The biological effects of diluted bitumen (dilbit) on two species of Pacific salmonid: Sockeye (Oncorhynchus nerka) and pink salmon (Oncorhynchus gorbuscha)

The major petroleum product derived from the Canadian Alberta oil sands is bitumen, which is commonly mixed with diluents to produce several blends of diluted bitumen (dilbit). The prospected expansions of dilbit transportation capacity in coastal regions of British Columbia (BC) increase the risks of accidental releases of dilbit into freshwater and marine environments of particular concern are the potential risks of exposure to sensitive Pacific salmonids. The central goal of this research was to generate new empirical data to characterize the toxicity of the water-soluble fraction (WSF) of unweathered Cold Lake Blend dilbit to two Pacific salmon species: sockeye (Oncorhynchus nerka) and pink salmon (Oncorhynchus gorbuscha). A comprehensive suite of studies examined the acute and chronic toxic outcomes including lethality, effects on growth, swimming performance, exercise recovery capacity, body energetics, the interrenal stress response, iono-osmoregulatory ability, immune function, and genetic responses. Exposure of sockeye from the fertilized embryos to swim up stage resulted in increased mortality, impaired growth, as well as reductions in both critical (Ucrit) and burst swimming speed (Uburst) in free-swimming fry. These effects correlated with alterations in energy substrate reserves at all stage and an interference in the utilization of lipid energy sources and the ability to mount a physiological stress response. Exposure of juvenile salmonids to the WSF of dilbit (at TPAC concentrations at the ppb level) resulted in sublethal effects that included a classic physiological stress response, and alterations in iono-osmoregulatory homeostasis and immunological performance. Reductions in swimming performance were correlated with a significantly diminished aerobic scope following exposure and recovery following burst exercise was altered. In experiments with juvenile pinks, A 3 month exposure at varying salinity and temperature showed that higher temperatures and salinities affected dilbit-induced mortality, growth, osmoregulation, and energy storage. In a larger context, the findings here provide necessary toxicological information required for the development of risk assessment plans for managing salmon populations and restoring habitat in the event of potential pipeline failures or tanker spill.