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Dispersants: A Guided Tour - Part Five
What Are Some Environmental Impacts from Dispersant Use?
Both dispersants and dispersed oil particles are toxic to some marine organisms. But because concentrations of dispersed oil are quickly diluted in the ocean, organisms are likely to be exposed only for short time periods. To try to understand how badly marine organisms might be harmed by dispersant application operations, researchers conduct experiments with specialized laboratory equipment. (See the section, A Toxicity Test Apparatus, below.)
In any particular situation, the decision to use dispersants involves balancing the potential advantages of dispersant use--removing oil from the water surface and avoiding some shoreline impacts--with the potential disadvantages, such as impacts to plankton or other water column organisms. Part of the work of planning the response to potential oil spills is the difficult task of evaluating these tradeoffs, which requires careful consideration of the resources and issues involved.
Because coral reefs can be harmed by dispersed oil, dispersant use in the vicinity of coral reefs is usually restricted to areas where dispersed oil is unlikely to contact coral. These are areas far from the reefs, or located where currents would carry the dispersed oil away from the coral.
(For more information about dispersant and oil toxicity, check Chapters 2 and 5 of our online training manual, Introduction to Coastal Habitats and Biological Resources for Spill Response.)
A Toxicity Test Apparatus
The drawing above shows a laboratory system designed to mimic the real environmental conditions that organisms might experience if they were exposed to dispersed oil. A pulse of oil and dispersant is added to the flow-through tank, and then test organisms are observed for a set period of time, such as 24 or 48 hours. Changes which may denote toxic impacts are noted. These could include cessation of feeding, inability to swim or move, sluggishness, or other conditions.
How are Dispersant Applications Monitored?
Dispersant applications are monitored for both effectiveness and environmental impacts. The SMART program (Special Monitoring of Applied Response Technologies, a joint project of several Federal agencies, including NOAA, that respond to oil spills) includes components for monitoring dispersants as well as in-situ burning.
At right, U.S. Coast Guard officers and a NOAA researcher prepare to deploy a fluorometer, an instrument used to detect dispersed oil below a slick.
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