State of Knowledge on Chemical Dispersants for Canadian Marine Oil Spills

Abstract

Chemical dispersants represent one of many oil spill response measures. Following its large-scale application during response operations during the Gulf of Mexico Oil Spill in 2010 there has been significant advancement in the scientific understanding of dispersants. As a result, a large volume of literature has been produced detailing the results and findings of many studies and assessments. A literature review was conducted to consolidate and evaluate the state of knowledge of chemical dispersants in a Canadian context. Specifically, the literature review investigates how dispersants interact with the fate, behavior, and transport of oil in the environment, pathways of effects of dispersed oil for marine biota, potential effects, and impacts of dispersed oil on biota. Furthermore, in light of environmental concerns, consideration is given to specific monitoring and oil trajectory modelling needs during response operations when dispersants are used. The findings of the literature review suggest that chemical dispersants change the oil’s transport, fate, and potential effects by changing the chemical and physical properties of oil. As dispersants enhance the movement of oil into the water column as small oil droplets, dispersants may alter the level of exposure for certain species. For example, dispersants may enhance the bioavailability of the oil to some species. However, based on the results of laboratory toxicity assessments, at oil loadings <100 mg/L (a common value for most oil spill scenarios), chemically-dispersed oil and untreated oil (without dispersant application) appear relatively similar in terms of their effects on marine biota. A significant trade-off of dispersant use is that while dispersants may reduce impacts of oil slicks to wildlife at the water surface (e.g., marine mammals, seabirds), and the subsequent transport of oil to vulnerable and biologically rich coastlines and coastal habitats, they may increase impacts within the water column and sediments of the offshore environment. There are currently numerous ongoing studies focused on the evaluation of long term impacts of dispersant use on biota in the offshore marine environment to address knowledge gaps. Proper use of dispersants within Canada must take into consideration the unique circumstances and conditions of each oil spill scenario, including the dynamic nature of the marine environment and the role of environmental, physiochemical, and ecological factors.