22 Aug 2018 Story Ecosystems

Wastewater treatment plants – a surprising source of microplastic pollution

RaceforWater Peter Charaf.

A lot of attention has been drawn recently to microplastics in freshwater and marine environments, and the threat they pose to ecosystems and people’s health.

The source of microplastics is generally thought to be well known: most plastic items are not recycled or incinerated when they are discarded. Plastic waste therefore ends up in landfill or in our rivers and oceans where it gradually breaks down into smaller and smaller pieces and particles. Microplastics are defined as pieces of plastic 5mm in diameter or less.

A new study, however, concludes that treated sewage effluents are also key sources of microplastics – the implication being that wastewater treatment plants are not effective at filtering them out.

Published in July 2018, a study in the United Kingdom titled Wastewater treatment plants as a source of microplastics in river catchments looked at six river catchments in the north of England.

“The fact that the quantity of microplastics present in receiving waters was greater downstream of each of the six wastewater treatment plants studied confirms that treated sewage effluent is a key source of microplastics,” concluded the authors.

The study also found microplastics upstream of water treatment plants. These, in turn, come from sewage sludge applied to agricultural land as fertilizer, the diffuse release of secondary microplastics, and aerial deposition.

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Sewage sludge containing microplastics is often spread on agricultural land with as yet unknown consequences. Flickr

One surprising finding was that while the composition of microplastics varied spatially and temporally, it was dominated by fibres, fragments, and flakes, as opposed to beads and pellets.

“Management efforts to reduce microplastic concentrations in rivers and oceans must focus on a diverse range of microplastic sources,” according to the study, in addition to addressing the treatment facilities’ failure to filter out the micropollutants.

An additional reason for concern is that microplastics can also trap, or act as a vehicle for the dispersal of, harmful chemicals. These chemical-laced particles can be ingested by small organisms, which are eaten by bigger animals and so on up the food chain and onto our plates.

Studies have linked the additives that leach out of certain microplastics to endocrine disruption in fish, affecting their reproductive ability and the hormone system of vertebrates and invertebrates alike.

UN Environment is focusing the topics of this year’s World Water Day, World Water Development Report and Stockholm World Water Week on “nature-based solutions” for water.

World Water Week, in Stockholm from 26-31 August, is an opportunity to raise awareness about the interplay between microplastics and chemical pollution in our freshwater and marine environments.

For further information, please contact Birguy Lamizana Diallo: birguy.lamizana[at]un.org or Elisabeth Mullin Bernhardt: lis.bernhardt[at]un.org