Plastics and Litter in the Environment

Introduction

Plastics are cheap, light, strong, waterproof and easy to shape, which is why they are used for everything from drinks bottles to car parts. But the same properties that make plastics so useful make them a serious pollution problem. A plastic bag used for a few minutes can last for decades or more in the environment. This page explains why plastics persist, how they harm wildlife, and why tiny fragments called microplastics are now found almost everywhere on Earth.

Core explanation

What plastics are. Most plastics are polymers : enormous molecules made by joining thousands of small monomer molecules into long chains. Poly(ethene), used for bags and bottles, is made from ethene; poly(propene) and PVC are other common examples. Most are made from crude oil.

Why they persist. Microorganisms break down natural materials such as paper, wood and food because they have enzymes that can attack their bonds. Most plastics have long chains held together by strong carbon–carbon bonds, and few microbes have enzymes that can digest them. Plastics are therefore non-biodegradable . Sunlight and weathering do slowly make them brittle, but they break into smaller and smaller pieces rather than disappearing.

Effects of plastic litter.

Problem Effect --- --- Entanglement Seals, turtles and birds get caught in nets, rings and packaging, and drown or are injured Ingestion Animals mistake plastic for food; stomachs fill and they starve Visual pollution Litter spoils beaches, parks and rivers, harming tourism Blocked drains Litter can block drains and worsen floods Landfill Plastic takes up space for a very long time

Microplastics. Pieces smaller than 5 mm are called microplastics. Some are made small on purpose, such as the pellets used to manufacture plastic goods. Many more form when larger items break down, or are shed as fibres when synthetic clothes are washed and as dust from car tyres. Microplastics have been found in the deep ocean, Arctic ice, soil, drinking water and inside animals. Tiny organisms eat them, so they enter food chains. Their long-term effects on health are still being studied.

Dealing with plastic waste.

- Landfill — simple but uses land and the plastic lasts for a very long time. - Incineration — releases energy that can generate electricity, but produces carbon dioxide and, without careful control, other harmful gases. - Mechanical recycling — plastics are sorted, washed, melted and remade; it saves crude oil and energy but needs careful sorting by type. - Reducing use — reusable bags and bottles and less packaging stop waste at the source. - Biodegradable plastics — some newer plastics made from plant materials can be broken down by microbes, usually only in industrial composting conditions.

Step-by-step reasoning

To explain how a plastic bottle becomes part of a fish's diet:

1. The bottle is littered and reaches the sea. 2. Sunlight and waves make it brittle. 3. It breaks into smaller fragments, then microplastics. 4. Small animals such as zooplankton eat the particles. 5. Fish eat the zooplankton, taking in the plastic.

Visual explanation

Picture a timeline beneath a drinks bottle floating in the sea: after a year it is faded and cracked, after ten years it is a scatter of flakes, and after many decades it is a cloud of tiny specks drifting through the water, some of them inside plankton and fish.

Real-world analogy

A long polymer chain is like a necklace of thousands of beads held on strong wire. Natural materials are more like beads on thread that a hungry mouse can chew through. Microbes are the mice: they can nibble thread, but not wire, so the plastic necklace stays intact.

Real-world example

The Great Pacific Garbage Patch is a region of the North Pacific where ocean currents gather floating debris. Most of it is not a solid island but a soup of plastic fragments, nets and microplastics spread over a vast area, and it shows how rubbish from many countries ends up in one place.

Why?

Why did the introduction of charges for plastic carrier bags work so well? A small fee made people think about each bag. In the UK, the number of single-use bags handed out by large supermarkets fell by more than 90% after charges were introduced, showing how reducing use cuts waste at its source.

Common misconception

"If a plastic breaks up until you cannot see it, it has gone." Breaking into microplastics is not biodegradation. The polymer molecules are still there; they are just spread through water, soil and living things where they are harder to remove.

Worked example

Question: A town produces 500 tonnes of plastic waste a year. If 30% is recycled and 20% incinerated, how much goes to landfill, assuming no other routes?

Reasoning: Recycled + incinerated = 30% + 20% = 50%. Landfill = 100% − 50% = 50%. 50% of 500 tonnes = 250 tonnes.

Answer: 250 tonnes go to landfill.

Quick check

1. What size are microplastics? Answer: Smaller than 5 mm.

Exam focus

Explain non-biodegradability by referring to microorganisms: "microbes cannot break down plastics", not simply "plastics do not rot". When evaluating disposal methods, give an advantage and a disadvantage for each, such as incineration producing energy but also carbon dioxide.

Advanced insight

Scientists have discovered bacteria that produce enzymes capable of breaking down PET, the plastic used in drinks bottles. Researchers are engineering faster versions of these enzymes, which could one day allow plastics to be broken back into monomers and made into new plastic of the same quality, an approach called chemical or enzymatic recycling.

Summary

Plastics are polymers, mostly made from crude oil. Microbes lack enzymes to break their strong chains, so most plastics are non-biodegradable and persist. Litter entangles and is swallowed by wildlife, spoils landscapes and blocks drains. Larger items break into microplastics, found in oceans, soil and food chains. Reducing use, reusing, recycling and responsible disposal all limit the harm.

Practice questions

1. Explain why most plastics are described as non-biodegradable. Answer: Microorganisms cannot break them down because they lack enzymes to attack the strong bonds in the long polymer chains. 2. Give two ways plastic litter harms marine animals. Answer: Animals become entangled and drown, and they swallow plastic, which fills their stomachs so they starve. 3. Name two sources of microplastics. Answer: Any two: breakdown of larger plastic items, fibres from washing synthetic clothes, tyre dust, manufacturing pellets. 4. Give one advantage and one disadvantage of burning plastic waste. Answer: Advantage: energy is released to generate electricity. Disadvantage: carbon dioxide and possibly toxic gases are produced.