Each type of crude oil and refined product has distinct physical properties that affect the way oil spreads, breaks down and affects the environment and man-made resources.
For example, light refined products, such as gasoline and kerosene, spread on water surfaces and penetrate porous soils quickly. Fire and toxic hazards are high, but the products evaporate quickly and leave little residue. Alternatively, heavier refined oil products may pose a lesser fire and toxic hazard and do not spread on water as readily. Heavier oils are more persistent, however, and may present a greater remediation challenge.
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.
Oil exposure to the shoreline depends on wave energy and tides, substrate type, and slope of the shoreline. Shoreline type is classified by rank depending on how easy the oil would be to clean up, how long the oil would persist, and how sensitive the shoreline is.
Shorelines can vary dramatically in their forms and compositions:
The composition and structure of the beach will determine the potential effects of oil on the shoreline.
Oil may persist longer than expected based on microclimates. Some of the weathered crude may develop a thin "skin" which when disturbed during cleanup, releases fresher oil.
Oil may not weather into a semi-solid tar because of the water emusification and organic matter and vegetation mixed into the mousse.
Seabirds are amongst the most vulnerable inhabitants of open waters since they are easily harmed by floating oil. Species that dive for their food or which congregate on the sea surface are particularly at risk. Although oil ingested by birds during attempts to clean themselves by preening may be lethal, the most common cause of death is from drowning, starvation and loss of body heat following fouling of plumage by oil.
Cleaning and rehabilitation after oiling is often attempted, but for many species it is rare for more than a fraction of oiled birds to survive cleaning and rarer still for those that survive to breed successfully after release. Penguins are an exception and are much more resilient than most other birds. When handled properly, the majority are likely to survive the cleaning process and rejoin breeding populations.
When oil that washes up on the shoreline, it coats and clings to every rock and grain of sand. Oil slick rocks cause increased slip, trip and fall hazards to emergency responders and cleanup workers.
If the oil washes into coastal marshes, mangrove forests or other wetlands, fibrous plants and grasses absorb the oil, which can damage the plants and make the whole area unsuitable as wildlife habitat.
Since most oils float, the creatures most affected by oil are animals like sea otters and seabirds that are found on the sea surface or on shorelines if the oil comes ashore. During most oil spills, seabirds are harmed and killed in greater numbers than other kinds of creatures. Sea otters can easily be harmed by oil, since their ability to stay warm depends on their fur remaining clean. If oil remains on a beach for a while, other creatures, such as snails, clams, and terrestrial animals may suffer.
Ultimately, the severity of environmental damages caused by a particular oil spill depends on many factors, including the amount of the oil spilled, the type and weight of the oil, the location of the spill, the species of wildlife in the area, the timing or breeding cycles and seasonal migrations, and even the weather at sea during and immediately after the oil spill.
Source: National Oceanic and Atmospheric Administration (October 21, 2013)NOAA
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