Accumulation of ⁹⁰Sr by Pinus sylvestris and Betula pendula in the zone of radioactive contamination (East Ural Radioactive Trace, Russia)

Introduction. The studies were carried out in 2010–2020 on the territory of the East Ural radioactive trace (EURT), formed in 1957 as a result of an accident at the "Mayak Production Association". Currently ⁹⁰Sr is main pollutant. Forest ecosystems are mainly represented by secondary birch and mixed forests. Purpose of the study: to study the patterns of ⁹⁰Sr accumulation by woody plants (Pinus sylvestris and Betula pendula), which have been growing in the gradient of radioactive contamination for more than 60 years. Materials and methods. We have selected test sites in automorphic territories located at a distance of 5–30 km from the epicenter of the accident. The soil contamination density decreased with distance from 70 to 0.4 MBq/m². Control plots (0.002 MBq/m²) were selected outside the EURT area. Few Scots pine stands were found in the head part of the EURT only in areas where the soil contamination density does not exceed 10 MBq/m². We took samples of soils and aboveground organs of trees: leaves (needles), small branches 1–5 years old, large branches 5+ years old, trunk (wood, bark). The ⁹⁰Sr content in soil and plant samples was determined by the radiochemical method. The beta activity of the preparations was measured on a UMF-2000 radiometer (Russia) with a lower detection limit of 0.2 Bq. Results. Concentration of ⁹⁰Sr in air-dry matter and plant ash increased with increasing soil contamination density in accordance with the power function. Evaluation of ⁹⁰Sr accumulation in various organs of pine and birch growing on the territory of EURT showed that the radionuclide concentrations decrease in the following order: bark> needles (leaves)> small branches> large branches> wood. With an increase in the soil contamination density by ⁹⁰Sr (from background values to 70 MBq/m²), the aggregated transfer factors for aboveground organs of P. sylvestris decreased from 1⸳10^-2 to 1⸳10^-4, and for B. pendula, from 5⸳10^-2 to 5⸳10^-5. Similar results were obtained by us earlier for herbaceous plants, mosses and lichens. Conclusion. White birch accumulates ⁹⁰Sr in larger quantities than Scots pine. The concentrations of ⁹⁰Sr in air-dry matter and plant ash were increased with increasing soil contamination density in accordance with the exponential dependence. (author)