Japanese researchers say they have detected potentially dangerous organic fluorine compounds from blood samples of people living near a US base in Tokyo. They say the levels of the substances were much higher than the figures in an earlier nation-wide survey.

Harada Koji, the Associate Professor at Kyoto University, along with a civic group have conducted the blood testing of 280 people living near the US Yokota Air Base.

They said on Monday that the preliminary results show the levels of PFOS and PFOA detected in 87 people were more than three times the concentration reported in a 2021 government survey at three locations across the country.

Harada said such levels of the compounds will not immediately affect people's health. But he urged the central and municipal governments to identify the sources of the chemicals and look into their impact.

The blood tests were conducted in response to the detection of the substances in rivers and groundwater near US bases in Okinawa and Kanagawa Prefectures.

Their concentrations were above the provisional safety standards set by the Japanese government.

Similar levels of the substances were also found in wells and groundwater in several places in central Tokyo.

The civic group says it plans to test a total of 600 residents through March and analyze the results.

Organic fluorine compounds were once used in fire-fighting foam and stain repellents.

The United States has strict guidelines for the compounds including no amount allowed in drinking water.

The Japanese government has set up an expert panel to come up with a package of measures as it has yet to establish safety standards for the chemicals.

At the first panel meeting on Monday, environment ministry officials explained a WHO-proposed method to measure those substances in drinking water.

The panel aims to come up with science-based measures and to set an effective PR policy about the chemicals.