An Environment Ministry decision to allow reuse of radioactively contaminated soil emanating from the Fukushima nuclear disaster in public works projects has prompted experts to warn against possible dumping of such soil under fake recycling.

The ministry formally decided on June 30 to allow limited use of soil generated from decontamination work after the Fukushima No. 1 nuclear power plant disaster in mounds under road pavements and other public works projects, as long as the soil contains no more than 8,000 becquerels per kilogram of radioactive cesium. The decision was made despite questions raised during a closed meeting of the ministry over incompatibility with the decontamination criteria for farmland soil.

The Act on the Regulation of Nuclear Source Material, Nuclear Fuel Material and Reactors sets the safety criteria for recycling metals and other materials generated from the decommissioning of nuclear reactors at no more than 100 becquerels per kilogram, and requires materials whose radiation levels exceed that level to be buried underground as "radioactive waste." The figure of 100 becquerels is derived from the International Commission on Radiological Protection's standards that annual radiation exposure of up to 0.01 millisieverts poses negligible health risks.

However, the Fukushima disaster has disseminated radioactive materials outside the crippled nuclear plant across far wider areas than expected. Under the special measures law on decontamination of radioactive materials, which was fully put into force in January 2012, waste whose radiation levels top 8,000 becquerels per kilogram is called "designated waste" and must be treated by the government, while waste with radiation levels of 8,000 becquerels or lower can be treated in the same way as regular waste. The figure of 8,000 becquerels comes from the upper limit of annual radiation exposure doses for ordinary citizens under the reactor regulation law, which is set at 1 millisievert. Regarding the double safety standards of 100 becquerels and 8,000 becquerels, the Environment Ministry had earlier explained that the former is for "reuse" and the latter for "waste disposal."

However, the recent Environment Ministry decision to allow the reuse of contaminated soil in public works projects runs counter to its earlier explanation. The ministry is trying to reconcile that difference by insisting that the radiation levels of tainted soil could be kept under 100 becquerels if mounds using such soil were covered with concrete and other materials to shield radiation. During a closed meeting of the ministry that discussed the matter, some attendants raised questions over inconsistencies with the decontamination criteria for farmland soil.

In April 2011, in the aftermath of the Fukushima meltdowns, the Ministry of Agriculture, Forestry and Fisheries restricted rice planting in paddies whose radiation levels topped 5,000 becquerels per kilogram of soil. While the restriction was effective for just one year, the same criteria has been in place for ensuing decontamination, where surface soil of more than 5,000 becquerels is removed and surface soil under that level is replaced with deeper layers.

It is inconsistent to strip away soil of more than 5,000 becquerels while recycling soil with the same level of radiation. However, attendants of the closed meeting never discussed the matter in detail, nor did the issue come up for discussion at an open meeting.

The radioactivity concentration of contaminated soil is higher than that of earthquake debris, whose treatment caused friction across the country on the heels of the Fukushima crisis. Therefore, officials attending an open meeting of the ministry discussed the introduction of incentives for users of tainted soil, with one saying, "Unless there are motives for using such soil, regular soil would be used instead."

Kazuki Kumamoto, professor at Meiji Gakuin University specializing in environmental policy, criticized the ministry's move, saying, "There is a high risk for inverse onerous contracts, in which dealers take on contaminated soil in exchange for financial benefits." There have been a series of incidents involving such contracts, in which waste was pressed upon dealers under the guise of "recycled materials," such as backfill material called ferrosilt and slag generated from iron refining.

"If contaminated soil was handed over under inverse onerous contracts, there is a risk that such soil could be illegally dumped later. Reuse of tainted soil would lead to dispersing contamination," Kumamoto said.