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Associated Press
Radioactive cesium has been found in plankton about 375 miles from the Tokyo Electric Power Co.'s tsunami-crippled Fukushima Dai-ichi nuclear power plant.

TOKYO (MCT) — Radioactive cesium believed to have been released during the crisis at the Fukushima No. 1 nuclear power plant in Japan following last year's major earthquake has been found in plankton about 375 miles east of the facility, according to a Japan-U.S. joint research team.

The amount of cesium detected in the plankton was far below the government's provisional limit of 500 becquerels per kilogram for marine products, according to the team led by Jun Nishikawa, research associate at the University of Tokyo's Atmosphere and Ocean Research Institute.

However, follow-up studies will be necessary because the radioactive cesium is likely to have accumulated in fish that eat plankton, the team said.

The findings will be reported to a conference of the Oceanographic Society of Japan set for Tuesday.

The research team collected animal plankton at 17 locations between 18.6 miles and 372.8 miles east of the plant in June last year, about three months after the March 11 earthquake and tsunami that triggered the nuclear crisis.

Cesium-137 was detected in all of the collected plankton, which in a dry state was found to contain 0.3 to 56.4 becquerels per kilogram. The farther away the plankton was collected, the less radiation it contained, according to the team.

Results of a similar survey conducted by the team before the crisis showed that plankton contained between 0.1 and 0.4 becquerels of cesium-137 per kilogram.

In the latest survey, the team also found cesium-134 — which has a two-year half-life — in plankton at the same levels as cesium-137, whose half-life is three decades.