The use of leucine incorporation to determine the toxicity of phenols to bacterial communities extracted from soil

The toxicity of different phenols to the soil bacterial community was studied in the laboratory using the leucine incorporation technique. The effects of environmental factors such as pH, temperature and binding strength to soil particles were also assessed in order to deduce confounding effects due to the chemical and physical conditions in the soil from which the bacterial community was extracted. Bacterial growth varied with temperature and pH, the optima being at around 33 degrees C and pH 7 in a soil with a natural pH of 7. The toxicity of different phenols varied less than bacterial growth as a function of temperature and pH, but the toxicity of 2,3,6-trichlorophenol increased at lower temperatures and pH. The pH affected the toxicity in the same way in soils with naturally different pH values and when the pH was changed using buffers, showing that this was a direct effect of pH and was not due to different communities in different soils. The degree to which the bacteria were bound to soil particles had no effect on the toxicity of phenols. Neither did freezing nor thawing the soil have any effect on toxicity, although the bacterial growth was lower in frozen soil than in non-frozen soil. Increasing numbers of substitutes on the phenols increased their toxicity to soil bacteria, and chlorine substitutes were more toxic than the corresponding methyl substitutes. The toxicity of the phenols studied to the whole soil bacterial community was correlated with literature data on the toxicity to the single species Pseudomonas putida. Applying the leucine incorporation technique to the bacterial community extracted from soil was shown to be a rapid and sensitive method of estimating toxicity. The methodology also allowed differentiation between the effects of environmental factors on toxicity to the soil bacterial community and changes in the tolerance of the community. Thus, the development of pollution-induced community tolerance in phenol- and 2-chlorophenol-polluted soils could be shown. (c) 2007 Elsevier B.V. All rights reserved