Toxic waste sites exposed in Michael Sheen documentary are 'tip of the iceberg'
Michael Sheen took up the job of investigating Douglas Gowan's concerns about an international chemical giant dumping carcinogenic waste in Wales
A former Monsanto worker who spent three years helping seal toxic waste underground said staff had "cheap" protective equipment and were not told what they were burying.
Stephen Constance worked at the chemical giant's Newport factory in the 1990s and came forward after the BBC documentary Buried with Michael Sheen highlighted Wales' toxic waste legacy.
But the 14 sites identified in the programme are just the tip of the iceberg and there are about 20,000 high-concern sites in the UK, said Dr David Megson, the scientist involved in the documentary.
Eastman Chemical Company, which is responsible for Monsanto's legacy production in the UK, did not respond when asked to comment.
Constance was one of dozens of people who contacted BBC Wales after coverage of Sheen's investigation into Monsanto and the dumping of polychlorinated biphenyls (PCBs).
Researcher and whistleblower Douglas Gowan spent 50 years trying to persuade authorities to investigate what he believed was widespread dumping of industrial chemicals.
These included PCBs, which he called "some of the worst contaminants known to man", and were widely used in the 20th Century, including for lipstick and white goods.
They were banned in the UK in the 1970s and have since been banned by 151 countries.
Douglas Gowan spent 50 years trying to make people listen to his concerns about chemical contamination in Wales
Constance, 61, said working for Monsanto was "absolutely dreadful".
Looking back, he said it was "quite evident that nobody was fully appraised of the potential hazard that they were exposed to".
The material was already buried when Constance arrived and it was his job to dig a 6m-deep trench around the outside of the mound before it was sealed using plastic membrane sheets and liquid clay.
While he believes this prevented airborne contamination, he is unsure if it would have stopped contamination into the Earth due to the high water table linked to the tides.
PCB material was covered over with plastic membrane and liquid clay
When asked if he felt safe, he said: "In terms of what we knew was there and what we were potentially exposed to, no."
Constance is in remission from cancer after having follicular lymphoma.
"I'm not suggesting in any way at all that it's linked, but the thought did cross my mind," he said.
Stephen Constance says he does not feel safe now he knows what chemicals he was exposed to
In the documentary, journalists Dan Ashby and Lucy Taylor reveal a memo from Monsanto dated to 1972 which found that it knew PCBs were a danger to human health and was closing its site in the US as a result of legal action from a town.
However, it then increased its work at the plant in Newport.
"The government in the UK told the industry 'we're not going to put any restrictions on importing PCBs'," said Ashby.
"So they begin importing from around the world, hundreds of tonnes of PCBs."
Dr David Megson says only public pressure can motivate governments to take action
Dr Megson, a reader in chemistry and environmental forensics at Manchester Metropolitan University, led the scientific data collection in the documentary.
He said: "The country is in a really dire place.
"Public pressure is the only thing that's going to make this action happen. This is our only chance, if I'm being brutally honest.
"What our data shows is those sites are leaking and those sites are a chemical cocktail. Whether it's the PCBs alone is up for debate.
"PCBs are suspected carcinogens, so we think they can cause cancer."
The data he found stunned him after having met people who had been worried about PCB levels near their family home for more than 30 years, saying he found levels that were "pretty much the highest I've ever seen in anything we've tested".
He added: "It's made me feel quite uncomfortable about some of those sites and what could have happened to all of those people's friends and loved ones.
"The polluter just keeps getting away with stuff left, right and centre."
There are 12 locations in Wales which were sites of concern for Douglas Gowan
These chemicals are hard to clear up, but not impossible.
Ralph Davies, who has been in the chemical remediation industry for about 35 years, said he proposed a way of cleaning up the acid tar lake in Llwyneinion near Ruabon in 2007, but never heard back from Wrexham council.
He said was "amazed" how close it was to people's homes when he visited nearly 20 years ago.
"People are still saying it does not meet the threshold for remediation, that both angers me and saddens me," he added.
"The fact it is still there, untouched, is mind blowing."
Ralph Davies visited the acid tar lagoon in 2007 to propose how to clean it up
A report by an environmental engineering consultancy in 2006, seen by BBC Wales, shows that the acid tar lagoon - one of the sites in the documentary - was known to be contaminated as early as 1979.
Among the known contaminants dumped at the site is 93,100 tonnes of acid sludge from Burmah Castrol and barrels of unknown substances suspected to be from Monsanto, the report said.
Over the next 27 years, there were 18 investigations, two remediation proposals and five treatment trials but, as of 2026, the acid tar lagoon remains.
The report identified 105 possible ways contamination from the site could affect people, wildlife, property or water supplies.
This included three uncapped mine shafts beneath the lagoon that were suggested as potential pathways for contaminant movement.
In the 1980s, Clwyd County Council bought the site and legally agreed to protect the previous owner from any past, present or future claims, costs or liabilities arising from the "escape or nuisance of noxious wastes".
BP, which is responsible for Burmah Castrol, said it had no comment to make.
The lagoon is near Llwyneinion and has had many remediation trials, yet it remains
Emeritus professor Sue Jordan, a researcher at Swansea University, said further monitoring and investigation was needed.
After reading the BBC article about the documentary, she said she and her colleagues thought it was "an eye-opener" and it made them think "maybe there is something in this pollution".
She added that researchers still did not fully understand why some health outcomes, including congenital anomalies and stillbirths, appear higher in Wales than in parts of the UK, and believes further research is needed.
"I would very much like the minister to turn around and say Public Health Wales will look at this," she said.
"We don't want anything brushed under the carpet."
John Browne said cases involving contamination are difficult but not impossible
John Browne, a lawyer specialising in industrial disease claims at Slater and Gordon, said cases involving historical contamination were difficult to investigate - but not impossible.
"Time passing makes cases more difficult to prove," he said.
"Witnesses' memories fade and locating [eye]witnesses becomes increasingly challenging and difficult."
However, he said scientific, medical and forensic evidence could help establish what happened and whether exposure to hazardous substances contributed to illness.
The key question is not simply what the law was at the time, but what was known about the risks, he said, adding: "Communities affected by contamination deserve transparency and clear answers."
Public Health Wales said its Welsh cancer intelligence and surveillance unit had collected and analysed "every single case of cancer" since the 1970s.
It added: "Based on the evidence currently available, there is no indication that historical environmental pollution is responsible for an increased risk of cancer, or any other disease or illness, in these areas."
Natural Resources Wales said the Environment Agency, its predecessor, investigated the acid tar lake in 2006 and 2008 but tests concluded it did not meet the legal definition of contaminated land.
"Therefore, responsibility for the site returned and remains with Wrexham County Council as regulator."
Wrexham council said, since these investigations 20 years ago, ongoing monitoring had not identified any significant changes and there was no statutory requirement for remediation.
The Welsh government said addressing contaminated land was one of its key priorities.
"A survey of local authorities carried out by Natural Resources Wales in 2015 identified more than 9,000 potential sites requiring further investigation.
"While not all of these sites will pose a risk to human health or the environment, this figure demonstrates the scale of the issue facing regulators in Wales.
"We now intend to develop a Wales-wide strategy to progressively restore post-industrial land, so that communities are no longer exposed to potential risks."
The UK government referred the BBC to the Welsh government when asked to comment.
Buried with Michael Sheen is available on BBC iPlayer
