Comparison of three microbial assay procedures for measuring toxicity of chemical compounds: ToxAlert®10, CellSense and Biolog MT2 microplates Original Research Article

Methods for measuring toxicity or respiratory activity of microbial cultures can be used as tools for assessing the impact of chemicals or waste streams on biological wastewater treatment plants. Easy-to-use and highly standardised toxicity tests are gaining wide acceptance due to their capability to make an assessment of the overall composite toxicity of the discharge. In this study we evaluate the relative sensitivity and performance of three microbial assay procedures for measuring toxicity of nine commonly used organic compounds in pharmaceutical processes: ToxAlert® (using Vibrio fischeri), CellSense biosensors (using activated sludge, Pseudomonas putida and V. fischeri sensors) and Biolog MT2 microplates (using industrial activated sludge). Results were statistically compared and characteristics of the three procedures are discussed in terms of their sensitivity, reproducibility, representativity and ease of execution. All tests were found to be easy to perform. ToxAlert® gave the best quantitative results, best reproducibility and repeatability followed by Biolog MT2. The uncertainty in the estimates for CellSense was found to be large, leading to wide confidence intervals. Although ToxAlert® gave the best quantitative results the Biolog MT2 microplates which used industrial activated sludge were found to be more representative of the microflora present in industrial biological treatment plants. The microplate respiration tests are recommended for screening large number of toxicants or wastewater samples. CellSense gave poor reproducibility, however, it is a method with potential since it uses whole cell biosensors which allow different species to be easily and quickly tested.