How clean is clean?
The Guardian reports:
Following the nuclear disaster at Chernobyl 25 years ago, the Soviet government chose long-term evacuation over extensive decontamination; as a result, the plants and animals near Chernobyl inhabit an environment that is both largely devoid of humans and severely contaminated by radioactive fallout.
The meltdown last March of three nuclear reactors at the Fukushima Daiichi nuclear power plant in Japan also contaminated large areas of farmland and forests, albeit not as severely or extensively as at Chernobyl. But lacking land for resettlement and facing public outrage over the accident, the Japanese government has chosen a very different path, embarking on a decontamination effort of unprecedented scale.
Beginning this month, at least 1,000 sq km of land — much of it forest and farms — will be cleaned up as workers power-spray buildings, scrape soil off fields, and remove fallen leaves and undergrowth from woods near houses. The goal is to make all of Fukushima livable again. But as scientists, engineers, and ordinary residents begin this massive task, they face the possibility that their efforts will create new environmental problems in direct proportion to their success in remediating the radioactive contamination.
“Decontamination can be really effective, [but] what you have is a tradeoff between dose reduction and environmental impact,” says Kathryn Higley, a radioecologist at Oregon State University who has studied several decontamination sites in the United States. That’s because the radioactive particles the Japanese are trying to get rid of can be quite “sticky”. Removing them without removing large amounts of soil, leaves, and living plants is nearly impossible. The Ministry of Environment estimates that Fukushima will have to dispose of 15 to 31m cubic metres of contaminated soil and debris by the time the decontamination projects end. Costs are predicted to exceed a trillion yuan…
Past studies have shown that cancer rates rise in populations exposed to a dose of 100 millisieverts (mSv) of radiation. They reveal much less about the situation in Fukushima, where lower doses will remain for many years. (Measurements taken in Fukushima City in late December, for instance, ranged from .33 to 1.04 microsieverts per hour; sustained for a year, that adds up to doses of 2.9 to 9.1mSv.) The International Commission on Radiological Protection recommends that the general public be exposed to a yearly dose of no more than 1 to 20 mSv following a nuclear accident; those two numbers represent the difference between a decontamination effort confined to about 500 sq km and one encompassing much of Fukushima prefecture and beyond.