Effect of Soil Buffer Capacity on the Transformation of Lead and Cadmium Compounds

Abstract—

The aim of this work is to study the transformation of priority pollutants compounds, i.e., of Pb and Cd in soils with different buffer capacity and pollution level. The object of study is southern chernozem (Haplic Chernozem), calcareous, heavy loamy, collected in a virgin site in the Rostov-on-Don region, the layer 0–20 cm. Lead and Cd nitrates were added separately in doses of 2, 5, 10 approximately permissible concentration (APC) of metal (130 mg/kg for Pb and 2 mg/kg for Cd) into soil samples of the model experiment containing quartz sand in the ratios 1 : 0.25, 1 : 0.5, 1 : 0.75 of the soil mass. The buffer capacity of soils in relation to Pb and Cd was assessed according to the method of V.B. Il’in (1995), based on the content of physical clay, organic matter, carbonates, R₂O₃, and pH. The ability of soils to firmly bind Pb and Cd was studied proceeding from the results of fractional group composition of metals using a combined fractionation scheme. In unpolluted heavy loamy Haplic Chernozem, the buffer capacity of soils in relation to Pb and Cd is high and is ensured by strong retention of metals by silicates and clay minerals (50–64% of the total fractions). Dilution of the initial soil with quartz sand reduces its buffer capacity from high to medium and low. When soil is contaminated, organic matter plays the most active role in the interaction with Pb; and Fe–Mn oxides are most important in the case of Cd. With a decrease in soil buffer capacity and growing pollution, the group of loosely bound compounds increases by 6–54%, mainly due to complex compounds in the case of Pb, and due to exchangeable and specifically sorbed by Fe–Mn oxides in the case of Cd. At the application dose of 10 APC Pb, the soil buffer capacity changes from low to very low. The data obtained are important for predicting and normalizing pollution of soils with different physicochemical properties.