Freshwater pollution

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Temps de lecture : 4 minutes  

pollution des eaux douces
The Earth’s water stocks should be able to renew themselves. Unfortunately, some of mankind’s activities (domestic use, industry or agriculture) seriously pollute watercourses and water tables which are sources of drinking water. As well as damaging the ecosystem (sometimes irreparably), this pollution kills 2.2 million people every year, especially in the poorest countries which are in dire need of a water treatment system.

Soft water, unlike hard water and seawater, contains very little dissolved salt. It makes up 3% of the hydrosphere. Almost three quarters is polar ice, a little less than a quarter is underground water and a minute part is superficial water. In the end, only about 0.01% of soft water on Earth is directly usable. Water circulates continuously between the different reservoirs (seas and oceans, continental superficial and underground waters, atmosphere and biosphere). Thus, even if stocks are not limitless, some are always being renewed. If we give it enough time, water is a completely renewable resource.

However, human activity has caused the quality of water supplies to deteriorate. 25% of watercourses in Western Europe and Southern Europe are extremely polluted. Two billion people in the world and 40% of world agriculture depend on non-renewable underground water tables to supply them with drinking water and water for irrigation.

A vital resource

Soft water is for human consumption, for drinking, preparing food and irrigating crops. Poor quality water is dangerous for health. As the world’s population has increased, so has global water consumption but not everyone has access to clean water that is fit for consumption.

The lifestyle in developed countries has also contributed to the increase in water consumption (toilets, showers, leisure…). Moreover, the urban concentration of populations requires water being transported and treated on a larger scale and city-dwellers throw out polluted water. Thus, for cities, water distribution and water treatment are challenges that take up significant shares of budgets.

Causes of pollution

Industry, agriculture and domestic activities are responsible for polluting soft water. The pollution can be caused by organic (waste being thrown out without being treated) and microbiological matter. This type of pollution causes aquatic wildlife to asphyxiate.

Organic matter, especially human excrement is the prime cause of river pollution. On the one hand, it saturates the water and stops ecosystems functioning normally and on the other hand, it puts pathogenic microorganisms into the water. These can transmit diseases to Man if the water is not purified before consumption.

Pesticides contaminate watercourses as well as underground water by infiltration: they are scattered in the atmosphere and fall back down as rain. Aquifers are also affected by nitrates in fertilisers. Nitrate pollution, which is mainly caused by agriculture (66%), can have toxic effects on the human body if too many nitrates are ingested. Similarly to phosphates, they change the biological balance of aquatic environments and cause eutrophication problems.

Other types of pollution can degrade soft water: metallic pollution (non-biodegradable), radioactive pollution, thermal pollution (water is used as a cooling liquid) or acid pollution.

Watercourses being developed, especially dams being built, can have disastrous consequences on soft water. [See Dam summary]

Water-related diseases

In 2002, about 2.6 billion people lacked an adequate water treatment system. 80% of these people lived in Sub-Saharan Africa and South-East Asia.

Over 2.2 million people, mainly in developing countries, die from illnesses linked to poor water quality and appalling sanitary conditions every year. Every eight seconds, somewhere in the world, a child dies from an illness linked to dirty water. There are many microorganisms in dirty water because of animal and human faeces.

Some of these bacteria cause severe diarrhoea that can lead to the body being severely dehydrated. This results in death. In hot countries which do not have septic tank latrines, sick people’s faecal matter rapidly contaminates drinking water. Malaria and dengue fever are other examples of diseases where polluted water infects mosquitoes which then pass on the infection to humans.

Effects on ecosystems

An aquatic ecosystem becomes unsanitary or unhealthy when the balance of its natural state is disturbed. These disturbances can be physical (for ex: hot water being poured into a watercourse), chemical (for ex: toxic waste being poured out) or biological (for ex: the introduction and propagation of non-indigenous animal or vegetable species). Soft water pollution can cause: the death of certain species, eutrophication, tumours and deformations in animals, the development of bacteria…

Many symptoms of an ailing ecosystem occur at the same time. For example, the increased acidity of water in a lake can cause the death of certain species and thus allow the temporary proliferation of species that can withstand acidity better.

The water table in Bangladesh has been contaminated with arsenic and is threatening the lives of 75 million people (according to a British Geological Survey, there were more than 50 million people in the country drinking the contaminated water in 2001). The rock at the bottom of the Brahmaputra river basin where water is pumped to the surface by millions of wells contains arsenic. It can cause breast cancer, kidney and liver disease, respiratory problems and it can be fatal. Over 25% of these 4 million tubular wells which are the main source of drinking water contain dangerous amounts of arsenic. The WHO describes this situation as « the largest poisoning of a population in history » . An FAO report came to the conclusion that the inhabitants could be exposed to arsenic in drinking water but also indirectly through subsistence farming that is irrigated by the polluted water table. Indeed, about 95% of underground water which is drawn is for irrigation and 5% is for domestic use. In 2001, about 24 million people were already suffering from arsenic poisoning.

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