Microplastics reveal sewage in UK rivers

After a recent controversial vote in the UK Parliament and a subsequent government U-turn, the dumping of untreated sewage into rivers by water companies has gained a lot of attention. Sally Le Page spoke with Jamie Woodward from the Department of Geography at the University of Manchester to discuss his latest research, on how tracking microplastics in the riverbed allows us to monitor the dumping of untreated wastewater...

Sally - Jamie, why were you looking for microplastics in our rivers?

Jamie - Well, we decided a few years ago that because most of the research on microplastics is focussed very much on the ocean. So the contamination problem, the oceans, we started thinking about where those microplastics were coming from. So we started looking at UK rivers, particularly rivers in cities where we've got lots of industry and lots of population as a potential source of microplastics into rivers and into the ocean.

Sally - What are these microplastics? Where are they coming from?

Jamie - Well microplastics are pieces of plastic smaller than five millimetres in size but most of the microplastics we find are much smaller than that, smaller than one millimetre. They're mainly coming from wastewater, so we find fibres from commercial and domestic laundry. We find microbeads from industrial processes. We find fragments of plastics from a range of processes from road runoff to industrial processes. They mainly enter the river system through wastewater.

Sally - So every time I wash my synthetic jumper, I'm producing tiny microplastics, but surely that just going to get filtered out when all of that wastewater gets treated?

Jamie - What we've found in our latest work, and this is quite well established in the literature, is that existing wastewater treatments (water treatment plants, sewage treatment plants in the UK and elsewhere) are actually pretty effective at removing microplastics. They can filter out 99% of the microplastics in wastewater if the wastewater is treated properly. We've found lots of microplastics in high concentrations on riverbeds. The only way that microplastics can accumulate on riverbeds is if wastewater is being pumped into rivers at very low flows.

Sally - Oh, I see. So you weren't expecting to see microplastics in there, but it was a sign that the wastewater hadn't been treated properly.

Jamie - When it started we didn't know. We did a survey and found high concentrations of microplastics. What we found is after flood events those microplastics were washed away. So identifying that contamination was a new discovery as well as the process of them being washed away by flooding. The nice thing that comes out of that is that the rivers will clean themselves.Now, ultimately those microplastics will end up in the ocean. Then we started thinking as to how to join up the dots. Well, if floods remove microplastics and water companies are only supposed to put wastewater into rivers during high flows in exceptional rainfall. How on earth are the riverbeds getting contaminated in the first place? So the only way you can get high concentrations of microplastics accumulating on a riverbed is if you're putting untreated wastewater into a river when the river is actually at low flow and you haven't got exceptional rainfall.

Sally - And untreated wastewater, doesn't only contain microplastics, obviously contains faecal bacteria and other horrific things to think about. What harm overall does raw sewage cause to our river ecosystems?

Jamie - Everyone's talking about sewage at the moment, sewage in rivers and sewage in the sea, so basically this is untreated wastewater. It can contain bacteria like e-coli for example, that can make humans seriously ill, but also untreated wastewater can also contain lots of industrial pollutants, toxic chemicals, pharmaceuticals, other bacteria, detergents, pesticides, etc. So there are lots of nasties in untreated wastewater that you don't want in rivers and you don't want them in the ocean.

Sally - Is this happening just in the UK or is it happening in countries worldwide?

Jamie - This is a global problem. So wherever you've got people living in cities in high concentrations producing wastewater and you've got industry as well, you've got a wastewater issue. Where that wastewater is being treated is important. You can reduce the impact obviously on rivers and in the marine environment. There are circumstances when untreated wastewater gets into the river. This is a global problem, but it's become a particular problem in the UK as some of our wastewater systems are quite old. They're Victorian and the infrastructure hasn't been maintained as it should have been. So we get far too many spills of wastewater into rivers.

Sally - Indeed, we've been hearing about it a lot. It's been discussed in the House of Lords and the House of Lords even mentioned your research. That must have been quite validating as a researcher.

Jamie - Yeah, it's nice to do a piece of research that actually influences policy and people are talking about. What we're finding is that the microplastics, when found in high concentrations can be used as an indicator of poor wastewater management. So microplastics themselves can be used as a diagnostic tool to identify when the water companies are not doing what they should be.