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.

A landfill site

Air pollution

Combustion of fossil fuels and other fuels releases carbon dioxide. This contributes to the greenhouse effect and 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 world's major cities like Delhi in India and Karachi in Pakistan have dangerously high levels of air pollution.

A power station with smoke
Power stations give out sulfur dioxide

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 measure pollution.

Water pollution indicator species

Some freshwater animals are very sensitive to the 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.

Clean: stonefly nymph, mayfly larva. Some pollution: freshwater shrimp, caddis fly larva. Moderate: bloodworm, water louse. High: sludgeworm, red-tailed maggot.  Very high: no living insects.

In a sample of pond water there were a large number of water louse and red-tailed maggot. What does this tell you about the levels of pollution in the pond?

Water louse and red-tailed maggot are indicator species. They are able to live in water that is moderately to highly polluted. The pond must therefore be moderately to highly polluted.


The species living in a pond were monitored over a period of ten years. At the start of the ten years the pond mainly had stonefly nymph living in it and by the end of the ten years almost all of the stonefly nymph had gone. Explain what has happened to stonefly nymph.

Stonefly nymph can only live in clean water. As the ten years went on, the pond must have become more polluted. This killed off the stonefly nymph or they went to lie in a cleaner pond.

A bushy lichen

Bushy lichens need really clean air

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