Microbial Insights

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.