Depletion Monitoring with a Selected Biomarker

ESTCP Project #1011, Rhizosphere

Final Report

toxicity of the compounds. The FSH approach was developed based on these properties. Specific

FSH values are obtained similarly to TPH curves but, following extraction from soil and prior to

GC analysis, the petroleum materials are fractionated into aliphatic and aromatic components.

When quantifying the chromatogram for FSH, the ranges used to group compounds have been

chosen based on correlations with potential toxicity. The initial fractionation provides

quantitative measures for specific fractions of the petroleum material. Changes in FSH values

can be compared through time. Because different petroleum fractions have different transport,

bioavailability, and toxicity characteristics, FSH data can be more meaningful than TPH data.

FSH values are obtained using the HRGC/FID technique (see Appendix A). For statistical

analyses of data, TPH, summed PAHs, and aliphatic and aromatic fractions were all normalized

using a recalcitrant biomarker.

Polycyclic Aromatic Hydrocarbons (PAHs) and Diagnostic Heteroatomic Compounds. Using

high-resolution gas chromatography mass spectrometry (HRGC/MS; see Appendix A), mass

spectra can be obtained that show peaks corresponding to the molecular fragments of specific

petroleum compounds. Using this approach, we can determine the amounts of individual

polycyclic aromatic hydrocarbons (PAHs). PAHs are various arrangements of fused, aromatic

ring molecules. We can also identify heteroaromatic compounds, which are rings containing

elements in addition to carbon. This approach can be used to specifically identify PAHs that

have been listed by the US Environmental Protection Agency (EPA) as priority pollutants (see

Table 6 in Appendix A). Inclusion on this list generally indicates that the compound is

carcinogenic.

BTEX. Using appropriate handling, extraction, and analytical methods, we can characterize the

volatile organic compounds (VOCs) benzene, toluene, ethylbenzene, and xylene (BTEX). These

compounds are relatively volatile, are water soluble, and generally have low permissible levels.

In field soils, BTEX compounds are generally the first to leach and to volatilize. Their levels in

aged or weathered contaminated soil may be low. For these sites, BTEX was not considered an

issue.

Depletion Monitoring with a Selected Biomarker. For a site that is contaminated with a

relatively uniform type of contaminant, bioremediation effectiveness can be calculated relative to

a compound that is relatively non-degradable. These recalcitrant or stable compounds are often

referred to as biomarkers. As different fractions of the total suite of petroleum degrade, the

relative concentration of the recalcitrant fraction, or biomarker, increases. The compound α,β-

hopane (hopane) is often chosen as a biomarker because it appears in many petroleum

compounds and it degrades very slowly. Because it is often cited in petroleum literature, α,β-

hopane is a good choice for TPH degradation normalization studies. The HRGC/MS method (see

Appendix A) used for PAHs is used to quantify hopane.

Using this technique, the percent loss of TPH, FSH, and individual target benzene, toluene, ethyl

benzene, and xylene (BTEX) and PAH compounds can be calculated as follows:

Percent depletion of individual target analytes