Fingerprinting of Petroleum Hydrocarbons (PHC) and Other Biogenic Organic Compounds (BOC) in Oil-contaminated and Background Soil Samples

Total petroleum hydrocarbons (TPH) or petroleum hydrocarbons (PHC) are one of the most widespread soil contaminants in Canada, the United States and many other countries worldwide. Clean-up of PHC-contaminated soils costs the Canadian economy hundreds of millions of dollars annually. In Canada, most PHC contaminated site evaluations are based on the methods developed by the Canadian Council of the Ministers of the Environment (CCME). However, the CCME method does not differentiate PHCs from BOCs (the naturally occurring biogenic organic compounds), which are co-extracted with petroleum hydrocarbons in soil samples. Consequently, this could lead to overestimation of PHC levels in soil samples. In some cases, biogenic interferences can even exceed regulatory levels (300 ?g/g for coarse soils and 1300 ?g/g for fine soils for Fraction 3, C16-C34 range, in the CCME Soil Quality Level). Resulting false exceedances can trigger unnecessary and costly cleanup or remediation measures. Therefore, it is critically important to develop new protocols to characterize and quantitatively differentiate PHCs and BOCs in contaminated soils. The ultimate objective of this PERD (Program of Energy Research and Development) project is to correct the misconception that all detectable hydrocarbons should be regulated as toxic petroleum hydrocarbons. This can only be accomplished through improvements to the existing CCME PHC determination protocols and soil quality guidelines. During 2009-2010, soil and plant samples were collected from over forty oil-contaminated and paired background sites in various provinces. These samples were extracted by the ALS Laboratory and analyzed in the ESTS Oil Research Laboratory. The silica gel column cleanup procedure was applied to effectively remove all target BOCs from the oil-contaminated sample extracts. Furthermore, a reliable GC-MS method in combination with the derivatization technique, developed in this laboratory, was used for identification and characterization of various biogenic sterols and other major biogenic compounds in these oil contaminated samples. Both PHCs and BOCs in these samples were quantitatively determined. This paper reports the characterization results of this set of 21 samples. In general, the presence of petroleum-characteristic alkylated PAH homologues and biomarkers can be used as unambiguous indicators of the contamination of oil and petroleum product hydrocarbons; while the absence of petroleum-characteristic alkylated PAH homologues and biomarkers and the presence of abundant BOC compounds can be used as unambiguous indicators of the predominance of natural organic compounds in soil samples.

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