Six months after the nuclear meltdowns in Fukushima Prefecture, the public's awareness of the threat posed by radiation is entering a new phase: the realization that the biggest danger now and in the future is from contaminated soil.

The iodine-131 ejected into the sky by the Fukushima No. 1 power station disaster was quickly detected in vegetables and tap water — even as far away as Tokyo, 220 km south of the plant.

But contamination levels are now so low they are virtually undetectable, thanks to the short half-life of iodine-131 — eight days — and stepped up filtering by water companies.