A trial to compare the effects of pH, buffer concentration, and NaCl, on one fluorescent and two bioluminescent...

Of all the bioassays to determine acute toxicity described in the literature, those that employ bacteria as indicator organisms are usually the most rapid and the most economic, although alone they cannot predict the possible toxic effect of any type of substance. When bioassays are employed to test the toxicity of known substances and of compounds in samples from waste discharges they have to work in very different conditions from those for which they are designed. The effects of three factors, pH, buffer concentration, and NaCl, on the performance of a fluorogenic bioassay based on the beta-glucuronidase activity of Escherichia coli were investigated. The results of this test were compared with those of two known biluminescent bacteria tests. The fluorogenic bioassay has a more restricted optimum pH range, while the influence of buffer concentration was similar for the three tests. E. coli glucuronidase activity was affected at a concentration as low as 128 mg/l of NaCl. Changes in the pH or buffer concentrations or chloride ions, greatly influenced the respectives toxicities of four substances, acridine orange, TEMED, 2-mercaptoethanol, and mercuric chloride.