Causes of Water Pollution

The Industrial development Urbanization and for achieving more comforts in life, the human has polluted the

surrounding including the aquatic environment. Most of the available water either surface or underground is severely

polluted. A number of factors causing to contaminate potable water are;

• Municipal Wastes: It comprise of the human excreta, sewage, kitchen wastes and storm water allowed to flow into

drains, sewers, canals, and rivers in untreated state, causing to pollute water bodies. The sewage is also used for

irrigation without undergoing proper treatment. The wastewater has certain amount of nitrates, phosphates and

potassium (NPK), which provide the essential nutrients for the growth crops.

• Human and animal wastes contains pathogenic microorganisms like bacteria, viruses, protozoa and worms. These

harmful organisms caused to make the surface and subsurface resources polluted. The human beings and other

animals are affected when they come in contact or consume the contaminated aquatic life. Wastewater is produced at

a rate of 70-80% of the consumed quality. This contains biological, inorganic, organic and industrial compounds,

therefore more BOD is required for its treatment.

•Industrial Effluents: Industrial effluents consists of organic and inorganic salts, pathogenic organisms, toxic

materials, metal scraps, acids, alkalis, heavy metals etc. Pakistan is facing the serious dilemma of industrial pollution.

The wastes and effluents are being dumped in water courses untreated. At least 50 metals have been detected in the

effluents and these includes Mercury, Cadmium, Chromium and lead which are extremely harmful for human health.

Water Pollutants

Clean water has to be used for intended purpose, and then returned will be polluted. The agents caused to pollute

water is pollutant. The major pollutants are (i) Oxygen Demanding wastes (ii) Nutrients (iii) Pathogenic organisms

(iv) Suspended solids (v) Salts and other dissolved solids (vi) Toxic metals and Organic compounds (vii) Heat

Oxygen Demanding wastes (ODW): Oxygen demanding wastes are substances that oxidize in water. As

microorganisms decompose these wastes, they utilize oxygen dissolved in water, which reduce the concentration of

DO. As DO drops, fish and other aquatic life are threatened and in extreme case, killed. The critical level of DO

varies greatly among species. Like trout and salmon species of fish required cold water with DO of 7.5 mg/l, while

carp can survive at 3 mg/l. The US-EPA recommended 4 mg/l of DO for various species of fish survival. The low

level of DO produced undesirable odor, tastes and color reduce the attractiveness for domestic and for recreational

purposes. ODW are biodegradable organic and inorganic substances present in municipal wastewater or in effluents

from various industries like food processing and paper production. Similarly the natural organic matters like plant

leaves and dead animals if disposed up in water contribute to oxygen depletion. There are several measures of DO

like COD and BOD.

Nutrients: Nutrients are chemicals like nitrogen, phosphorus, carbon, sulfur, calcium, potassium, iron manganese,

cobalt and boron that are essential to the growth of plants. In case of water quality, nutrients are pollutants when

high concentration caused growth of algae. The presence of algae adversely affect the quality of water for drinking

and recreational purposes. The decomposition of algae used DO from water leaving less concentration for other

aquatic life. Algae and decaying materials add color, turbidity, and objectionable taste to water, that are difficult to

Water Pollutants

to remove. Aquatic species require a number of nutrients for their growth and reproduction. The three important

nutrients are carbon, nitrogen and phosphorus. Plants require large amounts of these three nutrients and the deficiency

caused to limit the growth. The nutrients that is less available than the demand is known as limiting nutrients. The algal

growth can be controlled by reducing the supply of these nutrients. The Carbon is usually available from various

sources like alkalinity, dissolved CO2 from atmosphere and decaying organic matter, so it is not a limiting nutrient.

The major sources of Nitrogen are municipal wastewater, runoff from animal feedlots, chemical fertilizers and nitrogen

deposition from atmosphere, certain bacteria and blue-green algae. It is very difficult to control nitrogen specially in

lakes. Nitrogen presence in drinking water is usually in the form of Nitrate (NO3), which it self is not toxic. However

certain bacteria found in the infant intestinal convert Nitrate to high toxic Nitrite (NO2) . Hemoglobin in the blood

stream has more affinity for nitrite than oxygen and when oxygen is replaced by nitrites it is known as

methemoglobinemia. It causes a bluish discoloration of the infant, and is commonly known as blue baby syndrome.

Phosphorus is another essential nutrient for plant growth. Human sources of phosphorus are the agricultural runoff

of heavy fertilizers and domestic sewage. In sewage phosphorus is from human feces and part of Detergents.

Phosphorus in detergents is usually in the form of sodium tripolyphosphate Na2 P3 O10. when wash water

containing this ingredient is discarded the following reaction occurs and slowly releases the orthophosphate

ion, PO4 3- ; P3O5 5- + 2H2O ------- 3 PO4

3- + 4H+ .Tripolyphosphate reacts with water producing

othrhophosphate . It is easily available to plant and its control is essential not to release in water bodies.

