UK researchers deploy mussell cages in pilot project to reduce marine plastic pollution

Scientists from Plymouth Marine Laboratory (PML) in the UK have installed cages filled with mussels at three marinas as part of a trial project to establish how effectively they can remove microplastics from tidal, estuarine waters.

Earlier laboratory experiments conducted by the PML team using a custom-designed flume tank have shown that a cluster of 300 blue mussels (Mytilus edulis) totalling around five kilograms could filter out over 250,000 microplastics per hour.

This is achieved by harnessing the natural filtering power of the mussels, which get their food by filtering seawater, sieving out plankton and other nutritious particles and flushing out unwanted particles from their digestive systems. As part of this process, microplastics are ejected in their normal faecal matter – which can then be collected as it sinks.

A scaled mussel filtration reef/system would not only remove microplastics but have multiple other benefits. The mussel’s hardy nature and water filtration capabilities mean they can improve overall water quality, reduce pathogen numbers, and soak up pollution while increasing local biodiversity and seafood quality in a given area.

With technical support from PML’s commercial subsidiary PML Applications, the specially-designed cylindrical PML cages currently being deployed contain 50 kilograms of mussels and feature receptacle tubes to collect the filtered waste. This enables the scientists to collect the faeces – and the microplastics – which can then be hauled in and removed from the seawater.

The organisation’s computer modelling has indicated that mussels sited near the mouths of rivers and estuaries could filter between 20 and 25 per cent of small, waterborne microplastics. The factors are complex, with physical parameters to consider including depth, currents, tides, temperatures, and varying plastic supply.

However, the findings suggest that a mussel-based clean-up system deployed closer to the source of microplastics (e.g. waste water treatment works or storm water drains) could potentially be rolled out at scale with significant positive effects.

The theory is now being scaled up to testing it in selected locations around the River Plym. Cages have been anchored under pontoons at Plymouth Yacht Haven, Yacht Haven Quay, and Turnchapel Wharf and they will be collected at the start of 2023 before being analysed. All three sites are within marinas operated by the Yacht Havens Group.

Flint Engineering Solutions, which is also located in Plymouth, constructed the cages being used in the project.