PRECAUTIONS FOR ROUTINE USE OF INT-REDUCTASE ACTIVITY FOR MEASURING BIOLOGICAL-ACTIVITIES IN SOIL AND SEDIMENTS

To evaluate toxicity of xenobiotics on microflora of soils and sedimen ts, reduction of tetrazolium dye 2-p-iodophenyl-3-p-nitrophenyl-5-phen yltetrazolium chloride (INT) or 2,3,5 triphenyltetrazolium chloride (T TC)] by dehydrogenase activities is commonly used, but many questions are posed about the biological relevance of this test. In th is work, INT was chosen to evaluate the influence of so me experimental factors on reductase activity. INT adsorption to soil, concentration of INT, and sterilization methods were tested on different soils and sediments to determine bioavailability of INT, saturation concentration, and in tensity of chemical reduction. INT adsorption shown dramatic variation s vs type of soil, from 0 to 100%, and was particularly linked with ca tion exchange capacity. Formaldehyde seems to be the best method with irradiation to determine abiotic reduction, particularly with sediment s. However, it must be stressed that the tetrazolium reduction in micr obial systems can be carried out by other enzymatic systems than malat e dehydrogenase. INT is an excellent substrate of membrane hydrogenase s found in numerous anaerobic bacteria. This was observed with experim ents conducted with Rhodobacter capsulatus in our laboratory. (C) 1995 by John Wiley & Sons, Inc.