SOURCES OF oil in our waters
The single largest human cause of oil pollution in the oceans is oily waste illegally spilled from ships, according to the National Academy of Science.
Intention dumping from ships accounts for 46% of the oil entering the world’s oceans from human sources each year.
Intention dumping from ships accounts for 46% of the oil entering the world’s oceans from human sources each year.
Ship leaving an oily trail.
Photo credit: US Department of Justice
People dump between 190 million and 706 million gallons of crude oil or its refined products into the sea each year, according to the National Academy of Sciences. This represents more than half (fifty-two percent) of all the oil entering the ocean each year. The remainder comes from natural underwater seeps.
Source: American Academy of Sciences, Oil in the Sea III, 2003
Exxon Valdez Oil Spill. Credit: NOAA
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While industrial accidents like the Exxon Valdez, which spilled 11 million gallons of oil in 1989, or British Petroleum’s Deepwater Horizon, which released 210 million gallons of oil in 2010, attract the most media attention, industrial accidents like these represent just 18% of all the oil released into the water as a result of human activity.
Intentional illegal dumping of oil from ships represents 46% of the oil spilled into the world's waters, which is equal to eight new Exxon Valdez oil spills every year. |
Extent of illegal dumping
Source: US Department of Justice
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The world’s shipping fleet is comprised of nearly 88,000 vessels. About 50,000 of these ships trade internationally.
It is believed that 85-90% of the world fleet complies with the law. Unfortunately, that means between 5,000-7,500 vessels, routinely and intentionally discharge between 70 million to 210 million gallons of waste oil into the water each year. From aerial surveillance by governments around the world, we can see that illegal dumping by commercial ships is commonplace. It is also highly illegal. Learn about the laws against marine oil pollution. |
WHY DO MARINERS POLLUTE?Oil pollution is illegal, not to mention extremely harmful to the environment. So why do some ship owners and crew members still decide to pollute? It comes down to money.
Modern cargo and container ships are powered by oil-based fuels and lubricants, and leaks are commonplace. The heavy fuel oil that propels these ships produces an oily sludge when burned, and nearly all of the foul water, liquid waste and oil leaked from machinery drains down and accumulates in the bilge tanks. Oil tankers, in addition to accumulating regular operational waste, must also wash out their tanks between each trip, adding thousands of gallons of sludgy waste oil which must also be emptied regularly. A 2002 report by the European Organization for Economic Cooperation and Development estimated that the average annual cost of meeting the MARPOL regulations runs from $30,000 a year for an average sized cargo ship to $55,000 for a large container vessel, and the cost can rise to $150,000 per year for a very large oil taker. These costs represent, on average, between 3.5% and 6.5% of a ship's overall operating expenses. 
A "Magic Pipe." Source: US Department of Justice
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Source: US Department of Justice
Some ship operators and owners try to save money or the time it takes to unload waste oil in port by breaking the law by installing a pipe or hose, known in the shipping industry as a “magic pipe,” to bypass the ship's oily water separator and pump oily water directly into the ocean. This behavior was outlawed by the international marine pollution treaty known as MARPOL, which banned the dumping of oil into the water. Learn more about MARPOL and other Laws |
Environmental Impact of OIL types
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HEAVY OILS
Heavy oils, such as bunker fuels, crude oil, and No. 6 fuel oil, are the most common type of ship fuel. When spilled, these oils create thick, dark slicks that do not evaporate when exposed to sunlight. They eventually spread out to form smaller, discrete patches or streaks. Environmental Impacts: Heavy oils impact every area of the marine environment. They can coat birds and fish, restricting their movement, covering their airways, and smothering them to death. When responders act quickly, heavy oils can be contained and collected by skimmers or vacuum pumps. They can float at the surface, remain suspended in the water column, or sink to the seafloor, where they can remain for many years. Direct contact with heavy oil is toxic to fish. It can also bioaccumulate in crabs and other shellfish, making then unsafe for human consumption. Birds and mammals are also affected by direct contact or ingesting the oil. |
Tar ball washed up on a beach.
Source: NOAA
Heavy oil can form tar balls when mixed with air and agitated by the movement of waves in a process known as weathering. Tar balls can travel great distances and eventually wash up on shore.
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LIGHT OILS
Marine diesel and No. 2 fuel oil, used for smaller commercial vessels and recreational boats, are categorized as “light oils.” They usually create a dull, dark colored film when spilled into the water, which spreads quickly creating a rainbow or silvery sheen on the water. A sheen is a thin layer of oil (less than 0.0002 inches or 0.005 mm) floating on the water’s surface. One gallon of light oil can cover more than a full square mile, forming the tiniest film on the surface at one-hundredth of a millimeter thick. Environmental Impacts: Light oils evaporate or dissipate quickly from the surface of the water and are easily mixed into the water column. They do not usually settle on the seafloor, but can be absorbed into sediments or dispersed into small droplets that stay suspended in the water. While light oil spills might seem to disappear quickly, it can take months for the last traces to leave the environment. Even very thin sheens can do great harm to these animals. 
Silvery sheen spill. Source: NOAA
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MEDIUM OILS
Most crude, or naturally occurring oils, fall into the category of medium oils. The Deepwater Horizon spill of 2010 released an estimated two hundred and ten million gallons of medium crude oil into the Gulf of Mexico.  BP Deepwater Horizon on fire. Source: NOAA
Environmental Impacts: While roughly one-third of spilled crude oil will evaporate within 24 hours, medium oil spills can cause serious long-term contamination. Medium oil is heavy enough to settle down onto the seafloor, which means that it can take years for it to finally leave the environment. |