No life without water
The contamination of streams, lakes, underground water, bays or oceans by substances that are harmful for living creatures is called water pollution. Water pollution is a serious business, because water is a necessary condition for all life on earth. There can be no life without water. All organisms consist of water, some live in water, others drink water. Animals and plants are not satisfied with just any type of water however. The water needs to be of a certain quality. If water contains toxic substances or dangerous micro organisms, plants and animals can become sick and may even die. When water pollution is very large-scaled, huge numbers of fish, birds and other animals may die. For humans, the sight of polluted rivers, lakes and bays is not very attractive either. Besides, fish and shellfish from polluted waters can be unsafe to eat.
Types of pollution
There are seven major types of water pollution. The polluters are as follows:
1. Petroleum products
2. Pesticides and herbicides
3. Heavy metals
4. Dangerous waste
5. A surplus of organic material
7. Contagious organisms
Petroleum products which are, among others, used for fuels, smears and the manufacture of plastics can end up in the water through the draining of ships and tankers, and the leaking of pipe lines and underground storage tanks. Oil can contain dangerous polychlorobifenyls (PCBs), which are chemical compounds that are very toxic and difficult to decompose. For that reason, an oil disaster within a short distance to a coast is often a catastrophe for the nature and the environment.
Pesticides and herbicides, the chemicals that are used for pest and weed control can be carried along by rain water, especially when too much pesticide is used. Some of the chemicals do not decomposed and remain dangerous for a long time. When animals eat plants which are sprayed with these non-decomposable chemicals, the substances may be absorbed into their tissue or organs. When other animals eat these contaminated animals, the chemicals move up through the food chain. The higher in the food chain, the higher the pollution concentration. When humans eat contaminated fish, their health can be harmed too. Humans can have contact with pesticides through contaminated drinking water. More than 14 million Americans drink water that is polluted with pesticides every year. Nitrates, which are often from fertilizers, can cause a mortal form of anaemia in children.
Heavy metals, such as copper, lead, mercury and selenium can end up in water in many different ways. The most likely sources are industry, car's exhaust fumes, mines and even natural dirt. Like pesticides, the concentration of heavy metals increases when you get higher in the food chain. With heavy metals this can have many negative effects. The cadmium in fertilizer, which is produced from sewer soil, can be absorbed by crops. When these crops are consequently eaten by humans in the right amounts, cadmium can cause diarrhoea and in the long term liver and kidney cancer.
Dangerous waste is chemical waste that is toxic, reactive, corrosive or flammable. When these substances are not treated with care, they can pollute water supplies. In 1969 the river Cuyahoga in Cleveland (Ohio, USA) was so badly polluted it caught fire. PCBs, a type of chemical that was generally used in electrical machines, can end up in the environment through oil leaks.
Fertilizers and other nutrients are used to make plants grow faster. When too much fertilizer is used, it is often drained away with the ground water. The nutrients initially stimulate the growth of plants and algae in the water. When these plants die and sink down into the soil, they are decomposed by micro-organisms. During this decomposition process, the micro-organisms use oxygen, which is absorbed from the water. The oxygen content in the water can decrease so much, that animals which depend on the water, may die. This process of reducing oxygen levels is called eutrophication.
Ground parts which are present in large amounts within beds, lakes or oceans can also pollute the ground. Because of ground erosion, the amount of nutrients in the water can rise very high. Ground erosion occurs when, for example, water drains away the ground on surfaces where trees first held the ground. The sediments that are swept away can also cover the gravel layer on the sides of the river. This can have negative consequences for many types of fish, such as salmon and trout, which lay their eggs in the gravel.
Research by the American Centre for Control and Prevention of Diseases (CDC) estimated that in 1994 about 900,000 Americans became sick because of organisms in the drinking water. According to this estimation, one person out of every 1,000 of those sick, dies. Many pathogenic organisms which occur in very small amounts in nature, are considered as pollutants when they occur in drinking water. Parasites such as giardia, lamblia and Cryptosporidium may occur in urban water supplies. In 1993, a break out of Cryptosporidium in the water supply of Milwaukee (Wisconsin, USA) made 400,000 people sick and caused 100 deaths.