Storage and transportation 60% through the sea route of petroleum products make deliberate and accidental oil spills not so uncommon.According to the estimates of National Research Council in the US which is a private nonprofit institute that provides science,technology and health policy advice to the American government on an average,over 700 million gallons of oil pollutants enter the oceans every year,of which big spills account for only 5%.The largest contributors of oil to the oceans are drains and urban street run-offs accounting for 51% of the oil put into the oceans worldwide every year.

Routine maintenance,including boat bilge discharge and other ship operations,contributes 19%,air pollution 13% and natural seepage from the seafloor 9% of the annual oil discharged into the oceans.Crude oil spills from tanker accidents and offshore drilling hit the headlines because of the size of the spill and the immediate impact.

How does an oil spill affect the ecosystem

Various parts of the oil behave in different ways after coming into contact with water volatile organic parts partially evaporate reducing the mass of the spill by 20-40 %,the water soluble parts get dissolved,some of the oil sinks,while the remaining oil keeps floating on the water.Over a long period of time,most of this waste disintegrates,but this period sometimes stretches to decades.The major impact of oil contamination is on marine life.Animals living on the surface get coated with the oil and hence cant keep themselves warm.Also,ingested toxins could result in death.The animals that dont die immediately develop liver and reproductive diseases,which might have a long term impact on the ecosystem.

Oil spills also kill marine larvae.Oil waste poisons the organic substrate,interrupting the food chain of fish,and hence impacts the fishing industry in various ways.Across the world,coastal areas are thickly populated and the livelihood of a substantial number of this population is based on water bodies,starting from food processing to various tourism-related services,all of which get affected by oil spills.The contamination can also affect the weather conditions of the coastal areas.

How can the contaminated water be purified

After a spill,the oil forms a layer that floats on the water.With the spread of the oil,the thickness of this layer keeps decreasing.Purification simply means dealing with this slick layer and the methods depend on a lot of variables like waves,weather,water current,time duration,marine population,distance from the coast and so on.If the cleaning crew can reach the spill within a few hours,the first step is containment of the spill,which is done by using long skirt-fitted booms.The booms float on the surface and the skirts keep the oil from spreading out.The surface oil can be skimmed off using various methods.

Oil slicks may also be absorbed by sponge sorbents,or may simply be burnt by the cleaning crew,depending on their distance from the coastline.Another method uses chemicals called dispersants.Although these chemicals break down the oil,they can pose danger to marine life.Oil spills can also be treated by using biological agents.Fertilizers are spread over the spill area,promoting the growth of microorganisms,hence speeding up the hydrocarbon breaking up process.Although science offers several ways of cleaning the spill,these contaminants have long-term effects on the spill areas,sometimes even lasting for decades.

Why is Deepwater-Horizon such a global concern

Deepwater Horizon was a semisubmersible offshore drilling rig which sank on April 22,2010,causing a major oil spill.The rig was owned by Transocean Ltd and leased to BP until 2013.The spill was the result of an explosion.There have been no confirmed estimates of the damage done,because from the original 1,000 barrels the estimates have reached up to the 25,000-barrel mark.The spill could become the third largest oil spill of all time after the Gulf War oil spill in 1990 and the blowout of the Ixtoc I exploratory well off the shore of Mexico in 1979 streets ahead of the much publicized 1989 Exxon Valdez tanker spill in offshore Alaska.