Multi-element compound specific isotope analysis reveals aerobic biodegradation of 2,3-dichloroaniline at a complex site

Compound specific isotope analysis (CSIA) is an established tool for evaluating in situ transformation of organic contaminants. To date, CSIA has never been applied to understand the in situ fate of 2,3-dichloroaniline (2,3-DCA). Although persistent in the environment, several microorganisms were identified as able to degrade 2,3-DCA, thus making this contaminant a potential candidate for bioremediation. Using a controlled-laboratory experiment, we determined, for the first time, negligible carbon and hydrogen isotope fractionation, and a significant inverse nitrogen isotope effect during aerobic 2,3-DCA biodegradation via dioxygenation using a mixed enrichment culture. The corresponding AKIEN values ranged from 0.9938±0.0003 to 0.9922±0.0004. The ε_(N,bulk) values, ranging from +6.2±0.3 to +7.9±0.4‰ was applied to investigate the potential in situ 2,3-DCA biotransformation at a contaminated site, where the field-obtained carbon and nitrogen isotope signatures suggested aerobic biotransformation by native microorganisms. Under the assumption of the applicability of the Rayleigh model at the field site, the extent of 2,3-DCA transformation was estimated at up to 80 to 90%. This study proposes multi-element CSIA of 2,3-DCA as a novel application to study 2,3-DCA fate in groundwater and surface water.