Quantifying the mineralization of contaminants using stable carbon isotope ratios

Current techniques used to monitor in situ degradation of organic contaminants require time intervals of days to months to measure significant changes in concentration. In addition, these methods are unable to monitor mineralization or measure absolute degradation of complex mixed wastes. The ability to continuously and definitively monitor mineralization (conversion to CO₂ and H₂O) would greatly enhance the ability to study the fate of contaminants. The objectives of this study were to show that in environments with appropriate background δ¹³C signatures, simultaneous measurement of CO₂ production and δ¹³C signatures of the produced CO₂ will allow both the quantification and qualification of contaminant mineralization. In laboratory microcosm studies the mineralization of hexadecane was monitored by both traditional ¹⁴C radiorespirometry techniques and by measuring the δ¹³C ratio and total amount of produced CO₂. The total mass of hexadecane mineralized determined by each technique was statistically the same. More importantly, the first order rate constants calculated from the respective mineralization curves were virtually identical. These results indicate that stable carbon isotope ratios are an appropriate means of monitoring aerobic mineralization of contaminants in environments in which differences in δ¹³C ratios exist between contaminant and natural organic matter.