The Asahi Shimbun reported Tuesday that the mud in 468 reservoirs outside of the Fukushima evacuation zone contain levels of cesium high enough to be designated waste that must be removed. The mud in the Myotoishi reservoir, 55 kilometers west of the stricken Fukushima plant, had a cesium level of 370,000 becquerels per kilogram, a level the newspaper described as "mind boggling". The central government has classified levels over 8,000 becquerels as material that must be removed; however the Environment Ministry says it has no plans to remove the contaminated mud. This report highlights serious deficiencies in another report, released the same day, which concluded that radiation exposures outside the exclusion zone were "comparable with variations in the background dose".
Between February 2012 and December 2013, a joint survey by the Fukushima prefectural government and the Japanese farm ministry tested the sediment on the bottom of 1,939 of the 3,730 agricultural reservoirs in Fukushima Prefecture. Of those, 576 reservoirs exceeded the 8,000 becquerel per kilogram federal action level for contaminated soil, with 14 reservoirs exceeding 100,000 becquerels per kilogram. 468 of those reservoirs were located outside of the evacuation order zone, including five of the most highly contaminated reservoirs. Most of these reservoirs are located in the center of Fukushima prefecture, far from the coastal nuclear plant, with a number of the contaminated reservoirs in the cities of Fukushima and Date. That such vast quantities of cesium drifted so far from the power plants bodes ill for the many Japanese who were exposed to this fallout.
As The Asahi Shimbun explains:
Officials with the prefectural government’s farmland management section said cesium that was discharged from the nuclear plant immediately after the accident attached to dust in the air and fell to the reservoirs along with the rain. Cesium that ended up on surrounding mountains was washed down into the reservoirs along with earth and sand, they added.
“As reservoirs are shaped like earthenware mortars, it is easy for earth and sand to accumulate,” said an official of the section. “Because of that, contaminated soil in surrounding areas often ends up in the reservoirs, making their contamination levels high.”
However, the Myotoishi reservoir is located on a hilltop, so this explanation rings hollow. The Myotoshi reservoir is in the middle of a residential area, ringed by 392 homes and a high school. The fact that a plume of cesium so concentrated that 370,000 becquerels per kilogram remains in the mud passed through this community 55 kilometers (34 miles) from the nuclear disaster raises serious questions about the exposures received by these and other residents far outside the evacuation zones.
On the same day that this report was released, another study was posted to the Proceedings of the National Academy of Sciences of the United States of America. In this study, 483 residents of three towns outside the exclusion zone, 20-50 kilometers away from the triple meltdown, wore personal dosimeters from August through September of 2012. From this data, total exposures from "groundshine" was extrapolated for the next fifty years. The exposure from food and inhalation was estimated, and considered to be relatively insignificant. The bottom line was that post-2012 doses estimated for this population would increase the lifetime risk of cancer by about 1.37 percent.
But it is clear that there are obvious issues in the study. One of the most important was emphasized by the researchers themselves - that it did not take into account exposures in the direct aftermath of the accident, but rather only exposures after 2012. Obviously the vast majority of the exposure occurred in the immediate aftermath of the meltdowns. Another issue was that the three study sites selected were all areas with the LOWEST radiation exposures - although the study participants showed typical exposures of 1-3 mSv/y, other areas over thirty kilometers away from the meltdowns had exposures over 50 mSv/y, and evacuation orders are "ready to be lifted" in areas with less than 20 mSv/y. Finally, and pertinent to the residents living near these contaminated reservoirs, it was assumed that very little cesium would be re-lofted into the atmosphere.
Although an Environment Ministry ministry official in charge of decontamination work stated that “Radiation levels in the air (around the reservoirs) are not high enough to have an adverse effect on the health of residents,” in some of the reservoirs where cesium measurements were high officials noted that water levels were lower in summer and, as a result, the mud was exposed to the elements. In those instances, the exposed mud posed a health hazard to residents.
Prefectural authorities, fearing that contaminated mud from the reservoirs may create a health hazard for residents, are asking the central government to remove the waste. However, the Environment Ministry says it has no plans to dredge the reservoirs to remove the contaminated sediment. The central government says that reservoirs, many of which are located in residential areas, are not covered by its decontamination program.
Kiyoshi Ishii, 71, who lives near the reservoir and is head of the local community association, was unable to hide his anger.
“If the reservoir dries up and the dirt in the mud rises into the air, we will not be able to remain here. Does the administration have any intention to do something to prevent that from happening?"
One thing is clear - the true exposures of this community, and the many others that were hit with plumes of radionuclides after the triple meltdown at Fukushima, are unknown. While it appears that every effort is being made to minimize public perceptions of the severity of this disaster, the victims of this denial continue to live at risk in order to protect the image and profits of the nuclear industry.