Radioactive plutonium particles from U.S. nuclear weapons tests in the Pacific some 50 years ago have been detected for the first time in Japanese waters. The particles were found in soil samples from Sagami Bay, about 50 kilometers (30 miles) southwest of Tokyo, researchers at the National Institute of Radiological Science said. The plutonium particles matched the fallout from the blasts at the Bikini Atoll in the Marshall Islands, but they pose no environmental risk, said research team leader Masatoshi Yamada.