U.K. Ministry of Defense investigates 14 former chemical weapons facilities

The U.K. Ministry of Defense recently investigated a total of 14 former chemical weapons facilities in Britain for signs of contamination.

Since World War I, tens of thousands of tons of mustard gas, phosgene and other chemical agents have been produced, burned and dumped at sites located around the country, according to the Guardian. Some areas are still restricted in order to protect the public, according to the Guardian.

Project Cleansweep, as the operation was called, detected no significant risk to the public health or environment from the sites.

At least one expert, Prof. Alastair Hay from the University of Leeds, has questioned the results of the investigation. Hay has argued that there is still no scientific proof that all harmful traces of the weapons were removed. He said more sampling might be needed at the sites. Mustard gas in particular, Hay warned, can remain in the environment persistently.

"The more problematic areas are where physical destruction took place," Hay said, the Guardian reports. "Incineration is a well-recognized method of disposal, but you need to ensure all is burned. We have no details of these procedures."

The MoD began Project Cleansweep in 2007. Initially, 46 sites were considered for inspection, but in the end only 14 were chosen. Two former U.S. chemical weapons stores and a workshop were included in the project.