The use of double ratio plots of polynuclear aromatic hydrocarbon (PAH) alkyl homologues for petroleum source identification

Abstract

Regulatory agencies and trustees of natural resources are increasingly trying to identify parties responsible for accidental or uncontrolled releases of petroleum and other hazardous chemicals into the environment in order to assess associated environmental damages and recover the costs for cleanup and restoration. The identification process in a given situation is often compounded by the presence of multiple sources of contamination when accidental releases occur in heavily industrialized settings which are influenced by chronic waste inputs. Identifying and differentiating sources of chemical contamination in receiving waters, soil and sediments, involves combinations of chemical analyses to establish a chemical "fingerprint." Conventional chemical fingerprinting methods for petroleum hydrocarbon identification have involved the use of gas chromatography/flame ionization detection (GC/FID) techniques to establish the basic chemical constituents of the source(s) which are then matched (through pattern recognition) with the same constituents in environmental samples. These conventional fingerprinting techniques are limited in their ability to distinguish between similar petroleum sources in environments that include multiple sources and often result in false positive identifications. More importantly, as petroleum weathers and biodegrades, the classic chemical fingerprint used in conventional fingerprinting techniques (i.e., saturated hydrocarbons) often disappears. Chemical fingerprinting and subsequent source identification of petroleum in mixed-pollutant environments can clearly be enhanced by methods and techniques that are capable of more accurately distinguishing between sources of similar chemical composition and that utilize chemical constituents that are resistant to weathering and bio-degradation. One such method involves the use of cyclic alkane corn-pounds (steranes and triterpanes), or biomarkers. Biomarkers are stable compounds that are highly resistant to biodegradation and often have unique distributions in petroleum from different sources. The petroleum industry has traditionally used biomarkers to distinguish between source rock formations during exploratory drilling operations. However, the use of biomarkers is limited in that it requires non-routine analyses, the target analyses are often present at very low concentrations, and biomarkers are not present in many refined petroleum products. Another technique involves the use of polycyclic aromatic hydrocarbons (PAH) and selected series of alkylated PAH (alkyl homologues). The advantages of this method are that determination of PAH is a routine analysis, they are present in petroleum at relatively high concentrations, and they are present in many refined petroleum products.