A new study on the transport of per- and polyfluoroalkyl substances (PFAS) from the River Mersey, in the north west of England, out to sea reveals that yields of certain PFAS chemicals in the Mersey basin are among the highest recorded globally.

The researchers say their study is the first to consider temporal variability in flows and loads of PFAS, rather than just annual averages, and therefore provides the first robust estimates of PFAS transport in a European river system.

Mersey River

Source: © Shutterstock

The new study measured PFAS levels in the River Mersey and flow rates over the course of a year.

‘The Mersey is one of the largest river basins in the UK and it’s also one of the most densely populated – it has a very well-documented industrial past,’ says Patrick Byrne, a hydrology and environmental pollution researcher at Liverpool John Moores University and lead author of the study.

‘We know PFAS are found pretty much everywhere around the world now, but if you want to study a natural laboratory of how PFAS behaves in the environment … the River Mersey is a very good case study and the results [will] hopefully be representative of other similar industrialised urbanised river catchments around the world.’

Byrne and colleagues took a different approach to PFAS measurements by looking at the load or ‘flux’ of the chemicals: how much PFAS is being transported off the land, into the river and out to the sea. The team sampled the levels of 17 PFAS chemicals at different points in the river between August 2022 and July 2023, and measured the river’s flow rate at those times. Combining these measurements, they were able to estimate that around 68.1kg of PFAS is being exported from the River Mersey into the sea each year, with loads for two specific PFAS compounds perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) estimated to be 9.81 and 14.36kg/year, respectively.

Dividing these loads by the catchment’s 2030km2 area gives annual yields of PFOS and PFOA in the basin. Comparing those figures with published data from around the world, the team found that these yields are amongst the highest in the world; only two watersheds, one in Japan and one in the US, had higher levels.

‘We need to regulate these chemicals, if there’s regulation this will force the water companies to invest more in better treatment techniques,’ says Byrne. ‘But there is a consequence of that … [the] cost to upgrade all of our wastewater treatment systems to effectively remove PFAS across the UK; the estimate … is something like £23 billion.’

The researchers also conclude that tackling PFAS contamination in urban rivers should not focus only on wastewater treatment. The study revealed that PFAS entering the Mersey from river and wastewater treatment plants only accounts for a portion of the total PFAS flux: around half of the PFOS being transported out to sea came from these sources. The researchers also suggest that approximately a third of PFOA emitted from treatment plants could be stored within river channels. Confirming the other sources of PFAS will be the focus of the group’s future work.

David Megson, reader in chemistry and environmental forensics at Manchester Metropolitan University says the numbers reported in the study were ‘very large’. ‘I find it interesting that 50% was from non-point sources, which you’d expect to be direct industrial discharges out of plants and factories in industry around the area, or just general leaching from the environment because we’ve managed to contaminate it so badly and it’s all flowing into that river and going out,’ he adds.

Megson says there are some ‘worrying’ discharge consents regarding the amount of PFAS companies can legally excrete into the environment. ‘You just need to go round a few areas and find a tonne of PFAS a year can legally be discharged directly into our water bodies. We know this stuff’s toxic … we’ve just not got our hands around the regulations.’

He says that the figures reported in the study are just the tip of the iceberg: ‘the 17 [PFAS] that were mentioned in that study probably make up about less than 5% of the total PFAS that are going out into the environment.

‘This study does a really good job to say “hold on a minute, we’ve got a big problem here”, but I think we’ve got a massive problem and we need much more support from government to introduce stronger environmental regulation.’

In October 2023, the Royal Society of Chemistry (RSC) called on the UK government to reduce the current cap on individual PFAS in drinking water from 100ng/l to 10ng/l, warning that levels above this pose a significant risk to public health.


This article was updated on 7 March 2024 to make it clear that the study found yields of PFOA and PFOS in the Mersey basin are among the highest globally, rather than total mass, and to clarify the terms load and yield in this context.