Distribution and behaviour of naturally occurring radionuclides within a Scots pine forest grown on a CaF2 waste deposit related to the Belgian phosphate industry. (July 2021)

• Record Type: Journal Article
• Authors: Vanhoudt, Nathalie; Van Gompel, Axel; Vives i Batlle, Jordi
• Is Part Of: Journal of environmental radioactivity. Volume 233(2021)
• Publication Date: 2021-07
• Subjects: Isotopic ratio -- Radionuclide cycling -- Seasonal variation -- Solid-liquid distribution coefficient -- Terrestrial ecosystem -- Transfer factor; Radioactivity -- Periodicals; Radiation, Background -- Periodicals; Radioecology -- Periodicals; Radioactive pollution -- Periodicals; Environmental Pollutants -- Periodicals; Radioactive Pollutants -- Periodicals; Radioactivity -- Periodicals; Radioécologie -- Périodiques; Pollution radioactive -- Périodiques; Fond de rayonnement -- Périodiques; 539.752
• DOI: 10.1016/j.jenvrad.2021.106591
• Languages: English
• ISSNs: 0265-931X

Abstract

Abstract: 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 238 U, 226 Ra, 210 Pb and 210 Po 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 238 U, 226 Ra (using Ba as analogue) and 210 Pb based on adsorption-desorption batch tests. Results indicated higher 238 U, 232 Th, 226 Ra, 210 Pb and 210 Po 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 238 U: 226 Ra ratio in the soil while the 226 Ra: 210 Pb 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, 210 Pb and 210 Po were mostly present in the bark, needles and twigs. Furthermore, 238 U 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 238 U and 210 Pb 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. Graphical abstract: Image 1 Highlights: Increased U and Pb solid-liquid distribution through acidification of soil. Seasonal variability 226 Ra: 210 Pb ratio in soil, possible link with radon exhalation. Tree roots serve as translocation barrier. 210 Pb and 210 Po present in bark, needles and twigs. Role for mosses as indicators for long-term exposure to 238 U and its progeny.