Two people have been taken to hospital for treatment to burns and minor respiratory problems after discovering mustard gas canisters from World War Two.
The area around Roughton Woods near Woodhall Spa has been cordoned off after the canisters were found by people bottle digging on Sunday, October 1.
A man aged 38, from Lincoln, has also been arrested on suspicion of being in possession of a noxious substance. He remains in custody.
Police sent the canisters to Porton Down, the Defence Science and Technology Laboratory, to identify what they contained.
It is believed that the mustard gas canisters have been in situ since the site was an operational RAF base.
The area formally known as RAF Woodhall Spa opened in February 1942 as a satellite of RAF Coningsby and closed in the mid 1960s.
A Lincolnshire Police spokesperson said: “No-one has been seriously injured; two people who found the canisters were taken to hospital and received treatment for burns and minor respiratory problems on Sunday, they returned home the same day.
“If anyone has recently recovered any bottles or other containers from this area they are asked to contact 101.
“We are working with other emergency services, military and health partners to ensure the continued safety of anyone who uses the woods and to establish if any further canisters are present.
“We would ask people to avoid the area for the time being.”