Descriptive statistics of particle-size classes G1 - G6 (%), pH, TOC (%), ChE total concentrations and mobile fractions (mg/kg), and mobility of ChEs (%) in Chernozems and Planosols
Soil samples from the pits studiedwere analysed at the MSU (Lomonosov Moscow State University) Faculty of Geography by standard techniques. The analyses included total organic carbon (TOC), рН and the particle-size distribution. The Russian system of particle-size classes was used, i.e., G1 – clay (particles <1 µm), G2 – fine silt (1 – 5 µm), G3 – medium silt (5 – 10 µm), G4 – coarse silt (10 – 50 µm), G5 – fine sand (50 – 250 µm) and G6 – medium and coarse sand (250 – 1000 µm). Total content of 24 ChEs was determined at the IGEM RAS (Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry of the Russian Academy of Sciences) using an Axios X-Ray fluorescence spectrometer (made by PANalytical, Netherlands) and Russian Soil Standard samples (SSs of ‘Chernozem’ and ‘Albeluvisol’),. The analysed fractions of the ChEs were defined as follows: • F1 – weakly bound acid-soluble (exchangeable ions readily available to plants), • F2 – complexed (fulvate and humate substances potentially available to plants), • F3 – bound with Fe and Mn hydroxides (unavailable to plants) and • F4 – residual fraction. Mobile fractions F1, F2 and F3 were obtained according to the extraction procedure by (Solov’ev, 1989) with the use of the following reagents: (1) F1 – with NH4Ac (ammonium acetate buffer) and the soil:solution ratio of 1:5, (2) F2 – with 1% EDTA (ethylenediaminetetraacetic acid) and the soil:solution ratio of 1:5 and (3) F1 and F3 – with 1M HNO3 (nitric acid) and the soil:solution ratio of 1:10. Soil suspensions (50 ml) were prepared from soil subsamples (5-10 g) by incubation for 18 hours. Concentrations of the extracted ChEs (Al, As, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, Pb, Se, Si, Sr and Zn) in the filtrates were determined using an Elan-6100 ICP-MS System (Inductively Coupled Plasma Mass Spectrometer by PerkinElmer Inc., USA) and an Optima-4300 DV ICP-AES System (Inductively Coupled Plasma Atomic Emission Spectrometer by PerkinElmer Inc., USA) at the VIMS (N. M. Fedorovskii All-Russia Institute of Mineral Raw Materials). The procedure (Solov’ev, 1989) is regularly used in Russian soil quality assessments for analysing mobile fractions of ChEs from polluted and background soils (Minkina et al., 2018; Siromlya, 2009). Another normality of NH4Ac, EDTA and HNO3 extracts is used all over the world (e.g., Anderson, 1976; Bakircioglu et al., 2011; Dudas and Pawluk, 1977; Kelepertzis et al., 2018; McBratney et al., 1982; Takeda et al., 2004; Torri and Lavado, 2009a, 2009b). The ChE mobility is defined as a ratio of the element’s mobile fractions (F1+F2+F3) to its total content, multiplied by 100%.