Water Pollution

ü Water is essential for life. Without water there would be no life. We usually take water as granted for its purity, but we must ensure the quality of water.

ü Pollution of water originates from human activities. Through different paths, pollution reaches surface or ground water. Easily identified source or place of pollution is called as point source.

ü Non point sources of pollution are those where a source of pollution cannot be easily identified, e.g., agricultural run off (from farm, animals and crop-lands), acid rain, storm-water drainage (from streets, parking), etc.

Causes of Water Pollution:

Ø The most serious water pollutants are the disease causing agents called pathogens. Pathogens include bacteria and other organisms that enter water from domestic sewage and animal excreta. Human excreta contain bacteria such as Escherichia coli and faecalis which cause gastrointestinal diseases, these are known as pathogens.

Ø The other major water pollutant is organic matter such as leaves, grass, trash etc. They pollute water as a consequence of run off. Excessive phytoplankton growth within water is also a cause of water pollution. These wastes are biodegradable.

Ø Oxygen reaches water either through atmosphere or from the process of photosynthesis carried out by many aquatic green plants during day light. However, during night, photosynthesis stops but the plants continue to respire, resulting in reduction of dissolved oxygen. The dissolved oxygen is also used by microorganisms to oxidise organic matter.

Ø This causes oxygen dependent aquatic life to die. Thus, anaerobic bacteria (which do not require oxygen) begin to break down the organic waste and produce chemicals that have a foul smell and are harmful to human health. Aerobic (oxygen requiring) bacteria degrade these organic wastes and keep the water depleted in dissolved oxygen.

Ø Thus, the amount of oxygen required by bacteria to break down the organic matter present in a certain volume of a sample of water, is called Biochemical Oxygen Demand (BOD).

Ø Water is an excellent solvent, water soluble inorganic chemicals that include heavy metals such as cadmium, mercury, nickel etc. constitute an important class of pollutants. All these metals are dangerous to humans because our body cannot excrete them. Over the time, it crosses the tolerance limit. These metals then can damage kidneys, central nervous system, liver etc.

Ø The organic chemicals are another group of substances that are found in polluted water. Petroleum products pollute many sources of water e.g., major oil spills in oceans.

Ø This process in which nutrient enriched water bodies support a dense plant population, which kills animal life by depriving it of oxygen and results in subsequent loss of biodiversity is known as Eutrophica.

Industrial Effluents:

Ø The water after it is used for industrial purpose cannot be reused for the same purpose without treatment.

Ø Such effluents have no definite composition, as anything which is not required is carelessly dumped into its stream. Such unwanted disposable material is contributed by chemical firms, food and beverage industry, textile and apparel industries, electronics and electrical material industries, or thermal power plants.

Ø The disposal of arsenic compounds by paper industry, or toxic chemicals by fertiliser plant had caused serious problem in western India.

Ø In many places, town authorities have not hesitated to let up sewage into streams or brooks or rivers, presuming that dilution would solve the pollution problem.

Ø Unfortunately, biological matter and bacteria such as coliforma, streptococcii, fecal coliforma, crenthronix, are not eliminated by mere dilution. Such water needs chemical treatment, like disinfection. This would also kill pathogenic bacteria.

International Standards for Drinking Water:

Fluoride:

· For drinking purposes, water should be tested for fluoride ion concentration. Its deficiency in drinking water is harmful to man and causes diseases such as tooth decay etc. Soluble fluoride is often added to drinking water to bring its concentration upto 1 ppm or 1 mg dm^–3.

· The F^– ions make the enamel on teeth much harder by converting hydroxyapatite, [3(Ca₃(PO4)₂.Ca(OH)₂], the enamel on the surface of the teeth, into much harder fluorapatite, [3(Ca₃(PO₄)₂.CaF₂].

Lead:

· Drinking water gets contaminated with lead when lead pipes are used for transportation of water. The prescribed upper limit concentration of lead in drinking water is about 50 ppb. Lead can damage kidney, liver, reproductive system etc.

Sulphate:

· Excessive sulphate (>500 ppm) in drinking water causes laxative effect, otherwise at moderate levels it is harmless.

Nitrate:

· The maximum limit of nitrate in drinking water is 50 ppm. Excess nitrate in drinking water can cause disease such as methemoglobinemia (‘blue baby’ syndrome).

Chemical	Concentration	Effects
Fluoride:	upto 1 ppm or 1 mg dm^–3	Tooth Decay
Lead:	in drinking water is about 50 ppb	damage kidney, liver, reproductive system etc
Sulphate:	<500 ppm	laxative effect
Nitrate:	<50 ppm	methemoglobinemia (‘blue baby’ syndrome).