Comparison of bacterial toxicity tests based on growth, dehydrogenase activity, and esterase activity of Pseudomonas fluorescens.

Bacterial test systems that are used to assess the environmental risk of chemicals show considerable differences in sensitivity to toxic chemicals. This variation may be caused by differences in sensitivity between species and test parameters of the test systems. In this study, the differences in sensitivity of three test parameters, growth, esterase activity, and dehydrogenase activity, using Pseudomonas fluorescens as the test organism, were studied. The effect of eight substances was tested: pentachlorophenol, 2,4-dichlorophenol, aniline, trichloroethylene, nonylphenolethoxylate, tetrapropylene benzene sulphonate, copper, and nickel. None of the three test parameters was the most sensitive to all substances, although dehydrogenase activity showed a high sensitivity in most cases. The observed differences in sensitivity among the three test parameters were of the same order of magnitude as those previously observed for different strains of bacteria. It was concluded that the choice of test parameter is just as important as the choice of test species to the sensitivity of a test system. The differences in sensitivity between test parameters and between species may account for a great deal of the observed variation between test results obtained with different methods.