Content and mobility of copper, chrome and nickel in humus horizons of soils in the Republic of Tatarstan

A geochemical survey and contamination levels assessment of humus horizons for different land use types (natural, agricultural and urban) was carried out in the territory of the Republic of Tatarstan. The regression trees method was used to evaluate the dependencies of heavy metals content and mobility on the content of organic matter, physical clay, Fe, Mn, and soil pH. The regional background level of metals was estimated using the samples of natural zonal soils and amounted to 16.4 ± 7.8 mg/kg for Cu, 23.3 ± 12.7 mg/kg for Cr and 29.8 ± 18.8 mg/kg for Ni. The geochemical zones of elevated Ni and Cu content were observed in the eastern Zakamskaya and Bugulminskaya soil-climatic zones of the Republic of Tatarstan. Elevated Cr content was observed in the eastern part of the Fredkamskaya, north-western part of the Fredvolzhskaya and the Bugulminskaya soil-climatic zones. Cr content in agricultural soils was elevated comparing to natural soils. Significant copper pollution was observed in the soil samples collected in the cities of Kazan, Naberezhnye Chelny and Almetyevsk. Copper and nickel showed similar structures of geochemical interactions. The total content of Cu and Ni increases with increasing Mn content. The mobility of Cu and Ni in the topsoil was controlled by Fe content. The content and mobility of Cr was determined by its siderophilic properties.