Water pollution is caused by emission of domestic or urban sewage, agricultural waste, pollutants and industrial effluents into water bodies. Nowadays, its main source is the waste material discharged by industrial units. Waste materials like acids, alkalies, toxic metals, oil, grease, dyes, pesticides and even radioactive materials are poured into the water bodies by many industrial units. Some other important pollutants include polychlorinated biphenyl (PCB) compounds, lubricants and hot water discharged by power plants. The pollutants unloaded into the water bodies usually dissolve or remain suspended in water.
Sometimes, they also accumulate on the bottom of the water bodies. Another important pollutant, that can endanger marine life, is the oil spilled by oil tanks. As per the estimates of the United Nations, 1. 3 million barrels of oils are spilled annually into the Persian Gulf, and about 285 million gallons are spilled into the oceans every year. In the United States, the industries contribute to more than half of the total water pollution. The industrial effluents contain pollutants like asbestos, phosphates, mercury, lead, nitrates, sulfur, sulfuric acid, oil and many other poisonous materials.
In many countries, industrial water is not treated adequately before discharging it into rivers or lakes. This is particularly true in the case of small-scale industries that do not have sufficient capital to invest in pollution control equipment. In many instances, the researches and studies carried out to determine the toxicity of these pollutants are focused on the individual effect of the toxic elements. Therefore, sometimes these researches lead to an underestimation of the total toxicity of these harmful materials.
Besides, their toxicity is assessed with the help of tests carried out on bacteria, which also fails to take into account the accurate toxic effects on other organisms. These harmful pollutants are a major contributor to many grave diseases such as diarrhea, cholera, hepatitis, dysentery and salmonellosis. Besides, many of the pollutants are also carcinogenic i. e. they can cause cancer. Some pollutants like sodium can cause cardiovascular diseases, while mercury and lead cause nervous disorders. DDT is another toxic material which can cause chromosomal changes.
Excess fluoride in water may damage the spinal cord, while arsenic can cause significant damage to the liver and the nervous system. In addition to all these, organic compounds present in the polluted water facilitate the growth of algae and other weeds, which in turn use more oxygen dissolved in the water. This reduces the amount of oxygen dissolved in the water and the consequent shortage of oxygen for other aquatic life. In recent times, to control the menace of water pollution, various legislations have been introduced by different countries.
The legislations undertaken by the United States include Federal Water Pollution Control Act (1972), the Marine Protection, Research, and Sanctuaries Act (1972) and the Safe Drinking Water Act (1974). Besides, Federal Insecticide, Fungicide, and Rodenticide Act was also amended in 1988. For the success of these legislations, cooperation of the citizens and industrial units is an important prerequisite. In addition to the enforcement and proper use of these rules and regulations, availability of efficient and cheaper pollution control techniques is also required to tackle the threat posed by water pollution.