Field and in vitro evidence for in-situ bioremediation using compound-specific C-13/C-12 ratio monitoring

This work describes the use of delta(13)C values of residual hydrocarbons a s a method for demonstrating in-situ biodegradation. Microbial growth, hydr ocarbon loss and increase in delta(13)C values were demonstrated in vitro u sing benzene and styrene as carbon substrates. Isotope evidence of biodegra dation were subsequently sought in four field sites contaminated with a wid e variety of hydrocarbons. Analysis of residual hydrocarbons in the field i ndicated that an overall increase in the delta(13)C generally accompanied l oss of hydrocarbons, an observation consistent with in-situ biodegradation. The field samples were analyzed using vapor or soil extracts, and the incre ases in delta(13)C were observed using both types of samples. Vapor samplin g is of practical interest because stable isotope ratio monitoring of soil vapor could dramatically reduce the number of wells required for monitoring of ongoing remediation efforts. Our preliminary studies of contaminated fi eld sites allude to the potential of compound-specific isotopic monitoring techniques as a cost-effective measure of in-situ biodegradation. (C) 1999 Elsevier Science Ltd. All rights reserved.