Assessing 134Cs & 137Cs levels in abiotic and biotic samples in British Columbia following the Fukushima Nuclear Accident

Abstract

The Fukushima nuclear power plant accident on March 11, 2011 raised global concerns due to the uncontrolled release of radioisotopes into the atmosphere and Pacific Ocean. With the aim to investigate potential Fukushima-associated radioactive contamination in British Columbia, detailed analysis of 134Cs and 137Cs activity levels in abiotic (soil and clay) and biotic (wild Pacific salmon including, Chinook, Oncorhynchus tshawytscha; chum, O. keta; and sockeye, O. nerka, as well as roof plant-material) samples collected in British Columbia was performed using gamma-ray spectroscopy. The extended source shape of each sample was modeled using the GEANT4 software package, previously developed to model the Germanium Detector for Elemental Analysis and Radioactivity Studies (GEARS), in order to measure the larger environmental samples. 134Cs and 137Cs activity levels were compared relative to 40K, a (Naturally Occuring Radioactive Material (NORM), to examine the impact of anthropogenic radiation relative to existing natural background radiation. In abiotic samples, the maximum 134Cs and 137Cs activity concentrations measured were 1.33(17) and 155.6(19) Bq/kg respectively while in the salmon biotic samples, the maximum 137Cs activity concentrations measured was 2.8(4) Bq/kg. 134Cs was not detected in any of the salmon samples. In the single plant biotic sample, the activiy concentrations for 134Cs and 137Cs were measured to be 13.1(2) and 54.4(8) Bq/kg. The Minimum Detection Limit (MDL) was calculated for samples where neither 134Cs and 137Cs were detected to provide an upper limit for the amount of each radioisotope present. The maximum ratio of anthropogenic activity to naturally occurring activity in all of the samples measured was 0.0336(9) and 0.68(2) for 134Cs/40K and 137Cs/40K respectively, though the required ratios to give equal dose contributions from man-made and naturally occurring radioactivity would be 3.17 and 2.67. It was observed that in the samples where 134Cs was positively identified, 7Be was also detected suggesting the contribution of 134Cs into these samples may have been through the atmospheric deposition rather then through ocean currents. For all samples, the measured activity concentration of 134Cs and 137Cs were below 1000 Bq/kg, the 134Cs and 137Cs action level for commercial food and beverages established by the Canadian Guidelines for the Restriction of Radioactively Contaminated Food and Water Following a Nuclear Emergenc