assays of the inhibition of respiration test using baker's yeast and P. fluorescens. Also, the genotoxic effect of the assayed metals was evaluated by using the Ames test, the Escherichia coli WP2 test, and the SOS test. The sensitivity to metals decreases in most of the toxicity and genotoxicity assays; in general, higher sensitivity thresholds (EC20) in wastewater than in water solutions were determined. Each test shows different sensitivities to each metal, which is related to different sensitivities of the organisms used in the assays, as well as to other factors.

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