3. Agricultural Discharges
With population explosion and advancement of science and technology, the demand for more crops from the same land leads to excessive uses of fertilizers and pesticides. This injudicious use of chemicals results in water pollution as these are washed off the lands through irrigation, rainfall and drainage and carried into river and streams. Excessive use of fertilizes results in accumulation of nitrogen, phosphorous and water on land. These are washed off the land with water through rainfall and irrigation into water bodies such as streams and rivers. Excessive storage of potassium and phosphorous enhances a luxuriant growth of algae in water bodies which goes on to decrease the dissolved oxygen content thereby leading to eutrophication. On the other hand nitrogenous fertilizers get converted to nitrates and get deposited in water bodies. When these nitrates enter the human body they are transformed to nitrites by intestinal bacteria. These nitrites combine with hemoglobin to form methaemoglobin. Methaemoglobin prohibits the formation of oxyhaemoglobin and causes damage to the vascular and respiratory system and blue colouration of skin leading to skin cancer.
Pesticides on the other side not only kill the targeted pest but they also affect the untargeted helpful organisms. BHC, PBs and DDT have been detected in Arctic region as well.
4. Shipping or coastal water pollution
Pollution of coastal water occurs due to discharge of sewage and industrial effluents through open drains or closed pipes, rubbish from ships, in course of transportation of oil, exploration or exploitation of sea bed and ocean floor for obtaining crude petroleum. The chance of seashore water pollution is more from sewage and industrial effluents, but deep ocean surface water is contaminated with a layer of oil generally extended to a long distance. The source of this oil is, in most cases,accidents that take place during shipping and transferring. The greatest sufferers of this situation are marine birds, aquatic mammals and fishes. The birds lose their power of flight and external and aquatic mammals have agonies due to closure of eyes, ears and obstruction in locomotory activities.
5. Thermal and Radioactive Plants
Different industries and nuclear power plants use water for cooling and discharge the heated water into nearby streams or water bodies. Nuclear reactors, nuclear explosions, nuclear war, medicinal use and research laboratories are the main sources of radioactive waste. These are most toxic as their effect persists for a number of generations.The long suffering people of Hiroshima and Nagasaki are a living example of radioactive pollution.
Detergents as water pollutant
The term detergent, means cleansing agent, has come to mean a soap substitute. They include ingredients like surfactants, builders and additives such as anticorrosive sodium silicate, stabilizers and soil suspending carboxymethyl cellulose. Etc. Both surfactants and builders of detergents create serious pollution problems in water. ABS (Alkyl benzene sulphonates )are considered as surfactants. The ABS has one serious disadvantage that it is non-biodegradable. Consequently,the detergent stay around in water supplies more or less indefinitely, causing some rivers and sewage treatment plants or ponds to become covered with mountains of foams. So now completely biodegradable linear alkyl benzene sulphonates (LAS) are used. Lauryl sulphate is an excellent surfactant and like LAS is also biodegradable.