Performances of three bacterial assays in toxicity assessment

Three differing bacterial toxicity assays were compared: the Microtox test, (Photobacterium phosphoreum luminescence inhibition assay), the oxygen consumption of activated sludge assay (ISO 8192), and the Glucose U-¹⁴C mineralization assay (the rate of release of ¹⁴CO₂ by Escherichia coli ). Metals, amines, halogenated alcans, chlorophenols, aromatic hydrocarbons, surfactants, and pesticides were screened for their toxic activity.Results showed satisfactory repeatability of the three bacterial assays with variation coefficients between 5 and 32%. The Microtox assay was the most sensitive test evaluated under our conditions. The lower sensitivity of the oxygen consumption assay may have been due to high concentrations of substrates which modify toxicant bioavailability, and also to a high biomass/toxic substances ratio. The Glucose U-¹⁴C mineralization assay was selective, and low in sensitivity; but the specific species used in this test — Escherichia coli — may have been responsible for this selectivity.The Microtox test appears to be well adapted to the detection of aquatic environmental pollution, and to the toxicity screening of complex solid waste effluents and/or leachates. The oxygen consumption assay can be advantageously used to measure the impact of sewage on activated sludge in biological treatment plants. The Glucose U-¹⁴C mineralization assay, which does not require high biomass, can be useful for in situ studies using field microorganisms.