Ecological and human impact assessment in the legacy enhanced and naturally occurring radiation areas - human and ecological impact assessment in the legacy enhanced and naturally occurring radiation areas

The Fen Complex in Norway is an area well-known with its specific magmatic bedrock rich in thorium (Th), iron (Fe), niobium (Nb) and rare earth elements (REE). During several past centuries, intensive mining was conducted at sites in the area, giving rise to enhanced radioactivity levels. Previous human health studies demonstrated exposure doses among the highest in Europe. In the current work, contamination status with respect to radionuclides (232Th, uranium (238U)) and trace elements (arsenic (As), chromium (Cr) and lead (Pb)) and possible impact on humans and biota were investigated at legacy NORM and undisturbed surrounding NOR rich sites in the Fen Complex area. Significantly heterogeneous radionuclides (232Th, 238U, and daughters) distribution was found in soil at both legacy NORM and undisturbed NOR rich sites. Thorium activity concentration levels exceeded screening levels for radioactive waste material given by Norwegian Pollution Control Act. Based on sequential extraction results, mobility of 232Th and trace elements were low, although higher at legacy NORM than at undisturbed NOR rich sites. Uranium was present at considerable levels (up to 50 %) in pH and redox sensitive soil fraction, as well as bound to soil organic compounds. However, no further transport towards biggest water source Norsjoe Lake was observed, as concentration levels of all investigated elements in water samples were extremely low. Long-term surveys of outdoor terrestrial gamma dose rates, thoron (220Rn) and radon (222Rn) concentrations in the air demonstrated elevated values (up to 9.2 μGy/h, 5000 Bq/m3 and 200 Bq/m3, respectively) with significant seasonal variation. Calculated annual exposure doses to humans due to outdoor exposure could exceed 10 mSv, i.e., be higher than 1 mSv dose constraint given by ICRP. Roughly summarized with previously published data on indoor doses for Fen village population, total annual exposure dose could reach 20 mSv, what is given as limit for occupational radiation exposure (UNSCEAR, ICRP). However, existing uncertainties in dose estimation must be considered. To assess the impacts on biota, wild plant species, free-living earthworm species, wild berries and mushrooms were collected from both former mining sites (legacy NORM) and undisturbed NOR rich sites. Biota levels of radionuclides (232Th and 238U as well daughters 228Ra, 228Th, 226Ra and 210Po) were in accordance with worldwide published literature, but actual transfer was lower than expected from total soil activity concentrations. Radiation dose rates, calculated by the ERICA Tool with site-specific data, were in range 2.3 - 10.8 μGy/h, with maximal value estimated for lichen and bryophytes. Although higher than typical background dose range of terrestrial organisms 0.02 - 0.44 μG/h, biota exposure doses do not implicate any risk. The radionuclide main contributor to the dose was 228Th. Based on overall results, several 'hot spots' in the Fen Complex were identified including both legacy NORM and undisturbed NOR rich sites and consideration of intervention actions is recommended. (authors)