The Sublethal Effects of Chemically-Dispersed Access Western Blend and Cold Lake Blend Diluted Bitumen on Rainbow Trout Embryos (Oncorhynchus mykiss)
An increased demand for Canadian diluted bitumen has resulted in new proposals, such as the Enbridge Northern Gateway pipeline, for transportation to coastal ports for shipment to foreign markets. Access Western Blend (AWB) and Cold Lake Blend (CLB) are identified as the highest-volume dilbit products currently shipped in Canada, each with varying physical properties and chemical compositions. Though dilbit is similar to conventional crude oils in physical properties, the volatility of polycyclic aromatic hydrocarbons (PAHs) present in dilbit during oil spill scenarios causes changes to its environmental fate and behavior. This study characterizes the physiological effects of rainbow trout (Oncorhynchus mykiss) embryos in response to chemically-dispersed dilbit to establish salmonid sensitivity for populations at risk from dilbit spills caused by transportation or pipeline failures. Embryos were exposed for 23 days to dilutions of chemically-enhanced water accommodated fractions of AWB and CLB dilbit. Toxicity was determined by measuring mortality rate as well as the development of blue sac disease (BSD) in embryos at the end of the 23-day exposure. Physiological effects were assessed through mortality, prevalence of malformations, and measurement of gene transcripts associated with phase I (cyp1a), phase II (hsp70, gst, gpx, nfe2, gsr, sod, cat), xenobiotic metabolism (ahr, arnt), and cell cycling and mutation response (p53). Complete mortality was observed at the highest treatments of 1 % v/v due to dispersant toxicity. Malformations were measured in the second highest treatments (0.1 % v/v) of AWB and CLB dilbits. Significant changes in gene expression were observed in ahr, cyp1a, gsr, p53, and sod1 in response to the upper nominal loadings of CEWAF dilbits. This is the first study on the physiological effects of chemically-dispersed dilbit exposure in a native Canadian fish species and may provide a baseline of physiological effects for other economically-important salmonids with varying life strategies and environmental sensitivities.