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Millions of tonnes of treated sewage sludge is spread on farmland across the UK every year despite containing forever chemicals, microplastics and toxic waste, and experts say the outdated current regulations are not fit for purpose.
An investigation by the Guardian and Watershed has identified England’s sludge-spreading hotspots and shown where the practice could be damaging rivers.
Sludge – the solid matter left over after sewage treatment – is laden with Pfas “forever chemicals”, flame retardants, pharmaceuticals, microplastics, and toxic waste from homes and industry. Water companies rebrand it as biosolids and give or sell it to farmers as a nutrient-rich fertiliser.
It is spread over vast areas under light-touch regulation and minimal scrutiny, unmonitored for toxic substances.
“On the outside it appears to be ‘black gold’ – containing nitrogen and phosphates valuable for soil,” a water industry expert said. “But hidden within it are microplastics, Pfas forever chemicals, endocrine disruptors, pharmaceuticals and heavy metals.”
About 87% of the UK’s 3.6m tonnes of sewage sludge is applied to farmland. An Environment Agency (EA) officer, speaking anonymously, said: “People have seen the sewage in rivers … they need to know about the sludge, where it goes and what’s in it.”
The water industry’s own chemicals investigation programme found hormone-damaging nonylphenols and phthalates, the banned carcinogen PFOS, antibiotics, antimicrobials and anti-corrosion chemicals in every sample tested from 11 treatment works.
Scientists from Cardiff and Manchester universities estimate that 31,000 to 42,000 tonnes of microplastics are spread on European farmland annually via sludge, with the UK possibly facing the worst contamination.
Rules set in 1989 require testing only for a few heavy metals, and EA insiders say they are “not fit for purpose”.
The investigation identified about 34,000 registered sites in England where sludge is stored, usually before being spread at the same site or on a field nearby, although it can sometimes be transported long distances. Of these, about 33,000 sites are defined as being agricultural land.
In 2023 alone, more than 768,000 tonnes of dry solids were spread across 152,000 hectares. Figures from the past decade consistently fall between 715,000 and 800,000 tonnes.
Some counties are more affected than others: Hampshire, Lincolnshire, North Yorkshire and Essex have the highest number of sites, with 6,371 between them.
Sludge-spreading is governed by waste exemptions, allowing companies to store or apply waste on land without an environmental permit, provided certain conditions are met such as avoiding significant risk to water, soil, air or wildlife. But enforcement is weak. “No one checks. No one cares,” said one EA insider.
An EA officer explained that sludge toxicity depends on local sources: “Anywhere with an industrial estate will likely produce more contaminated sludge than a rural area.”
Industrial waste, such as landfill leachate, is often tankered into sewage works, mixed with domestic waste, and the resulting sludge is spread under the same rules as any biosolid.
Contaminated fields become silent sources of pollution. Even uncontaminated sludge can be a problem if mismanaged. When too many nutrients reach rivers, they fuel algal blooms that block sunlight and starve aquatic life of oxygen – a process called eutrophication.
The investigation found that one in 20 sludge storage sites in England are within 100 metres of a river, and 1,277 sites are within 500 metres of waters already classed as eutrophic by the EA.
The investigation found that 73% of all sludge sites – 23,844 – are within nitrate vulnerable zones (NVZs), where strict rules apply due to pollution risks. In England, no rivers meet chemical standards and just 14% meet ecological ones.
Sludge-spreading occurs in Wales and Scotland, too. Almost a quarter of sludge storage sites in Scottish locations that could be identified are within NVZs. A study from the James Hutton Institute found microplastic levels rose by 1,450% after four years of sludge-spreading in North Lanarkshire and remained elevated 22 years later. In Northern Ireland, most sludge is incinerated.
Richard Benwell, Wildlife and Countryside Link’s chief executive, said: “Though sludge could be a beneficial fertiliser, it is mixed with the dregs of chemical pollutants. Damaging Pfas, BPA and glyphosate are prevalent in sludge. Regulation must be strengthened to protect public health and the environment.”
Prof Rupert Hough, of the James Hutton Institute, said: “At the moment, sludge will only be checked for metals and the receiving environment is checked for metals but I don’t think it gets checked rigorously.
“We all put chemicals down the drain, take medicines – these end up in the sludge and on land, and can enter the food chain.” He said the alternative options – landfilling and incineration – had capacity limits and high costs.
“The cost of removing chemicals from sludge is also prohibitively expensive … the industry has few options,” he said.
A water industry source said: “Colleagues in the industry are not out to commit evil in their public service of water management. They’re just constrained by a lack of research and development.”
A spokesperson for Water UK said water companies were backing research and trialling new uses for bioresources, including as aviation fuel. “The UK has banned some products with microplastics – we need the same for Pfas, plus a national cleanup plan funded by polluting manufacturers. Contaminants cross borders, which is why we’re calling for coordinated action across Europe.”
Shubhi Sharma, of the charity Chem Trust, said the government used lack of funding as an excuse for “failing to prevent our farmlands from being poisoned”. She called for tighter chemical restrictions and a “polluter pays” model. “France has already introduced taxes for Pfas polluters. The UK should follow,” she said.
The EA said sludge must not harm soil or water, and that it enforced strict rules, including through more than 4,500 farm inspections last year, resulting in more than 6,000 pollution-reducing actions.
The Department for Environment, Food and Rural Affairs said it wanted safe, sustainable sludge use and it has launched an independent water commission to review the regulatory framework in collaboration with the EA, farmers and water companies.
