On Sept. 10, Tokyo Gov. Yuriko Koike revealed that the people in charge of the soil remediation work for the Toyosu market, the relocation site for the famed Tsukiji fish market in Chuo Ward, ignored the recommendations of outside safety experts.

The discovery has reignited public concern about the environmental safety of the man-made area 2 km south of Tsukiji, adjacent to Tokyo Bay.

Will the soil pose a health risk to the market’s produce, workers and consumers? Let’s take a closer look.

What problems have emerged at the new site?

The soil at the Toyosu site, which was formerly a Tokyo Gas Co. production plant, was contaminated with toxic chemicals including benzene and cyanogen.

Under the relocation plan, the Tokyo Metropolitan Government was to remove and decontaminate the top two meters of soil at the Toyosu site and return it to the compound. That was then supposed to be topped off with a 2.5-meter layer of fresh, clean soil before construction began.

But on Sept. 10, Koike revealed this 4.5-meter layer of soil was missing from under the five main structures at the new market. So instead of sitting on a foundation of clean soil, the five structures were built on hollow concrete utility rooms filled with pipes and electrical cables. These undisclosed structures occupy about a third of the 40-hectare Toyosu site, which was built on reclaimed land.

The revelation has shattered the credibility of Tsukiji relocation plan, which has been dogged by environmental concerns from the very beginning.

What kind of health risks will the missing layer of soil pose?

Experts are not sure, but some warn that, over time, toxic gas or chemicals might seep to the surface or accumulate in the buildings’ hollow foundations, posing health risks to those working there.

The rooms’ vulnerability to contamination may already be evident in the form of large pools of tainted water found in the utility rooms of three of the five facilities, which are destined for use by seafood, vegetable and fruit wholesalers. The pools were discovered by assemblymen from the Japanese Communist Party.

Testing has found the pools in two of the five facilities to be tainted with arsenic and chromium at density levels around 10 to 35 percent of the legal limit.

The metropolitan government said the groundwater might have seeped in through their sides during the heavy rains in August.

Akio Hata, former president of the Japan Association on Environmental Studies, said the presence of a substance like chromium proves groundwater can come to the surface and speculated that any clean soil provided to protect the site has been re-contaminated, raising the chance that the density levels of the toxins will rise in the future.

He also raised issues with the site’s underground water control system, which is supposed to monitor water levels at the site and pump any excess into the sewage system, and its susceptibility to powerful earthquakes.

The metro government, meanwhile, said the pump system is still running in test mode and that all the water on the floors will be drained once it enters full operation.

Hata also said that, since chromium and arsenic don’t evaporate, the chemicals will likely remain underground, waiting to be freed by an event large enough to cause liquefaction, as happened at Toyosu during the March 2011 Great East Japan Earthquake.

Kazuko Mizunoya, an architect who was hired to observe the decontamination work as an outside expert, said in an email that the metro government should have dug deeper at Toyosu when collecting soil samples.

She said the revetment work carried out by the contractors wasn’t sufficient to stabilize the ground in the area, pointing out that parts of the Toyosu site liquefied during the March 2011 quake, bringing sand and stones to the surface.

Do the toxic substances found at Toyosu pose a health threat right now?

Probably not. The Tokyo Metropolitan Government said recent groundwater and air surveys at the site have shown the density of the chemicals, including benzene, to be within legal limits.

Minoru Yoneda, a professor at Kyoto University Graduate School of Engineering’s Division of Integrated Biosciences, believes the Toyosu market’s current condition doesn’t pose any health threat.

He said the safety limit for benzene is based on the consumption of 2 liters of groundwater every day, which is impossible at the Toyosu site.

While traces of benzene are still in Toyosu’s air, its density level is within the safety limit, according to metropolitan government data.

Has the Tokyo Metropolitan Government violated any public safety regulations?

Metro officials say no. Koji Yoshida, one of the officials in charge of the Tsukiji relocation project, said “all has been done to ensure safety” under measures required by law.

In 2008, an environmental advisory panel recommended that the Toyosu site be blanketed by a 4.5-meter layer of soil. The metro government apparently ignored this advice and assumed the walls of the secret concrete utility rooms would be sufficient to shield the market buildings instead.

Yoshida said there were no legal requirements for further measures to be taken as long as the groundwater at Toyosu is not to be used.

Although not required to do so, Tokyo has sampled groundwater at the Toyosu site nine times since November 2014 to reassure the public, Yoshida said.

The results of the last sampling test in November will be released in January.

Why was the environment panel’s advice ignored and who made the decision?

This is not clear yet.

According to the daily Mainichi Shimbun, a senior official in the metro government said the hollow utility spaces were built to let power shovels or other heavy equipment be brought in to handle any new soil contamination problems.

Quoting a former metro official, the newspaper said the change in the Toyosu construction plan was kept secret because the planners feared that revealing it to the public would fan unfounded fears of pollution.

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