This question is probably referring to radioactive materials carried by the ocean. This image shows a simulation generated by the GEOMAR Helmholtz Centre for Ocean Research, Kiel. It illustrates the spread of radioactive materials 16 months after the March 2011 disaster. Currents are shifting contaminated ocean water in the Pacific towards North America, but due to strong ocean gyres and winter storms it is already highly diluted. Scientists have calculated that the first radioactive debris will take around three years to reach the North American coast, i.e. 2014. At that point, the radioactivity will be just slightly lower than the value still measured in the Baltic Sea today following the Chernobyl disaster. The levels of radioactivity in the Baltic are around about 20 becquerels per cubic meter of water, which is only slightly higher than the normal value, but still considerably below the safe limit for drinking water. Any materials from Fukushima that reach the North Sea and Baltic Sea coasts of Germany will not be measurably radioactive.
Dr Susann Beetz from the Ideas2020-Team answered this question in collaboration with Dr Andreas Villwock, Head of Communications and Media Relations at the GEOMAR Helmholtz Centre for Ocean Research, Kiel.