The effects of diluted bitumen and the dispersant Corexit 9500A on Pacific marine organisms

Canada is expected to significantly increase the production and exportation of bitumen in the next decade. Raw bitumen is diluted with natural-gas condensates to produce diluted bitumen (dilbit), facilitating its flow through pipelines. Few data currently exist on dilbit toxicity to Pacific marine species, either alone or in combination with recently approved chemical dispersant Corexit 9500A. The current study investigated the toxicity of the water-accommodated fraction (WAF) of dilbit, Corexit 9500A, and the chemically enhanced water-accommodated fraction (CEWAF) of dilbit to representative marine species of the west coast of Canada. Oil chemically dispersed by Corexit showed evidence of higher toxicity than dilbit WAF to each test species including juvenile mysids (Mysidopsis bahia), juvenile topsmelt (Atherinops affinis) and adults spot prawns (Pandalus platyceros). Additionally, purple sea urchin (Strongylocentrous purpuratus) fertilization showed high susceptibility to Corexit toxicity, both with and without dilbit present, as nearly 100% of eggs exposed to Corexit remained unfertilized. Overall these results suggest that the use of Corexit as a remediation technique may increase the toxic impacts to Pacific marine species over those caused by a dilbit spill alone.