USE OF A H-3 LABELED SUBSTRATE TO MEASURE MICROBIAL BIODEGRADATION IN MARINE WATERS

A method is described in which a high specific activity (SA) H-3-labeled substrate was used to measure microbial biodegradation of p-cresol in coastal marine waters. [2,6-H-3]p-cresol with a SA of 11 Ci mmol(-1) was added to marine waters collected off Southern California. After short incubations of 12 h, subsamples were filtered to collect bacterial cells, respired (H2O)-H-3 and H-3-labeled biodegradation intermediates were collected, and residual [2,6-H-3]p-cresol was isolated using C-18 solid phase extraction columns. Activity in each of these fractions was used to calculate biodegradation kinetics. Filter effects, substrate adsorption, and extraction efficiency were determined with formalin treated abiotic controls. The method has broad applicability and since H-3-labeled substrates are commercially available with about three orders of magnitude greater SA than for C-14-labeled compounds, the method can detect biodegradation rates at extremely low levels of target organics. Also, the method allows for use of smaller sample volumes and, as a result, smaller amounts of radioactive waste are produced. In environments where contamination is present and its concentration can be determined, isotopic dilution can be calculated and radioactivity can be related to total contaminant concentration. The method has broad applicability for assessing the kinetics of p-cresol (and other H-3-labeled phenols) biodegradation in areas of contamination.