via ScienceDaily.com / June 11, 2103 / Researchers from the Institute for Environmental Science and Technology (ICTA) and the Department of Physics of the Universitat Autònoma de Barcelona (UAB) have studied the spread of radioactive strontium in the coastal waters of eastern Japan during the three months following the Fukushima nuclear accident, which happened in March 2011. The samples analysed show the impact of the direct release of radioactive materials into the Pacific Ocean, and indicate that the amount of strontium-90 discharged into the sea during those three months was between 90 and 900 Tbq (terabecquerels), raising levels by up to two orders of magnitude. The highest concentrations were found to the north of the Kuroshio current, which acts as a barrier preventing radioactive material from being carried to lower latitudes.
This study measures the concentrations of the main strontium radioisotopes (90Sr and 89Sr) released into the sea over the three months following the accident at the Fukushima Dai-ichi nuclear power plant. The researchers took part in an oceanographic campaign led by Woods Hole Oceanographic Institution, in June, 2011. They analysed samples of water from the surface and from up to 200 metres in depth in an area between 30 and 600 kilometres off the eastern coast of Japan. This work was carried out in collaboration with the University of Seville.
The concentrations found were up to 85 Bq·m-3 (becquerels per cubic metre) for strontium 90 and 265 Bq·m-3 for strontium 89. These findings point to an increase of up to two orders of magnitude — a hundredfold- in concentrations of strontium-90 in the sea, with respect to the background values for this part of the Pacific before the Fukushima accident, which were 1.2 Bq·m-3. The presence of strontium-89, with a half-life of only 50 days, was further proof of a recent release. The highest concentrations of radioactive strontium were found 130 kilometres from the coast, in the eddies that form at the meeting point between the Kuroshio and Oyashi ocean currents.