Pollution

Pollution & the sea - like oil and water

One significant impact of human activity upon the oceans is marine pollution. It is not just oil pollution from accidents and illegally discharged tank cleaning wastes. Despite the high visibility of oil spills upon marine environments the total quantities involved are dwarfed by those of pollutants introduced from other sources (including domestic sewage, industrial discharges, leakages from waste tips, urban and industrial run-off, accidents, spillage, explosions, sea dumping operations, oil production, mining, agriculture nutrients and pesticides, waste heat sources, and radioactive discharges).

Land based sources are estimated to account for around 44 percent of the pollutants entering the sea and atmospheric inputs account for an estimated 33 percent. By contrast, maritime transport accounts only for around 12 percent.

Dawn of the dead: Creeping Dead Zones

The impacts of pollution vary. Nutrient pollution from sewage discharges and agriculture can result in unsightly and possibly dangerous "blooms" of algae in coastal waters. As these blooms die and decay they use up the oxygen in the water. This has led, in some areas, to 'creeping dead zones' (CDZ), where oxygen dissolved in the water falls to levels unable to sustain marine life. Industrial pollution also contributes to these dead zones by discharging substances which, as they degrade, also use up the dissolved oxygen

Gone fission

Radioactive contamination in the sea has many causes. Historically the testing of nuclear weapons has contributed. The normal operation of nuclear power stations also pollute the sea, but by far the single biggest point-sources of man-made radioactive elements in the sea are the nuclear fuel reprocessing plants at La Hague in France and at Sellafield in the UK. These discharges have resulted in the widespread contamination of living marine resources over a wide area; radioactive elements traceable to reprocessing can be found in seaweeds as far away as the West Greenland Coast and along the coast of Norway

Toxic chemicals

The input of man-made chemicals to the oceans potentially involves a huge number of different substances. 63,000 different chemicals are thought to be in use worldwide with 3000 accounting for 90 percent of the total production tonnage. Each year, anywhere up to 1000 new synthetic chemicals may be brought onto the market.

Of all these chemicals some 4500 fall into the most serious category. These, known as persistent organic pollutants (POPs). They're resistant to breakdown and have the potential to accumulate in the tissues of living organisms (all marine life), causing hormone disruption which can, in turn, cause reproductive problems, induce cancer, suppress the immune system and interfere with normal development in children.

POPs can also be transported long distances in the atmosphere and deposited in cold regions. As a result, Inuit populations who live in the Arctic a long distance from the sources of these pollutants are among the most heavily contaminated people on the planet, since they rely on fat-rich marine food sources such as fish and seals. POPs include the highly toxic dioxins and PCBs (Polychlorinated Biphenyls) together with various pesticides such as DDT and dieldrin. These chemicals are also thought to be responsible for some polar bear populations failing to reproduce normally.

Are you eating fish 'n' POPS tonight?

Scarily, seafood consumed by people living in temperate regions are also affected by POPs. Oily fish tend to accumulate POPs in their bodies and these can be passed to human consumers. When oily fish are rendered down into fish meal and fish oils and subsequently used to feed other animals, then this too can act as a pathway to humans. Farmed fish and shellfish, dairy cattle, poultry and pigs are all fed fish meal in certain countries, and so meat and dairy products as well as farmed and wild fish can act as further sources of these chemicals to humans.

Mining

Trace metal pollution from metal mining, production and processing industries can damage the health of marine plants and animals and render some seafood unfit for human consumption. The contribution of human activities can be very significant: the amount of mercury introduced to the environment by industrial activities is around four times the amount released through natural processes such as weathering and erosion.

Oil

The most visible and familiar form of pollution is oil pollution caused by tanker accidents and tank washing at sea, and in addition to the gross visible short term impacts, severe long term problems can also result. In the case of the Exxon Valdez which ran aground in Alaska in 1989, biological impacts from the oil spill can still be identified 15 years after the event. The Prestige, which sank off the Spanish coast late in 2002, resulted in huge economic losses as it polluted more than 100 beaches in France and Spain and effectively destroyed the local fishing industry.

More on oil spills.