Magnetic susceptibility provides an inexpensive and valuable estimate of the quantity of magnetite (Fe3O4) present in environmental samples. Magnetite (Fe3O4) is a naturally occurring iron mineral that can mediate abiotic degradation of PCE, TCE, cis-DCE, vinyl chloride, and carbon tetrachloride. For long dilute plumes and sites undergoing monitored natural attenuation (MNA), abiotic degradation can be a substantial or even the primary attenuation process.
MAGNETIC SUSCEPTIBILITY ADVANTAGES:
While no direct chemical test is available, magnetite is the most abundant mineral in natural sediments that exhibits magnetic behavior. Therefore, magnetic susceptibility provides an inexpensive and valuable estimate of the quantity of magnetite in environmental samples.
Magnetite has been shown to be capable of abiotic degradation of PCE, TCE, cis-DCE, vinyl chloride, and carbon tetrachloride.
ZERO VALENT IRON (ZVI)
Magnetic susceptibility has also been used to evaluate the distribution of ZVI materials used for in situ chemical reduction of chlorinated hydrocarbons.
Low, medium, or high magnetic susceptibility? The MI Database can provide percentile rankings of your results versus other sites.
HOW TO USE MAGNETIC SUSCEPTIBILITY:
As part of a multiple lines of evidence approach, use magnetic susceptibility to identify aquifers where it is plausible that chlorinated compounds may be degraded through an abiotic mechanism.
Use magnetic susceptibility to help answer…
- Is magnetite present along the dissolved plume?
- Is abiotic degradation of chlorinated compounds plausible at my site?
- Is abiotic degradation a reasonable explanation for decreasing contaminant concentrations/mass?
- TCE and cis-DCE masses are decreasing so why don’t I see daughter products?
X-Ray Diffraction (XRD)
XRD can provide relative abundances of reactive iron bearing minerals including pyrite and the crystalline form of mackinawite. Both minerals will transform PCE, TCE, and carbon tetrachloride.
While less well studied than the other iron-bearing minerals, various phyllosilicate clays have been shown to be capable of degradation of PCE, TCE, cis-DCE, vinyl chloride, and carbon tetrachloride.
14C TCE Rate Constant
Prof. David Freedman from Clemson University has developed an innovative 14C assay to determine TCE degradation rate constants from environmental samples as part of a recent ESTCP project.
QuantArray®Chlor or CENSUS® qPCR
In addition to abiotic degradation, aerobic cometabolism (co-oxidation) of TCE and other chlorinated solvents can be an important component of MNA. QuantArray®Chlor and CENSUS®qPCR are used to quantify functional genes encoding enzymes such as soluble methane monooxygenase that are capable of cometabolism of TCE.
Compound Specific Isotope Analysis (CSIA)
While contaminant and pathway dependent, aerobic cometabolism and abiotic degradation can result in significant isotopic fractionation and CSIA can be a strong supporting line of evidence in evaluating degradation mechanisms that contribute to MNA.