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Increasing human population has led to an increase in pollution. Some of this is due to:

• more fossil fuels being burnt for heat and power
• more food being grown
• land taken over for industry and housing

Land pollution

The rubbish we throw out that is not recycled goes into a land fill. These are huge holes in the ground into which our rubbish is dumped. Some things like batteries cannot be put into landfill sites because of the toxic chemicals they contain. They must be recycled. Other land pollution comes when some people dump rubbish in public or other private places, often to avoid paying for it to be disposed of. This is called fly tipping and is illegal.

Air pollution

Combustion of fossil fuels and other fuels releases carbon dioxide. This contributes to the greenhouse effect and the vast majority of scientists think this leads to global warming. It also releases sulfur dioxide and nitrogen oxides which can cause acid rain. Air pollution can also be caused by tiny particulates from smoke which can cause smog. Some of the most polluted cities are in Bangladesh, Pakistan and India.

Water pollution

Nitrate fertilisers are very soluble in water and are easily washed off fields by the rain and then into rivers and reservoirs. Because nitrates are all soluble, they cannot easily be removed from the water.

Pesticides used by farmers to kill weeds or insects may be washed or blown into streams and rivers.

Pollution indicators

The level of pollution in air or water can be indicated by the species living there. This is known as an indicator species. Data obtained using indicator species will only show if an area is polluted or not. Indicator species cannot measure pollution levels - only chemical analysis using electronic meters and laboratory tests can.

Water pollution indicator species

Some freshwater animals are very sensitive to oxygen levels, such as stonefly larvae and freshwater shrimps. If these animals are found in a river, it shows that the river is clean. However, some animals are adapted for surviving in polluted conditions, for example blood worms and sludge worms. Presence of these species indicates there is a high level of water pollution.