Dispersants: A controversial oil spill response | Guest Column

By William King, Brendan Cowan and Megan Dethier

A major oil spill in San Juan marine waters would impact much that we value in our island community: the environment, the economy and our health. Vessels sailing local waters pose spill risks, and we are wise to consider our spill response strategy in advance. Chemical dispersants are a potential response method embroiled in controversy due to inherent environmental tradeoffs. A recent review from the University of Washington Friday Harbor Laboratories examined the scientific literature to better understand the implications of using dispersants for the islands.

Dispersants, which contain chemicals similar to laundry detergents, break up large oil slicks on the ocean surface into tiny oil droplets. Ideally, waves then mix the droplets deeper into the ocean, diluting the oil and its toxic effects on organisms and potentially increasing oil degradation by marine microbes. Dispersant effectiveness depends on specific spill conditions; the type of oil spilled, water conditions (including temperature), and time since the spill occurred all affect dispersant effectiveness. During a spill, decision-makers must consider both the potential benefits and environmental consequences of using (or not using) dispersants.

Controversy on dispersant use centers on the environmental tradeoffs. Oil is highly toxic; oil spilled into the ocean will inevitably kill many organisms, and deciding to use dispersants means attempting to decrease the overall damage. Ideally, dispersants break up an oil slick at the ocean surface away from shore, preventing oil contact with sensitive shoreline habitats, orcas, and other marine birds and mammals. This benefit would come at the cost of putting oil droplets deeper into the ocean, where they may contact other organisms, including salmon.

Current federal spill response policy for the San Juans considers dispersants a secondary option (to traditional clean-up methods) that can be used on a “case-by-case” basis. For dispersants to be used, decision-makers go through a formal environmental assessment involving state and federal authorities.

The recent review from Friday Harbor Laboratories suggests that, based on the best-available science, San Juan County should remain “case-by-case” for dispersant use. The review found substantial uncertainty in the scientific literature about the environmental tradeoffs of using dispersants. Dispersant effectiveness and consequences on organisms depend heavily on the specific spill conditions, and current scientific knowledge cannot reliably predict the net benefits of using dispersants. Although dispersants are toxic, they are not more toxic than oil alone. Under certain conditions, using dispersants may reduce overall environmental harm – therefore, dispersants should be kept open as an option to spill responders.

No response can completely undo the harm of an oil spill, but having the right tools can help responders lessen the inevitable significant damage to natural resources. Policy makers, responders and concerned citizens continue to debate the tradeoffs involved in using dispersants. We hope that island residents continue to learn about spill prevention and response, helping to shape future response decisions and ensure that we are as ready as possible for an oil spill in the San Juans.

Read the full review on dispersant use in San Juan County from Friday Harbor Laboratories on the Encyclopedia of Puget Sound at www.eopugetsound.org/articles/oil-dispersant-effectiveness-and-ecological-consequences-san-juan-county-marine-waters.