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Environmental Forensic Analysis Using Enhanced Petroleum Hydrocarbon Testing | TestAmerica Laboratories

Enhanced Petroleum Hydrocarbon Testing

Environmental Forensic Testing

Crude oil and oil products contain a complex mixture of hydrocarbons as well as minor amounts of sulfur, oxygen, nitrogen, nickel and vanadium.  Due to variations in crude oil and refining processes, environmental samples have unique chemical fingerprints that can provide the basis for identifying and distinguishing the sources of released oil or oil products.  The release of hydrocarbons into the environment can require extensive environmental cleanup activities as well as an assessment of the potential damages to terrestrial, aquatic and/or marine natural resources. In certain situations, the spatial and temporal extent of damages may need to be assessed using chemical fingerprinting.

Chemical Fingerprinting

Chemical fingerprinting allows for the comparison of unique diagnostic chemical features of potentially impacted environmental samples.  Data is used to assess potential liability as well as monitor short and long term environmental impacts.  Chemical fingerprinting can include the determination of petroleum hydrocarbons as petrogenic, pyrogenic and/or biogenic based on patterns.

Environmental forensic chemists use data generated from specialized environmental hydrocarbon testing methods such as those for Saturated Hydrocarbons (SHC), Polycyclic Aromatic Hydrocarbons (PAHs) and their alkylated homologs and/or Petroleum Biomarkers.  Saturated hydrocarbons and biomarkers are used together to track source signatures of petroleum in the environment.  Saturated hydrocarbons can identify the petrogenic source (distillates, residual petroleum or coal).  Biomarkers can be used to distinguish petroleum sources.

Saturated Hydrocarbons (SHCs)

SHCs are the simplest and most dominant class of hydrocarbons in crude oil.  They contain only single bonds between carbon atoms and each carbon atom is saturated with hydrogen.  Cycloalkanes are also SHCs since they are single bonded carbon atoms joined in a ring structure.

Pristane and phytane are the dominant saturated hydrocarbon biomarker isoprenoid components of crude oils.  The pristane/phytane (Pr/Ph) ratio is used as an indicator of the oil source. These correlations are based on the concept that the composition of biomarkers in spill samples does not differ from those of the source oils.  The ratio of the pristane to n-alkane C17 (Pr/n-C17) and phytane to n-alkane C18 (Ph/n-C18) are a rough indication of the relative state of biodegradation.  The SHC analysis provides for the distribution of alkanes from C8 to C40, as well as selected isoprenoids [pristane & phytane] & cyclohexanes.

Polycyclic Aromatic Hydrocarbon (PAH) & Alkylated Homologs (aPAH)

PAHs have two or more fused aromatic-ring compounds consisting solely of carbon and hydrogen molecules.  The PAHs most commonly encountered in the environment contain two to seven fused benzene rings.  PAHs in petroleum products range from one- to five-ring combinations.

The unsubstituted aromatic structures are referred to as the parent PAHs.  These PAHs can also have branched or alkyl group substitution on their ring structures that are referred to as Alkylated PAHs. The alkyl groups generally have one to four saturated carbon atoms, and thus can produce many different structural homologs for each aromatic hydrocarbon family. The most abundant aromatic hydrocarbon families have one to four carbon atom alkyl group substitutions denoted by C1-, C2-, C3-, and C4.  Parent PAHs in petroleum products are usually present in low concentration since crude oils contain primarily the alkyl PAHs.   In contrast, parent PAHs in coal tar can be found in high concentrations. Therefore, a full PAH signature including the alkylated homologs is required for an environmental forensic evaluation.

Biomarkers

Biomarkers are complex molecules derived from the formerly living organisms that are the basis of the crude oil.  Biomarkers are unique in that they are weather resistant and show little or no change to the parent organic molecules. Due to the wide range of geologic conditions, these compounds retain most of their organic chemical structure from their original product, and are the source signatures of petroleum.  These compounds provide more information about the oil source than any other compounds.  In comparison to the other components of crude, they are often found in low concentrations. The chemical analysis of these compounds and diagnostic ratios are frequently used for oil release identification by environmental forensic chemists.   

TestAmerica’s Analytical Approach to Enhanced Petroleum Hydrocarbon Testing

Conventional lists of chemical compounds in U.S. EPA methods do not include the important constituents of petroleum and refined petroleum products.  As a result, TestAmerica modifies U.S. EPA SW 846 methodologies to provide the data necessary for chemical fingerprinting for an environmental forensic investigation.  Enhancements include:

  • expanded targeted analyte lists to characterize and differentiate petroleum;
  • sufficient analytical sensitivity to measure the low levels that are needed;
  • selectivity to minimize matrix interference and false positives;
  • applicability to a wide variety of matrices including oil, NAPL, coal tar, MGP oil,  water, soil, sediment, and tissue. 

