How does Oil Turn into a Pollutant?
How does petroleum (oil products) become a pollutant in the coastal and marine environment?
Accidental or deliberate, operational discharges and spills of oil from ships, especially tankers, offshore platforms and pipelines, is the most obvious and visible cause of oil pollution of the marine environment. As summarized by NOAA: ‘The kind of oil spill we usually think about is the accidental or intentional release of petroleum products into the environment as result of human activity (drilling, manufacturing, storing, transporting, waste management). Examples would be things like well blowouts, pipeline breaks, ship collisions or groundings, overfilling of gas tanks and bilge pumping from ships, leaking underground storage tanks, and oil-contaminated water runoff from streets and parking lots during rain storms’.
However, oils enter the ocean from a variety of sources, and both natural sources (large quantities) and land-based sources account for a large part of the total annual input of oil to the marine environment.
Also, hydrocarbons enter the ocean not merely as ‘wet’ oil products but also as gaseous air pollutants. Hydrocarbons from vapours deriving from the loading and unloading of oil at different stages from extraction to consumption, in the form of non-methane volatile organic compounds (nmVOCs), is one example. Polycyclic aromatic hydrocarbons (PAHs) from incomplete combustion (exhaust gases and flue gases) is another category of gaseous hydrocarbons that enter the marine environment as oil pollution.
In a report published in 2002 by the National Research Council (NRC) of the U.S. National Academy of Sciences, the average total worldwide annual release of petroleum (oils) from all known sources to the sea has been estimated at 1.3 million tonnes. However, the range is wide, from a possible 470,000 tonnes to a possible 8.4 million tonnes per year. raymond mill:http://www.hx-china.com/13.html
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In a report published in 1980, the total input of oil to the ocean was estimated at 3,2 million tonnes. Half of that amount (1.5 million tonnes) was estimated to come from vessels (about 1.2 million tonnes of which from operational, deliberate discharges). The source ‘discarded lubricants’ (from both sea-based and land-based sources?) was estimated to account for about 1.3 million tonnes. As pointed out in a recent comment to these figures, ‘oil pollution from ships probably reached its peak in 1979. Despite the publicity that oil spills always attract, even in 1979 only a small fraction of the oil entering the sea came from tanker accidents. Most came from routine operations, and discarded lubricants – such as engine oil poured into drains – accounted for a much higher percentage of the total. Since 1979, the amount of sea getting into the sea as a result of shipping operations has declined dramatically.’
Sources of oil input to the marine environment are often divided into natural, sea-based and land-based sources cone crusher. In the NRC report, the perspective of ‘following the oil’ is used, with four main categories of sources: discharges through natural seeps, discharges during the extraction of oil, discharges during the transportation of oil, and discharges during the consumption of oil (including both sea-based and land-based sources dryer machine). There are also other ways of placing accidental or operational/deliberate discharges of oils into different main categories.
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