Water Pollutants• Pathogenic organisms: Pathogens are disease causing microorganisms that grow and multiply within the host.

The growth of microbes in a host is infection. Pathogens may be bacteria, viruses and protozoa responsible for

several diseases like cholera, dysentery, typhoid, hepatitis, malaria etc. The intestinal discharges of an infected

individual, a carrier may contain billions of pathogens, which if allowed to enter in water supply can cause

epidemic diseases. The carrier may not necessary to have symptoms of diseases, which makes it even more

difficult to protect water supply from contaminations. If concentration of pathogens are high, such water may

also not fit for swimming and fishing purposes. Certain shellfish can be toxic because they concentrate

pathogenic organisms in their tissue, making the toxicity levels in the shellfish much greater than the levels in

the surrounding water.

• Suspended Solids: Organic and inorganic particles that are carried by the wastewater into a receiving water is

termed suspended solids. When the speed of water is reduced by flowing into a lake or reservoir, many of these

particles settles to the bottom as sediments. Similarly when eroded soil particles are being carried by water and

are not settled are sediments. Colloidal particles when do not settle easily caused turbidity. Organic suspended

solids may also exert DO. When sediments are deposited in lakes and reservoirs their usefulness is reduced. In

some rapidly moving mountain streams, sediment from mining and logging operations has destroyed many living

places for aquatic organisms.

• Salts and other Dissolved solids: Water naturally accumulates a variety of dissolved solids and salts as it passes

through soils and rocks on its way to sea. The salts includes cations such as Sodium, Calcium, Magnesium, and

potassium while the common anions are Chloride, Sulfate and bicarbonate.

Water Pollutants

The presence of these dissolved cations and anions are termed as total dissolved solids (TDS). Fresh water usually

have less than 1500 mg/l TDS. Brackish water have up to 5000 mg/l, saline water above 5000 mg/l and sea water

more than 30,000 mg/l. The concentration of TDS is an indicator of the usefulness of water for various applications.

Like drinking water upper limit is 500 mg/l, livestock upto 10,000 mg/l. For crop production more than 500mg/l is a

problem for salt tolerance crops, while more than 2100 mg/l need proper drainage system. All naturally occurring

water has some amount of salt in it. A number of industries discharge high concentration of salts and urban runoff

may contain large amounts where salts is used to keep ice from forming on roads in winter season.

Similarly, the evapotranspiration increases salinity problem. The concentration in soils is usually controlled by

flushing the salts with additional amount of irrigation water. This process increase the cost as well as contaminate

water. If proper drainage is not available, then water table raises up along with dissolved salt and damage crops.

Toxic Metal and Organic Compounds: Most metals are toxic, like aluminum, arsenic, cadmium, chromium, mercury

Lead, iron and zinc. Some of these metals like chromium and iron are essential nutrients in out diet, but in high

doses they can cause a range of adverse impacts on the body, including nerves system and kidney damage

etc. Metals are non degradable and creates problems for human beings if their concentration increases in body.

The chemicals that can be used for killing of organisms are insecticides, herbicides, rodenticides and

fungicides..The three main group of synthetic organic insecticides are organochlorines also known as chlorinated

Water Pollutants

hydrocarbons, organophosphates and carbamate. The most widely used organochlorine is DDT

(dichlorodiphenyl trichloethane) is widely used to control insects, but are very persistent and soluble. It is very

toxic to human beings and caused a number of diseases including cancer. Agricultural runoff often contains

such agro-chemicals that has been applied on crops. Industrial wastewater contains either toxic metals or

organic compounds if discharged in large quantities, make water unfit for intended purposes. Many toxic

Compounds are concentrated in food chain, making fish unsafe for human consumption. Thus even small

quantity of toxic compounds in water can be incompatible with the natural ecosystem and human use.

Heat: The thermal and nuclear electric power plants requires large amount of cooling water. For example

nuclear power plant warms about 150,000 m3/hr of cooling water by 10C0 as it passes through the plant

condenser. If that heat is released to a local river or lake, the resulting rise in temperature can adversely affect

life in the vicinity of thermal plume. For some fish like trout any increase in temperature is life threatening,

while for other warm water is beneficial upto certain extent. Also the sudden change in temperature caused by

plant can disturb the local ecology. Similarly the water releases by different industries are much hotter than the

receiving waters. In some case hot water increases the metabolic activities of fish, causing more population.

The demand of dissolved oxygen increases with the same rate, but the concentration reduces due to more

consumption as well as the absorb capacity for DO is less in hot water than cool water. Similarly high

temperatures increase the rate of oxygen depletion when oxygen demanding wastes are presents.