Iodine 129 measurements by gamma spectrometry in biological samples. Results in seaweeds (Fucus serratus et laminaria digitata)

A iodine selective radiochemistry method was developed to measure 129I(period 1,57 x 10 107 years) by gamma spectrometry in biological samples. This method avoids using neutron activation analysis or accelerator mass spectrometry. The method is based on iodine extraction from samples in order to obtain an aqueous matrix with no attenuation agent except 127I(stable isotope). The parallel determination of 127I allows to correct 129I measurements for self attenuation and also monitor seasonal changes in iodine metabolism in biological species. Measurements were performed in two seaweed species (Fucus serratus and Laminaria digitata) samples in the area of La Hague reprocessing plant discharge between January and February 1997). Samples from stations close to the point of release (Goury and Herquemoulin), showed 129I activities around 60 Bq kg-1 dry weight in Fucus serratus and around 300 Bq kg-1 dry weight in Laminaria digitata. 300 km away from the realize point, 129I activities were 10 Bq kg-1 dry weight in Fucus serratus and 171 Bq kg-1 dry weight in Laminaria digitata. 127I concentrations were between 547 and 1,232 mg kg-1 dry weight in Fucus serratus and between 6,624 and 14,296 mg kg-1 dry weight in Laminaria digitata. (authors)