Photo/Illutration Towel rail fittings are seen with black splotches in a private residence in Yashio, Saitama Prefecture, on Oct. 2. (Shun Nakamura)

YASHIO, Saitama Prefecture--Metallic fittings on cars and indoor metal fixtures mysteriously started to tarnish after a sinkhole swallowed a truck in this city north of Tokyo in January.

Residents were at a loss to explain the phenomenon, but authorities now say it was likely due to hydrogen sulfide escaping from a ruptured sewer pipe, the source of the deadly cave-in.

The prefectural government here has signaled it is willing to pay for damages on a case-by-case basis.

Fumie Kinoshita, whose home stands 70 meters from the sinkhole that claimed the life of truck driver, became aware of the problem in June.

She said the emblem of one of her family’s two cars turned black. The same thing happened with the sideview mirrors of the other vehicle.

Kinoshita, 56, said metal fixtures on the bathroom shower also became discolored.

Another resident, Tadao Haseda, had a similar experience.

“I had never seen anything like it during the 54 years I’ve lived here,” said Haseda, 84.

A woman living about 20 meters from the accident site said she noticed in May that her shower fittings were tarnished.

The 70-year-old resident said she initially thought it was mold and rubbed the spot with detergent, but the stain didn’t come out.

The prefectural government mounted an investigation after residents complained.

A lab test turned up traces of sulfur on car emblems at 30 to 100 times normal levels. An expert suspected hydrogen sulfide was the cause.

Prefectural authorities have so far confirmed 33 cases of tarnish on cars, three on metal bathroom fittings, two on bicycles, two on precious metals, one on a faucet and one on kitchenware.

Hiroaki Kitagishi, a Doshisha University professor of organic chemistry, told The Asahi Shimbun that even a tiny amount of hydrogen sulfide can cause metals to change color through a chemical reaction.

He noted there had also been cases of tarnish occurring at hot spring resorts.

The prefectural government is planning to pay a flat rate for damages to residents and businesses located within a 200-meter radius of the sinkhole site or facing roads that were slapped with traffic restrictions because of the sinkhole accident.

Prefectural officials are planning to offer a 30,000-yen ($198) handout to each affected household plus 20,000 yen per person, whereas the payments to businesses will be a flat 100,000 yen per office.

Officials said they are also making arrangements to offer damages, on a case-by-case basis, for incidents where a causal relationship has been established.

Authorities have been measuring hydrogen sulfide concentrations around the sinkhole site since February. The data is available for free viewing on a website.

A peak concentration, so far, of 6.4 ppm was registered on Aug. 10. The measurements were zero on most days in September.

Under current safety standards, hydrogen sulfide concentration should not exceed 10 ppm at work sites and elsewhere.

“The measurement results to date indicate that a negative impact on public health is unlikely,” Kitagishi said.

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