Source apportionment of elevated PAH concentrations in sediments near deep marine outfalls in Esquimalt and Victoria, BC, Canada: Is coal from an 1891 shipwreck the source?

Abstract

Previous studies have suggested that coal from the 1891 shipwreck of a collier off Victoria, BC, Canada is responsible for elevated parent (unsubstituted) PAH concentrations in sediments near deep marine outfalls from Esquimalt and Victoria in the Strait of Juan de Fuca. To resolve this question, we analysed a comprehensive suite of resolved and unresolved complex mixture (UCM) alkanes, tricyclic terpane, hopane and sterane biomarkers, and parent and alkyl polycyclic aromatic hydrocarbons (PAHs) in samples of coal, wastewater and sediments. Composition patterns, principal components analysis (PCA) models and PAH and biomarker ratios all indicate that coal from the collier does not make a dominant contribution to any sediment sample. Mass balance calculations based on the n-C24 content and 24/4 tetracyclic terpane to 26/3R tricyclic terpane ratio in coal provide a particularly good match between predicted and observed alkyl PAH concentrations for sediments with high alkyl naphthalenes and phenanthrene/anthracenes and low UCM, but the predicted coal contribution substantially underestimates the measured parent PAHs for all sediment samples. Methylbenz[a]anthracene/chrysene profiles for sediments with a dominance of parent PAHs are very close to coal tar, with a marked predominance of methylbenz[a]anthracenes and the possible 10-methylbenz[a]anthracene as a major constituent, while the methylchrysenes predominate in coal. Hence, coal from the collier could account for most alkyl PAHs in the sediments, but dredged sediment containing pyrolised coal waste from a former coal gas plant in Victoria Harbour is a more likely source for the samples with elevated parent PAHs. PAH ratios indicate that these sources are superimposed on combustion PAHs introduced by a combination of atmospheric deposition and delivery via stormwater and the outfalls. Parent PAH distributions also suggest that PAHs in wastewater that originate from oils and soot in liquid fossil fuel combustion are dispersed and degraded, while the larger wood char particles (containing PAHs more protected from degradation) settle closer to the outfalls. Overall, results suggest that PAHs have predominant sources in wood combustion, coal and possibly coke, with a likelihood of much lower bioavailability than would be expected from wastewater dominated by oils and soot from vehicle combustion.