Approximately 48,000 liters of water contaminated with PFAS synthetic chemicals overflowed from a firefighting training area at the U.S. Yokota Air Base in western Japan during heavy rainfall in August, the Asahi Shimbun reported recently, citing the Tokyo metropolitan government.

Tokyo officials received the report on October 3 from the U.S. military through the Japanese Defense Ministry, according to Asahi Shimbun.

On October 4, a council composed of officials from the metropolitan government and affected municipalities told Japanese Defense Minister Gen Nakatani that the significant delay in reporting the incident was deeply regrettable, the Japanese media reported.

The council also requested that the Japanese government take responsibility for investigating and analyzing the leak's potential impact on groundwater and other environmental resources.

PFAS is a general term for a group of over 10,000 artificial chemicals that include PFOS, or perfluorooctanesulfonic acid, and PFOA, or perfluorooctanoic acid, the two most representative forms of PFAS.

PFAS, used in various products such as frying pan coatings and water-repellent clothing, have been detected in high concentrations at places near Self-Defense Forces and U.S. military bases as well as industrial areas in Japan.

In June, Japan's Food Safety Commission said that the effects of chemicals known as PFAS on birthweight loss and reduced immunity are "undeniable" in its first health assessment of the substances, after their detection across the country fueled concern among local residents.

Since last year, regions in Japan including Okinawa, Osaka and Tokyo have successively reported excessive levels of PFAS in their water bodies, and abnormal blood tests of nearby residents.

(With input from agencies)