Background Contents of Heavy Metals in Soils and Bottom Sediments in the North of Western Siberia

Resumo

Background concentrations of heavy metals (Cu, Zn, Ni, Co, Fe, Mn, Cr, Pb, Hg, Cd, Ba, Sr, and Sc) in soils and bottom sediments were determined for the background and anthropogenically disturbed (oil and gas extraction) areas in the north of Western Siberia on the basis of long-term studies (1993–2017). It was found that the soils are characterized by relatively low concentrations of heavy metals. The major factors affecting the variability of the chemical composition of the environmental components are the lithological and chemical composition of the parent materials and the zonal–azonal geochemical differentiation related to peat accumulation. The statistical analysis and the method of ranked geochemical spectra suggested that background element concentrations should be separately determined for organic soil horizons, for mineral (illuvial) horizons in coarse-textured and heavy-textured soils, and for peatlands. Minimum concentrations of most of the studied heavy metals were determined in peatlands: they were 2–8 times lower than the concentrations of these metals in the clayey and loamy illuvial horizons. Mercury and cadmium were the exceptions: their concentrations in the peatlands were 3–4 times higher than those in the illuvial mineral horizons. Background metal concentrations in bottom sediments were separately calculated for three categories: clay and peaty clay sediments, silts, and fine-grained sands. Metals concentrations in clay sediments were significantly higher than those in sandy sediments: by 11 times for Fe and Mn; by 8.5 times for Ni; by 6.5 times for Co; and by 5 times for Zn, Cu, Cr, and V. The concentrations of metals were determined by the ICP MS method. The obtained data on the background concentrations of heavy metals can be recommended for the assessment of technogenic impact on local soils and bottom sediments in the course of the environmental monitoring.