Pollution Types & Effects IGCSE Biology 0610

Pollution: Types, Sources and Effects on Ecosystems

Biology editorial review is supported by the named review panel. Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.

Key concept

Pollution is the release of harmful substances into the environment. It includes water pollution (sewage, fertiliser runoff, toxic chemicals), air pollution (smoke, sulfur dioxide, carbon dioxide) and land pollution (pesticides, herbicides, non-biodegradable plastics).

Pollution questions require students to link a specific pollutant to its source, describe its effect on organisms or ecosystems, and often suggest how the pollution can be reduced. Biological indicator species provide evidence of pollution levels.

Water pollution

Sewage released into rivers or seas introduces organic matter that bacteria feed on. As bacteria decompose the sewage, they use up dissolved oxygen in the water through respiration. This reduces the oxygen available for aquatic organisms, potentially causing fish kills and loss of biodiversity.

Fertiliser runoff from farmland causes eutrophication (covered in detail in a separate guide). Toxic chemicals such as heavy metals (mercury, lead) from industrial discharge can accumulate in organisms through bioaccumulation and become more concentrated at higher trophic levels in food chains.

Air pollution

Carbon dioxide from burning fossil fuels contributes to the enhanced greenhouse effect and global warming. Sulfur dioxide and nitrogen oxides from burning fossil fuels dissolve in rainwater to form acid rain, which damages leaves, acidifies lakes and soils, and corrodes buildings.

Smoke and particulates from combustion can cause respiratory diseases in humans and reduce light reaching plants, decreasing photosynthesis. Carbon monoxide from incomplete combustion is toxic, binding to haemoglobin and reducing oxygen transport in the blood.

Land pollution

Non-biodegradable plastics persist in the environment for hundreds of years, accumulating in landfills, oceans and habitats. Marine organisms can become entangled in plastic or ingest it, causing injury or death. Microplastics enter food chains and have been found in organisms at every trophic level.

Pesticides and herbicides can contaminate soil and water. Some pesticides are persistent and accumulate through food chains (bioaccumulation). Nuclear waste remains radioactive for thousands of years and must be stored safely to prevent contamination.

Indicator species

Indicator species are organisms whose presence or absence indicates the level of pollution. For water pollution: bloodworms and sludgeworms indicate high pollution (they tolerate low oxygen), while freshwater shrimp, stonefly larvae and mayfly larvae indicate clean water (they need high oxygen levels).

For air pollution: lichens are sensitive to sulfur dioxide. Areas with diverse lichen growth have clean air; areas with few or no lichens are likely to be polluted. Monitoring indicator species is a biological method of assessing pollution without expensive chemical testing.

Try a focused question (4 marks)

A river downstream from a sewage outlet has very few fish but many bloodworms. Explain these observations.

Show the answer and marking guidance

Sewage provides organic matter that bacteria decompose.
Bacterial decomposition uses dissolved oxygen through respiration.
Low dissolved oxygen means fish cannot survive as they need oxygen for respiration.
Bloodworms are indicator species that can tolerate low oxygen levels, so they thrive where fish cannot.

Original Cambridge-style practice written for this site. It is not an official Cambridge past-paper question.

Common mix-ups to avoid

Check these points against your own answer before moving on.

Saying sewage directly poisons fish (it is the oxygen depletion by bacterial decomposition that kills them).
Confusing bioaccumulation with eutrophication.
Listing types of pollution without explaining the biological effects.
Not linking indicator species to the specific conditions they indicate.