TOKYO (Kyodo) -- The Japanese government said Friday that it has conducted an on-site inspection of the U.S. Yokota Air Base in western Tokyo over the possible leakage of so-called PFAS chemicals that may have harmful effects on human health.

Officials from the defense, foreign and environment ministries, the Tokyo metropolitan government as well as local municipalities entered the base in the morning to inspect a firefighting training area where an extinguishant containing PFAS is believed to have been used, according to the Japanese Defense Ministry.

Acknowledging local concerns over the chemicals, Defense Minister Gen Nakatani told a press conference that the government will work to ensure that "environmental measures in and around U.S. military facilities in Japan will be effective."

The inspection was conducted at the request of nearby municipalities after the United States informed the Japanese government in October of the possible leakage of water containing PFAS from the firefighting training area following heavy rainfall in late August.

PFAS, or polyfluoroalkyl substances, used in a wide variety of products including fire extinguishers are known as "forever chemicals" because they break down very slowly over time and can accumulate in people, animals, plants and the environment.

The U.S. military in Japan has already stopped using extinguishers that include PFAS, but past U.S. investigations had detected in reservoirs levels far above Japan's nonbinding interim standards.