Plastic ‘bio-beads’ from sewage plants are polluting the oceans and spreading superbugs

A recent spill of bio-beads – small plastic pellets used by some wastewater treatment facilities since the 1990s – has brought renewed attention to a problem that has been quietly accumulating in coastal waters for years.

Millions of bio-beads recently washed up onto the beach at Camber Sands in East Sussex. But this is not just another form of plastic pollution. Bio-beads can carry potentially dangerous bacteria.

Plastic bio-beads are used in wastewater treatment plants to help break down waste. They resemble the plastic pellets known as nurdles that are used as a feedstock by the plastic industry which are often found on beaches.

Bio-beads, however, are compressed, like a concertina, to maximise their surface area-to-volume ratio. This promotes the growth of bacteria that form a biofilm on their surface. These bacteria break down nutrients in the wastewater effluent and help process sewage.

Bio-beads are a relatively cheap and efficient method for treating waste. However, this efficiency comes with a significant environmental cost when these plastics escape.

The UK’s water industry insists that bio-beads shouldn’t escape from treatment facilities. They are supposed to be contained within the system by mesh screens.

Yet water companies are known to have to top up their bio-bead supplies which raises the question of how much of this plastic pollution is being released, and why.

The answer probably lies in ageing infrastructure. Many wastewater treatment works have outdated retention mechanisms that aren’t fit for purpose. Storage is another weak point.

Bio-beads have been seen in large dumpy bags or strewn across the ground in wastewater treatment plants, so they can spill before treatment processes begin.

Like any plastic, bio-beads will gradually break up into smaller particles. Fragmented bio-beads could escape into the environment as soon as they are smaller than the mesh screens used.

Bacteria-laden plastics

What makes bio-beads particularly concerning isn’t just the plastic itself – it’s what they carry. These pellets are designed to maximise bacterial growth, and when they come from sewage treatment facilities, that biofilm may include harmful bacteria, including E. coli and other pathogens dangerous to humans.

More worryingly, research – including our own studies – shows these plastics can harbour “superbug” bacteria that are resistant to antibiotics.

Our latest research has examined how bacteria grow on bio-beads and other substrates such as polystyrene, wood and glass in the environment. By collecting samples at various points along two Cornish rivers – from hospital wastewater, upstream near Truro to the marine environment of the Fal estuary – we’ve demonstrated that antimicrobial-resistant pathogens are found on plastics sampled from source to sea.

Protected within their biofilm, each bio-bead can become a tiny vehicle transporting potential pathogens from sewage works to beaches, swimming areas and locations where shellfish are cultivated.

Our 2024 review of this rapidly growing research area suggests that plastics may promote horizontal gene transfer, the process by which antimicrobial resistance can spread between bacteria. The implications are sobering: these small plastics could be facilitating the spread of antibiotic resistance across marine environments.

Reports from 2017 show there were at least 55 wastewater treatment works around the UK using bio-beads, serving a population of at least 2 million people. There are over 10,000 sewage treatment works in the UK, so those using bio-beads comprise a very small proportion.

While exact figures on bio-bead losses remain elusive, their presence on beaches tells another story. Historic spills, including a major incident near Truro in Cornwall in 2010, have deposited billions of these pellets into coastal waters. Their black or grey colour makes them easily mistaken for food by marine wildlife, from commercially important fish and, once broken or fragmented, shellfish and organisms at the base of the food chain.

Some bio-beads pose also additional chemical risks. Many were manufactured from recycled electronics materials and contain substances like lead and bromine.

If bio-beads are found accumulated on beaches, they can be removed – but with caution. Like any material from sewage systems, they should be handled with care. And any cleanup efforts are only treating symptoms. The solution must be at source.

A solvable problem

Alternative wastewater treatment methods exist. Not all wastewater treatment works use bio-beads, proving they’re not essential. Some facilities use different plastic designs (large flat surfaces rather than floating pellets) or denser materials such as ceramic or stone that are less likely to escape.

Some plants use activated sludge (a biological treatment process where wastewater is mixed with a community of microbes) that breaks down organic pollution. Other treatment stages, such as UV processing, add further layers of protection, though these complement rather than replace the bacterial breakdown process.

By collaborating with water companies, we’re investigating whether certain plastic polymers promote antimicrobial resistance more than others. If we can identify which materials pose the greatest risk without compromising treatment efficacy, we could recommend safer alternatives.

This issue demands transparency and accountability. If water companies disclose how many bio-beads they use and how frequently they require replacement, the scale of losses could be quantified. It’s equally important that spillages are reported and pressure for more environmentally sustainable methods is sustained.

Improvements in policy based on robust scientific data are also required, in the UK and elsewhere. This was highlighted in a 2024 report) from the Ospar convention (the Oslo-Paris convention for the protection of the marine environment for the north-east Atlantic) – of which the UK is a signatory.

Better management and a phase out of bio-beads is possible. This isn’t a technical challenge. Investing in alternative treatment methods and modern infrastructure can eliminate this unnecessary source of contaminated plastic pollution from our rivers and ocean.

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This article is republished from The Conversation, a nonprofit, independent news organization bringing you facts and trustworthy analysis to help you make sense of our complex world. It was written by: Pennie Lindeque, Plymouth Marine Laboratory and Emily Stevenson, University of Exeter

Dr Emily May Stevenson is a director of Beach Guardian CIC.

Pennie Lindeque does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.