Soil Polycyclic Aromatic Hydrocarbons Across Urban Density Zones in Shenzhen, China: Occurrences, Source Apportionments,and Spatial Risk Assessment

Urbanization may cause increased exposure levels to polycyclic aromatic hydrocarbons （PAHs） and associated health risks for over half of the world＇s population living in cities, but little evidence has shown a direct spatial relationship between urbanization and soil PAH pollution. Based on the monitored PAH concentrations in 188 topsoil （0-5 cm） samples in Shenzhen, the most rapidly developing city in China, in recent decades, we applied geographical demarcation to determine the occurrences, source apportionments, and spatial ecological risks of soil PAHs across five zones of varying urban densities. Mean concentrations of the 16 US Environmental Protection Agency （EPA） priority PAHs （∑16PAHs） and the 7 carcinogenic PAHs （2E7CarPAHs） both followed the order： Zone D （60%-80% constructive land density （CLD）） 〉 Zone E （80%-100% CLD） 〉 Zone C （40%-60% CLD） 〉 Zone B （20%-40% CLD） 〉 Zone A （0%-20% CLD）, suggesting that the highest PAH levels occurred in the suburban-urban center transitional zone （Zone D） rather than the urban center zone （Zone E） in Shenzhen. There were significant correlations of ∑16PAHs to TOC and sampling altitude across all samples but not within highly-urbanized regions （Zones D and E）, implying a considerable disturbance of urbanization to the soil PAH pool. Source apportionments suggested that soil PAHs of all zones were mainly derived from fossil fuel combustion, with Zone E showing the highest contribution from oil sources among different zones. Spatial ecological risk analysis showed that the contaminated area （467 km2; 23.9% of total area; toxic equivalency quotients 〉 33 ng g^-1） had a higher contribution from the highly-urbanized regions （Zones D and E） than the uncontaminated area （42.3% vs. 18.1%）. Overall, our study highlighted a strong spatial relationship between urbanization and soil PAH pollution.

Level of polycyclic aromatic hydrocarbon emission in the ambient air and residual ash from a typical municipal solid waste open burning site in Nigeria

Open burning of municipal solid waste(MSW)is a common practice in Nigeria.Emission of compounds of polycyclic aromatic hydrocarbon(PAHs)in ambient air and ash residues from burning of these wastes pose a great danger to the environment.This study investigated the contribution of open burning of MSW to the levels of PAHs in ambient air and ash residues from the burning site.Ash samples were obtained from six sampling locations at a MSW burning site.Polyurethane foam passive samplers were used in collecting ambient air samples.Quantification of PAHs was carried out using GC-MS operated in selected ion monitoring mode.The trend of ambient concentration of PAHs was;ΣPAHs AS-A(4.023)>AS-B(3.798)>AS-D(3.468)>AS-C(3.288),while average concentration of PAHs in the ash was 6.12 mg/kg.Concentrations of PAHs in ash samples ranged from 5.69-6.34 mg/kg.Principal component analysis(PCA)showed that most of the PAHs in the ambient were from MSW combustion.The results obtained suggest that concerted effort of the government and the relevant stakeholders is required to safeguard the environment and humans from PAH pollution from open burning of MSW.