Transfer of natural radionuclides from hay and silage to cow's milk in the vicinity of a former uranium mine.

After the closure of the former Žirovski Vrh uranium mine in Slovenia, mining and milling wastes were deposited on two waste piles, which are located close to the mine. These wastes contain elevated levels of natural radionuclides from the uranium decay chain. Due to different migration processes (erosion, aerial deposition, through groundwater), these radionuclides can be transported via fodder into cow's milk, which is an important foodstuff for Slovenian people. Therefore, natural radionuclides were analysed in the transfer food chain from soil to cow's fodder and cow's milk. After sampling, (238)U, (234)U, (230)Th, (226)Ra, (210)Pb and (210)Po were determined using radiochemical separation methods and alpha spectrometry or proportional counting. Hay and silage to milk concentration ratios (kg dry weight L(-1)) were calculated and were 0.260 for (238)U, 0.255 for (230)Th, 0.070 for (226)Ra, 0.021 for (210)Pb and 0.019 for (210)Po. The calculated annual ingestion dose due to milk consumption for the natural radionuclides analysed was 9 μSv/year for adults and 389 μSv/year for infants with the highest contribution of (210)Po (51% for adults and 63% for infants) and (210)Pb (36% for adults and 24% for infants). This study provides new data quantifying the transfer of natural radionuclides to milk, which is a parameter for which there have been very few previously reported values.