Lanthanides and Actinides in Humic Acids of Soils and Paleosols of Forest-Steppe Conditions in the Southern Urals

Abstract

This article analyzes the lanthanum, cerium, samarium, europium, terbium, ytterbium, lutetium, uranium, and thorium content in humic acids within soil and paleosol surface horizons from the southern steppe in the Southern Urals. Research demonstrates similar accumulation levels of these elements in paleosols isolated from both the active medium between 3.6 and 3.3 thousand years ago and in recent background soils. Despite the lack of significant differences, research has shown a growing content among the rarest metals in the series “the buried paleosols–man-modified paleosols of settlement–recent background soils”. Research has detected the lowest content of La, Ce, Sm, Eu, Yb, Lu, and Th in preparations of humic acids of recent background soils. This reveals a close content to most elements in humic acids of paleosols buried under barrows and ancient settlement paleosols. Additionally, it indicates the virtual absence of anthropogenic impact on binding lanthanides and actinides by humic acids in ancient times. The contribution of humic acids into the common pool for each element was evaluated using a special approach. Research showed that there was less than half the share of elements associated by humic acids of paleosols than in the recent background chernozems in the total pool of lanthanides and actinides. This article considers the prospects of using humic acids of recent and ancient soils in identifying behavioral patterns of metal complexes through time.