The effects of diluted bitumen on marine intertidal vascular plants

Canada has the third largest oil reserves in the world, most of which exist in the form of bitumen in the oil sands of the Western Canada Sedimentary Basin. Plans are underway to increase the export of petroleum products including diluted bitumen (dilbit) and crude oil to overseas markets, highlighting the potential risk of a spill into the Canadian marine environment. Understanding and evaluating risk, and the development of chemical management plans require information on the toxicity of dilbit to key marine species. Little information exists regarding the toxic effects of most petroleum products to intertidal vascular plants. The objective of this project was to determine the lethal and sublethal toxicity of environmentally relevant concentrations of dilbit to eelgrass (Zostera marina), an intertidal vascular plant and keystone species in the Pacific Northwest. Eelgrass was collected from the intertidal zone of an uncontaminated site in the Strait of Georgia, near Boundary Bay, British Columbia. A short-term, 9-d exposure and a long-term 28-d exposure of shoots to multiple concentrations of a water-accommodated fraction (WAF) of dilbit were performed. Endpoints assessed in shoots from the short-term exposure included: total reactive oxygen species (ROS), activity of catalase and superoxide dismutase, and protein oxidation. Shoots from the long-term exposure were assessed for biological endpoints including plant growth, chlorophyll-a content, and the effective quantum yield of Photosystem II.