Despite extensive characterisation of 137Cs in Lithuanian soils and vegetation, key uncertainties persist regarding radionuclide compartmentalisation and post-depositional dynamics in forest ecosystems, particularly in the context of the recently commissioned Belarusian Nuclear Power Plant (BelNPP). Integrated assessments combining legacy 137Cs, background 210Pbex, and short-lived 7Be tracers within a single moss–soil system remain scarce, limiting discrimination between historical contamination, contemporary atmospheric inputs, and secondary remobilisation. This study quantified atmospheric deposition, moss interception, and soil profile distribution of 137Cs, 7Be, and 210Pbex in eastern Lithuanian pine forests during 2019–2023, and evaluated current 137Cs levels against pre-operational baselines. Atmospheric flux measurements established the reference ratios for subsequent interpretation: the mean annual 210Pbex flux (92 Bq·m−2 year−1) was consistent with regional values, while contemporary 137Cs deposition (1.22 Bq·m−2 year−1) yielded a 137Cs/210Pbex atmospheric input ratio of 0.013 - the critical baseline for interpreting moss and soil inventories. Mean moss inventories were 130 Bq·m−2 (210Pbex), 236 Bq·m−2 (7Be), and 8 Bq·m−2 (137Cs); 7Be capture efficiency ranged from 0.56 to 1.00 with a surface equilibrium inventory of 356 ± 6 Bq·m−2. Ratio analysis spanning 7Be, 137Cs, and 210Pbex cross-referenced against 40 K identified an active exchange interface between the atmosphere, moss, and the uppermost soil horizon (< 5 cm). Within this interface, 7Be/210Pbex ratios decreased systematically from deposition through moss to surface soil, reflecting differential retention driven by 7Be’s shorter half-life and higher mobility. The 137Cs/210Pbex ratio in moss (0.06) exceeded the atmospheric input ratio by a factor of 4.6, demonstrating that moss 137Cs inventories are sustained primarily by legacy fallout recycled from surface soil rather than by current atmospheric deposition. No 137Cs signal attributable to BelNPP operations was detected, providing a quantified post-commissioning baseline against which future possible operational releases can be assessed.

A study of atmospheric deposition of fallout radionuclides, their interception by moss, and distribution in soil profiles in a forest environment of eastern Lithuania

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2026年7月23日

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Vitaliy Romanenko,
Žana Skuratovič,
Olga Jusis Jusis Jefanova,
Ieva Baužienė,
Rimantas Petrošius,
Jonas Mažeika

摘要

Despite extensive characterisation of ¹³⁷Cs in Lithuanian soils and vegetation, key uncertainties persist regarding radionuclide compartmentalisation and post-depositional dynamics in forest ecosystems, particularly in the context of the recently commissioned Belarusian Nuclear Power Plant (BelNPP). Integrated assessments combining legacy ¹³⁷Cs, background ²¹⁰Pb_ex, and short-lived ⁷Be tracers within a single moss–soil system remain scarce, limiting discrimination between historical contamination, contemporary atmospheric inputs, and secondary remobilisation. This study quantified atmospheric deposition, moss interception, and soil profile distribution of ¹³⁷Cs, ⁷Be, and ²¹⁰Pb_ex in eastern Lithuanian pine forests during 2019–2023, and evaluated current ¹³⁷Cs levels against pre-operational baselines. Atmospheric flux measurements established the reference ratios for subsequent interpretation: the mean annual ²¹⁰Pb_ex flux (92 Bq·m⁻² year⁻¹) was consistent with regional values, while contemporary ¹³⁷Cs deposition (1.22 Bq·m⁻² year⁻¹) yielded a ¹³⁷Cs/²¹⁰Pb_ex atmospheric input ratio of 0.013 - the critical baseline for interpreting moss and soil inventories. Mean moss inventories were 130 Bq·m⁻² (²¹⁰Pb_ex), 236 Bq·m⁻² (⁷Be), and 8 Bq·m⁻² (¹³⁷Cs); ⁷Be capture efficiency ranged from 0.56 to 1.00 with a surface equilibrium inventory of 356 ± 6 Bq·m⁻². Ratio analysis spanning ⁷Be, ¹³⁷Cs, and ²¹⁰Pb_ex cross-referenced against ⁴⁰ K identified an active exchange interface between the atmosphere, moss, and the uppermost soil horizon (< 5 cm). Within this interface, ⁷Be/²¹⁰Pb_ex ratios decreased systematically from deposition through moss to surface soil, reflecting differential retention driven by ⁷Be’s shorter half-life and higher mobility. The ¹³⁷Cs/²¹⁰Pb_ex ratio in moss (0.06) exceeded the atmospheric input ratio by a factor of 4.6, demonstrating that moss ¹³⁷Cs inventories are sustained primarily by legacy fallout recycled from surface soil rather than by current atmospheric deposition. No ¹³⁷Cs signal attributable to BelNPP operations was detected, providing a quantified post-commissioning baseline against which future possible operational releases can be assessed.