Ocean pollution

Posted: 19 March 2008

The oceans are the ultimate sink for all pollution, 70-80 per cent of which originates from land-based sources. Globally, some 450 cubic kilometres of wastewater - from untreated or partially treated sewage, industrial effluents and agricultural runoff - are carried into coastal waters by rivers and streams every year. Nearly everywhere in the developing world coastal cities dump their untreated wastes into the sea. No place in the world's seas is immune from pollution, as ocean currents transport pollutants to the far corners of the world.

Oiled Jackass penguins, South Africa.
Oiled Jackass penguins, South Africa.
Oiled Jackass penguins, South Africa. © International Fund for Animal Welfare (IFAW).

Filthy facts:

  • The toxic tide of pollution is increasing in scope and intensity. In the Gulf of Mexico an environmental "dead zone" now covers over 7,700 square miles and is expanding. No marine life, other than bacteria, survives there. Agricultural and industrial pollution from the vast Mississippi River Basin is responsible.

  • Somewhere between 50 and 60 million tons of untreated (or partially treated) municipal wastes flow daily into the Yellow Sea from China's coastal towns and cities.

  • Every year, rivers and streams transport roughly 25 billion tons of eroded sediment into coastal waters, smothering near shore ecosystems and fouling shallow waters habitats.

  • Every year ships at sea discharge somewhere between 5 and 50 million tons of oil. Most of this is the result of the routine discharge of engine wastes and bilge slops, in direct violation of international treaties.

  • The countries surrounding the Mediterranean Sea dump 30-50 million tons of untreated or partially treated urban wastes and sewage into coastal waters every year.

  • Calcutta and Mumbai (Bombay), India, dump 400 million and 365 million tons, respectively, of raw sewage and other municipal wastes into coastal waters every year.

  • Australia's northern beaches are being swamped by tons of marine debris - plastic bottles, rubber thongs, fishing nets and weather balloons. It took 10 people 10 days to clean up nine km of beach in remote north-east Arnhem Land. Of greatest concern are the large numbers of fishing nets which are lethal to wildlife.

  • Over 46,000 pieces of plastic litter are floating on every square mile of ocean today. In the Central Pacific, there are up to 6 pounds of marine litter to every pound of plankton.

  • Beluga whales swimming in the highly polluted St Lawrence River, which connects the Atlantic with North America's Great Lakes, have such high levels of PCBs in their blubber that, under Canadian law, they now qualify as "toxic waste dumps".

  • The rapid build-up of pollution, particularly oxygen-consuming phosphorus and nitrogen from agricultural activities (fertilizers), has turned 100,000 square kilometres of the Baltic's deeper waters into an oxygen-starved "dead sea".

  • Of the Black Sea's 537,000 cubic kilometres of brackish water, 90 per cent of it is anoxic (devoid of oxygen) - a natural process made infinitely worse by pollution.
Human impacts on oceans map
Human impacts on oceans map
Red and orange areas indicate highly impacted areas of the ocean. © Science/ B S Halpern. Click on map to enlarge.
Coral reefs:

Scientists say that pollution may be a major contributor to the worldwide decline of coral reefs, playing as big a role as global warming. A combination of human sewage and shipyard discharge may be responsible for the development and spread of deadly black band disease in corals.

Both pollution and global warming stress the tiny polyps which build reefs, making them more vulnerable to disease. According to the US National Marine and Fisheries Service, diseases of stony corals have skyrocketed over the last decade. Studies have shown that coral diseases are affecting greater numbers of coral species, are increasing in frequency and distribution, and are spreading to new regions faster than ever recorded in the past.

In recent years, a number of new coral diseases have emerged, with new types of symptoms not observed in the past. Several of these diseases kill coral tissue at rates much faster than ever observed before.

According to University of Illinois geologist, Bruce Fouke, many more tests are needed to identify what is killing the coral. "But the present trilogy of disease distribution, high metal concentrations and presence of human pathogens creates a signpost, at least, that human pollution is playing a role."

A new study by the US National Center for Ecological Analysis and Synthesis estimates that over 40 per cent of the world's oceans have been heavily affected by human land-based activities; only 4 per cent of ocean waters "remain relatively pristine".

See Map charts human toll on oceans