| Low level releases of 131I and other fission products in the environment, such as seawater, may be difficult to detect by standard methods. Seaweeds have a high iodine concentration and absorb 131I to levels measurable by gamma-ray spectroscopy. A gamma-ray detection system was designed and validated to use for the detection of low level activities. The detection limit and minimum detectable activity of 131I for the system were determined to be 0.28 +/- 0.07 Bq and 0.09 +/- 0.02 Bq, respectively. Samples of seaweeds were collected on the East and West coasts of Canada. Ascophyllum Nodosum and the Saccharina Latissima were sampled in Shearwater, NS (Eastern Passage) in December 2006 and had 131I average dry weight activity of 30 +/- 2 Bq kg-1 and 175 +/- 7 Bq kg-1, respectively. Fucus gardneri samples were harvested from the western shoreline of Vancouver Island in Bamfield, British Columbia, at low tide in January, March and November of 2008. The average concentration of iodine in Fucus gardneri determined using INAA was 290 +/- 50 mug g-1 dry weight. Assuming an average concentration of iodine in seawater at the sampling location in Bamfield, BC, in the range of 0.03-0.05 mug g-1 and the average concentration of iodine in the Fucus gardneri, the equilibrium constant for iodine between Fucus gardneri and seawater in this study was 5800-9700 mL g-1. The equilibrium of 131I between seawater and Fucus gardneri can be established within hours and can be modelled using first order equilibrium kinetics. The average equilibrium constant, measured experimentally using first order equilibrium kinetics, for Fucus gardneri is 78 +/- 46 mL g-1 based on wet weight and 480 +/- 270 mL g-1 based on dry weight. The average rate constants kf +kb, kf and kb are 0.57 +/- 0.22 h-1, 0.55 +/- 0.21 h-1 and 0.012 +/- 0.011 h-1, respectively. It was found that seaweed samples can be stored for up to one week in temperatures ranging from --17°C to 25°C without any loss of 131I, indicating that samples may be kept for later analysis, as necessary. Fucus gardneri exposed to reactor container water from the SLOWPOKE-2 Facility absorbs the low level fission products within 4 hours. The fission products include radioisotopes of iodine, metals and noble gases. |
