TOKYO - White foam was seen overflowing from a manhole near a US base in Japan's Okinawa Prefecture on Thursday, prompting local authorities to investigate a possible link to per- and polyfluoroalkyl substances (PFAS) contamination.

A police officer on routine patrol discovered the foam leaked from the sewer linked to the US Marine Corps Air Station Futenma around noon in the city of Ginowan.

The city government is investigating the cause of the incident and has collected foam samples to analyze whether it contains PFAS and other potentially harmful substances.

The latest overflow echoes earlier incidents reported in 2020, when extinguishant containing potentially harmful PFAS chemicals leaked from the Futenma base, causing white foam to spread through surrounding residential areas, Kyodo News reported.

The report said the US military denied any involvement in the case, saying it had no confirmation that foam fire extinguishers or similar equipment were used.

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PFAS encompasses over 10,000 synthetic chemicals, which were once used for water-repellent finishing and foam-extinguishing agents.

A Japanese government survey in 2023 has found concentrations of PFAS chemicals in rivers and groundwater exceeded the country's provisional standard at 242 locations nationwide, raising concern about possible health risks such as cancer.