Abstract
This study investigates the distribution of 137 Cs, 90 Sr, 241 Am, and 239+240 Pu in soil micro-aggregate fractions of various sizes in a waterstream area emerging through a tunnel cavity at the Degelen site of the Semipalatinsk Test Site, where an underground nuclear test was conducted. The objective was to identify radionuclides distribution patterns in soil micro-aggregate fractions and key mechanisms of radioactive soil contamination resulting from prolonged contact with contaminated water. Results show that radionuclides distribution among soil micro-aggregate fractions is uneven and depends on fraction size and composition. Mineral components (40–1000 μm sand particles) are significantly depleted in radionuclides, while organic matter (partially decomposed plant residues, humus) demonstrates high accumulation, especially of 239+240 Pu. A general trend was observed indicating that radionuclides concentration, especially 137 Cs, increases with decreasing particle size. However, this pattern is less expressed for 90 Sr, 241 Am, and 239+240 Pu due to their significant enrichment in organic matter. Thus, sorption processes in the “soil-water” system, increasing radionuclide accumulation as particle size decreases, and the formation of organic substances with uniformly high radionuclide content, which tends to level out typical sorption trends, are identified as the main mechanisms shaping radionuclide distribution in soil micro-aggregate fractions. Additionally, the presence of highly radioactive individual particles (“hot” particles) may locally enhance enrichment of particular fractions. • Sand particles (40–100 μm) are significantly depleted in radionuclides • Organic matter (plant residues, humus) is substantially enriched with radionuclides • Radionuclide content increases with decreasing soil particle size due to sorption • Radionuclide-enriched organic matter levels out the typical sorption patterns • 137 Cs, 90 Sr and 241 Am, 239+240 Pu exhibit different spatial distribution patterns