127I and 129I/127I isotopic ratio in marine alga Fucus virsoides from the North Adriatic Sea

The only stable iodine isotope is 127I and the natural 129I/127I ratio in the biosphere has increased from 10−15–10−14 to 10−10–10−9, mainly due to emissions from nuclear fuel reprocessing plants. In Europe they are located at La Hague (France) and Sellafield (England), where the ratio of 129I/127I is up to 10−4. The marine environment, i.e. the oceans, is the major source of iodine with average concentrations of around 60 μg L−1 iodine in seawater. Brown algae accumulate iodine at high levels of up to 1.0% of dry weight, and therefore they are an ideal bioindicator for studying the levels of 127I and 129I in the marine environment. A radiochemical neutron activation analysis (RNAA) method, developed at our laboratory, was used for 129I determination in the brown alga Fucus virsoides (Donati) J. Agardh, and the same technique of RNAA was used for total 127I determination. The samples were collected along the coast of the Gulf of Trieste and the West coast of Istria in the North Adriatic Sea in the period from 2005 to 2006. Values of the 129I/127I ratio up to 10−9 were found, which is in agreement with the present average global distribution of 129I. The levels of stable iodine found were in the range from 235 to 506 μg g−1 and the levels of 129I from 1.7 to 7.3 × 10−3 Bq kg−1 (2.6–10.9 × 10−7 μg g−1), on a dry matter basis.