Confirming Biodegradation with Stable Isotope Probing
Stable Isotope Probing (SIP) is an innovative method to track the environmental fate of a 13C-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 carbon dioxide (CO2) or dissolved inorganic carbon (DIC).
How Does SIP Work?
A Bio-Trap® is “baited” with a specially synthesized form of the contaminant containing “heavy” carbon (13C) as the label. Since 13C is rare, carbon originating from the labeled contaminant is readily distinguished from carbon (predominantly 12C) from other sources. The Bio-Trap® is deployed in a monitoring well, and the 13C-labeled contaminant is subject to the same physical, chemical, and microbiological processes as the site contaminants. Following in-well deployment, which is typically 30-45 days, the Bio-Trap® is recovered and two methods are used to document in situ biodegradation of the contaminant into biomass:
- Phospholipid Fatty Acids (PLFA)—PLFA are a major component in the membranes of all microbes, so incorporation of the 13C-label into PLFA unequivocally shows incorporation of the contaminant into biomass.
- Dissolved Inorganic Carbon (DIC)—Enrichment of 13C-labeled DIC (CO2 and carbonates) demonstrates contaminant mineralization.
What compounds can be used in a SIP Study?
SIP studies can be performed for any compound that microorganisms use carbon and energy sources. Although remediation sites may have a mixture of contaminants present, when planning a SIP project, it is recommended to choose the contaminant of greatest concern for the study. Commonly used compounds include:
SIP Applications in the Lifecycle of a Remediation Site
There are many points during a remediation project where a SIP study can provide actionable data to increase confidence in site management decisions and help gain stakeholder acceptance.
Remedy selection: SIP can be incorporated into a pilot study or in situ microcosm study to determine which remedial amendment(s) that effectively enhance biodegradation.
Site Monitoring: Once a remedy is applied on a large scale, a SIP study can provide a line of evidence demonstrating the treatment’s efficacy.
Transitioning to Monitored Natural Attenuation: A SIP study can be used as a third line of evidence to support monitored natural attenuation where incorporation of the 13C label into biomass and DIC conclusively demonstrates that contaminant biodegradation is occurring in situ.
Closure: If stakeholders require proof of monitored natural attenuation for site closure, SIP can yield evidence of biodegradation under the current site conditions.
Is SIP Right for My Site?
SIP can provide conclusive evidence of biodegradation of benzene and other petroleum hydrocarbons, fuel oxygenates, and even some emerging contaminants. Contact Microbial Insights’ project success team at 865-573-8188 or [email protected] to learn more about the benefits of a SIP study and receive guidance tailored to your project goals.
