Water pollution is any chemical, biological,

or physical change in water quality that has

a harmful effect on living organism or make

water unsuitable for desired uses.

Table of Sources, pollutants, and

effects of water pollution

Pollutants Sources Effects

Nitrates, Phosphates Fertilisers from farms, sewage

effluent

Lead to eutrophication

Pesticides, herbicides Farm, agricultural run-off Harmful to humans when passed

through food chains

Detergents Domestic sewage Contains phosphates which leads

to eutrophication

Oil, Grease Oil spills, industril effluent May cause death of aquatic

organisms

Suspended Solids, Rubbish Domestic wastes, Industrial

effluent

Reduce light penetration into

water

Heavy Metals

(Copper, Mercury, Lead)

Industrial plants

Electronics factories

Mining industries

•Mercury can cause blindness

•Pass to consumers through food

chains and are very toxic

Chemical, Radioactive Waste

Substances

Nuclear power stations,

research laboratories

Excess acids or alkalis effect the

lives of aquatic organisms

Microorganisms

(Virus, Protozoa,Bacteria)

Untreated sewage, human

faeces, animals wastes

Harmful to human if untreated

water is used

Addition of oxygen not sufficient to

support life.

Addition of oil destroys life by reducing

oxygen and catching fine, destroying

ecosystem.

Reduced reproduction rate of animals.

Increased incidence of diseases.

Imbalances created in secondary food

chains

Reduced activity of immune system.

• Eutrophication is a natural

process whereby an aquatic ecosystem

becomes enriched with nutrients causing

an excessive growth of aquatic plants.

• Nutrients can come from many sources such as:

Fertilisers (especially Nitrates and

Phophates) from agricultural fields.

Sewage treatment plant discharges.

Run-off of animal waste.

• Algal blooms endanger the ecosystem

in 2 main ways.

1,

• The densely populated algae cover the water surface and block

sunlight. Unable to carry out photosynthesis, the aquatic plants

die.

• When these plants die, aquatic animals lose their food sources and

habitats. As a result, the food chain and ecosystem change.

• Algae also reduce the level of dissolved oxygen in the water.

2,

• When the algae and other aquatic organisms die, decomposing

organisms especially saprophytic bacteria use up oxygen to

decompose the dead organic materials.

• This reduce the oxygen content in the water.

• A depletion in oxygen results in an increase in

biochemical oxygen demand (BOD).

• Eutrophication increase the BOD value in the water.

• BOD refers to the amount of oxygen utilised by

microogranisms to oxidise all organic matter in one litre

of water.

• The higher the BOD value, the more polluted the water as

the dissolved oxygen level decrease.