Contamination is the industry word for the wrong thing in the right bin. It sounds mild. In practice it is the single biggest reason material collected for recycling does not get recycled, and a small number of items cause a wildly disproportionate share of the damage. Some of them are obvious once explained. Others are things put in the bin by people trying to do the right thing, which is why they keep happening.
What actually goes wrong
Your dry recycling goes to a materials recovery facility, where it travels along a line of screens, magnets, eddy current separators and optical sorters that identify materials and blow them off the belt into the right bunker. It is fast, largely automated and remarkably good at what it was designed for. It is also easily defeated.
Contamination causes three separate problems. It can stop the plant, when something wraps around a rotating shaft and a team has to climb in and cut it out. It can spoil the material, when a liquid or a food residue soaks into paper and card and destroys the fibre. And it can get the load rejected outright, when the level of non-target material is high enough that the facility refuses the delivery and the whole lorry goes for disposal instead.
That last one is why a single household can matter. A kerbside lorry carries the recycling from hundreds of homes, and a rejected load takes all of it with it.
The worst offenders
Plastic bags and film
The classic. Soft plastic wraps around the spinning shafts of the screening equipment and builds up until the machine has to be stopped and cleared by hand. Bagging your recycling makes it worse, not better, because a sealed bag cannot be sorted and is usually pulled off the line and binned unopened along with everything inside it.
Put recycling in loose. Film, bread bags, salad bags and carrier bags go to supermarket front-of-store collection points until kerbside film collections arrive.
Food waste and liquids
A half-full sauce jar or a bottle with juice still in it leaks over everything around it. Paper and card absorb it and become unusable. This is exactly why paper and card are supposed to be collected separately from glass and plastics wherever that is practicable.
A rinse is enough. Nobody expects washing-up-liquid clean, and using hot water and detergent on every container has its own environmental cost. Tip out the residue, swill it with the last of the washing-up water, leave it to drain.
Nappies and hygiene waste
Consistently reported by councils as one of the most common and most damaging items found in recycling. They contaminate everything they touch, they are a health hazard for the people picking the line by hand, and there is no route by which they become anything useful. General waste, every time, unless your council runs a separate hygiene collection.
Textiles, cables and hoses
Anything long, flexible and stringy behaves like plastic film in the machinery, only stronger. Clothes, bedding, garden hose, phone chargers and Christmas lights all tangle in the equipment. Textiles go to a clothing bank, a charity shop or a council textiles collection. Cables are electrical waste.
Batteries and anything containing one
The most dangerous item on this list by a distance. A lithium battery crushed in a bin lorry or a baler can catch fire, and the number of battery fires in the UK waste stream rose above 1,200 a year, an increase of 71% on the 700 recorded in 2022. These fires destroy vehicles and burn down recycling facilities.
Loose batteries, vapes, power banks, electric toothbrushes and any gadget with a built-in cell must never go in any household bin. They go to a battery collection point or an electrical recycling point.
Crockery, pyrex and drinking glasses
These look like glass and are not. Pyrex, ceramics and toughened drinking glasses have a different melting point from packaging glass, and a single fragment can ruin a whole batch of remelted cullet by creating a weak spot. Only bottles and jars belong in glass recycling. Broken crockery goes to general waste or the tip.
Black plastic trays
The optical sorters that identify plastics work by bouncing infrared light off the material and reading what comes back. Carbon black pigment absorbs that light, so a black tray registers as nothing at all and falls off the end of the line with the residue. Manufacturers have been moving away from it, but it is still out there.
Aerosols and gas canisters
Many councils accept empty aerosols in with metals, but plenty do not, and a partly full one is a genuine explosion risk in a baler. Camping gas canisters and butane cartridges should never go in a household bin under any circumstances. Check your council's A to Z for aerosols specifically, because this is one of the most variable items in the country.
If in doubt, leave it out
The instinct to put a doubtful item in the recycling and hope is understandable and it is the wrong call. One item in the general waste bin is one item lost. One wrong item in the recycling can cost a whole load. When you genuinely do not know, general waste is the safer error, and then look it up before next week.
The things that are fine and people worry about
- Envelope windows. Fine. The pulping process screens the plastic out.
- Staples and paperclips. Fine. Magnets and screens remove them.
- Labels on jars and bottles. Fine. They come off in processing.
- A bit of moisture. Fine. Rinsed and drained does not mean bone dry.
- Bottle caps left on. Usually preferred now, because a loose cap is too small to sort and falls through the screens. Check your council, but leaving it on is increasingly the advice.
Why it matters more than it used to
England's waste from households recycling rate was 43.8% in 2024, marginally down on 44.0% the year before. Of the 25.2 million tonnes of waste local authorities managed in 2024/25, 41.2% went for recycling, 50.3% went to incineration and 5.5% to landfill.
More of our waste is burned than recycled. Every load rejected for contamination moves material from the first column to the second, and it does so after the fuel has already been burned collecting it. The margins here are not comfortable enough to waste.
A two-minute household fix
Print your council's A to Z and stick the first page inside a cupboard door. Put a small container by the sink for batteries and small electricals so they never reach a bin at all. Keep a bag for soft plastics that goes to the supermarket with you. Rinse as you go rather than at the end of the week.
None of it is difficult, and it removes almost every route by which a household ends up contaminating a load.