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COMPARING STABLE CARBON ISOTOPE AND RESPIROMETRIC TECHNIQUES FOR EVALUATING BIODEGRADATION
Citation:
Mills**, M A., J R. Haines*, S Wright*, AND E Kleiner*. COMPARING STABLE CARBON ISOTOPE AND RESPIROMETRIC TECHNIQUES FOR EVALUATING BIODEGRADATION. Presented at 32nd ACS Central Regional Meeting (CMACS 2000), Covington, KY, 05/16-19/2000.
Description:
Biodegradation of petrochemical contaminants such as crude oil and polychlorinated biphenyls has been determined to remove these contaminants from the environment. The biological processes that result in the contaminant degradation have been determined primarily through bench-scale studies. Though some field scale demonstrations of bioremediation technologies have been conducted, few have had the adequate experimental design to fully evaluate the efficacy of these technologies.
One primary limitation to adequate field-scale demonstrations has been the cost associated with monitoring the biodegradation process. Traditionally, monitoring required the quantification of the microbial population and the contaminant concentration, both of which are time-consuming and expensive. This information was used to evaluate the efficacy of the treatments. Neither of these techniques measured the biodegradation directly. A common laboratory process used to directly measure the biodegradation of contaminant is respirometry. A technique by which one measures either the gases produced during biological activity or the gas used during respiration. This procedure commonly used in the laboratory has been successfully applied to evaluating various bioremediation treatments. A limitation to this procedure is the possibility that the gases either produced or used are not directly involved in the biodegradation of the contaminant especially in environmental samples. Ratios of the stable carbon isotope (13C) to the most abundant carbon isotope (12C) can be used to differentiate the source of the respired CO2. Petrochemicals have a distinct 13C/12C ratio compared to present day carbon. The respired gases from the biodegradation of a petrochemical contaminant should reflect the isotopic ratio of the source material.
A series of experiments were designed to verify the gas (CO2) produced during the respiration of organic contaminants reflect that of the source materials. One set of experiments used six petroleum products to demonstrate the degradability of these six products and the differences in their isotopic ratios. The experiments were conducted in respirometers with the CO2 produced removed with alkaline solutions. These solutions were repeatedly exchanged and archived. The archived solutions were later acidified and the CO2 was analyzed. The results indicate that the CO2 directly reflected the isotopic ratios of the source material.
Results indicate that monitoring the gases produced during the biodegradation of organic contaminants may compliment existing methods of monitoring. Additionally, this method of analysis may reduce the need to collect and analyze as many samples for the expensive and time-consuming traditional monitoring methods.