Officials in Yokohama, Japan’s second largest city, are investigating soil samples after a radioactive substance was found in sediment atop an apartment building about 155 miles (250 kilometers) from the Fukushima No. 1 nuclear plant, according to news reports.
The discovery has raised concerns that leaked radiation from three Fukushima reactors that suffered meltdowns after the March earthquake and tsunami may be more widespread than thought, The Japan Times reported Wednesday.
The findings come after a travel alert issued by the U.S. government last week, warning Americans in Japan to avoid areas near the stricken reactors.
The alert recommends that U.S. citizens stay away from areas within 20 kilometers (12 miles) of the nuclear facility. The State Department also admonished Americans to stay away from territory northwest of the plant in a zone that Japan calls the "Deliberate Evacuation Area." The zone includes Iitate-mura, the Yamagiya district of Kawamata-machi, Katsurao-mura, Namie-machi and parts of Minamisoma.
The radioactive isotope strontium-90 was detected on a rooftop by a private agency responding to a resident's request, The Japan Times reported.
Strontium-90 has been found in Japan at concentrations up to 20 becquerels before the nuclear crisis, The Japan Times said. The latest discovery found the strontium-90 level at 195 becquerels, according to the paper.
Since strontium-90, which has a half-life of 29 years, is widely dispersed in the environment and the food chain in trace amounts, external exposure is minimal, according to the Environmental Protection Agency. With internal exposure at high concentrations, strontium-90 can accumulate in the bones and is “one of the more hazardous constituents of nuclear wastes,” according to the EPA.
Meanwhile Wednesday, Tokyo Electric Power Co., the embattled utility whose territory includes the nuclear crisis zone, held a disaster drill at the Fukushima No. 1 nuclear power, according to news reports.