ATMOSPHERIC TRANSPORT OF 129I FROM FUKUSHIMA TO BRITISH COLUMBIA, CANADA AND ITS DEPOSITION AND FLUX INTO LOCAL GROUNDWATER

The Fukushima-Daiichi nuclear accident (FDNA) released large amounts of fission product radionuclides to the environment in the spring and summer of 2011. Along with short lived fission products, iodine-129 (15.7 million year half-life) was also released. ¹²⁹I is recognized as a useful environmental tracer due to its mobile geochemical behaviour. Rain samples were collected in Vancouver from March 2011 to March 2012 and used to test if FDNA-released ¹²⁹I was reaching Canada. Precipitation samples from Environment Canada’s station on Saturna Island and from the National Atmospheric Deposition Program in northern Washington State were also measured to establish a regional pre-accident ¹²⁹I background. Groundwater from the Abbotsford-Sumas Aquifer was sampled to determine the persistence of ¹²⁹I in regional groundwater recharge. The mean regional pre-accident background for ¹²⁹I in rain samples is 38.15 x 10⁶ atoms/L (n=4). Days after the FDNA, ¹²⁹I values increased sharply to 218.7 x 10⁶ atoms/L and within weeks returned to near-background levels. This 6-fold increase in ¹²⁹I concentrations from both Vancouver and Saturna Island rain samples are synchronized and occur directly after the initial FDNA release. In addition, sporadic pulses of elevated ¹²⁹I in rain samples continued for several months, which were primarily due to local ¹²⁹I resuspension from the ground surface. Results of shallow (<1.4 yr ³H/³He age) groundwater samples showed variability in ¹²⁹I through March 2013 with an average of 10.83 x 10⁶ atoms/L (n=31) coincident with measured atmospheric and modelled vadose zone travel times for FDNA ¹²⁹I fallout. The minimal groundwater response suggests that ¹²⁹I input was partially retarded in soil, as is consistent with its geochemical behaviour; however we propose that there is adequate variability (and coincident timing) for attribution of FDNA-derived ¹²⁹I in regional groundwater, although it is of limited use as a groundwater tracer.