Wang, Z; Yang, Z; Yang, C; Hollebone, B; Brown, CE; Landriault, M; Sun, J; Mudge, SM; Kelly-Hooper, F; Dixon, DG
"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 or remediation 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 matter), which are co-extracted with petroleum hydrocarbons in soil samples. The CCME method can misidentify and quantify soil BOCs as regulated PHCs. Consequently, this could lead to overestimation of PHC levels in soil samples. In some cases, biogenic concentrations can cause false exceedences of the CCME Fraction 3 (C 16-C34) fine and course soil standards, which are 1300 mg/kg and 300 mg/kg respectively. Resulting false exceedences can trigger unnecessary and costly cleanup or remediation of non-contaminated soils. Therefore, it is critically important to develop new protocols to characterize and quantatively 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. Our goal is to provide the scientific rationale that is necessary for creating this significant degree of change. During 2008-2010, soil and plant samples were collected from over forty oilcontaminated and paired background sites. The sample collection sites included: (1) contaminated soil samples from 25-30 year old crude oil pipeline spill sites in a peatland; (2) remediated crude oil or diesel contaminated site samples; (3) tar contaminated soil sample from 30 years old distilled crude oil site; (4) diesel contaminated biopile woodchips and soil samples; (5) phytoremediation plant and soil samples; and (6) background soil and plant samples. These samples were extracted by the ALS Laboratory using the ALS Standard Method of "The determination of petroleum hydrocarbons (C10-C50) - F2, F3, F4, and F4G in soil and water" (modified from the CCME Tier 1 Method), and analyzed in the EST Oil Research Lab. A reliable GC-MS method in combination with the derivatization technique, developed in this lab, was used for identification, characterization and quantification of various biogenic sterols and other major biogenic compounds in these contaminated samples. Both PHCs and BHCs in these samples were quantified, and data will be used for assessment of the contamination sites and toxicity risks associated with the CCME Fraction 3 hydrocarbons. The characterization results of the first set of 21 samples indicated the following: (1) For background soil and plant samples (#1563-#1573, and #1579), the total GC-detectable hydrocarbons (without column cleanup) were determined to be in the range of 320 to 9960 μg/g or mg/kg sample (dry weight). After column cleanup, the total GC-TPH were determined to be only in the range of 60 to 1820 μg/g or mg/kg sample (dry weight). Clearly, ∼80% of the GC-detected hydrocarbons (without column cleanup) are attributed to polar natural organic compounds, which are removed by the silica gel column cleanup. These BOC compounds (often in the forms of resolved peaks and irregular small UCM humps) mainly fall in the n-C23 to n-C40+ carbon range (the CCME F3 and F4 range). (2) For contaminated soil samples (#1575-1578, and #1580-1584), the total GC- detectable hydrocarbons (without column cleanup) were determined to be in the range of 2310 to 501000 μg/g or mg/kg sample (dry weight). After column cleanup, the total GC-TPH were determined to be in the range of 2050 to 376000 μg/g or mg/kg sample (dry weight). Approximately 60% up to 100% of these GC-detecte hydrocarbons (without column cleanup) are attributed to petroleum hydrocarbons, indicating that these soil samples were highly contaminated by crude oils or refined products. (3) For most background plant and soil samples, odd-carbon number nalkanes are significantly abundant than even-carbon number n-alkanes. The CPI (carbon preference index) values were determined to be very high (in the range of 7-16). This is clear indication of biogenic origins for most n-alkanes in samples. For contaminated soil samples, the total n-alkanes were determined to be in the 4.9-3606 μg/g range; and the CPI values were in the 1.0-1.5 range, which clearly indicates the dominance of petroleum n-alkanes. Loss of low molecular weight nalkanes due to weathering and biodegradation was also apparent in these soil samples. (4) The total PAH concentrations were very low in most of the background soil and plant samples (at ppb level): only trace EPA priority PAHs plus C1- naphthalenes were detected, but no other petroleum-characteristic alkylated PAH homologues were detected. Correspondingly, almost no oil-characteristic biomarker terpanes (m/z 191) and steranes (m/z 217/218) were detected in these samples. On contrast, most contaminated soil samples demonstrate very high concentrations of both total target PAHs (2835-3442847 ng/g soil) and biomarkers (16880-6180333 ng/g soil), clearly indicating contamination by oils/petroleum products. (5) Target biogenic organic compounds including target fatty acids, fatty alcohols, and sterols were detected in all samples, indicating the presence of BOCs in the total detected hydrocarbon concentrations. They were, however, much more abundant in background samples than in the contaminated soil samples. In general, the absence of petroleum-characteristic alkylated PAHs and biomarkers and the presence of abundant BOC compounds can be used as unambiguous indicators for the predominance of natural organic compounds in soil samples.