Authorities in Tokyo put the stopper on wells supplying fresh drinking water in the western Tama suburb last year after high levels of organic chemicals were discovered.

An expert noted that the level of contamination posed no immediate health hazard to those who drank the tap water, but called for a thorough investigation as the chemicals can remain in the body for many years.

The Asahi Shimbun obtained documents from the Tokyo metropolitan government about water quality after submitting a request for information disclosure.

The chemicals found in the water supply in western Tokyo were Perfluorooctane Sulfonate (PFOS) and Perfluorooctanoic Acid (PFOA).

In 2016, the U.S. Environmental Protection Agency issued a drinking water health advisory that limits the combined presence of PFOS and PFOA to 70 nanograms per liter of water. The advisory states that no health effects would arise if an individual drank two liters a day of water with that level of chemicals for 70 years.

While other nations have standards for the chemicals in their drinking water, the levels are different. Japan has no such standards but plans to call for the Ministry of Health, Labor and Welfare to set such standards this spring.

Groundwater pumped from wells in Tama helps supply the western suburb but not the 23 wards in central Tokyo.

The documents obtained by this newspaper showed that the metropolitan government conducted tests for the chemicals since May 2019 at six water purification facilities where comparatively high levels of chemicals were detected in the past. A total of 71 water purification facilities provide water to most of the 30 cities, towns and villages in western Tokyo.

The water at the Higashi-Koigakubo facility in Kokubunji had a combined total of 101 nanograms of PFOS and PFOA.

The metropolitan government has established its own guidelines calling on purification facilities to keep the combined levels of PFOS and PFOA at 35 nanograms per liter, or half the U.S. standard.

But a test last year at the Fuchu-Musashidai facility detected a total of 60 nanograms, while a 2018 test at the Kunitachi-Naka facility detected a level of 38 nanograms.

Based on those results, the metropolitan government last June stopped using well water from some wells that supply those three facilities. Nearby rivers helped pick up the slack and the levels of the chemicals decreased as a result.

The three facilities supply tens of thousands of households.

"We became more cautious because of our concerns for Tokyo residents," said an official at the Bureau of Waterworks.

The metropolitan government began testing for the presence of PFOS and PFOA in the water supply in western Tokyo from about 2005. The area covers Yokota Air Base. A test in 2019 of four wells in the vicinity of the base found levels of the two chemicals that were 19 times the U.S. standard.

Records of the water testing only remain for the period between fiscal 2011 and 2018. Tests at the Higashi-Koigakubo and Fuchu-Musashidai facilities were conducted between one and 12 times a year depending on the level of chemicals detected. The maximum figures detected for the period ranged between 79 and 150 nanograms.

While metropolitan government officials believe that chemicals used in the past that had seeped into groundwater may account for the high levels, they added that no specific cause had been found.

"I am surprised that some of the drinking water supplied in Tokyo had such high levels of the chemicals," said Mineo Takatsuki, a researcher affiliated with Tokyo's Waseda University who attended a U.N. conference in 2019 related to regulations on toxic substances in water.

"The figures in the Tokyo data are not at levels that would lead to immediate health effects," Takatsuki added. "Even so, the local governments that use the groundwater for their water supply need to carry out proper investigations because factories and airports in the area also used that water in the past."

About 1,000 water supply operations in Japan provide drinking water, but there are no legal requirements calling for testing of the two chemicals, according to health ministry officials.

They said tests for the presence of the chemicals were only conducted at a small percentage of the 6,400 or so water purification facilities around Japan.

The World Health Organization has not evaluated the health effects from ingesting PFOS and PFOA. But research has found that the chemicals lead to higher blood cholesterol levels.

A study in the United States found that people who drank water with extremely high levels of PFOA were at risk of developing six types of illnesses, including testicular and kidney cancer and ulcerative colitis.

(This article was written by Yuji Moronaga, Kei Fujiyama and Ayako Suzuki.)