Rapid and cost-effective multiparameter toxicity tests for soil microorganisms

Abstract

Three biochemical parameters, DNA quantification in soil samples and two enzymatic activities, β-galactosidase and dehydrogenase have been assessed as potential end-points for the use in cost-effective toxicity tests on soil microorganisms. The assessment included the development of a classical dose–response 24-h assay and the incorporation of measurements of the effects on microbial activities in soil column leaching studies and multispecies miniaturised terrestrial systems (MTS). Four different chemicals, copper, a new herbicide, thiabendazole and fenthion were studied. A rapid fluorescence DNA quantification technique did not produce adequate responses. The efforts to quantify DNA after extraction and clean-up procedures failed due to the presence of humic acids. From the protocol of the technique one could see that the technical procedure is time-consuming and expensive and, for this reason, not suitable for use as a parameter in rapid and cost-effective tests. However, the enzymatic activities showed their potential as toxicity end-points. Copper produced a concentration/response inhibition of β-galactosidase and dehydrogenase with EC 50 values of 78.39 and 24.77 mg Cu/kg soil, respectively. In the soil column study, these endpoints allowed the measurement of the microbial activities through the column. The effects of the new herbicide on β-galactosidase and dehydrogenase activities were statistically significant for the highest application dose (40 g/ha). Thiabendazole affected the microbial activity when mixed within the soil, but no effects were observed when this fungicide was applied on the soil surface. Fenthion produced effects when applied either in the soil or on the soil surface. These results can be explained by the low mobility of thiabendazole. The results show the capabilities of these biochemical parameters to be included as endpoints in cost-effective bioassays.