Benzo[<i>a</i>]pyrene in urban environments of eastern Moscow: pollution levels and critical loads

Polycyclic aromatic hydrocarbons (PAHs), particularly benzo[<i>a</i>]pyrene (BaP), are toxic compounds emitted from various anthropogenic sources. Understanding the BaP concentrations, dynamics and decomposition in soil is required to assess the critical loads of BaP in urban environments. This study is the first attempt to evaluate all major input and output components of benzo[<i>a</i>]pyrene (BaP) balance and to calculate the permissible load on the urban environment in different land-use zones in the Eastern district of Moscow. BaP contamination of the snow cover in the Eastern district of Moscow was related to daily BaP fallout from the atmosphere. In 2010, the mean content of the pollutant in the snow dust was 1942 ng g⁻¹, whereas the average intensity of its fallout was 7.13 ng m⁻² per day. Across the territory, BaP winter fallout intensities varied from 0.3 to 1100 ng m⁻² per day. The average BaP content in the surface (0–10 cm) soil horizons was 409 ng g⁻¹, which is 83 times higher than the local background value and 20 times higher than the maximum permissible concentration (MPC) accepted in Russia. The variations in soil and snow BaP concentrations among different land-use zones were examined. A significant contribution of BaP from the atmosphere to urban soils was identified. Based on the measurements of BaP atmospheric fallout and BaP reserves in the soils, the critical loads of BaP for the land-use zones in the Eastern district were calculated for different values of degradation intensity and different exposure times. It was established that at an annual degradation intensity of 1–10 %, ecologically safe BaP levels in the soils of all land-use zones, excluding the agricultural zone, will only be reached after many decades or centuries