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Marine pollution

Prior to 1972, the crash of some seabird populations caused by DDT, outbreaks of Minamata disease in Japan from mercury-contaminated seafood, and the Torrey Canyon and other oil spills focused the attention of the Stockholm Conference on marine pollution. Policy responses included bans on production and use of some substances, regulations to reduce discharges, and the prohibition of ocean dumping, as well as a significant scientific effort to improve the status of knowledge about these pollutants. These responses are enshrined in a number of international agreements, including the 1972 London Dumping Convention and its 1996 Protocol, the 1989 Basel Convention on the Control of Transboundary Movement of Hazardous Wastes and their Disposal, and the 1995 Global Programme of Action for the Protection of the Marine Environment from Land-based Activities. Marine pollution is also an important focus of UNEP's Regional Seas Programmes that have been established in many parts of the world.

Globally, sewage remains the largest source of contamination, by volume, of the marine and coastal environment (GESAMP 2001a), and coastal sewage discharges have increased dramatically in the past three decades. In addition, because of the high demand for water in urban neighbourhoods, water supply tends to outstrip the provision of sewerage, increasing the volume of wastewater.

Disease burden of selected common and marine-related diseases
disease DALYs/year
economic impact
malaria 31.0 124.0
diabetes 11.0 44.0
trachea, brachia and lung cancer 8.8 35.0
stomach cancer 7.7 31.0
intestinal nematodes 5.0 20.0
upper respiratory tract infections 1.3 5.2
trachoma 1.0 4.0
dengue fever 0.75 3.0
Japanese encephalitis 0.74 3.0
diptheria 0.36 1.4
diseases related to marine contamination
related to bathing and swimming 0.4 1.6
seafood consumption (hepatitis) 1.8 7.2
seafood consumption (algal toxins) 1.0 4.0
sub-total 3.2 12.8

Note: one DALY (Disability-Adjusted Life Year) equals one person-year of productive life lost through death or disability

Source: GESAMP 2001a

Public health problems from the contamination of coastal waters with sewage-borne pathogens were well known in the 1970s, and in many developed countries improved sewage treatment and reduction of the disposal of industrial and some domestic contaminants into municipal systems have significantly improved water quality. In the developing world, however, the provision of basic sanitation, as well as urban sewer systems and sewage treatment, has not kept pace. High capital costs, the explosive pace of urbanization, and in many cases limited technical, administrative and financial capacities for urban planning and management and ongoing operation of sewage treatment systems are barriers to efficient sewage treatment (GESAMP 2001a). Removal of these barriers, as well as alternative approaches, is urgently needed.

Recent evidence suggests that bathing in waters well within current microbiological standards still poses significant risk of gastrointestinal disease, and that sewage contamination of marine waters is a health problem of global proportions (see box, GESAMP 2001a, WHO 1998).

A primary concern at the Stockholm Conference was the introduction of nutrients to coastal and marine waters. Human activities now account for more than half of global nitrogen fixation (Vitousek and others 1997a), and the supply of fixed nitrogen to the oceans has greatly increased. Sewage discharges are often the dominant local source near urban areas but global inputs are dominated by agricultural run-off and atmospheric deposition. The highest rates of riverine transport of dissolved inorganic nitrogen to estuaries from all sources occur in Europe and in South and East Asia (Seitzinger and Kroeze 1998). Nitrogen levels are exacerbated by widespread loss of natural interceptors such as coastal wetlands, coral reefs and mangrove forests.

At the time of Stockholm, agricultural nutrient run-off was 'not yet a major global problem'. Most fertilizer use was in developed countries but the rapid increase of fertilizer use in developing countries was already foreseen (SCEP 1970). Fertilizer use has stabilized in developed countries but is increasing in developing ones (Socolow 1999), a trend expected to continue. Fertilizer use has undoubtedly been enhanced by widespread subsidies, which reflect the high political priority of increasing food production and reducing food costs.

Seasonal zones of oxygen-depleted waters

Red dots on the map indicate seasonal zones of oxygen-depleted waters resulting from human activities

Source: Malakoff 1998 after Diaz and Rosenberg 1995

Atmospheric inputs, derived primarily from vehicle and industrial emissions and in some areas evaporation from animal manure and fertilizer, dominate anthropogenic nitrogen inputs to some coastal areas. They are expected to rise with increasing industrialization and vehicle use, especially in developing regions (GESAMP in prep.). Atmospheric nitrogen inputs to the nitrogen-limited open oceans will also increase, with potential significant impacts on primary production and the carbon cycle.

