Definition of Pollution

- This is the introduction of foreign material, poisonous compounds and excess nutrients or energy to the environment in harmful proportions.
- Any such substance is called a pollutant.

Causes of Pollution

- Industrialisation and urbanisation are the main causes of pollution.
- As human beings exploit natural resources the delicate balance in the biosphere gets disturbed.
- The disturbance leads to the creation of conditions that are unfavourable to humans and other organisms.

Sources of Pollutants in Air and Water

• Motor vehicles release carbon (II) oxide, sulphur (IV) oxide, and nitrogen oxides and hydrocarbons.
• Agricultural chemicals, fertilisers and pesticides.
• Factories, manufacturing and metal processing industries.
• They release toxic substances and gases as well as synthetic compounds that are bio-undegradable.
• They release solid particles or droplets of poisonous substances e.g. arsenic, beryllium, lead and cadmium.
• Radioactive waste: Leakages from nuclear power stations and testing sites release radioactive elements like strontium-90 which can eventually reach man through the food chain.
• Domestic waste and sewage are released raw into water bodies.
• Oil spills from accidents in the seas and leakage of oil tankers as well as from offshore drilling and storage and processing.

Water Pollution

- In most cases, chemical wastes from industries are discharged into water.
- Toxic chemicals such as mercury compounds may be ingested by organisms.
- Insecticides like DDT, and weedkillers eventually get into the water and contaminate it.
- Oil and detergents also pollute water.
- Excess nitrates and phosphates from sewage and fertilisers cause overgrowth of algae and bacteria in water.
- This is called eutrophication.
- As a result there is insufficient oxygen which causes the deaths of animals in the water.

Air Pollution

- Smoke from industries and motor vehicles contains poisonous chemicals like carbon (II) oxide, carbon (IV) oxide, sulphur (IV) oxide and oxides of nitrogen. - When sulphur (IV) oxide and oxides of nitrogen dissolve in rain, they fall as acid rain. - Accumulation of carbon (IV) oxide in the atmosphere causes the infrared light to be confined within the atmosphere, the earth's temperature rises. - This is called the greenhouse effect. - Carbon particles in smoke coat the leaves of plants and hinder gaseous exchange and photosynthesis. - The particles also form smog in the air. - Lead compounds are from vehicle exhaust pipes. - All these have negative effects on man and the environment.

Soil/Land Pollution:

- Plastics and other man-made materials are biologically non-degradable i.e they are not acted upon by micro-organisms.
- Scrap metal and slag from mines also pollute land.
- Failure to rehabilitate mines and quarries also pollute land.

Effects of Pollutants

1. Chemical pollutants e.g. nitrogen oxides, fluorides, mercury and lead cause physiological and metabolic disorders to humans and domestic animals.
2. Some hydrocarbons as well as radioactive pollutants acts as mutagens (cause mutations) and carcinogens induce cancer.
3. Radioactive pollutants like strontium, caesium and lithium are absorbed into body surface and cause harm to bone marrow and the thyroid gland.
4. Communicable diseases like cholera are spread through water polluted with sewage.
5. Thermal pollution result in death of some fish due to decreased oxygen in the water.
6. Oil spills disrupt normal functioning of coastal ecosystems.
7. Birds that eat fish die due to inability to fly as feathers get covered by oil.
8. Molluscs and crustaceans on rocky shores also die.

Control Air Pollution

• Use of lead-free petrol and low sulphur diesel in vehicles.
• Use of smokeless fuels e.g electricity or solar.
• Filtration of waste gases to remove harmful gases.
• Liquid dissolution of waste gases.
• In Kenya, factories are subjected to thorough audits to ensure that they do not pollute the environment.
• Factories should be erected far away from residential areas.
• Reduce volume or intensity of sound.
• Use of ear muffs.
• Vehicle exhaust systems should be fitted with catalytic oxidisers.
• Regular servicing of vehicles to ensure complete combustion of fuel.

Control Water pollution:

• Treatment of sewage.
• Treatment of industrial waste before discharge into water.
• Use of controlled amounts of agrochemicals.
• Organic farming and biological control.
• Avoid spillage of oils and other chemicals into water.
• Good water management.
• Stiff penalties for oil spillage.
• Use of Pseudomonas bacteria that naturally feed on oil and break it up.

Control Soil pollution:

• Addition of lime to farms to counteract the effect of agrochemicals.
• Recycling of solid waste.
• Compacting and incineration of solid waste.
• Use of biodegradable materials and chemicals.
• Good soil management to avoid soil erosion.