Mixed zooplankton samples were sampled using Bongo nets (mesh size = 300 micromol and Methot net (mesh size = 4mm) to collect gelatinous zooplankton, larger crustaceans and fish. Samples collected were pooled together from several casts to achieve biomass needed for radioanalysis. Samples were frozen prior to freeze-drying. Samples that were freeze-dried and ground were stored and analyzed in straight side Nalgene 4oz jar; powdered mass was compressed by a polyacrilamide ring placed on top to assure uniform distribution of the sample in the jar. Biological samples were analyzed using a planar low energy germanium detector - LEGe, Canberra, Model GLP 3830 with a 3800 mm2 active area; Genie 2000 software was used for spectrum analysis.
Counts and concentrations of Cs134, Cs137, Ag110m, and K40 detected in zooplankton and small fish samples are reported. Samples were collected as part of a radioecological study of biota in order to assess the impact of radiation leaks from the Fukushima Daiichi nuclear power facility, damaged by a March 11, 2011 earthquake and tsunami. Radionuclide results were determined from high purity germanium detectors and calibrated against IAEA standards as described in Buesseler et al. (PNAS, 2012).
Total counting efficiencies that accounted for sample geometry and for energy emission were calculated based on standards composed of Se-75, Cs-137 and Eu-152 (265 keV, 662 keV and 1408 keV, respectively). We also accounted for the branching ratio and the concentrations were decay-corrected back to April 6th, 2011 The error reported reflects the % counting error. The lower end of the detection was decided based on the lowest among the samples radionuclide concentration minus one error. We did not correct for coincidence summing. An algorithm used for making these corrections - i.e. total % counting efficiency was: CEtot% = ((-6.24 * ln(sample volume) + 48.23) * (13.74 * energy * ^(-0.79)))/100;
\nnd = not determined
\nbd = below detection