Origin, baseline contents, and vertical distribution of selected trace lithophile elements in soils from nature reserves, Russian Far East

PURPOSE: Despite extensive studies, little is known about the natural trace lithophile element contents and the relationship between contents of these elements and soil properties in the natural environment. The objectives of this study are as follows: (i) to quantify the natural baseline total trace lithophile element contents in soils, (ii) to identify the main factors controlling the vertical distribution and accumulation of elements, and (iii) to evaluate the anthropogenic influence on the soils in the territory of reserves. MATERIALS AND METHODS: In this work, we collected 42 soil samples from conditionally pollution-free Dystric Cambisols of three large natural reserves on the coast of the Russian Far East. Soil samples were analyzed for total trace lithophile elements (Ga, Rb, Sr, V, Y, and Zr), total oxides of some major elements (Si, Al, Fe, and Mn), pH(KCl), organic C, total H, and clay content. The total contents of elements were determined via energy dispersive X-ray fluorescence spectroscopy. The correlations between soil properties and contents of the trace lithophile elements were analyzed. Estimation of additional inputs of trace lithophile elements from external sources was assessed by using corrected technogenic index (Tg) of the elements. RESULTS AND DISCUSSION: Natural baseline total element contents (mg kg⁻¹) were as follows: Ga (5.77–7.27), Rb (68.72–113.55), Sr (56.14–154.70), V (106.90–168.99), Y (18.02–20.98), and Zr (189.74–249.28). Rubidium and Y in soils from all reserves include additions from external sources. These elements tended to accumulate in the upper parts of the soil profiles. Contents of Rb and Y were dependent largely on organic C content, total H content, and Mn-containing compounds of soil. In the territories with the maximum levels of Tg, we identified increased associations of total soil Ga and Sr with organic C content and Mn-Fe-containing compounds, Zr with Fe-containing compounds. Distribution and accumulation of V were mainly controlled by natural soil-forming factors and were mostly dependent on Al₂O₃ and SiO₂ contents in soils. CONCLUSIONS: The levels of trace lithophile element contents in the soils from natural reserves depend on the mixed influence of natural environmental conditions (main soil-forming factors, peculiar geographic area) and additional inputs of elements originating from atmospheric deposition of long-distance transported pollutants. Technogenic index (Tg) indicated progressive contamination of soils from all reserves by Rb and Y, and local contamination of soils by Ga, Sr, and Zr. In our study, V was an uncontaminated element.