Dispersants, also called dispersing agents, are chemical agents used to break up oil into smaller droplets in the water column. Dispersants can be applied on surface oil or below the surface, closer to an uncontrolled release of crude oil from a well blowout source. In an oil spill, these smaller oil droplets disperse into the water column where they are transported by currents and subjected to other natural processes such as dissolution and biodegradation. Dispersant use is one of several response tools that may be considered in coastal waters to minimize the overall environmental impacts of an oil spill.
Oil released to the environment undergoes a variety of physical, chemical, and biological processes that begin to transform or “weather” the oil almost immediately. Dispersants are most effective when applied immediately following a spill, before the oil has weathered.
Multiple environmental factors influence the effectiveness of dispersants including water salinity, water temperature, and conditions at sea. The type of oil will also influence the effectiveness of dispersants; heavy crude oils generally do not disperse as well as light- to medium-weight oils.
Subpart J of the National Contingency Plan (NCP) governs the use of chemical agents, including dispersants, in response to oil spills. Under these provisions, EPA prepares a list, known as the NCP Product Schedule, that includes dispersant products, as well as chemicals and substances that may be considered for removing or controlling oil spills. Subpart J also provides the framework for how these products are authorized for use.