pollution

pollution is the introduction of substances and energy in concentrations that result in harm to the marine environment and its fauna and flora. But see also environmental issues.

Dumping.

Disposal of waste and raw sewage into the sea from ships and land became commonplace in the 19th and 20th centuries. At the time it provided a relatively cheap and very effective way of keeping the land clean and, following the construction of the sewage systems that discharged wastes either into rivers or the sea, the health of city-dwellers improved immensely. Sea water was thought to be effective in cleansing human waste and killing the pathogens, but after the Second World War (1939–45) it became clear that eating contaminated fish and shellfish from polluted water created a serious health risk, and even swimming in the sea could be hazardous and was linked to poliomyelitis.

At the end of the Second World War there was a major problem of what to do with large quantities of redundant munitions and toxic chemical agents. The solution, which seemed innocuous at the time, was to dispose of them in the sea. Similarly, when the newly emerging nuclear industries started to generate large quantities of dangerous radioactive waste, this too was dumped in the deep ocean. The first of the campaigns by Greenpeace led to banning of the disposal of radioactive waste in the sea and eventually to a complete reappraisal of marine dumping and a tightening of international regulations.

Once the relevant annexe of the 1978 International Convention for the Prevention of Pollution from Ships, known as MARPOL, came into force, throwing and discharging most wastes from ships was also banned. All wastes now have to be off loaded in port, and the oceans are awarded greater protection from dumping of industrial waste than is afforded to the land or the atmosphere.

Toxic Chemicals.

Marine ecosystems do have a limited capacity to cope with low levels of naturally occurring toxic chemicals. Organisms that take up some pollutants like heavy metals (e.g. mercury and lead), either directly from the water or via their food, can regulate their contents to some extent. Once the pollutant is absorbed into the body it may be excreted or converted into a non-toxic form and stored in the liver or in fatty tissues. However, if a predator eats prey containing such detoxified pollutants, it too absorbs and stores the pollutant and so it accumulates—a process known as biomagnification. Top predators tend to accumulate high concentrations of the pollutants in their tissues, and humans are, of course, the ultimate top predator. For example, in the Faeroe Islands the traditional hunt for pilot whales has been abandoned because the whales are too heavily contaminated with heavy metals and PCBs (polychlorinated biphenyls) to be safe to eat.

Chemical industries continue to synthesize many thousands of novel substances each year. Many of these are specifically designed to be toxic and persistent. Ecosystems have no built-in ability to deal with novel substances, and so they have the potential to cause chronic long-term problems. Intensive agriculture, aquaculture, and industry all have high demands for chemicals that will boost production, control pests, and limit corrosion. The high cost of such chemicals favours the selection of persistent substances, which reduces the number of applications. The problems accruing from the synthesis and use of such novel substances were first recognized with DDT. Post-war, this was the most effective insecticide, particularly successful in controlling malaria-carrying mosquitoes and agricultural pests. However, DDT accumulated in body fat and interfered with the laying down of eggshells in birds, including seabirds; populations of many charismatic species declined catastrophically. This was the first indication of a much greater environmental disaster as DDT residues were found to be accumulating not only in Antarctic species but also in human tissues, which persuaded governments to curb its manufacture and use.

Likewise the manufacture of PCBs (polychlorinated biphenyls), once widely used as lubricants and coolants, was halted in 1977, when they were found to be accumulating in both man and animals. By the time their manufacture was banned about 2 million tonnes had been synthesized, most of which still exist today as they are highly stable. About a third is in waste stores and the rest is out there contaminating the environment.

The use of TBTs (tributyltins) in antifouling paints was so effective at controlling fouling organisms that they were rapidly and widely adopted. Soon their devastating impact as hormone disruptors was discovered; marine animals turned into sterile sexual intermediates, and some think reductions in human sperm counts have a similar cause. TBTs have largely been phased out, but they are so persistent that many harbours and yacht basins still have substantial traces of TBTs in their sediments, which are inhabited by very aberrant faunas.

Atmospheric Disruption.

Marine pollution is not all about direct impacts, it also involves the disruption of environmental processes. For example chorofluorocarbons (CFCs), once widely used as refrigerants, are inert in sea water and have no direct effect on the ocean life. But high in the earth's atmosphere, they lead to the breakdown of the ozone layer, which normally shields the surface of the earth from the damaging effects of the full intensity of the ultraviolet light coming from the sun. Once a hole appears in the ozone layer marine plants and animals are exposed to the full intensity of UV radiation. The productivity of the Southern Ocean has probably been reduced by more than 10%. It may also have contributed to the increasing prevalence of coral bleaching in coral reefs. It is estimated that it will take over 50 years for the ozone hole finally to return to normal. Also, the increase of greenhouse gases in the atmosphere, particularly carbon dioxide from the burning of fossil fuels, is threatening to cause climate change that will disrupt the global ecosystem, including the oceans, in an unpredictable manner.

Garbage.

Marine garbage, some thrown from or washed off ships, but most being carried in by rivers and blown into the sea from land, is not only unsightly but also causes real environmental problems. It accumulates in slicks where it becomes a major cause of premature death in turtles (see marine reptiles) through their mistaking plastic bags that block their guts for the jellyfish they feed on. Three hundred albatross chicks examined on the Pacific island of Midway, about as far as one can get from ‘civilization’, all had plastic items in their stomachs.

Inputs of some pollutants can be reduced by cleaning up our rivers and ground waters, and stopping direct discharges from land and ships. But controlling the inputs that arrive via the atmosphere will be much harder. The switch to unleaded fuel for vehicles has substantially reduced the lead entering the oceans from the atmosphere. Now anthropogenic radioactivity adds less than 1% to the natural background levels of radiation.

Oil Pollution.

Another source of pollution is the foundering of large vessels carrying damaging cargoes. The effects of massive oil spills after notorious tanker disasters, such as the Torrey Canyon and the Exxon Valdez, have been well publicized and have resulted in considerable improvements in navigation, ship safety, and routeing that have curtailed the frequency of such accidents. However, human error ensures the risks can never be eliminated while we continue to transport materials around the oceans and exploit seabed minerals. The only sure way to stop marine pollution is to cease the manufacture, use, and transportation of the major pollutants, but so long as the human population continues to grow, marine pollution problems will continue.

Bibliography

Clark, R. , Marine Pollution (1997).
Website on PCBs: www.atsdr.cdc.gov/tfacts17. html

www.epa.gov/owow/oceans/www.pewoceans.org/inquiry/marine/

M. V. Angel