Three people have now been arrested following an incident involving the discovery of bottles of mustard gas in woods near Woodhall Spa.
A 38-year-old man from Lincoln was arrested on Tuesday night, and a woman was arrested yesterday. They remain in custody.
A third person - a man from Woodhall Spa - was arrested this morning, and specialist teams will conduct a search at a property in Woodhall Spa today.
Police added that a search at an address at Longdales Road, Lincoln, has been completed and no noxious substances were found.
Two people required hospital treatment for burns after the discovery of the canisters in woodland off Kirkby Lane on Sunday (October 1).
Police have described events as a ‘major incident’ and have appealed for people to stay away from the scene.
Other agencies have been involved including army bomb disposal units.
The location - Roughton Woods - is popular with walkers.
This afternoon (Thursday), a police spokesman said: “Our joint enquiry with the military into the items found at Roughton continues, with our primary focus on maximising the safety of the public in the local area.
“There is not thought to be any risk to the public, but advice remains not to go to areas where there is an ongoing police presence.