Sewage sludge applied to land in a farm north of Hull in Yorkshire. Photo: Alice Russell / Unearthed

Revealed: salmonella, toxic chemicals and plastic found in sewage spread on farmland

Secret Environment Agency report finds sewage sludge destined for English fields contaminated with microplastics, weedkiller, and “persistent organic pollutants”

Sewage sludge applied to land in a farm north of Hull in Yorkshire. Photo: Alice Russell / Unearthed

Revealed: salmonella, toxic chemicals and plastic found in sewage spread on farmland

Secret Environment Agency report finds sewage sludge destined for English fields contaminated with microplastics, weedkiller, and “persistent organic pollutants”

Sewage sludge applied to land in a farm north of Hull in Yorkshire. Photo: Alice Russell / Unearthed

A secret report obtained by Unearthed has revealed serious weaknesses in the Environment Agency’s controls on an industry that spreads millions of tonnes of sewage sludge on farmland each year.

Investigators commissioned by the agency found sewage waste destined for English crops contaminated with dangerous “persistent organic pollutants” like dioxins, fuerans, and polycyclic aromatic hydrocarbons at “levels that may present a risk to human health”. 

They reported evidence that these sludges, which are routinely spread as fertiliser on hundreds of farms, were widely contaminated with microplastics that could ultimately leave soil “unsuitable for agriculture”. 

They found various cases of sludge treated with lime in an attempt to kill harmful bugs, but which still tested positive for salmonella or “high concentrations of e-coli”. These bacteria can cause serious or even fatal infections. 

And they warned that the task of regulating this “landspreading” industry was “becoming more difficult”, because the Environment Agency (EA) staff responsible were being hit with “increased time pressures and reduced budgets”. 

The report – which proposed a suite of reforms to landspreading regulation – was handed to the agency in late 2017. But neither the environmental regulator nor the government has so far made changes in response, and the findings have remained secret until now. 

Farmland is the ultimate destination for the majority of the UK’s sewage sludge, which is the human faeces and other solids left behind when wastewater is cleaned. According to the water industry, around 78% of the country’s treated sludge – 3.6m tonnes – is spread over agricultural land each year. 

But the EA probe obtained by Unearthed warns that rules governing this practice were written decades ago, and have not changed to reflect the complex mix of contaminants sludge now contains. 

In addition to widespread contamination with organic pollutants such as polychlorinated biphenyls (PCBs) and perfluorooctanesulfonic acid (PFOS), the investigators discovered that almost all treated sludge samples they tested contained the weedkiller glyphosate and the antimicrobial triclosan, which scientists believe may cause antibiotic resistance.

Despite this, investigators reported, sewage sludge is not routinely tested for any of these contaminants before spreading. There are no legal limits to the amount of these chemicals that can be present in landspreading sludge. For the most part, the report states, scientists have not established what amount of these contaminants can be present in sludge without risk to the food chain.

This report can only now be made public after it was obtained by Unearthed under freedom of information laws. Unearthed has shared the document with the Telegraph newspaper and the BBC’s File on 4, which will air a documentary on the sludge spreading industry tonight. 

The consultants who ran the EA’s landspreading probe proposed a far-reaching list of possible reforms, including the introduction of checks by independent experts and the threat of trading bans for persistently misbehaving farmers or waste companies. 

But neither the agency nor the environment, food and rural affairs department (DEFRA) have yet made any significant changes. Sources close to the issue believe the lack of action is due to lack of resources, and the fact that landspreading is not seen as a political priority. 

An EA spokesman said: “We take our responsibility to protect the environment very seriously, which is why we commissioned this report to inform our upcoming sludge strategy and make sure our regulations are based on the latest scientific data.”

However, he declined to say why the agency was yet to take any visible action in response to the report, more than two years after it was completed. He also declined to directly answer questions on why the agency’s landspreading team have faced “reduced budgets”. 

He added that in 2018 the agency increased its permit charges “to better fund our compliance activities”. 

Toxic mix

Scientists who reviewed the EA report concluded landspreading regulations were not “fit for purpose” and said the probe had revealed it was worryingly easy to find “non-compliance” with rules that are “essential for our safety”.

Andrew Singer, a senior soil scientist at the UK Centre for Ecology and Hydrology, said the fact that sludge treatment centres had proven unable thoroughly to kill e-coli and salmonella could have serious implications for the fight against antibiotic resistance. 

Salmonella is supposed to be completely eliminated – and 99.9999% of all bacteria destroyed – before sewage sludge is spread on fields. But this was not the case for processed sludge tested at a number of sludge treatment sites.

“That sludge has e-coli in it, plus antibiotics, plus biocides, plus metals – all of that breeds something called an antibiotic-resistant bacteria,” Dr Singer told Unearthed. 

“So you’re effectively disseminating [in the environment] the very thing we should be trying to eliminate.”

