This study investigates the levels, sources, spatial distribution, and toxicity of polycyclic aromatic hydrocarbons (PAHs) in urban soils of Tyumen, Russia. Observations of PAHs in cities of Western Siberia accomplished by a representative set of samples are very rare, even though it is one of the most urbanized parts of Russia. Therefore, it is important to estimate the status of PAHs in soils of urban environments representing vast Siberian regions. Tyumen, as one of the most intensively developing cities of Western Siberia, is a good object for such studies. Topsoil samples (0-10 cm) were collected from 241 sampling sites on a regular grid within Tyumen city limits. It was found that total concentration of 12 priority PAHs ranged from 33.4 to 2147.9 mu g kg(-1), with a median value of 280.3 mu g kg(-1). High-molecular-weight (HMW) PAHs were dominant, accounting for the majority (62%) of the total PAHs. Among the PAHs in soils, 4-ring compounds were predominant in all studied samples, followed by 5- and 6-ring PAHs. Phenanthrene, pyrene, fluoranthene, and benzo(ghi)perylene had values of 28%, 19%, 15%, and 10% of total PAHs, respectively. Results showed that large high-contrast anomalies of HMW PAHs were related to low-residential and transport areas. The diagnostic ratios, as well as hierarchical cluster analysis (HCA) and principal component analysis (PCA), confirmed that sources associated with the transport were the most significant, while biomass combustion played an important role as a source of PAHs in agricultural, low-residential, and recreational areas. Levels of individual PAHs, as well as total PAHs in urban soils of Tyumen, were comparable with those in non-industrial cities with similar populations but were significantly lower than those in large industrial centers. Assessment of soil toxicity using toxic equivalent quantity (TEQ(BaP)) showed that the TEQ(BaP) values varied from 2.0 to 388.2 mu g kg(-1), with a mean value of 34.9 mu g kg(-1) and median of 19.8 mu g kg(-1), and were lower than those in heavy industrialized cities, but higher than those in soils of cities specializing in consumer and service industries.
