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Toxic compounds detected again at water treatment plant on US Navy base in Japan

The front gate of the U.S. naval base in Yokosuka is seen in Kanagawa Prefecture in this May 27, 2022, file photo. (Mainichi/Toshiaki Hashimoto)

YOKOSUKA, Kanagawa -- The amount of possibly cancerous organic fluorine compounds detected in drainage water from a major U.S. naval base here exceeded Japanese government-set limits during a July investigation led by U.S. authorities, the Yokosuka Municipal Government announced on Sept. 12.

    The investigation followed a report that contaminated water was being discharged from the base.

    According to the latest U.S. finding, which was relayed to the municipal government by a senior official at the Japanese Defense Ministry's South Kanto Defense Bureau the same day, a combined 112 nanograms of perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) per liter of drainage water were detected in the July survey. That topped the Japanese government-set provisional target value of 50 nanograms per liter.

    The city said the survey was conducted on July 6 at four locations in a wastewater treatment plant, following the collection of samples on May 9. Of the four, 112 nanograms of the organic fluorine compounds were detected at a domestic wastewater discharge point -- the same amount found in the May survey. The U.S. report was quoted as saying that the cause of the possible compound leaks was unknown.

    Meanwhile, when the South Kanto Defense Bureau checked seawater samples collected on June 30 in three locations near the U.S. Fleet Activities Yokosuka base, it detected 1.6-1.8 nanograms per liter of the compounds.

    Yokosuka Mayor Katsuaki Kamiji had an online meeting over the issue with U.S. Navy Region Japan Commander Rear Adm. Carl Lahti on Sept. 12. As the U.S. continues to discharge contaminated water into the ocean via the treatment plant, Kamiji demanded that the U.S. Navy improve the situation, saying, "We cannot help but believe that the release of PFOS and other compounds has become continuous."

    Rear Adm. Lahti responded that the U.S. Navy will exhaust all efforts to find the cause of the leak, and told Kamiji that in the meantime they would install filters that adsorb the chemical compounds and continue surveying samples from the treatment plant.

    (Japanese original by Toshiaki Hashimoto, Yokosuka Local Bureau)

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