INTRODUCTION In an increasingly technological era, we have become more dependent upon petroleum products to help us maintain our high standard of living. Products derived from petroleum, such as heating oil and gasoline, provide fuel for our automobiles, heat for our homes, and energy for the machinery used in our industries. Other products derived from petroleum, including plastics and pharmaceuticals, provide us with convenience and help to make our lives more comfortable. However, petroleum must be stored and transported, usually in large volumes. As a result of exploration activities, or during storage or transport, oil and other petroleum products are sometimes spilled onto land or into waterways. When this occurs, human health and environmental quality may be at risk. Every effort must be made to prevent oil spills, and to clean them up promptly once they Occur. The purpose of this brochure is to provide information about oil spills. This volume contains individual sections that outline what oil spills are, their potential effects on the environment, how they are cleaned up, and how various agencies prepare for spills before they happen. Details about one oil spill cleanup -- that of the Exxon Valdez spill of March, 1989-- is provided to offer an example of the complexities that can potentially be involved in oil spill cleanup activities. THE BEHAVIOR AND EFFECTS OF OIL SPILLS IN THE MARINE ENVIRONMENT INTRODUCTION Spilled oil can pose serious threats to the marine environment. The severity of impact of an oil spill depends on a variety of factors, including characteristics of the oil itself. Even large spills of refined petroleum products such as gasoline evaporate quickly and cause only short-term environmental effects. On the other hand, crude oils, heavy fuel oils, and water-in-oil mixtures may cause widespread and long-lasting physical contamination of shorelines. Natural conditions, such as water temperature and weather, also influence the behavior of oil in the marine environment. PHYSICAL PROPERTIES OF OIL The term oil describes a broad range of natural hydrocarbon-based substances and refined petroleum products. (Hydrocarbons are chemical compounds composed of the elements hydrogen and carbon.) Most refined petroleum products are mixtures of many types of hydrocarbon-based substances. Commonly used products refined from crude oil include fuel oil, gasoline, kerosene, and jet fuel. Each type of crude oil and refined product has distinct physical and chemical properties. These properties affect the way oil will spread and break down, the hazard it may pose to marine and human life, and the likelihood that it will pose a threat to natural and man-made resources. The rate at which an oil spill spreads will determine its effect on the environment. Most oils tend to spread horizontally into a smooth and slippery surface, called a slick, on top of the water. Factors which affect the ability of an oil spill to spread include surface tension, specific gravity, and viscosity. Surface tension is the measure of attraction between the surface molecules of a liquid. The higher the oil's surface tension, the more likely a spill will remain in place. If the surface tension of the oil is low, the oil will spread even without help from wind and water currents. Because increased temperatures can reduce a liquid's surface tension, oil is more likely to spread in warmer waters than in very cold waters. Specific gravity is the density of a substance compared to the density of water. Since most oils are lighter than water, they flat on top of it. However, the specific gravity of an oil spill can increase if the lighter substances within the oil evaporate. Viscosity is the measure of a liquid's resistance to flow. The higher the viscosity of the oil, the greater the tendency for it to stay in one place. (Honey is an example of a viscous liquid.) THE FATE OF SPILLED OIL Natural actions are always at work in the marine environment. These can reduce the severity of an oil spill and accelerate the recovery of an affected area. Some natural actions include weathering, evaporation, oxidation, biodegradation, and emulsification. Weathering is a series of chemical and physical changes that cause spilled oil to break down and become heavier than water. Wave action may result in natural dispersion, breaking a slick into droplets which are then distributed throughout the water column. These droplets can also form a secondary slick or thin film on the surface of the water. |