Radioactive iodine-131 readings taken from seawater near the water intake of the Fukushima No. 1 nuclear plant's No. 2 reactor reached 7.5 million times the legal limit, Tokyo Electric Power Co. admitted Tuesday.
The sample that yielded the high reading was taken Saturday, before Tepco announced Monday it would start releasing radioactive water into the sea, and experts fear the contamination may spread well beyond Japan's shores to affect seafood overseas.
The unchecked radioactive discharge into the Pacific has prompted experts to sound the alarm, as cesium, which has a much longer half-life than iodine, is expected to concentrate in the upper food chain.