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Tanker accidents :
As with other shipping , a large number of accidents involving oil
tankers happen every year . Most result in little or no spillage of oil ;
the accident may not rupture the cargo compartments , a damaged
vessel may be salvaged , or its cargo may be off-loaded into other
tankers.
Major shipping disasters involving large tankers are usually a different
matter . some very large tankers have been lost in the open ocean far
from land through hull failure , or fire and explosion ; the oil
disappeared
into the sea without coming ashore and had no
detectable impact . If the wrecked tanker is on fire , much oil may be
burned off and so reduce the amount entering the sea.
Atmospheric inputs :
Previously it was thought that the chief input of hydocarbons to the
atmosphere was from the incomplete combustion of petrol or diesel in
motor vehicles. Incomplete combustion of gas flared off at oil platforms
was regarded as another major source. This input to the atmosphere is
washed out in rain either directly to the sea or indirectly by
contributing to river run-off .
Environmental impact of oil pollution :
Rocky shores :
Rocky shores are high-energy beaches and stranded oil is quickly
removed by wave action and water movement. The more shelterd the
shore , the longer the oil remains .
A considerable variety of animals and the more sensitive red and green
algae are killed by exposure to fresh oil , but much of the oil reaching
beaches is bunker fuel or crude oil that ahs been at sea for several days
and lost most of its toxic
constituents ;it poisons few
organisms.
However if it is relatively non-toxic , a weathered oil may still cause
damage because of its physical properties.