Evidence gaps no excuse for inaction on microplastics, Royal Society analysis says

Acting now to limit microplastics entering our soils and waterways could help limit risks to human health, animals and the wider ecosystem, analysis by the Royal Society suggests.

The risks from microplastics may only become fully apparent in the future, as concentrations of microplastics within the environment increase. However the expert review of Microplastics in Freshwater and Soils found significant evidence gaps around their effects, particularly on the wider ecosystem.

Experiments using higher plastic concentrations have found they have the potential to cause harm. In fish, this included damage to the mouthparts and internal organs, while earthworms in plastic-polluted soils had reduced growth as a result of damage to their digestive tract – which could have implications for soil health.  

While microplastic concentrations in the environment are currently low the impact of long-term exposure is unclear and these levels are expected to rise in future. This is in part because sources of plastic waste are so widespread and also because plastics become almost impossible to remove as they break down in the environment.

If this rise continues, the evidence review suggests that the likelihood of negative consequences emerging in the future is high.

Professor Charles Godfray FRS, Director of Oxford Martin School at Oxford University and chair of the Royal Society’s Living Landscapes programme, of which this evidence synthesis is a part, said: “Ocean plastic pollution has gained significant attention in recent years. Yet we know comparatively little about the presence and impact of plastics in our rivers and on land.

“This analysis summarises the existing literature, and highlights the gaps where research can help us understand microplastics’ impacts on the wider ecosystem. 

“But we should not let what we don’t know paralyse us: the existing evidence shows we need to act now to limit current risks and likely worse future ones.

“These same waterways and landscapes provide us with clean water, food, flood protection, and many other benefits some of which may be jeopardised in future through a combination of stressors, including microplastics.”

A circular economy

As removing microplastics from the environment is such a challenge, preventing plastics entering waterways and soils in the first place will be key.

Legislation implemented, or planned, so far by the UK, EU and others, has tried to reduce single-use plastic waste like carrier bags and bottles with levies – or ban them entirely, in the case of microbeads used in some personal care products.

But the report notes that the items targeted to date represent a small proportion of the total environmental microplastics. Many other sources, from the plastic fibres shed by synthetic fabrics in the wash, to wear and tear on car tyres, have hardly been considered and may not have practical alternatives.  

So this report identifies the need to move towards a more “circular economy” which gives more thought to plastics throughout their lifecycle, in particular how they may be designed to maximise reuse, recycling and other alternatives to the landfill.

Around 8.3 billion tonnes of plastic was produced between 1950 and 2015, of which 5.8 billion tonnes has now been discarded. Just 9 per cent of this discarded plastic waste was ever recycled, while 79 per cent is now in landfills, or our seas, rivers and landscapes.

This balance is shifting, but is likely that a wide array of new legislation, incentives and penalties, coupled with the efforts of industry, the public and governments around the world, will be needed to take account of the wide array of scenarios where plastics are used.

“There’s a limit to how many things you can ban,” said Richard Thompson, Professor of Marine Biology at the University of Plymouth and a member of the report’s review group.

“It’s about cutting out plastics we didn’t need in the first place, but where plastics are the best material for the job, it’s about using them responsibly and thinking about what happens at the end of their lifespan. 

“That’s where the circular economy comes in, it’s what has largely been missing in the design of plastics and plastic products.”

Nanoplastics 

The evidence synthesis also reviewed studies on the smallest particles, so-called nanoplastics, which are between 1-100nm in size. In the environment, most microplastics will eventually degrade to become nanoplastics and they are almost impossible to see, measure or remove - and therefore almost impossible to control.

While microplastics research is in its infancy, the report suggests that our understanding of nanoplastics is “embryonic”, so firm conclusions about their effects cannot be made.

Yet initial research into their potential impact suggests that they may pose a greater risk to animals than larger particles such as microplastics. For instance, it appears that they can enter cells of the body and potentially disrupt proteins and other cell functions – some may even be able to cross the body’s protective blood-brain barrier.