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

The impact of the Fukushima-derived radiostrontium ((90)Sr and (89)Sr) on the western North Pacific Ocean has not been well established, although (90)Sr concentrations recorded in surface seawater offshore of the damaged Fukushima Dai-ichi nuclear power plant were in some areas comparable to or even higher than (as those in December 2011 with 400 kBq m(-3)(90)Sr) the (137)Cs levels. The total amount of (90)Sr released to the marine environment in the form of highly radioactive wastewater could reach about 1 PBq. Long-term series (1960-2010) of (90)Sr 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 (90)Sr 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.