Study: Toxic hydrocarbon hotspots in BC coastal sediments, threatening Southern Resident killer whales and Chinook salmon

A new study reveals that toxic hotspots for polycyclic aromatic hydrocarbons (PAHs) in marine sediments exist in parts of the British Columbia coast, threatening endangered Southern Resident killer whales and the Chinook salmon they depend on.

The study, conducted by researchers from Ocean Wise, Raincoast Conservation Foundation, Metro Vancouver, Fisheries and Oceans Canada, and Simon Fraser University, was published in the international scientific journal Archives of Environmental Contamination and Toxicology.

In this large-scale study, 76 different PAH compounds were analysed at 98 sediment sites spanning the BC coast from Victoria to Prince Rupert. The study found significant PAH hotspots in urbanized and industrialized areas including Victoria Harbour and Burrard Inlet. 

Polycyclic aromatic hydrocarbons in sediments come from a combination of natural background sources including coal formations and volcanoes, but human activities add a toxic layer of these pollutants from accidental fuel spills, and the combustion of wood, coal, and fossil fuels. Sediments provide a historical record of PAH contamination, but they also serve as a source of these pollutants to the adjacent food web where they can harm wildlife. Sediments are often used as an indicator of ocean health. 

Chemical fingerprinting in this study revealed that PAHs along the coast originate from coal-related activities, including mining, processing, and transporting. Exhaust and effluent from commercial vessels, and spills associated with recreational and commercial shipping likely account for localized contamination hotspots. 

Vessel traffic, particularly in the south, continues to grow, with over 400,000 vessels transiting the coast each year, including tankers, cargo ships, tugs, fishing vessels, ferries, and cruise ships. This portents a future of heightened PAH-associated risks to killer whales and their prey.

The study showed that health impacts are expected for Chinook salmon in nearshore habitats, as well as for both Southern and Northern Resident killer whales within their Critical Habitats. Health risks were higher in the Critical Habitat of Southern Resident killer whales than that of the Northern Resident killer whales.

Said co-author Dr. Peter Ross, Senior Scientist at Raincoast Conservation Foundation: “These troubling findings indicate that heightened attention to source controls, spill response, and best practices in harbours and aboard vessels is imperative, as the recovery of killer whales hangs in the balance.”

Many PAHs are toxic and can affect development, growth, swimming performance, and energy reserves in fish, resulting in an increased risk of death. They have also been linked to gastrointestinal cancers, reproductive impairment, lung disease, and liver damage in heavily exposed marine mammals.

Said lead author Dr. Joseph Kim: “Hydrocarbon releases into the Salish Sea add to the list of threats to the habitat of Endangered Southern Resident killer whales. Coupled with the potential for an oil spill from increased tanker traffic, hydrocarbons appear poised to grow as a conservation concern.”

Abstract

Polycyclic aromatic hydrocarbons (PAHs), a class of persistent, bioaccumulative, and toxic contaminants, represent a threat to at-risk populations of Resident killer whales (Orcinus orca) in the northeastern Pacific Ocean, and their primary prey, Chinook salmon (Oncorhynchus tshawytscha). Concentrations of 76 PAHs in subtidal surface sediments (1 to 435 m depth) from 98 sites along the coast of British Columbia (BC), Canada, were analyzed to evaluate their distribution patterns and potential sources. A subset of parent and alkylated PAHs, including the 16 priority PAHs, was evaluated to assess biological risks to Resident killer whales and Chinook salmon. Principal component analysis (PCA) revealed site-specific PAH patterns in sediments, characterized by heavier parent PAHs (4–6 aromatic rings) and lighter alkylated PAHs (2–3 aromatic rings). Polycyclic aromatic hydrocarbon distribution and profiles were strongly influenced by octanol-water partition coefficients (Log Kow) and total organic carbon (TOC) (p < 0.001), with water depth exhibiting a gradient from heavier PAHs in shallow sediments to lighter PAHs in deeper sediments (p < 0.001). Hotspots of pyrogenic and petrogenic sources were identified along the BC coast, with most areas being contaminated by pyrogenic inputs primarily associated with combustion of lignite and bituminous coal, and petrogenic inputs mainly associated with coal and diesel oil. Biological risk, based on sediment quality guidelines (SQGs), risk quotients (RQs), and toxic equivalents (TEQs), suggested varying degrees of direct and indirect impacts for Chinook salmon in nearshore Conservation Units (CUs), as well as for Resident killer whales within their Critical Habitats. Among Resident killer whale Critical Habitats, the greatest impacts were expected in the Southern Resident Killer Whale (SRKW) Critical Habitat around southern Vancouver Island, from both potential direct and indirect effects, with direct impacts from alkylated PAHs requiring special consideration. These findings highlight the urgent need for targeted management actions to reduce PAH emissions from both point and non-point sources in coastal environments to support conservation efforts for Chinook salmon and Resident killer whales. In particular, for Resident killer whales, such efforts should be prioritized within the SRKW Critical Habitat surrounding southern Vancouver Island.

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