Nature has always dealt with waste. Leaves fall, animals die, and bacteria break it all down into something useful again. Pollution is what happens when we hand ecosystems more than they can process, or hand them materials they have no way of breaking down at all.
📘 What you need to know
Producing, treating and disposing of waste causes air, water and soil pollution, and destroys habitat.
Decomposing organic waste in landfill releases methane, a potent greenhouse gas.
Waste has social impacts: health risks, poor living conditions and reduced quality of life, falling hardest on low-income communities.
Environmental injustice occurs when the harm from waste is felt disproportionately by poorer countries and communities.
The Basel Convention (UNEP, 1992) regulates the movement of hazardous waste between countries.
Pollution occurs when substances are added faster than ecosystems can process them into harmless forms.
Ecosystems act as natural filters — forests absorb carbon dioxide, wetlands absorb nitrogen and phosphorus — but their capacity has limits.
Biodegradability is how quickly natural processes break a substance down; half-life is the time for half of it to decay.
Environmental impacts
Pollution
Type
How waste causes it
Consequence
Air pollution
Burning waste, especially in open landfills, releases harmful gases including carbon dioxide; decomposing organic waste releases methane
Both gases contribute to climate change, and methane is a potent greenhouse gas
Water pollution
Improper disposal lets chemicals and hazardous materials leach into rivers, lakes and oceans
Harms aquatic life and contaminates drinking water sources
Soil pollution
Hazardous waste, chemicals and heavy metals from landfills seep into the ground
Contaminates soil, harms plant growth, and enters food chains through crops
Notice that the methane problem comes from the most harmless-sounding part of the bin. Food and garden waste are natural and biodegradable, but buried under tonnes of rubbish they rot without oxygen, and that is what produces methane rather than carbon dioxide. Sending organic waste to landfill is the mistake, not the waste itself.
Habitat destruction
Landfills and waste dumps take up large areas of land, which usually means destroying natural habitat and losing biodiversity. In Ghana, the Agbogbloshie e-waste dump polluted local water sources and destroyed large areas of natural land — a site that received electronic waste from far wealthier countries.
Social impacts
Waste management is not only an environmental issue. Its social consequences fall particularly on low-income communities and countries.
Health risks
Exposure to waste, especially e-waste and biohazardous materials, causes serious health problems including respiratory diseases, skin infections and cancers.
Low-income countries receiving waste from high-income nations often lack proper facilities to handle and treat it safely.
That leads to dangerous living and working conditions for the people who sort and burn the waste, often by hand.
Environmental injustice
High-income countries frequently export waste to low-income countries that struggle to manage it safely. The result is environmental injustice: the negative impacts of waste are experienced disproportionately by poorer countries, which did not generate it.
Key agreementThe Basel Convention, introduced by UNEP in 1992
Regulates movement of hazardous waste between countries, prevents export from high-income to low-income nations, and protects health and the environment from improper disposal
The treaty is important, but not a complete solution — illegal waste exporting and dumping still occurs.
Impact on local communities
Living near a landfill or waste processing plant lowers quality of life through bad smells, noise and possible contamination of local water and soil. Communities near waste sites also tend to suffer lower property values, reduced economic opportunities and poorer health outcomes.
The pattern worth naming. Waste sites are rarely placed in wealthy neighbourhoods. Cheaper land means sites end up near communities with the least political power to object, and once a site is there property values fall further, so those with means move away. The injustice is not a coincidence — it is built into how sites get chosen.
Ecosystems and pollution
DefinitionPollution occurs when harmful substances are added to the environment at a rate faster than ecosystems can process or transform them into harmless substances
Read that definition carefully: pollution is defined by a rate, not by a substance. Ecosystems naturally absorb and manage a certain amount of waste through processes such as photosynthesis and nutrient cycling. Trouble begins only when the amount exceeds their capacity.
The green line is not fixed. Cut down the forest or drain the wetland and it drops, so pollution appears at a lower rate of input than before.
Ecosystems as natural filters
Ecosystem
What it absorbs
How
Forests
Carbon dioxide
Trees absorb it during photosynthesis and release oxygen, reducing atmospheric carbon dioxide
Wetlands such as salt marshes and mangroves
Nitrogen, phosphorus and other pollutants
They trap the substances and use them for plant growth, filtering water before it reaches rivers and oceans
Grasslands and farmland
Nitrogen and phosphorus
Plants take them up from the soil as nutrients, reducing the impact of agricultural runoff
These are ecosystem services in action. Two matter most here:
Carbon sequestration: plants absorb carbon dioxide from the atmosphere and store it in their tissues, reducing greenhouse gases.
