| Polycyclic aromatic hydrocarbons (PAils), a group of ubiquitous persistent toxic substances possessing carcinogenic, mutagenic and immunotoxic properties, have become an issue of increasing concern in recent decades. PAHs are mainly originated from incomplete combustion of fossil fuel and biomass. PAHs tend to be strongly adsorbed to soil and are difficult to dissipate owing to their high octonal-water partition coefficients. Due to its high storage capacity, soil is considered as a major environmental reservoir for PAils. Liaoning province is one of typical traditional industrial bases in China. Over the last century, increases in population and industry in the region have resulted in high consumption of fuel. In addition, biomass burning is a traditional practice for heating and cooking in rural areas. Thus, it is expected that Liaoning suffered from severe PAHs pollution. However, the studies on PAHs in this area are very limited: So the investigation on PAH levels in soils is very important to understand the spatial distribution, sources, character of composition of PAils and risks on the ecological and human health.The levels and distributions of PAHs in Dalian soils were investigated. The PAH concentrations were high and/or comparable with other regions. Soil PAH concentrations showed an urban - suburban - rural gradient, with total concentrations up to 30 times higher in the urban areas than those in the rural areas. PAHs with 4-ring were dominated in the urban soils, while 3-ring PAHs in the rural areas. The composition profiles of PAHs also displayed the urban - suburban - rural gradient owing to their different transport potential. The cross plots of selected diagnostic ratios distinguished the four sampling areas, and suggested that soil PAHs were mainly from traffic emission in the urban areas and coal/wood combustion in the suburban and rural areas. The study also highlighted that benzo(a)pyrene (BaP) was a good indicator for assessing the potential toxicity of PAHs, and presented a promising toxicity assessment method for soil PAHs.For Liaoning soils, more than 50% of the samples were moderately and/or severely polluted with PAHs, and about 40% were weakly polluted. The high proportion of phenanthrene (Phe) in soil PAHs (16.3% on average) was observed in Liaoning. The results of Pearson correlation analysis and diagnostic ratios indicated that soil PAHs in the study area were mainly from the mixture of several sources with the characters of incomplete combustion of coal and biomass.An improved method, factor analysis with nonnegative constraints (FA-NNC) was employed to determine the primary sources of soil PAHs in Dalian and Liaoning based on the measured PAH concentrations. The FA-NNC model showed traffic average and coal related residential emission were two primary sources to Dalian soils, accounting for 74% and 26% of∑PAHs, respectively. In Liaoning, four primary sources were identified: coal combustion, coke oven, biomass burning and a labeled "other" source that may be a mixture profile. The contributions of these sources were quantified as 50.5% from coal combustion, 27.0% from coke oven, 19.4% from biomass burning and 3.1% from the "other" source.The incremental lifetime cancer risk (ILCR) of soil PAHs in Dalian were estimated employing the method of probabilistic risk assessment (PRA). For dermal contact and soil ingestion, the ILCRs of 90% cumulative probability were over 10-6, which indicated the potential cancer risk, while for soil particulate inhalation, the ILCR was below 10-6, revealing the cancer risk can be neglected: Due to various body weight and habits, there were differences between the ILCRs for children, adolescents and adults. The results of sensitivity analysis indicated that the most influential parameters were the BaP-based concentrations of soil PAHs and fraction skin area exposed (FE), which suggested that, to reduce the uncertainties of risk assessment, it was necessary to reduce the uncertainties of PAH concentrations and FE.
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