Water pollution Cambridge IGCSE Environmental Management revision
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In plain words
A river is the cheapest drain there is, which is why so much ends up in one. What goes in upstream comes out of somebody's tap downstream, or ends up inside a fish, in a far stronger dose than it went in.
9 things to know
- Sources of water pollution: domestic waste, sewage, plastic waste, industrial processes and agricultural practices.
- Sewage carries bacteria that cause infectious diseases. Cholera is caught by drinking water contaminated with the cholera bacterium.
- Industrial processes release toxic substances, such as compounds of mercury and lead. These accumulate in the water and in the mud of rivers and lakes.
- Bioaccumulation is the build-up of a toxic substance in a single organism over time. The organism takes the substance in faster than it can get rid of it.
- Biomagnification is the increase in concentration of a toxic substance as it passes up a food chain. Each animal eats many organisms from the level below, and keeps the toxin from every one. Top predators receive the highest dose.
- Acid rain makes rivers and lakes acidic. Fish and other organisms die, or cannot breed.
- Agricultural practices: fertilisers and manure are leached from fields. The nutrient enrichment, from organic content and inorganic ions, leads to eutrophication, in which algae grow fast, die and are decomposed by bacteria that use up the oxygen.
- Strategies for improving water quality. Improved sanitation keeps human waste away from water supplies. Treatment of sewage removes solids and harmful bacteria before the water is returned to a river.
- Pollution control and legislation: laws limit what factories and farms may release, with monitoring and fines.
Worked example
A factory releases a little mercury into a lake. The water has very little mercury in it, yet fish-eating birds are poisoned. Explain.
- Small organisms take in mercury and cannot get rid of it, so it builds up in each one. This is bioaccumulation.
- Small fish eat many of these organisms, and large fish eat many small fish.
- The concentration rises at each step of the food chain. This is biomagnification.
- The birds, at the top, receive the highest concentration, enough to poison them.
Tips and tricks
- Bioaccumulation happens in one organism over time. Biomagnification happens along a food chain. Use each word for the right thing.
- Sewage and fertiliser both cause eutrophication, because both add nutrients.
It lands in your notebook with its questions as flashcards.
Water pollution: 6 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
Which is a source of water pollution?
Untreated sewage carries bacteria and nutrients.
Which disease is spread by water contaminated with sewage?
The cholera bacterium is carried in dirty water.
What is biomagnification?
Each level concentrates the toxin further.
What does nutrient enrichment of a lake lead to?
Extra nutrients feed a rapid growth of algae.
How does treating sewage improve water quality?
Clean water is returned to the river.
A toxin is found at 1 unit in tiny water plants and 800 units in a fish-eating bird. What explains the difference?Stretch
That is biomagnification.
Quiz
6 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 8 marks. Write your answers on paper, then check them.
Water pollution
Cambridge IGCSE Environmental Management 0680 · 8 marks · papermunch.org
Name ______________________________ Date ______________
Define the term bioaccumulation.[2]
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The build-up of a toxic substance in a single organism over time.
Explain why top predators are the most affected by a toxic substance in water.[3]
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The substance is passed up the food chain. Each consumer eats many organisms from the level below and keeps the toxin from them. The concentration increases at each level, so it is highest in top predators (biomagnification).
Describe three strategies for improving the quality of water in a river.[3]
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Improve sanitation, so human waste does not reach the river. Treat sewage before it is released. Control pollution with laws that limit what factories and farms release, and enforce them.
Answers: Water pollution
- 1. The build-up of a toxic substance in a single organism over time.
- 2. The substance is passed up the food chain. Each consumer eats many organisms from the level below and keeps the toxin from them. The concentration increases at each level, so it is highest in top predators (biomagnification).
- 3. Improve sanitation, so human waste does not reach the river. Treat sewage before it is released. Control pollution with laws that limit what factories and farms release, and enforce them.