Controlling the spread of antibiotic resistance was “one of the highest global priorities in the world,” he added. 

“There is virtually no higher priority than this, other than maybe climate change, and it is a seemingly routine occurrence that we are spreading this onto our land.”

Supporters of landspreading argue that without it water companies would have to have to dump huge quantities of sludge in landfills or incinerate it. 

A spokesman for Water UK, the trade association for the UK’s major water companies, said there were “serious issues” with the report commissioned by the Environment Agency. He told Unearthed that it did not “represent the way that biosolids are actually treated and used, and describes a process which will be completely phased out in a few months anyway”. 

The industry complains the report only analysed the contents of sludge treated with lime by third party operators, whereas the majority of sludge is processed by the water companies themselves using anaerobic digesters and heat treatment. The water utilities say they are in the process of phasing out the use of these third-party treatment sites, but these represent a very small proportion of all sludge treated with lime. The industry will continue to use lime treatment at sewage works, which it says uses “bespoke equipment” and is quality assured. 

According to the industry’s Biosolids Assurance Scheme, in total 22% of sludge spread to land is lime treated.

The Water UK spokesman added: “Robust research from the UK and across Europe shows conclusively that sludge recycling allows nutrients and organic matter to be returned to the land in a way that is safe, sustainable, good for farmers, and good for the environment.”

However the EA itself does not dismiss the report’s findings. The agency’s land and contamination manager Barry Sheppard told a waste conference last week the “chemical makeup” of landspreading sludges was “very different from 30 years ago” and the regulator had “concerns” that this “chemical complexity” could have “ecological risks”.

Alistair Boxall, an environmental science professor at the University of York, told Unearthed the landspreading regulations were unfit for purpose. 

They were “developed 20 or 30 years ago” and only covered “a handful of substances.” Meanwhile, every few months researchers were “identifying new types of contaminants in sewage sludge, and the regulations just haven’t kept up with that”.

“We don’t know what the risk of those substances is, and whether they should be monitored or not,” he added.

However, we could expect sewage sludge to be contaminated with a “really complex mixture of substances”, and findings like those in the EA report were probably just “the tip of the iceberg”. 

Toxicity studies tend to examine one chemical at a time, Professor Boxall continued. 

“Yet we know that mixtures of chemicals can work together to enhance toxicity. 

“So it’s possible that toxic interactions of this complex mixture could be causing much more harm to the environment and human health than we’re predicting based on the single-compound data we have.”

‘Open to abuse’

UK regulations on sewage sludge in agriculture date back to the late 80s. Legal controls on pollutants in sludge have barely changed since then. They are largely focussed on killing bacteria and limiting concentrations of fluoride and a short list of heavy metals – the contaminants people were most worried about 30 years ago. 

However, the waste business has changed profoundly. So have the contaminants found in landspreading wastes.

In response to these changes, and to cases of unscrupulous middlemen spreading prohibited waste, in 2015 the EA launched an investigation into the landspreading industry. 

The purpose was to examine risks posed by “potentially inappropriate landspreading”, and to establish whether regulations needed to change.

It commissioned the consultants Aecom to undertake this probe, which ran between spring 2015 and autumn 2017. They tested soil, sludge and other wastes at more than 54 farms and eight third party lime treatment sites for sewage sludge. They reviewed paperwork for dozens more “deployments” of waste on farmland, and studied findings from other unpublished investigations.

They concluded the trade in sewage sludge and other wastes had changed radically, making it harder for the EA – or farmers – to know what was being spread on fields. 

In the past, a landspreading business would take waste from a single producer and spread it on a nearby farm. But this straightforward set-up was being replaced by “more convoluted chains which can include a number of different middlemen, including waste brokers, contractors and subcontractors”.

Instead of spreading sludge from a single source, these companies were increasingly mixing together wastes from more than one client. Waste was frequently ‘miscoded’, or labelled simply as “mixed waste” without “any further details”. 

All this, the report warned, increased the risk of land being contaminated by businesses that were using landspreading simply as a “cost effective method of waste disposal”. Worse, there was potential for “hazardous waste to be included within the mixed waste” and then to become impossible to track.

This, Dr Singer told Unearthed, was “probably the most worrying part of the report” – the “opportunities for things to get mixed into a waste stream that don’t belong there”.

The consultants even found cases where “waste producer, waste operator, contractor and farmer were all part of the same extended family or parent company”. The absence of “any independent parties” in these landspreading operations left them “open to abuse”, the report warned, such as the “deliberate masking of potential illegal spreading.”

The consultant proposed a range of reforms to strengthen regulations. These included financial penalties and trading bans for poor performers, and validation by independent experts to check landspreading was being done safely. They also suggested rule changes to reduce the number of different wastes that can be spread on land in one go, and to require landspreading companies to test soil after spreading, to check they had not contaminated the land. 

These proposals would require consultation with industry and – in some cases – legal changes. But the EA has not even begun consultations on reform. 

