Source and Fate of Weathered Polycyclic Aromatic Compounds: Canadian Boreal Site Case Study

This is the authors' abstract. We don't add key points for this paper.

The efficacy of polycyclic aromatic compound (PAC) diagnostic and weathering ratios was tested on a weathered petroleum-contaminated site located in the boreal region of northern Ontario, Canada. The site, a former petroleum distribution terminal (1920–1998) with documented spills and adjacent industrial activity (e.g., cement manufacturing), exhibited mixed petrogenic and pyrogenic PAC sources. Contaminated soil from the site was analyzed for unbranched, alkylated (Cn), nitrogen-, sulfur-, and oxygen-containing PACs using GC-MS-SIM, while hydrocarbon fraction concentrations based on effective carbon number were previously determined by GC-FID. Results underscore the limitations of several conventional diagnostic ratios in resolving mixed-source contamination, as overlapping chemical fingerprints from multiple inputs (diesel, fuel residues, and combustion byproducts) and site-specific weathering processes obscured clear source attribution. Weathering ratios may be used to observe changes in PAC composition over time and predict toxicity. Four weathering ratios suggested in earlier studies were validated: i. fluorene/(C1-anthracene/phenanthrenes), ii. C3-naphthalenes/(C2-anthracene/phenanthrenes), iii. dibenzothiophene/(C4-anthracene/phenanthrenes), and iv. benzo[e]pyrene/benzo[a]pyrene. Three newly proposed weathering ratios indicated weathering: i. acenaphthenone/acenaphthene (<1), ii. anthraquinone/anthracene (<1), and iii. benzanthrone/anthracene (>1). Novel weathering ratios may be established during photolysis, biodegradation, and other site weathering mechanisms for application to legacy polluted sites where the timing of contamination is unknown.