The Effects of Diluted Bitumen (dilbit) on Juvenile Salmon

We in British Columbia love our Pacific wild salmon and view them as keystone species and indicators of ecosystem wellbeing. Numbers have dropped significantly recently from multiple stressors including climate change, habitat loss, pollution and more.  With  current and proposed pipelines that will carry diluted bitumen (dilbit) from the oil sands through spawning habitat and migration routes of Pacific salmon, it is very important to understand the risks posed by oil spills to the salmon. The survival of juveniles to adulthood is influenced by multiple factors, and the combination of stressors, for example, oil exposure followed by an infection could seriously affect survival even if the contaminant exposure alone did not show much effect. This recent study by Lin et al. 20191 that used SGS AXYS’ extensive polycyclic aromatic carbons (PAHs and PACs) measurements is an excellent addition to the body of research that needs to be carried out to understand the effects of oil spills on BC’s salmon.

Researchers from Simon Fraser University exposed juvenile sockeye salmon to the water soluble fraction of a commercial dilbit blend. Most previous studies have focused on embryo/larval stages, so this was a unique study focusing on environmentally relevant concentrations in juvenile salmon.

The Early Life Stage (ELS) and juvenile salmonids are particularly vulnerable to potential dilbit spills due to their inability to avoid exposures spatially, and their apparent high sensitivity to some dilbit components.

They measured multiple biological indicators including stress response, immune response and osmoregulation. SGS AXYS measured the concentrations of the Polycyclic Aromatic Compounds (PACs) including PAHs in the exposure tanks using our extended PAH list of 70+ targets. This measurement is a key step in understanding actual exposure of the salmon to the PACs in dilbit. SGS AXYS’ extended PAC list provides a comprehensive measurement of the alkylated and substituted PACs that tend to dominate PAH signatures characteristic of oil. In this study, the EPA priority PAH list of 16 parent PAHs which is most commonly used to estimate total PAH concentrations, would have accounted for <15% of total PAC concentrations measured in the exposure. Especially for understanding PAH exposure from oils and for fingerprinting fossil fuels, it is critical to measure comprehensive PAH lists.

Researchers found that both acute (high) and subchronic (low) exposures altered these juvenile sockeyes significantly.

  • Acute and subchronic exposure significantly altered osmoregulatory functions.
  • Acute exposure to dilbit resulted in a transient classic physiological stress response.
  • A compromised immune system was demonstrated by higher mortality in fish challenged with Vibrio (Listonella) anguillarum following dilbit exposure.

These are all indications of significant sublethal effects.As researchers point out in the article. The researchers found significant evidence of compromised immune system performance in a 42-day exposure, which indicates chronic exposure could significantly impact survival. The authors state in their conclusion that:

These adverse effects will result in reduced fitness, particularly in 1+ year old juveniles that are expected to perform a seaward migration raising long-term conservation concerns for these populations. Continued efforts are clearly required to yield the necessary information to understand the potential risks associated with the transport and accidental release of dilbit into salmon habitat, and to appropriately regulate the production, transport and use of this mixture.

The salmon’s lifecycle is complicated and fraught with obstacles at every step, so these kinds of studies that help understand stressors are critical to helping revive BC’s wild salmon population.

Note: Salmon image from US EPA’s public domain reused under the US Government Works License


1. Lin F, Osachoff HL, Kennedy CJ. Physiological disturbances in juvenile sockeye salmon (Oncorhynchus nerka) exposed to the water-soluble fraction of diluted bitumen. Aquatic Toxicology. 2019; 105383. doi:10.1016/j.aquatox.2019.105383
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