Too much, too fast: Pollution is not about any waste at all: it is about waste added faster than nature can deal with it.
Absorbed or polluted?
- Ecosystems can absorb some waste: decomposers break it down and water dilutes it.
- Pollution happens when harmful substances are added faster than they can be broken down or made harmless.
- Pollution can be matter (chemicals, sewage, plastic) or energy (noise, light, heat).
- Pollution is a direct harm: it damages or kills organisms, which weakens food webs.
- The same waste can be absorbed in small amounts but overwhelm an ecosystem in large ones.
Remember it as: Pollution is too much, too fast for nature to clean up.
Matter and energy
- Plastic: an estimated 8 million tonnes a year enters the oceans; turtles mistake bags for jellyfish.
- Air: factory smoke causes smog and acid rain.
- Water: fertilisers cause algal blooms that kill fish.
- Energy: noise disturbs whales; light confuses migrating birds.
Real example: in the hot summer of 1858 so much raw sewage poured into the River Thames that its bacteria could not break it down. The river stank so badly that it was called the Great Stink, and London built new sewers to carry the waste away.
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How quickly an ecosystem can deal with waste depends first on how easily living things can break it down.
Biodegradability
- Biodegradability = how quickly a substance is broken down by living things (bacteria, fungi).
- Food, paper and cotton are biodegradable: they rot in weeks or months.
- Plastics, glass and metals have low biodegradability: they last for centuries.
- Plastic does not rot: it breaks into smaller pieces, down to microplastics under 5 mm.
- Breakdown is faster with warmth, water and oxygen; slow in cold, dry, airless places.
Real example: a plastic drinks bottle thrown into the sea is estimated to last about 450 years. It does not rot: sunlight and waves break it into smaller and smaller pieces.
Breaking up is not breaking down: Plastic that breaks into tiny pieces has not biodegraded. The microplastics are still plastic, spread further and are easier for animals to swallow.
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Half, then half again: Some pollutants decay or lose their activity over time. Their half-life tells you how long they stay harmful.
Half-life
- Half-life = the time for half of a substance to decay or lose its activity.
- After one half-life 50% is left, after two 25%, after three 12.5%.
- A long half-life means the substance stays harmful for a long time.
- Radioactive waste: caesium-137 about 30 years; iodine-131 about 8 days.
- Pesticides too: DDT in soil has a half-life of about 2 to 15 years.
Real example: the Chernobyl accident in 1986 spread caesium-137 across Europe. By 2016 about half of it had decayed; a quarter will still be there in 2046.
When a pollutant lasts a long time, every new amount adds to what is already there. That is why persistent pollutants cause long-term harm.
Persistent pollutants
- Persistent pollutants have long half-lives or low biodegradability.
- They accumulate: in soil, water and sediments, and in the bodies of living things.
- They build up in an organism (bioaccumulation) and up the food chain (biomagnification).
- Top predators carry the most and suffer most: poor health, fewer young.
- Examples: DDT, PCBs, mercury, plastics and the toxins they carry.
- People are exposed through food, water and air; some chemicals disturb hormones.
Non-persistent
- Breaks down fast
- Short half-life
- Harm is local and short
- Food waste, sewage
Persistent
- Breaks down slowly or not at all
- Long half-life
- Builds up for years
- DDT, PCBs, mercury, plastics
Real example: Lulu, a killer whale found dead in Scotland in 2016, had one of the highest levels of PCBs ever recorded, about 80 times the safe limit. She was at least 20 years old and had never had a calf.
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What non-biodegradable waste does: Questions ask for the impacts of non-biodegradable waste on ecosystems. Each impact needs the harm and what it does to organisms.
Impacts on ecosystems
- Animals swallow plastic, feel full and starve.
- Animals get tangled in nets, bags and rings and drown or are injured.
- Microplastics and chemicals bioaccumulate and biomagnify: fewer young, death.
- Heavy metals and chemicals leak into soil, water and groundwater.
- Waste covers soil and habitats: less light, less photosynthesis, less growth; broken glass injures.
- Fewer of one species means less food for the next trophic level.
Real example: on Midway Atoll in the Pacific, Laysan albatross parents feed their chicks plastic they mistake for food. Chicks have died with stomachs full of bottle caps and lighters.
What does not score: Greenhouse gases are not an impact of non-biodegradable waste here. 'Biodiversity falls' or 'it is toxic' alone score nothing: say how organisms are harmed.
How this comes up: Paper 2, Section A: a short Describe on how non-biodegradable waste harms ecosystems.
Plastic bags, glass bottles and metal cans are dumped along a river bank in a city.
Describe two negative impacts of this non-biodegradable waste on ecosystems.
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