The state's air checks for asbestos in fiscal 1981-1983 were conducted at only three of the 2,000-plus factories that handled the carcinogenic material, government sources said Wednesday.
Based on the study, the then Environment Agency, which conducted the survey, concluded in 1985 that the health "risk to the general public is small."
It also issued local governments notices urging them to take steps to curb asbestos emissions, but decided against proposing any regulations.
The research showed that the areas around the three factories, which were checked in fiscal 1981, showed no major differences in airborne asbestos concentrations compared with residential areas nearby.
"The research was intended to grasp asbestos concentration in broad areas in various environments," said an official at the Air Quality Management Division of the Environment Ministry. "It was conducted after listening to expert opinions, and we believe it was done appropriately."
Critics say the need for regulations would have been more apparent and that a warning issued by an agency panel in 1980 would have been taken more seriously if the checks had been more extensive.
The panel proposed taking specific actions immediately in areas around asbestos-emitting factories to lower health risks.
The Environment Agency was upgraded ministry status in 2001.
The 1981-1983 research was conducted in residential, industrial and agricultural areas, as well as areas along highways in Tokyo, Osaka, Fukuoka and other regions. A total of 190 locations were checked.
To check the effects of asbestos, however, only nine sites within 100 meters of three asbestos factories, in Hirakata and Osaka, both in Osaka Prefecture, and in Fukuoka, were included.