Sewage sludge spread on farmland is contaminating soil, water, and potentially the food chain with “forever chemicals,” according to whistleblowers from the Environment Agency, who argue that the current systems in place to prevent such pollution are “not fit for purpose.”

Investigations conducted by Watershed and the Guardian analysed samples of treated sewage sludge from five different catchments. The results revealed levels of per- and polyfluoroalkyl substances (PFAS) and flame-retardant chemicals that experts described as “exceptionally high.”

These forever chemicals persist in the environment for thousands of years, if they break down at all, and have been linked to serious health issues, including cancer. They are commonly found in consumer products and industrial processes, making their presence in soil particularly concerning.

Unlike some EU countries, the UK lacks statutory thresholds for forever chemicals in sewage sludge. However, all tested samples contained levels of a banned PFAS, PFOS, that exceeded what would be considered safe for allotments.

Dr David Megson, a forensic environmental scientist from Manchester Metropolitan University, said the “concentration of PFAS in the sludge samples poses a cause of concern. Concentrations of PFOS in all samples were greater than the recommended limit for an allotments site (2.7μg/kg). Uptake of PFAS in fruit and vegetables is poorly understood, but recent research has concluded that consumption of crops is a significant and underappreciated pathway for human exposure to PFAS.”

Prof Hans Peter Arp, an environmental chemist at the Norwegian University of Science and Technology, said he found the concentrations of flame retardants, used to coat materials to prevent them catching fire, “exceptionally high … Norway would consider 500μg/kg as contaminated, but these sludges range from 8,000 to 12,000μg/kg. I suspect the cause is fire-proof textile and/or textile manufacturing.”

Each year, vast amounts of sewage sludge—essentially human waste mixed with industrial residues—are spread on UK farmland. Although it is treated by water companies and regulated by the Environment Agency, many harmful substances remain.

Analysis of official figures by Watershed and the Guardian shows that the total volume of sludge spread has increased from 790,923 tonnes in 2012 to 819,001 tonnes in 2023. Over the same period, the land treated with sludge expanded by 12%, from 135,637 hectares to 151,921 hectares, with the majority applied to agricultural fields.

While the Environment Agency is responsible for overseeing this process, whistleblowers claim enforcement is severely lacking. Industrial waste, including landfill leachate—containing a toxic mix of chemicals—enters sewage treatment plants daily via the sewer system or by tanker. Insiders report that water company checks on the substances within waste are not always reliable.

Leachate disposal at sewage works is a cost-effective solution for waste producers, discouraging alternative disposal methods. While water companies profit from selling sludge to farmers, the agency reportedly has no clear records of where the sludge is ultimately spread.

Whistleblowers indicate that the agency has long sought to reform the system, but the Department for Environment, Food and Rural Affairs (Defra) has blocked such efforts.

One Environment Agency insider who asked not to be named said: “What’s going on at the moment is going to be adding potentially significant amounts of contaminants into the wastewater treatment system and therefore what comes out the other end in the final effluent, and what comes out in the sludge.”

“It’s a very lucrative area,” said the insider. Water companies charge industry to dispose of waste at their works, so there is a financial incentive to accept it. They said the water companies give the Environment Agency “assurances that they have a process in place for preassessment of the wastes but I am not in the least bit convinced that that is a very robust system … trade effluent and consenting is pretty much a self-policing system.

“An awful lot of tankered effluents are landfill leachates [which] are probably our greatest concern. You can imagine the number of substances, including PFAS, in them. They’re not going to be transformed or destroyed by the wastewater treatment process, they’re going to come out in the effluent or they’re going to end up in sludge.”

“It’s completely invisible to us,” said the insider. However the Environment Agency contends that it does know because it reviews water company registers.

The water industry wants to see the back of PFAS. A spokesperson for trade body Water UK said: “We want to see PFAS banned and the development of a national plan to remove it from the environment which should be paid for by manufacturers. In the meantime, water companies are exploring alternatives to spreading sludge to land on a precautionary basis.”

In March 2020, the Environment Agency proposed a strategy for the safe and sustainable use of sludge. However, delays in implementation have stalled progress, and insiders report that little action has been taken.

“The more industrial waste that is put into sewers for the profit of water companies, the more PFAS contaminated water will discharge from outfalls, and the more PFAS contaminated sludge will end up on agricultural land, and so in the food chain and local watercourses,” they said. “The same goes for all other discharge permits as none have PFAS as a limit or any sampling that requires it as a determinant. Nothing has changed over the last few years and there is nothing to suggest it will.

“The sewage sludge circle is highly profitable for all the parties involved. Heavy industry saves money by disposing [of] toxic waste down sewers, water companies are able to get rid of contaminated sludge on the cheap, and agriculture benefits from free fertiliser.”

The presence of PFAS in sludge has caused significant issues for farmers in the US. In 2016, high levels of PFAS were discovered in milk from a Maine dairy farm, traced back to sludge used as fertiliser. Since then, 78 farms across the state have been identified with PFAS contamination, and drinking water sources have been affected.

In response, Maine banned land application of PFAS-contaminated sludge and compost, established a fund to support affected farmers, and initiated legal action against PFAS manufacturers to recover costs for monitoring and treating contaminated wastewater. Similar regulatory measures may be necessary in the UK to prevent further environmental and public health risks.

Royal Society of Chemistry policy adviser Stephanie Metzger said: “Sludge spreading is an emerging issue of concern, and we need to do comprehensive monitoring in order to understand if contaminants such as PFAS are present, and if so what kinds and how much. It also represents a potential new contamination pathway that may result in PFAS contamination in previously unaffected areas.”

Defra said: “We recognise the damage agricultural runoff can cause, and we need to see the safe and sustainable use of sludge in agriculture to help clean up our waterways and promote healthy soil. As well as working closely with the Environment Agency to assess the current legal framework, we have also commissioned an independent review of the water sector to shape further legislation that will transform how our water system works and clean up rivers, lakes and seas for good.”

An Environment Agency spokesperson said: “Effective regulation in the safety of spreading sludge on land is vital and we are clear that sludge can only be used if it does not impair the quality of soil or surface and groundwater … we are undertaking a multi-year programme to better understand sources of PFAS pollution in England.”