After an organic fluorine compound content was detected in groundwater in Sezu City, Osaka Prefecture, Japan by more than 400 times, local civil society organizations organized blood tests for more than a thousand nearby residents. Survey results released not long ago showed that about 30% of the subjects had excessive levels of perfluorinated and polyfluoroalkyl substances (PFAS) in their blood. It is understood that PFAS is difficult to degrade and accumulates in the environment and human body. It is called a "permanent chemical". In 2023, the International Agency for Research on Cancer, a subsidiary of the World Health Organization, listed one of the representative substances, perfluorooctanoic acid (PFOA), as a carcinogen, and another representative substance, perfluorooctane sulfonic acid (PFOS), as a possible carcinogen. A water quality survey last year showed that the PFAS content in groundwater in a place in Sezu City, Osaka Prefecture reached 420 times that of Japan's provisional national standard. After more than 30 nearby residents were found to have abnormal blood tests at the end of last year, a non-governmental group decided to expand the scope of testing and conduct blood tests on more than a thousand residents. The results showed that about 30% of the 1190 residents in Osaka Prefecture and Hyogo Prefecture who received blood tests had excessive PFAS levels in their blood. The group asked the Japanese central government to conduct free blood tests for residents and take corresponding countermeasures.