A pollution pathway is the chain from a pollutant’s source to its effect. To explain one, write each step in order and say what causes the next step.
This lesson is part of environmental sustainability. After it, practise reading numbers in interpreting environmental indicator data.
How do I build a source to effect chain?
Start with the source, name the medium that carries the pollutant, then describe what changes in the environment and what that does to living things. Each link needs a reason, so ask “and then what happens?” after every sentence.
The frame has four slots: source, medium, change, effect. If a slot is empty, the explanation has a gap.
Worked example: fertiliser on a farm
An invented vegetable farm beside a stream spreads fertiliser before heavy rain. The question asks you to explain why fish in the stream die.
- The heavy rain washes fertiliser off the soil and into the stream. This is the source and the medium.
- The fertiliser contains nutrients, so algae in the stream grow and multiply quickly.
- A thick layer of algae blocks sunlight, so plants under it cannot photosynthesise and some die.
- When the algae and plants die, bacteria decompose them and use up the dissolved oxygen in the water.
- The fish do not get enough oxygen for respiration, so they die.
This is five linked statements. In an exam the marks would match the number of links you show, so a three-mark question needs three of them.
The mistake that costs marks
The common slip is the one-jump answer: “The fertiliser pollutes the water so the fish die.” Every step between “pollutes” and “die” is missing.
The corrected answer names the algae, the decomposition and the loss of dissolved oxygen. Those three terms are what a marking scheme looks for, because they show you understand how the harm happens.
A second pathway: smoke in the air
The same frame works for air pollution. An invented factory burns fuel that contains sulfur.
- Source: the factory chimney releases sulfur dioxide.
- Medium: the gas mixes with moisture in the air and forms acidic droplets.
- Change: rain carries the acid to the ground, making rain water and soil more acidic.
- Effect: plants take up nutrients poorly in acidic soil, so crops grow badly.
The steps differ from the fertiliser example, but the four slots are the same. That is the habit to practise.
Check yourself
An invented laundry behind a stream pours detergent water containing phosphates into it. Explain, in four linked statements, how this could reduce the number of fish.
Answer
- The detergent water enters the stream, so phosphate nutrients build up in the water.
- Algae grow and multiply quickly because of the extra nutrients.
- When the algae die, bacteria decompose them and use up dissolved oxygen.
- With less dissolved oxygen, fish cannot respire enough, so their number falls.
What to study next
Go on to comparing waste-management approaches to see how pathways change when waste is managed differently. Then work through the environmental sustainability practice set.
If a teacher checking each link of your chain would help, see online one-to-one Science tuition.