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Microplastics found in fifty percent of insects in South Wales rivers

October 10, 2018

The River Usk in South Wales. Half of the aquatic insects sampled in the river were found to contain microplastics. Image: Photo Monkey | Flickr Creative Commons

Microplastic pollution is a rapidly growing issue in aquatic ecosystems across the world. Microplastics are tiny pieces of plastic debris less than 5mm in size. They enter aquatic environments in two main ways. First, diffusely: through the erosion of larger plastic items such as drinks bottles, fishing nets and plastic bags. Second, directly: through the run-off of abraded road paints, textiles, and vehicle tyres, and in sewage containing plastic textile fibres from washing machines.

Plastics can take thousands of years to degrade and break down. As a result, understanding the impact of increasing microplastic pollution into aquatic ecosystems is an important emerging topic for environmental science and policy.

In marine environments, microplastics have been found in invertebrateszooplankton, shellfish, fish, and birds, and washed up on shorelines across the world. Whilst microplastics are present at all tropic levels in marine food webs, research is ongoing in understanding how this accumulation affects the feeding, growth, reproduction, and survival of aquatic communities. By comparison, our understanding of the extent and impacts of microplastic pollution in freshwater environments is relatively sparse (read our blog on the topic from 2015 here).

Microplastics widespread in South Wales rivers

A new open-access study by researchers from Cardiff University found that half of aquatic insects (or macroinvertebrates) sampled from three rivers in South Wales had ingested microplastics.

A research team led by Fred Windsor, a PhD researcher at Cardiff University School of Biosciences, sampled three different kinds of mayfly and caddis larvae at five sites on the Usk, Taff and Wye catchments. Each sampling site was located close to a waste water treatment plant, allowing macroinvertebrates to be sampled both above and below water outflows from each plant.

The researchers found microplastics at each of their five river sampling sites. These were found in individual insects across each of the three sampled macroinvertebrate species, regardless of their feeding methods, habitat preferences and ecological niche.

The research team found that, on average, microplastic levels were similar in river stretches both above and below waste water treatment plants. However, the researchers did observe that microplastic levels increased where waste water treatment plant outflows comprised a significant proportion of downstream river flows. This suggests that microplastic pollution originates from multiple sources – most likely transport networks and urban areas – across the wider landscape, rather than from discharge from waste water treatment plants alone.

Lead author of the study Fred Windsor says, “Every year, between eight and twelve million tonnes of plastics are thought to be entering the World’s oceans, but around four million tonnes of it passes along rivers. In some cases, there can be over half a million plastic fragments per square metre of river bed, so that ingestion by insects is very likely.”


Microscopic images of the microplastics (A and B) and plastic fibres (C) found by the researchers in the three rivers. Image: Study Authors

The emerging environmental risks of microplastic pollution

Co-author Professor Steve Ormerod, Co-Director of Cardiff University’s Water Research Institute continues, “Urban rivers in the UK have been recovering from decades of gross pollution, but growing information illustrates that plastics are a new risk for river organisms not just in towns and cities, but even in some rural areas.

Problems could arise from the physical effects of microplastics, from their direct toxicity or from pollutants that they transport. Plastics in insects mean that animals using them as prey could also be affected. At present, however, our understanding of the risks to wildlife and people is absolutely rudimentary. We need to improve this situation urgently to know how best to manage the problems.”

The research team conclude that more research is urgently required to understand the sources and transport of microplastics in freshwater environments, and how microplastics are ingested and transferred across different organisms in freshwater food webs. Such research could allow scientists and water managers to develop more complete biological risk assessment approaches for mitigating the potential impacts of microplastics on freshwater life.

Microplastic pollution: a key topic for environmental science and policy

Professor Isabelle Durance, Director of the Water Research Institute at Cardiff University, adds, “Although people are more and more aware of the damage caused to ocean wildlife from ingesting plastics, the potential problem of plastics in river ecosystems has been seriously overlooked.

“The water industry, environmental regulators, the plastics and packaging industries, and ordinary people concerned about the environment see this as an increasing priority, and this study provides yet more evidence that we need a fuller assessment of the sources, movements and effects of microplastics as they are transported between the land and sea along rivers.”

The interconnection of freshwater and marine environments highlighted by Prof Durance – in which microplastics are transported through river catchments out to estuaries and the open sea – is a key aspect of this emerging environmental issue. For example, another recently published paper by Alexandra McGoran and colleagues found microplastics in a third of fish sampled in the Thames and Clyde estuaries in the UK.

As a result, the management of microplastic pollution in coming years is likely to require close co-operation between scientists, policy-makers and water managers across both freshwater and marine realms, both to understand the extent of the microplastic problem, and what can be done to mitigate its effects on aquatic life.


Windsor, F. et al. (2018), Microplastic ingestion by riverine macroinvertebrates, Science of the Total Environment, Volume 646, 68-74 (open-access)

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