Airborne contamination continues to cross the western states, the new data shows, and Boise has seen the highest concentrations of radioactive isotopes in rain so far.
But the Korea Institute of Nuclear Safety said that although small levels of radioactive iodine and caesium particles had been found in rain falling in part of the country, they were not enough to cause concern over public health.
Radioactive isotopes accumulate in milk after they spread through the atmosphere, fall to earth in rain or dust, and settle on vegetation, where they are ingested by grazing cattle.