Self-purification of loamy-sandy agrosoddy-podzolic soils polluted by sewage sludge in the eastern Moscow region

For 12 years, the contents of Zn and Cd compounds in the plow horizons of the loamy-sandy agrosoddy-podzolic soils polluted due to the application of sewage sludge decreased by 2 times; the Cu and Ni concentrations became lower by 1.5 times. The thickness of the polluted layer increased from 20 to 45 cm. The reserves of Cd, Zn, and Cu in the 0- to 50-cm-thick layer decreased, on the average, by 22, 14, and 9%, respectively. The changes in the fractional composition of the metal compounds were found. The sum of the Cu and Ni compounds increased due to the fraction of these metals bound with organic matter; for the Cd compounds, due to the weakly adsorbed fraction.