Distribution and behaviour of naturally occurring radionuclides within a Scots pine forest grown on a CaF2 waste deposit related to the Belgian phosphate industry

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    The distribution and behaviour of naturally occurring radionuclides within a vegetated part of a CaF2 sludge heap from the Belgian phosphate industry was studied. A Scots pine forest plot was selected as study area. Trees were approximately 20 years old and showed a disturbed health state. Seasonal sampling campaigns of soil, roots, wood, inner and outer bark, needles and twigs gave insight on 238U, 226Ra, 210Pb and 210Po transfer and distribution between pine tree compartments. Soil samples were analysed for their texture, total organic and inorganic carbon, field capacity, pH and radionuclide content. Solid-liquid distribution coefficients (Kd) were experimentally determined for 238U, 226Ra (using Ba as analogue) and 210Pb based on adsorption-desorption batch tests.
    Results indicated higher 238U, 232Th, 226Ra, 210Pb and 210Po activity concentrations in the deeper soil layers while the first 20 cm contained less radionuclides but had a higher level of organic carbon. Additionally, results indicated no seasonal changes in the 238U:226Ra ratio in the soil while the 226Ra:210Pb ratio was significantly higher in spring compared to winter in the 20–60 cm soil layer. Pine tree roots served as natural translocation barrier for all radionuclides with high retention in the roots and low translocation to the above ground tree compartments. When considering the above ground compartments, 210Pb and 210Po were mostly present in the bark, needles and twigs. Furthermore, 238U and its progeny were highly accumulated in mosses. These results allowed us to establish more realistic soil-to-plant transfer factors. In addition, experimentally mimicking pore water acidification in the root zone resulted in lower 238U and 210Pb Kd values compared to using a standard CaCl2 solution.
    This study provides an integrated radioecological picture of knowledge and site specific data needed to study the long-term influence of vegetation on radionuclide dispersion in forest ecosystems.
    Original languageEnglish
    Article number106591
    Pages (from-to)1-11
    Number of pages11
    JournalJournal of environmental radioactivity
    StatePublished - Jul 2021

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