A joint survey by NHK and a civic group has found that the harmful construction material asbestos was used in more than 20,000 publicly run apartments across Japan.
Asbestos can cause lung cancer as well as a type of cancer called mesothelioma, and other health problems.
NHK and a group of patients and their families have obtained records on public housing kept by the central and local governments, through interviews and requests for information disclosure.
The survey found that asbestos was used in at least 22,000 apartment units.
Tokyo Institute of Technology Professor Takehiko Murayama estimates that about 230,000 people may have inhaled the harmful substance.
The public housing units in question were mostly built before removing or covering asbestos began in 1988.
Professor Murayama says the people are likely to develop illnesses due to asbestos exposure.
He is urging central and local government authorities to call the attention of former residents to the problem and provide them with information.
Source and image: NHK