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Due to the rapid expansion of cities, the impermeable area has increased. This exacerbated the accumulation of pollutants in road particles and made the road sediment one of the most widely distributed pollution carriers in the urban area. Urban-rural fringe is the frontier of urban expansion and the most dynamic area in the urban region, but less knowledge was available on the pollution status of the region. In this study, the occurrence, release behavior, and environmental risk of polycyclic aromatic hydrocarbons (PAHs) accumulated in road sediment in urban-rural fringe were systematically studied and compared with five other urban functional areas (i.e., commercial area, industrial park, residential area, traffic area, and leisure area) in Beijing, china. The concentration of ∑16PAHs in the road sediment followed in the order of petrol station (2.223 mg/kg)>crossroad (1.506 mg/kg)>main road (0.949 mg/kg)>university gate (0.841 mg/kg)>bus station (0.839 mg/kg). The PAHs concentration in the road sediment with different land use followed in the order of traffic area (3.030 mg/kg)>urban-rural fringe (1.338 mg/kg)>commercial area (0.946 mg/kg)>residential area (0.866 mg/kg)>industrial park (0.673 mg/kg)>leisure area (0.316 mg/kg). The cancer risk in the urban-rural fringe was second only to the traffic area. PAHs with low ring numbers were easier to release into the water, as indicated by that 20–95% nap could be released from the road sediment to runoff. In contrast, high-ring PAHs were more likely to accumulate in the particulate matter as <18.3% of PHE, FLA, and PYR (corresponding to 0.002–0.010 mg/kg) could be released into the water phase, which means that the removal of road sediment plays an important role in reducing pollution. Overall, this study reveals that pollution in the urban-rural fringe cannot be ignored and provides scientific data to support pollution control and risk assessment, especially for urban-rural areas. [ABSTRACT FROM AUTHOR]

To identify the distribution of heavy metals in sewer sediments and assess their potential harmfulness to the environment and human health, the occurrence of Pb, Zn, Cu, and Cd in the sewer sediment of six functional areas and two streets in an inner-city suburb of Beijing, China, was investigated by using a sequential extraction procedure. Results show that the concentrations of Cu, Zn, Cd, and Pb vary between 50 and 175, between 80 and 180, between 0.75 and 2.5, and between 20 and 110 mg/kg, respectively, and Fe-Mn oxide fraction is significant for all metals in sampling areas. Pollution assessment shows that 1–2% of Cu at Chegongzhuang Street and 1–3% of Zn at Fuwai Street in the exchangeable fractions are of low risk. 10–25% of Cd at six functional areas indicates medium risk. 40–60% of Pb at Fuwai Street existing in the exchangeable fractions is of high to very high risk. The sum of these metals associated with exchangeable, carbonate bound, and Fe-Mn oxide fractions is quite high; however, these three fractions represent the proportion of heavy metals that can be remobilized by changes in environmental conditions. [ABSTRACT FROM AUTHOR]