Lethal and sub-lethal defects demonstrate the chronic toxicity of chemically-dispersed diluted bitumen to rainbow trout embryos (Oncorhynchus mykiss)
MetadataShow full item record
Addition of a low molecular weight diluent to raw bitumen from Alberta’s Oil Sands produces diluted bitumen (dilbit), a physically and chemically distinct product from conventional oils. While thousands of kilometers of pipeline carry dilbit across Canada, relatively few studies have documented its environmental behaviour and toxicity to developing fish in the event of a spill to freshwater. In response, this study demonstrated exposure-response relationships between dilbit at a gradient of concentrations and toxicological responses of rainbow trout embryos under standardized laboratory conditions. Chronic toxicity was measured by exposing rainbow trout embryos for 25 days to two different winter dilbit blends, Access Western Blend (AWB) and Cold Lake Blend (CLB). Chemical dispersion of hydrocarbons from AWB and CLB dilbit into water (producing chemically enhanced water accommodated fractions, CEWAFs) was used to prepare exposure solutions. Endpoints to characterize chronic toxicity included mortality, impairment of growth and development, and select morphological deformities collectively called blue sac disease (BSD). Results indicated that cumulative mortality and the prevalence of sub-lethal defects (i.e. impairment of growth and development and onset of BSD) increased with increasing exposure concentration of dilbit CEWAF in water. Additionally, at the same volume of CEWAF, CLB had a higher total petroleum hydrocarbon content and higher lethal toxicity to rainbow trout embryos (25-d LC50 = 1200 g/L) than AWB (25-d LC50 = 1627 g/L). AWB and CLB were 2 and 2.7 times more toxic respectively when compared to a light crude oil (22-d LC50 = 3281 g/L), and 3.4 and 2.5 times less toxic respectively when compared to a heavy fuel oil (25-d LC50 = 473 g/L). This research contributes to developing a dilbit-specific assessment of toxicity and potential impacts (i.e., recruitment failure and declining populations of fish species whose spawning coincides with an oil spill) if the product is spilled into a freshwater environment.