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API Publ 4689-2001 pdf free download

This section describes the environmental fate processes and provides a brief overview of some considerations that need to be included in discussions about potential exposure. The information found in this section is based on referenced literature (F ingas, 1994, 1995; GE SAMP, 1993; Koons and Jahns, 1992; Mielke, 1990; NRC, 1985, 1989). A more complete description of the environmental fate and effect processes are found in the Fate and Environmental Effects of Oil Spills in Freshwater Environments (API, 1999). ENVIRONMENTAL FATE Introduction When oil is released into the environment, numerous processes begin to affect the environmental fate of oil components and the chemical-physical properties of the oil. The composition and physical/chemical properties of crude oil and refined products are variable; therefore, no two crude or refined oils will behave exactly the same in the environment. In addition, meteorological and oceanographic conditions will affect the movement and weathering of oil. Spreading, drift, evaporation, dissolution, and dispersion are processes that begin immediately once oil is spilled. Figure 2-1 illustrates these processes. One process can occur at a greater relative magnitude than another process. For example, in the early phases of an oil spill, spreading occurs at a greater rate than oil drift. Dispersion of oil occurs at a greater magnitude than dissolution since only small amounts of oil components are soluble in water. Emulsification, sedimentation, biodegradation, and photooxidation can occur within the first day of a spill, but these processes are not as predominant as spreading, evaporation, and dispersion. Some of the fate processes, for example, evaporation, may be most relevant to human health exposure. Other processes, such as photooxidation and sedimentation, are not important determinants of human exposure. The major processes are discussed here to provide a general understanding of the environmental fate of spilled oil.
Drift The combined action of wind, surface currents, and waves causes the oil slick to drift. Prediction of slick drift is necessary for spill response planning and operations. Slick drift is largely independent of spill volume, spreading, or weathering. However, a “thick” slick drifts faster than a “thin” slick, because wind interaction is increased with thicker oil in comparison to thinner oil. Therefore, the thicker portions of the slick often form the leading edge of an advancing spill. Local conditions such as river outflow, nearshore structures, or the presence of surface debris can also affect slick drift. Evaporation Evaporation is one of the primary weathering processes involved in the removal of oil from the sea. Evaporation begins immediately upon release of oil and is especially dominant during the first few days of a spill. During evaporation, volatile hydrocarbon components from the oil slick escape to the atmosphere. In the first few days following a spill, light crude oils can lose up to 75% of their volume due to evaporation. Medium crude oils and heavy crude oils may lose up to 40% and 10%, respectively, of their volume through evaporation.

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