Assessing the aerobic biodegradability of 14 hydrocarbons in two soils using a simple microcosm/respiration method

The aerobic biodegradability of 14 hydrocarbons in two soils was determined using a simple microcosm/respirometric method based on oxygen consumption. Biodegradability was assessed indirectly by measuring the depletion of oxygen over time in the headspace of microcosms containing soil and test chemicals. The microcosms consisted of small glass vials fitted with valves that allowed headspace gas samples to be collected, essentially resulting in a sealed system. Respiration data from control microcosms were obtained from identically treated microcosms with no test chemical. Control data were necessarily included in all calculations of percent of theoretical oxygen demand (%ThOD) for any given test chemical. Two experiments were performed to verify this simple biodegradation test method. First, an experiment was performed in which disappearance of n-tetradecane from the microcosms was measured directly by standard soil extraction and analytical techniques while simultaneously performing this simple respirometric method based on %ThOD with the same test chemical. Second, the method was compared to a well-established radiochemical technique using 14C-phenanthrene. Results of both comparisons showed that the method is both accurate and reliable. The consistent manner with which the data were produced in two different soils show that the method is also very reproducible. The method described here provides a simple and inexpensive method for determining the aerobic biodegradability of organic compounds in soils.