Marine and coastal eutrophication from elevated nitrogen inputs has emerged as a worrying trend not foreseen three decades ago. There is increasing evidence that blooms of toxic or otherwise undesirable phytoplankton are increasing in frequency, intensity and geographic distribution (Richardson 1997). Severe eutrophication has occurred in several enclosed or semi-enclosed seas, including the Black Sea (Zaitsev and Mamaev 1997, Balkas and others 1990). Elsewhere, elevated growth and subsequent decay of phytoplankton has caused widespread areas of seasonally oxygendepleted water (see map above). Phytoplankton blooms can have major economic impacts on fisheries, aquaculture and tourism (see table below).

At the time of the Stockholm Conference concerns for ocean health centred on pollution by POPs (particularly DDT and PCBs), heavy metals and oil (Goldberg 1976, Matthews and others 1971, UN 1972a, SCEP 1970). Some response measures have been effective, for example, introduction of unleaded gasoline helped to reduce lead levels in Bermuda (Wu and Boyle 1997, Huang, Arimoto and Rahn 1996); national regulations and international agreements such as the Convention on the Prevention of Pollution from Ships (MARPOL) resulted in the reduction of operational oil discharges from ships; and North American seabird populations affected by DDT recovered after this chemical was banned in the region.

In other cases, improved information has clarified some concerns. High levels of mercury in tuna and swordfish, for example, have been shown to have natural sources; the most dramatic effects of oil spills have proved to be localized and relatively transient; and heavy metal contamination, except for lead and mercury, has been found to be highly localized and has relatively minor impacts except at high concentrations.There are, however, other continuing concerns about these pollutants. The chemical residues of oil spills may have subtle long-term effects (Heintz, Short and Rice 1999), and chronic, small releases cause seabird mortality and other environmental effects (GESAMP in prep.). The effects of heavy metal contamination can be severe and are a significant concern in the Arctic (AMAP 1998).

Economic losses from red tides in fisheries and aquaculture
date location species loss
1972 Japan yellowtail ~47
1977 Japan yellowtail ~20
1978 Japan yellowtail ~22
1978 Republic of Korea oyster 4.6
1979 Maine, United States many 2.8
1980 New England, United States many 7
1981 Republic of Korea oyster >60
1985 Long Island, United States scallops 2
1986 Chile red salmon 21
1987 Japan yellowtail 15
1988 Norway and Sweden salmon 5
1989 Norway salmon, rainbow trout 4.5
1989-90 Puget Sound, United States salmon 4-5
1991 Washington State, United States oyster 15-20
1991-92 Republic of Korea farmed fish 133
1996 Texas, United States oyster 24
1998 Hong Kong farmed fish 32
Source: Worldwatch Institute 1999

The most serious concerns globally relate to POPs, many of which are transported globally via the atmosphere and are ubiquitous in the oceans. There is growing evidence that long-term, low-level exposures to some POPs cause reproductive, immunological, neurological and other problems in marine organisms, and possibly in humans, but the evidence for widespread ecological or human health impacts at current levels of contamination remains equivocal.

Another threat to the oceans, and in particular to living organisms, is non-biodegradable litter which enters the sea. Each year, large numbers of seabirds, sea turtles and marine mammals are killed by entanglement in or ingestion of non-biodegradable litter.

Human-induced changes in the natural flow of sediment have emerged since the Stockholm Conference as a major threat to coastal habitats. Urban and industrial development drives the construction of residential and industrial infrastructure which, depending on its nature, can alter sediment flow. In addition, agriculture, deforestation and construction typically mobilize sediments. Deltas, mangrove forests, beaches and other coastal habitats are sustained by the supply of sediment, while other habitats, such as coral reefs and seagrass beds, may be smothered or deprived of light. Sedimentation is one of the major global threats to reefs, particularly in the Caribbean, Indian Ocean, and South and Southeast Asia (Bryant and others 1998, Wilkinson 2000).