I spoke to the son of the man who died in or neighborhood. He told us that the doctor mentioned that it was possible that the cancer was caused by heavy metals. The doctor, the head of a hospital nearby, told him that there were dangerous levels of heavy metals in all Japanese water and that this information was being stifled by the Ministry of Health. The Ministry of Health in Japan is notoriously corrupt and have probably been under investigation for one thing or another for the last 30 years. I totally and completely don't trust them.
I also once met a toxologist who said that toxologists were coming to Japan to study because Japan was immersed in lots of chemicals that were illegal in other nations and there was a lot they could study.
My neighbor checked his well water for heavy metals and found enough to be a long term health concern. However, he was told that city tap water was even worse.
I don't have much expertise in this area, but it sounds like a good reason to leave Japan long term. I can only image it getting worse. Does anyone know more about this?