Radiostrontium in the Western North Pacific: Characteristics, Behavior, and the Fukushima Impact

The impact of the Fukushima-derived radiostrontium (Sr-90 and Sr-89) on the western North Pacific Ocean has not been well established, although 90Sr concentrations recorded in surface seawater offshore of the damaged Fukushima Daiichi nuclear power plant were in some areas comparable to or even higher than (as those in December 2011 with 400 kBq m(-3) Sr-90) the Cs-137 levels. The total amount of Sr-90 released to the marine environment in the form of highly radioactive wastewater could reach about 1 PBq. Long-term series (1960-2010) of Sr-90 concentration measurements in subtropical surface waters of the western North Pacific indicated that its concentration has been decreasing gradually with a half-life of 14 y. The pre-Fukushima Sr-90 levels in surface waters, including coastal waters near Fukushima, were estimated to be 1 Bq m(-3). To better assess the impact of about 4-5 orders of magnitude increased radiostrontium levels on the marine environment, more detail measurements in seawater and biota of the western North Pacific are required.