Does the Fukushima NPP disaster affect the caesium activity of North Atlantic Ocean fish?

Abstract. Fillet samples of marine fish collected from the East/West Greenland currents (GC) and from the Baltic Sea (BS) have been investigated by gamma-ray spectrometry within the regular German monitoring programme. In samples of the second half of 2011, ¹³⁴Cs traces have been detected that are suggested to originate from the Fukushima fallout that was deposited in March/April 2011 over the northern North Atlantic and accumulated by fish. The radionuclide ¹³⁴Cs (half-life 2 yr) was indeed detected with quite small activities at about 0.0036 Bq kg⁻¹ w.w. Existing box models describing the transport of Cs within seawater boxes of the northeast Atlantic allowed for estimation of ¹³⁴Cs contributions from other sources, i.e. from the Chernobyl fallout and from discharges by the two major European nuclear reprocessing plants; both were negligible around Greenland, while for the Chernobyl fallout a small ¹³⁴Cs background contribution to BS fish was estimated. Model results confirmed the level of ¹³⁴C measured in BS fish and showed its maximum to have occurred in winter 2011/2012 followed by a continuous decrease. It was also determined that ¹³⁴Cs activity, but not that of ¹³⁴Cs, showed a significant negative correlation with sampling depth (150–400 m) of GC fish; this strengthens our Fukushima fallout assumption. As a result, the Fukushima fallout in these sea areas only marginally enhanced (GC: 4%; BS: 0.1%) pre-Fukushima levels of individual dose rates received by human fish consumers; the addition was around 0.001 μSv following the consumption of 10 kg of fish per year, which is not expected to cause concern according to present guidelines for radiation protection.