Tens of thousands of tonnes of mustard gas, phosgene and other lethal chemicals have been made, stored, burned and dumped at sites in England, Wales and Scotland since the first world war. Some areas are still fenced off to protect the public today.
After a four-year investigation of the sites considered potentially hazardous – named Project Cleansweep – it has concluded that there is "no indication of significant risk to public health or environment" from the sites.
That has been questioned, however, by one expert, who pointed out that there was still no scientific proof that all harmful traces of the weapons have been removed, particularly after they were burnt.
Prof Alastair Hay, an expert on chemical weapons and who is a professor of environmental toxicology at the University of Leeds and an official adviser to the Health and Safety Executive, argued that more sampling might still be needed at the sites. Some areas should be kept secure as a failsafe because mustard gas can be very persistent in the environment, he warned.
"The more problematic areas are where physical destruction took place," he said. "Incineration is a well-recognised method of disposal, but you need to ensure all is burned. We have no details of these procedures."
Chemical weapons were extensively used by both sides in the first world war, and have been blamed for 100,000 deaths.
Soldiers particularly feared chemical gas attacks because they could cause blindness, blistering and a slow, painful death. The weapons are now outlawed by international agreement in most countries.
The MoD launched Project Cleansweep in 2007 to provide "reassurance" that residual contamination at UK sites did not pose a risk to human health or the environment. A briefing on the project has been released in response to requests under freedom of information law.
The project initially considered 46 sites, but whittled that down to 14 that required detailed investigation. Although sites may have been cleared in the past, "we do not have scientific evidence that all harmful traces of the agents were removed or disposed of", the MoD briefing stated.
The 14 sites included two former US chemical weapons stores at Aberfoyle in South Lanarkshire and at Worksop in Nottinghamshire. At Bowes Moor in Durham, 17,000 tonnes of chemicals were stored on 564 acres of moorland.
According to the MoD, areas historically used for the disposal of mustard gas are still fenced off at Riseley in Bedfordshire and at Spalford Warren in Nottinghamshire. Spalford Warren has also been designated as a site of special scientific interest because of "its importance as a grass-heath habitat".
The sites are now safe, the MoD briefing said, and "suitable for their current use, provided any management systems, restrictions or procedures remain in place". A comprehensive report on Project Cleansweep is due to be published later this year.
The 14 sites investigated for chemical weapons contamination
site / grid reference / comments by Ministry of Defence
Aberfoyle, South Lanarkshire / 263900, 704500 / “US Army chemical weapons store…Smoke generators were disposed of by burning.”
Kilmarnock, East Ayrshire / 235500, 651500 / “A chemical agent bomb filling plant…covering approximately 20 acres.”
Bowes Moor, Durham / 398065, 514440 / “The site stored weapons charged with mustard, phosgene and lewisite on an area of 564 acres of moorland. In total 17,000 tonnes of chemical agent was stored.”
Escrick, North Yorkshire / 463500, 440000 / “Part of the site was used for storage of mustard filled munitions.”
West Cottingworth, North Yorkshire / 467628, 442902 / “Was a Forward Filling Depot compromising two 250 ton underground mustard storage pots. In 1991 the pots were dug out and the site levelled.”
Southburn, Yorkshire / 499500, 453600 / “Was a CW [chemical weapons] storage site…Records indicate that the burning of 65lb LC [light case] bombs also took place.”
Harpur Hill, Derbyshire / 405800, 370500 / “Was a chemical (phosgene and mustard) storage site. Storage was on 104 acres of moorland.”
Norton Disney, Lincolnshire / 486100, 364500 / “The site included two 250 ton underground mustard storage pots and facilities for filling weapons.”
Spalford Warren, Nottinghamshire / 483300, 368100 / “Stored mustard and phosgene filled weapons…disposed of by burning…Areas historically used for disposal of mustard are fenced.”
Worksop, Nottinghamshire / 462500, 375500 / “US Army Storage Depot Worksop held stocks of mustard and phosgene…The site was developed to hold 40,000 tonnes of mixed ammunition, including chemical weapons.”
Valley, Flintshire / 320755, 366475 / “Was a large scale chemical agent manufacture, charging and storage site.”
Lords Bridge, Cambridgeshire / 539100, 253500 / “Was a Forward Filling Depot comprising two 250 ton mustard storage pots and held stocks of chemical weapons.”
Riseley, Bedfordshire / 504100, 264800 / “The site included three 500 ton underground mustard storage pots and facilities for filling weapons. Areas historically used for disposal of mustard are fenced.”
Little Heath, Suffolk / 585100, 278000 / “Was a Forward Filling Depot compromising three 500 ton underground mustard storage pots. Decanting and burning of munitions also took place.”
source: Ministry of Defence
An interactive map of the 14 sites is available at here at guardian.co.uk.
A copy of the two-page briefing on Project Cleansweep released by the Ministry of Defence can be downloaded here (786KB pdf).