ENVIRONMENTAL RADIOLOGICAL STUDIES OF KVARNTORPSHÖGEN Dose and Radiological Risk Assessments for Humans and Biota

Abstract

Background: The pile Kvarntorpshögen and the lakes Surpölen and Norrtorpssjön are the remains of an industry which mined and processed oil shales to extract oil during World War II. The pile mainly consists of shale ash, a waste from the production, while the lakes are nowadays water-filled mining pits. Both are by-products of an industry with “Naturally Occurring Radioactive Material” (NORM), making them “Technologically Enhanced NORM” (TENORM). The Kvarntorp area thus has somewhat increased concentrations of radionuclides, and the radiation exposure that may arise to humans and biota have to be assessed, to protect against radiation risks, both now and in the future. Aim: The aim of this project was to carry out a radiological characterisation on and around Kvarntorpshögen by measurements of 238U, 235U, 234U and 210Po in soil, water and plants in the area, and calculating the transfer of 210Po and U-isotopes in the soil-root-plant system. A second aim was to perform a radiological risk analysis for humans and biota by estimating effective doses and absorbed doses, respectively. Method: During the summer of 2020, samples of water, shale ash, soil and plants were collected on and around Kvarntorpshögen. The U-isotopes and 210Po were analysed by their alpha emission and the samples were prepared through radiochemistry, to be measured by alpha spectrometry. Transfer factors were calculated by ratios of activity concentrations in root and soil, plant and soil, and plant and root. The radiological risk analysis for humans was performed by conservatively estimating effective dose rates through ambient dose equivalent rates and comparing to average yearly effective doses. The radiological risk analysis for biota was performed by estimating absorbed dose rates with the ERICA Tool (Environmental Risk from Ionising Contaminants: Assessment Tool) Tier 1 and Tier 2. Results and Conclusions: External dose rates in the Kvarntorp area are highest by exposed alum shale walls at the pit lakes and by shale ash at Kvarntorpshögen. The activity concentrations of 238U, 235U, 234U and 210Po was seen to decrease in the soil-root-plant system at the pile. 238U, 235U, 234U and 210Po are in equilibrium in soil and roots, but not in plants, probably due to atmospheric deposition of 210Po. The activity concentration of 238U, 235U, 234U and 210Po in plants at the Serpentine ponds are in equilibrium, and are slightly lower than in plants at Kvarntorpshögen. For water in the Kvarntorp area, the highest activity concentrations were found mainly in Surpölen because of its acidity, second highest in Norrtorpssjön and lowest in the Serpentine ponds. In the water, 210Po was not in equilibrium with the U-isotopes due to differences in solubility. In the Serpentine ponds a decrease of activity concentration was seen the further away the ponds extend from the pile, showing that the treatment dams are working to reduce the concentration of radionuclides in the water.3 The radiological risk to biota at Kvarntorpshögen, the Serpentine ponds, Surpölen and Norrtorpssjön cannot be concluded as being of negligible concern. Further assessments are necessary to establish the risk. However, the radiological risk to humans at any site in the Kvarntorp area is of limited concern compared to average yearly effective doses.