Microplastics are a major concern when it comes to ocean pollution. These tiny pieces of plastic (less than 5mm) are ubiquitous in our oceans, and negatively affect all levels of organisms from plankton to humans. It is tricky collecting them from the water, as they are so small it is hard to remove them without also taking out organic material and marine life. However, Plymouth Marine Laboratory (PML) is looking into a natural solution to this increasing problem.

Nature’s solution

Dr Rachel Coppock, Marine Ecologist and one of the investigators on the project one of the investigators on the project, described how mussels are “voracious filter feeders”. They suck up a considerable amount of water in the area, ingesting algae and nutritious particles. One square meter of blue mussels (Mytilus edulis) can filter up to 150,000 litres of water in a day. Plymouth Marine Laboratory has been studying whether this amazing filtration can help reduce the levels of microplastics in the oceans. Dr Coppock and the PML team first looked at whether the ingestion of microplastics would cause harm to the mussels. Whilst some very small pieces called nanoparticles may slip through into the mussel’s tissue, the microplastics are too big. PML discovered that with the levels of microplastics naturally found in the environment, the exposure will not harm the mussels.

Fear not! 

Blue mussels are not traditionally sold for consumption, so these mussels aren’t the ones you will find on your dinner plate!

Mussel poo?

It was already understood that mussels could remove some levels of microplastics through their natural filtration system, excreting the microplastics through their faeces and pseudofaeces (a bit like their spit). The question was how this could work in flowing water. Would the faeces still sink and therefore be able to be removed, or would they float away – leaving the microplastics still in the water? The mussels went through a series of field trials, where they were placed in flow tanks, which mimic currents and water movement. They were placed on top of a cage where their waste could be collected and examined.

It was found that even with large quantities of buoyant plastic, the faeces and pseudofaeces still sank to the bottom – making their removal relatively easy. The experiments showed that a 5kg cluster (about 300 mussels) could filter over 250,000 microplastics per hour! If the faeces are removed, this could hugely impact the number of microplastics we can eliminate from our waterways.

Plymouth Sound, live test

The next step was to put these mussels to work in the real world. Clusters of mussels have been placed in Plymouth Sound in large baskets which have net-like receptacles to catch the faeces. From here the researchers will look at how much plastic is found in the mussel faeces, how much is rejected within the pseudofaeces, and what percentage of the total microplastics in the water, these make up. If these experiments go as well as the initial trials, then mussel clusters placed in strategic locations, like harbours and near waste treatment facilities, could potentially filter between 20-25% of waterborne microplastics.

There are even discussions about whether the microplastic excrement could be used as biofuel, as it is rich in carbon. This is still in the discussion stages at the moment; once the effective placement of the mussels and removal of their faeces has been established, the possibilities are endless!

Whilst it is obviously preferable to stop microplastics from entering the ocean in the first place, Dr Coppock talks of how this is a “fantastic natural solution”. By utilising mussels’ natural ecology, we can work with nature to make a real difference.

By: Rebecca Dodds