There is no life without clean 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, and 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 microorganisms, plants and animals can become sick and may even die. When water pollution occurs on a very large scale, 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. And fish and shellfish from polluted waters can be unsafe to eat.
Types of pollution: There are seven major types of water pollution. The top 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 take many years or even decades to decompose. For that reason, an oil disaster within a short distance to a coast is often a catastrophe for natural habitats and for the environment at large.
Pesticides and herbicides- the chemicals that are used for pest and weed control are carried along by rainwater, especially when too much pesticide is used. Some of the chemicals do not decompose and remain hazardous for a long time. When animals eat plants sprayed with these non-decomposable chemicals, the substances are absorbed into their tissues and organs. When other animals eat these contaminated animals, the chemicals move up through the food chain. The higher the organism 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, often found in fertilizers, can cause a fatal form of anemia 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, cars exhaust, 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 sufficient amounts, cadmium can cause diarrhea and, in the long term, liver and kidney cancer.
Dangerous waste is any toxic, reactive, corrosive or flammable chemical waste. 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 generally used in electrical machinery, can end up in the environment through oil leaks.
Fertilizers are additional nutrients which help 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 microorganisms. During this decomposition process the microorganisms use oxygen, which is absorbed from the water. The oxygen content in the water can decrease so much that animals that depend on the water may die. This process of reducing oxygen levels is called eutrophication.
Sediments are soil particles that are taken along by the water can also cause pollution. They can contain toxics or high nutrient levels, affecting the water quality. Normally the small quantities are not a problem, but it can become disastrous when large amounts of soil are washed away. This often happens in areas where forests are cut down, leaving behind vulnerable bare soil. Large amounts of sediment can block certain waterways or cover the gravel layer on the sides of the river. This can have negative consequences for many types of fish like salmon and trout that lay their eggs in the gravel.
Contagious organisms- Research by the American Centre for Control and Prevention of Diseases (CDC) estimated that in 1994, about 900,000 Americans became sick because of harmful organisms in their drinking water. According to this estimation, one out of every 1,000 diseased persons dies. Many pathogenic organisms that occur in very small amounts in nature are considered 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.