Photo/Illutration An expert, left, collects soil samples at the Futenma No. 2 Elementary School in Ginowan, Okinawa Prefecture, on Aug. 15. The school sits next to the U.S. Marine Corps Air Station Futenma. (Mika Kuniyoshi)

GINOWAN, Okinawa Prefecture--Extremely high levels of a suspected carcinogen were detected in the grounds of an elementary school next to the U.S. Marine Corps Air Station Futenma here, rekindling persistent health concerns over the handling of dangerous chemicals at U.S. military bases.

A reading of perfluorooctane sulfonic acid (PFOS) at one site of the Futenma No. 2 Elementary School was about 29 times that of PFOS levels deemed under U.S. environmental guidelines to carry risks in containing the contamination.

Koji Harada, an associate professor of health and environmental sciences at Kyoto University, expressed alarm over the findings, saying they underlined the need for on-site inspections at the Futenma airfield.

“The findings showed extremely high levels of the PFOS even on the ground surface where the contaminant tends to be washed away by rainwater,” he said. “The only way to resolve this problem is to open an investigation to identify the source of the contamination, given the high likelihood that soil lying deeper from the surface is polluted along with the groundwater.”

A waste pipe that is believed to originate in the Futenma base is located near the school premises.

An expert organization commissioned by a civic group that calls itself Ginowan Churamizu Kai (society working to maintain clean water in Ginowan) went ahead with an investigation of its own, saying it suspected that wastewater containing PFOS was released from the base through the pipe.

Its experts collected soil samples several centimeters below the ground surface at three sites on the school premises on Aug. 15 to determine the presence of PFOS. The group announced the findings on Sept. 5.

After receiving its report, the municipal education board notified parents and other concerned parties Sept. 7 that children will be prohibited from entering the area where figures are high.

In Japan, water quality guidelines for drinking, as well as river water, restrict the combined presence of PFOS and other substances to under 50 nanograms per liter of water as the preliminary limit.

In the United States, the Environmental Protection Agency’s soil screening guidance sets 38 nanograms per kilogram of soil as a level requiring more detailed examination for safety assessment.

The experts’ study turned up readings of 1,100 nanograms at one site.

A reading of 700 nanograms, about 18 times the U.S. level, was found at a second site. The level was so low at a third site that the gauge did not show a specific figure.

PFOS do not degrade in the natural environment and thus pose a threat to humans and ecosystems.

The chemical is widely used at military bases as well as the petrochemical industry as firefighting foam to quell fuel fires.

The use and production of PFOS was banned, in principle, in Japan in 2010.

However, a flurry of reports have emerged in Okinawa Prefecture since 2016 about high concentrations of the chemical in rivers and other sites near U.S. military installations.

The prefectural government has stated that it believes U.S. military facilities are the source of the contamination.

But the Japanese government and authorities in the southernmost prefecture have been denied access to the bases to carry out studies of their own despite repeated requests under the Japan-U.S. Status of Forces Agreement.

City officials placed safety cones at the sites where high levels of PFOS were detected to keep children away. Children were told to wash their hands and gargle carefully after playing in the school grounds.