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Oil in Marine Ecosystems

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A Spilling History

We also know that marine oil spills occur. The 1989 Exxon Valdez spill released more than 35,000 tonnes of crude. In 1998, there were 176 spills reported world-wide. Britain's 1995 record was 458 tonnes of oil accidentally or deliberately discharged, an 8.3 percent increase from the previous year. Some experts suggest much of that oil has been discharged from ships flying "flags of convenience".

With major spills, there's little that can be done exept to track the oil's path and impacts. Scientists tell us that only the deep-dwelling or "benthic" organisms are likely to escape the coating effects of oil, a particular threat to intertidal organisms and marine mammals and birds. Prior to drilling off Canada's east coast, government and oil companies were required to spend millions assessing such potential ecological impacts.

Oil and Salmon: An Aromatic Story

Scientists are also telling us that oil may inflict its greatest damage on organisms such as salmon. The risks appear to come mainly from the polycyclic aromatic hydrocarbons contained in the oil. Polycyclic aromatic hydrocarbons (PAHs) are compounds formed when organic substances coal, oil, wood, gasoline are heated without sufficient air for complete oxidation. Heat causes the oil, composed of hydrogen and carbon, to shed its hydrogen, a process called aromatization. The resulting carbon atoms, shorn of hydrogen (aromatic), recombine into rings (polycyclic) that can be perilous to life.

PAHs were first shown to be carcinogenic in a 1775 study of chimney sweeps (specifically, the benzo[a]pyrene in soot). PAHs pose a particular threat to bioaccum-ulating organisms, depending on the size (molecular weight) of the PAH. The smaller PAHs (2 and 3 rings) are acutely toxic to many organisms, especially crustaceans and molluscs. PAHs adsorb to sediment and bioaccumulate in these organisms, which lack efficient mixed-function oxidase detoxification mechanisms.

PAHs with four or more rings (heavier molecular weights) have mutagenic (deform-causing) and carcinogenic effects. Such PAHs such as Benzo[a]pyrene is suspected of causing cancer by covalent bonding to guanine residues on DNA, which is thought to lead to errors in reading the genetic code during transcription.

National Marine Fisheries Service biologists in Alaska recently reported that PAHs might pose an extremely grave threat to Pacific salmon for many years after a spill.

These scientists found that:

  • Buried oil pockets (from 1989) may act like "land mines" loaded with poisons;

  • Contamination by only one part per billion of crude oil caused significant growth and reproductive failure in pink salmon;

  • Exposure to oil [PAHs] in egg stage is "akin to taking a shotgun to DNA."
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