An Irish farmer had stored enough of the deadly substance cyanide to "kill most of the population" of his town, council workers have said.
The farmer had the hazardous waste for 45 years and had originally bought it to get rid of rabbits.
Suzanne Dempsey, Environmental Officer with Roscommon Co Council, said this would have been common practice: "The farmer had previously sought advice on how to dispose of it safely. The toxic expert on the day said the amount was enough to wipe out most of the county."
The man, whom she described as a 'lovely gentleman', had the material well secured in containers.
"We also had a quantity of the herbicide 2,4,5-T, one of the two ingredients of Agent Orange which was used in the Vietnam War. It was good to get these chemicals into safe hands."
Other waste products that farmers arrived with included one of the main ingredients in Agent Orange, a chemical weapon used in the Vietnam war.
The waste collection was led by the Environmental Protection Agency (EPA), with the involvement of Roscommon County Council and Teagasc (the Irish agriculture and food development authority).
Tim Hyde from Teagasc said the collections "provide an opportunity for farmers to dispose of materials that may be harmful to humans and animals". He said Saturday's event was the "biggest turnout for the seven collection days held nationwide so far this year".