When journalists first approached the agency with questions about the report, they were told the agency would launch its “sludge strategy” for reform at a late January conference for the water industry. But when Unearthed attended this conference last week, EA representatives admitted they were still not ready to reveal the strategy after all.

EA land and contamination manager Barry Sheppard told delegates he expected the strategy would be published within weeks.

However, he emphasised this “strategy itself will not deliver change”. It was intended only as a “starting point” for discussions with farmers and water companies, and it would not “look at the technical detail of the regulations”.

An EA spokesman later said in a statement: “While spreading waste can have beneficial impacts on the land when used as a substitute for manufactured fertilisers, we are clear this practice must not harm the environment. 

“We will not hesitate to take enforcement action against those who fail to manage any risks appropriately – including prosecution in the most severe cases.”

The food chain

The EA investigation confirmed there had been a “change in the composition” of landspreading waste to include a “range of potential contaminants” for which sludge is normally not tested. 

The “most widespread organic contaminants” of this kind included the herbicide glyphosate, triclosan – an antimicrobial chemical often used in household products, and a range of persistent organic pollutants (POPs), including PCBs, PFOS, dioxins, fuerans, and polycyclic aromatic hydrocarbons (PAHs). 

What are POPs?

Persistent organic pollutants (POPs) are so called because they do not break down in the environment. Because of this they can build up, or “bioaccumulate”, in the bodies of plants, animals and humans. They have been linked to a range of serious health conditions. Eating food contaminated with PCBs, for example, has been linked to reproductive failure and developmental delay. Many, including PCBs, are classified as human carcinogens. POPs found in landspreading wastes include PCBs, dioxins, fuerans, and polycyclic aromatic hydrocarbons (PAHs).

Many of these chemicals used to be used in industry or as pesticides – or are byproducts of manufacturing processes – but are now banned under the Stockholm Convention.

Because they do not break down, POPs are widely present in the environment, including in agricultural soils. The question for the EA investigation, therefore, was whether repeated spreading of contaminated sludge could raise concentrations of POPs in the soil – and ultimately the food chain – to levels that could be toxic to animals or humans. 

The report emphasises that it is hard to answer this question because “for many of the emerging toxics, not enough is understood about the toxicity and behaviour of these contaminants in the environment to derive suitable risk assessment criteria which are protective of human health, crops [and] livestock”. 

However, for some contaminants the investigators were able to use a landspreading risk assessment system built by the EA for assessing “potential risks to human health via the food chain”. They used this tool to analyse treated sludge samples, to identify potential risks of spreading it on agricultural land.

They concluded the sludges contained a range of contaminants at “levels that may present a risk to human health”, including manganese, dioxins, fuerans, dioxin-like PCBs, and benzo(a)pyrene. For the POP benzo(a)pyrene, the investigators found that spreading the sludge they tested would increase concentrations in the soil by up to 45%. Benzo(a)pyrene is and categorised as a Class 1 Carcinogen by the International Agency for Research on Cancer

Although there are no legal limits for the amount of these chemicals that can be present in sludge in the UK, the consultants did make use of a recent European Joint Research Centre study that proposes new legal limits for contaminants in sewage sludge.

For the carcinogenic PAHs, this study proposes a limit of 6mg/kg for biodegradable waste. In three quarters of the lime treated sludge samples analysed for the EA investigation, PAH levels were above this limit. In three of the samples tested, PAH levels were more than ten times the proposed limit.


The report states that “perhaps the biggest risk to the [country’s] landbank” from landspreading arises from the “spreading and incorporation of physical contaminants” like plastics and microplastics into agricultural soils. The risk, it explains, is that these will build up over repeated spreadings until the land becomes “unsuitable for agriculture”. 

Over 90% of microplastics in wastewater are retained in sewage sludge after treatment. 

The investigators did not test directly for plastic because there was “no standardised method” to do so in sludge. But they found phthalates – a group of chemicals commonly added to plastics, which are themselves linked to a range of health problems – in the majority of sludge samples tested. The report concluded that “the possible presence of plastics can be inferred” from the presence of these “organic contaminants”. 

Unearthed understands that the EA is working with WRAP, the National Farmers Union, and others on schemes to reduce plastic contamination in waste spread on farmland.

A DEFRA spokesman said: “We know soil is an essential natural asset and its careful management can help to provide a whole range of public goods. 

“That is why we’ve made sure that soil is specifically named in the [Agriculture] Bill, so we can provide financial assistance to farmers for protecting or improving its quality.”

You can hear File on 4’s documentary Sewage Sludge on BBC Radio 4 at 8pm tonight (Tuesday, February 4).

This story was updated at 11:18am on 4 February 2020, to incorporate further information received about the water industry’s criticisms of the EA report, and about the industry’s plans for phasing out the use of uncertified third party operators to treat sewage sludge with lime.