Field‐Scale qPCR Data to Estimate Rate Constants for Toluene Biodegradation in Groundwater

Biodegradation of petroleum hydrocarbons in groundwater occurs naturally and can be enhanced to support contaminated site management and remediation. Molecular biological tools can be used to assess the occurrence of biodegradation and monitor bioremediation efforts; however, the use of specific genes (i.e., biomarkers) to identify the rate constants of contaminant removal has not been explored for monoaromatic hydrocarbons. In this study, an approach was developed to estimate an apparent first‐order rate constant for anaerobic biodegradation of toluene based on toluene concentration and the abundance of the alpha subunit of the benzylsuccinate synthase gene (i.e., bssA ). The utility of the approach was evaluated by comparing the distribution of estimated rate constants to those from a published compilation at benchmark sites. There was good agreement between the distribution of rate constants calculated from the abundance of gene copies from soil cores and the distribution of rate constants at benchmark sites, while rate constants calculated from the abundance of gene copies in groundwater were lower than those from the benchmark sites. Given that groundwater samples are more common and convenient to obtain, it is proposed to use the rate constants estimated from groundwater samples to document whether the microbial community has acclimated for biodegradation of toluene. When practitioners use models to evaluate risk at petroleum release sites, they often assume a “typical” rate constant for biodegradation. If the abundance of the bssA biomarker demonstrates that the microbial community has acclimated, then it is appropriate to select and use a rate constant from benchmark sites to forecast biodegradation and attenuation of toluene at a site being evaluated.