Abstract

The impact of the Fukushima-derived radiostrontium (90Sr and 89Sr) on the western North Pacific Ocean has not been well established, although 90Sr 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 90Sr) the 137Cs levels. The total amount of 90Sr released to the marine environment in the form of highly radioactive wastewater could reach about 1 PBq. Long-term series (1960–2010) of 90Sr 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 90Sr 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.

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