Water filtration: wetlands and forests filter pollutants from water before it reaches rivers, lakes or oceans. Salt marshes along coastlines absorb heavy metals and excess nutrients, protecting marine ecosystems downstream.
Where the limits show
Excess carbon dioxide: forests absorb it, but deforestation reduces the number of trees, limiting their ability to manage rising levels.
Eutrophication: wetlands absorb nutrients, but when agricultural runoff carries too much nitrogen and phosphorus the system is overloaded, causing water pollution.
Biodegradability and half-lives
Biodegradability is how quickly natural processes break a substance down into harmless components.
Biodegradable materials such as paper and food waste decompose quickly, because bacteria and other organisms break them down into harmless materials.
Non-biodegradable materials such as plastic, glass and synthetic chemicals do not break down easily, and can remain in the environment for hundreds or thousands of years.
DefinitionHalf-life = the time taken for half of a substance to decay or break down
Each step down the red curve halves what is left, which is why long half-life pollutants never quite disappear — they just get harder to measure.
Long half-lives: pollutants such as pesticides (for example DDT) and radioactive waste persist in ecosystems for years or decades. DDT has a half-life of around 15 years, so it stays in soil and water for decades, affecting wildlife, food chains and whole ecosystems.
Short half-lives: substances such as organic waste decompose quickly, so their environmental impact is much smaller.
Worked examples
WE 1
Explain why pollution is defined as a rate
Explain why pollution occurs even though ecosystems can naturally absorb waste. (3 marks)
Point 1: natural capacity
Ecosystems absorb and transform a certain amount of waste through processes such as photosynthesis and nutrient cycling.
Point 2: the threshold
Pollution occurs when substances are added faster than the ecosystem can process them into harmless forms.
Point 3: an example
Wetlands absorb nitrogen and phosphorus, but heavy agricultural runoff overloads them, causing water pollution and eutrophication.
Not the substance, but the rate at which it arrivesthe word “rate” is the mark — a definition without it is incomplete
WE 2
Discuss the social impacts of waste exports
Discuss the social consequences of high-income countries exporting waste to low-income countries. (4 marks)
Point 1: health
Exposure to e-waste and biohazardous materials causes respiratory diseases, skin infections and cancers among those handling it.
Point 2: capacity
Receiving countries often lack proper facilities to treat waste safely, so it is burned or dumped, creating dangerous living and working conditions.
Point 3: injustice
This is environmental injustice — the harm falls on countries that did not generate the waste and gain least from the products.
Point 4: the counter-argument
Exporting can bring income and employment, and the Basel Convention of 1992 regulates hazardous transfers, though illegal dumping still happens.
Economic benefit for a few, health and environmental cost for manynaming the Basel Convention and its year is an easy way to show precise knowledge
WE 3
Explain the significance of half-life
Explain why pollutants with long half-lives are of particular environmental concern. (3 marks)
Point 1: what half-life means
Half-life is the time taken for half of a substance to decay or break down.
Point 2: persistence
A long half-life means the pollutant stays in the environment for years or decades — DDT’s is around 15 years, so a quarter remains after 30.
Point 3: the consequence
It remains in soil and water long enough to move through food chains, affecting wildlife and whole ecosystems far from where it was released.
Short half-life, short problem; long half-life, a problem for generationscontrast with organic waste, which decomposes quickly, to show you understand the comparison
💡 Exam tips
Define pollution using rate: added faster than ecosystems can process it.
Split impacts into environmental (air, water, soil, habitat) and social (health, injustice, community).
Remember methane comes from organic waste decomposing in landfill.
Learn the Basel Convention: UNEP, 1992, hazardous waste between countries.
Name specific ecosystem filters: forests for carbon dioxide, wetlands for nitrogen and phosphorus.
Quote DDT’s 15-year half-life as your example of a persistent pollutant.
⚠ Common mix-ups
Saying any harmful substance is pollution. It becomes pollution when the rate exceeds what can be processed.
Thinking ecosystems have unlimited capacity. Overloading is exactly what causes eutrophication.
Confusing biodegradable with harmless. Food waste in a landfill produces methane.
Treating half-life as full breakdown time. It is the time for half to go, and the rest takes far longer.
Listing only environmental impacts. Social consequences carry equal marks.
Assuming the Basel Convention solved waste exports. Illegal dumping continues.
Up next: How Waste Is Disposed Of. Every society has to put its waste somewhere, and there are six main options. None of them is free of drawbacks, and the next page compares them honestly.
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