Stable Isotope Probing

The big question – Is biodegradation occurring at the site?

Stable isotope probing (SIP) is an innovative method to track the environmental fate of a “labeled” contaminant of concern to unambiguously demonstrate biodegradation. The label serves as a tracer which can be detected in the end products of biodegradation (new biomass and CO2 or dissolved inorganic carbon).

Two stable carbon isotopes exist in nature – carbon 12 (12C) which accounts for 99% of carbon and carbon 13 (13C) which is considerably less abundant (~1%). With the SIP method, a Bio-Trap sampler is baited with a specially synthesized form of the contaminant containing 13C labeled carbon. Since 13C is rare, the labeled compound can be readily differentiated from the contaminants present at the site.

Following field deployment, the Bio-Trap is recovered and two methods are used to conclusively demonstrate biodegradation of the contaminant of concern.

  • Quantification of 13C enriched phospholipid fatty acids (PLFA) indicates incorporation into microbial biomass.
  • Quantification of 13C enriched dissolved inorganic carbon (DIC) indicates contaminant mineralization.

SIP studies can be performed for any compound that microbes use as a carbon source.  Some of the more common include:

  • Benzene
  • Toluene
  • Xylenes
  • MTBE (methyl tert-butyl ether)
  • TBA (tert-butyl alcohol)

A SIP study can also be incorporated into Bio-Trap In Situ Microcosm studies used to screen remedial alternatives.  For more information, please see Bio-Trap In Situ Microcosms.