The International Standard for Oil Spill Identification, 2002 SINTEF Method, recommends a tiered testing and data treatment approach for oil release investigations. The first tier is the SHC testing of samples from the suspected release and also the impacted samples.  If these samples are not a match, these samples can be eliminated from further testing. If there is any doubt, the process should continue through the next tier of testing for biomarkers and PAHs. Data evaluation and statistical analysis are then performed by an environmental forensic chemist to evaluate the oil release.

Tier I – SHC by GC/FID

For the SHC Tier 1, TestAmerica employs a high resolution gas chromatography/ flame ionization detector [GC/FID] based on US EPA SW 846 Method 8015 for the analysis of the total distribution of the hydrocarbons from C8 to C40 as well as selected isoprenoids, pristane and phytane. The method provides for a whole oil gas chromatographic analysis or chemical fingerprint of the sample.

Tier II - SHC, PAHs, aPAHs and Biomarkers by GC/MS

TestAmerica’s analytical approach for PAHs and aPAHs utilizes  a  high  resolution gas  chromatography /mass spectrometer [GC/MS] based on US EPA SW 846 Method 8270 [modified].  This method also provides for a whole oil analysis or chemical fingerprint of the samples. The identification of the calibrated target compounds is based on the detection of a peak at the appropriate retention time, except for the alkylated PAHs.  For the alkylated PAHs, the parent response factor is used for the concentration calculation of the alkylated PAHs. Quantification of the target compounds is based on their response relative to their associated internal standard.  SHC analysis provides quantitative analysis of individual n-alkanes and selected isoprenoids. 

Biomarkers can be detected in low quantities (low to sub ppm range) in the presence of other hydrocarbons using SW 846 Method 8270M SIM. Estimation of concentrations for biomarker compounds is achieved by using the response factor from a representative standard.  TestAmerica uses characterized crude oils, such as Alaskan North Slope, in its assessment of system performance and uses project specific crude oils as analytical comparison oils for the fingerprinting evaluation of field samples, if requested.  The method is also modified to include the PAHs which are not a part of Method 8270 list.  PAHs and their alkylated homologs can be performed simultaneously with the biomarker analysis.

TestAmerica’s Analytical Approach for Paraffins, Isoparaffins, Aromatics, Naphthenes, and Olefins (PIANO)

Gasoline is a complex mixture of hundreds of compounds, including hydrocarbons, oxygen containing ethers, alcohols, sulfur and nitrogen containing moieties.  Since no two refinery’s products are identical, gasoline can be chemically fingerprinted.  Hydrocarbons that are present in gasoline occur in five compound classes: Paraffins, Isoparaffins, Aromatics, Naphthenes, and Olefins, often referred to as PIANO. The PIANO target compound list provides data for chemical fingerprinting for forensic purposes for gasoline releases. Because PIANO methods are designed to distinguish gasoline types, they also include oxygenated additives such as MTBE, TAME, DIPE and ETBE as well as sulfur containing compounds such as thiophene, benzo(b)thiophene, 2 -methylthiophene and 2 -ethylthiophene.

TestAmerica’s analytical approach for PIANO uses a high resolution gas chromatography /mass spectrometer [GC/MS] based on US EPA SW 846 Method 8260 [modified]. The modification includes a far wider range of target analytes as compared to the traditional Method 8260 analysis,  including  11 paraffins, 33 isoparaffins, 26 olefins, 26 naphthenes, 37 aromatic compounds, MTBE, TAME, DIPE, ETBE ,Thiophene, benzo(b)thiophene, 2 -methylthiophene and 2 –ethylthiophene, as well as C3- C13.

TestAmerica’s Analytical Approach for Tetraethyl Lead (TEL)

To maximize performance, various additives were blended into gasoline, including lead alkyls in the early 1920’s.  Tetraethyl Lead was a lead alkyl substance added to automotive gasoline as an antiknock agent to improve octane performance.  TEL was phased out of gasolines for road vehicles in the United States pre-1996 (pre-1992 in California).  The measurement of TEL can be associated with the time of release of the gasoline in the environment.

TestAmerica’s approach for TEL uses a high resolution gas chromatography /mass spectrometer [GC/MS] based on US EPA SW 846 8270 Selected Ion Monitoring [SIM] [modified].