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

A method is described in which a high specific activity (SA) H-3-label ed 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 bacteri al cells, respired (H2O)-H-3 and H-3-labeled biodegradation intermedia tes were collected, and residual [2,6-H-3]p-cresol was isolated using C-18 solid phase extraction columns. Activity in each of these fractio ns was used to calculate biodegradation kinetics. Filter effects, subs trate adsorption, and extraction efficiency were determined with forma lin treated abiotic controls. The method has broad applicability and s ince H-3-labeled substrates are commercially available with about thre e orders of magnitude greater SA than for C-14-labeled compounds, the method can detect biodegradation rates at extremely low levels of targ et 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 c an be determined, isotopic dilution can be calculated and radioactivit y can be related to total contaminant concentration. The method has br oad applicability for assessing the kinetics of p-cresol (and other H- 3-labeled phenols) biodegradation in areas of contamination.