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The content of mobile compounds of Zn, Pb and Cu in the hydromorphic soil samples with natural humidity from southern European Russia turned out to be much higher than in samples stored in laboratory for 1 month and, particularly, 3 years. At the same time, the extractability of heavy metals is characterized by irregular kinetics: their solubility decreases rapidly during the first month when the dry soil sample loses the initial humidity, but slowly during its further storage for 3 years. Solubility of metals in natural humid soils is highly variable. Influence of the studied reagents (CH 3 COONH 4 , EDTA and oxalate) shows the following general trend: Zn > Pb ≫ Cu. Solubility difference of metals is smoothed over in the course of soil drying. In terms of the dissolution efficiency of mobile metal compounds in the hydromorphic ferruginated soils, the extractants are arranged in the following order: oxalate > EDTA > CH 3 COONH 4. Since the oxalate actively dissolves Fe(II)-compounds in soils, the solubility of metal is governed by the its siderophility. Zn is most intensely dissolved by oxalate, while Pb and Cu in soils demonstrate organophilic properties. However, Pb can also be sorbed on iron hydroxide particles. • The mobility of Zn, Pb and Cu is much higher in hydromorphic soil with natural humidity. • Heavy metals solubility decreases rapidly in the first month as dry soil loses humidity. • The discrepancy is the most significant for the metal solubility in the wet samples. • Solubility difference of metals is smoothed over in the course of soil drying. • Siderophility is the main factor governing the mobility of heavy metals in soil. [ABSTRACT FROM AUTHOR]

The speciation of Cu, Pb, and Zn compounds in Haplic Chernozem under the anthropogenic impact of a power plant mainly operating on coal was studied. General tendencies in the distributions of Cu, Pb, and Zn among the compound forms were revealed using selective sequential extractions (Miller method modified by Berti and Jacobs (1996)), which is based on the nature of metals and the participation of soil components. In an uncontaminated soil occurring far from the emission source, 55–85% of total Cu, Zn, and Pb fractions are concentrated in the residual fraction characterizing the metal bond with silicates. In uncontaminated soils, the contents of Cu, Pb, and Zn in crystallized Fe compounds are largely higher than in its amorphous forms. Metals accumulate in the soil occurring near the power plant, which increases the total contents of Cu, Pb, and Zn in 1.3–2.5 times and their mobile (water-soluble, exchangeable, and carbonate-bound) compounds in 2–12 times. The largest contributions to the adsorption and retention of metals are made by silicates, as well as soil organic matter for Cu and Pb and nonsilicate Fe compounds for Zn. A significant increase in the exchangeable Zn fraction is observed in studied soils. The estimation of the degree of metal fixation in the soil was calculated Partition index of element, which reflects the degree of metal-soil bonding. It showed that the highest parameter value for the studied metals was found for the soils located at 15 km from the NPP, where the Index values approach 1; the lowest Index value is noted for contaminated soils nearby from the enterprise. Thus, sequential extraction is an effective tool to check the affinity of the soil components for Cu, Pb and Zn. Image 1 • The metals fractional distributions in soil under contamination was studied. • Soil organic matter for Cu and Pb is the main soil binding compound under contamination. • Zn content bound to amorphous and crystalline Fe was increased under contamination. [ABSTRACT FROM AUTHOR]