Microplastics are plastic particles smaller than 5 millimetres. Some are deliberately manufactured at a small size, while many form when larger products and waste break apart. They have been found from beaches and surface water to sediments, sea ice, organisms and deep trenches.
“Microplastic” describes a size class, not one chemical. Particles differ in polymer, shape, additives, age and the organisms growing on their surface, so their movement and effects vary.
Primary and secondary microplastics
Primary microplastics enter the environment already small. Examples include pre-production pellets and some abrasive particles. Secondary microplastics are fragments or fibres shed from larger objects such as packaging, ropes, nets, paint, synthetic textiles and tyres.
Sunlight, heat, waves and abrasion make exposed plastic brittle. It fragments into smaller pieces but does not simply disappear; it can continue toward nanoplastic sizes that are harder to measure.
How they reach the sea
- Stormwater carries road dust, tyre wear and litter into drains and rivers.
- Wastewater receives synthetic fibres shed during washing and particles from households and industry.
- Poorly managed waste escapes from landfills, streets and coastlines.
- Fishing, aquaculture, shipping and recreation lose or shed plastic at sea.
- Airborne fibres and fragments can settle on water or land and later wash downstream.
Wastewater treatment can capture many particles, but performance varies and captured material may remain in sludge. Source reduction is therefore as important as end-of-pipe filtration.
What do microplastics do to marine life?
Organisms from plankton to whales can encounter or ingest particles. Laboratory and field studies report physical blockage, reduced feeding, inflammation or exposure to additives in some species and conditions. Effects depend on dose, particle properties and biology.
Microplastics can move through food webs, but scientists are still resolving exposure and health risks for people at real-world levels. Uncertainty is a reason for better research and prevention, not for sensational claims.
Can they be cleaned from the ocean?
Once tiny particles disperse through the water column and sediment, removal without harming plankton is extremely difficult. Capturing litter in rivers and harbours helps, but preventing loss upstream is more effective.
Ways to reduce microplastic pollution
Policies can improve product design, textile and tyre standards, pellet handling, wastewater and stormwater treatment, reuse systems and producer responsibility. Individuals can reduce unnecessary plastic, maintain clothing to limit fibre shedding, dispose of waste correctly and support community and policy action.
Microplastics are one part of the larger issue explored in the restored educational resource Lessons for the Planet: Pollution and Solutions.
Frequently asked questions
Are microplastics visible?
Particles near 5 millimetres can be visible, while smaller pieces and fibres often require microscopes or chemical identification.
Do biodegradable plastics solve the problem?
Not automatically. Many require specific industrial conditions and may persist in cold marine environments. Reduction, reuse and verified waste systems remain important.