Critical loads of benzo(a)pyrene on urban soils

The resistance of urban soils to organic contaminants and their capability for self-purification from benzo(a)pyrene were evaluated with the use of the concept of critical loads on urban landscapes. It is based on the balance equation between the input of benzo(a)pyrene with technogenic fallout and its decomposition in soil. The last component of the balance is described by the first-order kinetics model. The benzo(a)pyrene reserves in soils and precipitation from the atmosphere were determined and then used for calculation of its critical loads on soils in various land-use zones of the Eastern okrug of Moscow with respect to the degradation rate and the exposure period. It was revealed that when the degradation intensity is 1–10% per year, it will take many tens and hundreds of years to achieve a decrease in the benzo(a)pyrene content to an ecologically safe level in all the land-use zones except for the postagrogenic one.