Abstract
In the Fraser River Basin and the Strait of Georgia, a pristine hydrocarbon background is evident in older sediments and suspended sediments from remote regions. This natural background has been augmented over the past century by variable amounts of combustion PAHs and petroleum hydrocarbons derived from human activities, with impacts most evident near industrialised or highly populated regions. Traditional petroleum indicators, including alkane and alkyl PAH distributions and unresolved complex mixtures (UCMs), identify petroleum contamination in suspended particulates transported by the Fraser River and in modern sediments from lakes and rivers in the lower Fraser Basin and the Strait of Georgia. However, these markers have proven to be of limited quantitative use either because they overlap combustion PAH profiles or because they are prone to degradation in the environment. More specific and refractory petroleum markers such as the steranes, rearranged hopanes and tri- and tetracyclic terpanes are found where there are enhanced concentrations of traditional indicators, confirming previous assignments of petroleum contamination near industrial regions. Furthermore, the low or non-detectable quantities of these biomarkers in remote regions reinforce the conclusion that these areas remain pristine and suggest that these markers may provide useful indicators of any future contamination. Biomarkers of petroleum origin (reservoir location or age) do not provide incisive indicators of the origins of hydrocarbon contamination in the Fraser Basin but they have helped to narrow down the sources. In particular, the absence of structurally rearranged hopanes (25,28,30-trisnorhopane and 28,30-bisnorhopane) rules out contamination from Californian oils, while the presence of enhanced oleanane in samples from the lower Fraser River suggests a source in coal dust lost during railroad transportation to the coast.
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