A baseline assessment of the occurrence, characterization, source, and risk impact of petroleum-related hydrocarbons in sediments along the southeast shoreline of Vancouver Island and Southern Gulf Islands in British Columbia, Canada

Total petroleum hydrocarbons (TPH), n -alkanes, petroleum biomarkers, and polycyclic aromatic hydrocarbons (PAHs) were analyzed in 63 intertidal zone sediments from the southeast shoreline of Vancouver Island and the nearby Southern Gulf Islands, British Columbia (BC), Canada, using gas chromatography coupled with a flame ionization detector and mass spectrometry. All sites had TPH levels much lower than the Canadian Council of Ministers of the Environment thresholds for fine- and coarse-grained soils in agricultural and natural areas. Terrestrial plants were the main source of n -alkanes, though petrogenic n -alkanes were found in 13% of 63 samples, as indicated by the carbon preference index (CPI) and related characteristics. PAHs primarily originated from pyrogenic input, with some locations showing mixed petrogenic and pyrogenic inputs based on analyzing diagnostic ratios, like pyrogenic index and certain isomer ratios. Petroleum contamination was evident at sites with intensive human activities or oil spill history, such as Cowichan Bay, Octopus Point, Medicine Beach, Fulford Harbor, East Portland, Separation Point, Maple Bay, and Aldridge Point, marked by significant levels of petroleum biomarkers, petrogenic n -alkanes, and PAHs. While all PAHs pose minimal risk to benthic organisms, compounds like naphthalene, 2-methyl naphthalene, and certain 3–6 ring PAHs could potentially affect them at certain sites from Cowichan Bay, East Portland, Separation Point, Medicine Beach, and Maple Bay. • All detected TPH did not exceed the criteria regulated by CCME; • Higher levels of TPH were found in sites with extensive human activities or historical oil spills; • Most sites had primarily biogenic n -alkanes, while 12% of sites had primarily petrogenic n -alkanes; • Primary PAHs were pyrogenic, while mixed pyrogenic and petrogenic PAHs were present in some sites; • Sediment-dwelling organisms in a few sites may be affected by PAHs.