A number of materials have been used to remove or reduce oil slicks. Treating agents have been used to deal with accidents and field and laboratory experiments have been done to assess their usefulness and to develop the technology to use them. The types of agents which have been used to date are:

• Dispersants—chemicals forming oil-in-water suspensions;

• Sinking agents—materials that mix with the oil and create a mixture dense enough to sink;

• Burning agents—material put on the slick to assist ignition or enhance combustion of spilled oil;

• Biodegradants—substances that promote oxidation of oil by microbial action;

• Gelling agents—chemicals that form semi-solid oil agglomerates to facilitate removal;

• Herding agents—chemicals that concentrate the spilled oil in a small area;

• Sorbents—materials that absorb or adsorb oil to form a floating mass for later collection and removal.

Dispersants

Dispersants are chemical compounds that act to enhance the surface spreading of oil slicks and to emulsify the oil into the water beneath it. These effects increase the surface area of the slick so that more of it is susceptible to biodegradation. When emulsification (breaking the oil into very small droplets that become mixed with the water) occurs, the slick disperses vertically as well as horizontally. Toxicity of dispersed slicks is a major problem () and is due both to the effect of the dispersant and to the increased oil surface to which marine organisms are exposed. Considerable research has been devoted to the problem of dispersant toxicity.

The federal Council on Environmental Quality (CEQ) developed a National Oil and Hazardous Materials Pollution Contingency Plan in August 1971 (). This plan, enforced by the U.S. Coast Guard and the Environmental Protection Agency, requires that dispersants not be used:

• On any distillate fuel oil.

• On any spill of less than 200 barrels.

• On any shoreline.

• In waters less than 500 feet deep.

• In waters containing major fish populations, or breeding or passage areas for