Developing and optimizing a Saccharomyces cerevisiae-based cytotoxicity bioassay for toxicity assessment of contaminated waters.

Determination of toxicity levels in contaminated waters using bioassay methods is an important issue. Considering the shortcomings of bioassay methods, there is still a need to research new bioassay methods. This study introduces and optimizes a rapid, simple, and inexpensive microplate-based bioassay method for determining the presence of toxic substances (pesticides and heavy metals) in contaminated waters. Rapid cytotoxicity bioassay (RCB) method uses the yeast Saccharomyces cerevisiae and the colorimetric method of resazurin reduction inhibition. The toxic effects of two pesticides (bendiocarb and deltamethrin) and two heavy metals (arsenic and chromium) on Saccharomyces cerevisiae were investigated and an optimized protocol was presented. The Slow Cytotoxicity Bioassay (SCB) test, a standard yeast growth inhibition bioassay, was performed and compared to confirm its efficacy and validity. Pearson correlation coefficients between RCB and SCB data (r = 0.985-0.99, p-value < 0.0001) showed a strong and positive linear correlation. RCB method was 76 times faster than the SCB method. EC50 (the concentration that affects 50 % of the population) values for arsenic(III), bendiocarb, chromium(IV), deltamethrin, and a combination (arsenic + bendiocarb + deltamethrin) were 11.51, 332, 0.808, 139.4, 101.67 mg/L, respectively. As expected, confirmatory experiments using real samples showed 0-54 % cytotoxicity values. In conclusion, this study confirms the use of RCB as a reliable method for assessing the toxicity of contaminated waters alongside other methods.