Impacts of urbanization and landscape patterns on the accumulation of heavy metals in soils in residential areas in Beijing

PurposeIn metropolitan cities, residential land use is most closely related to inhabitants' daily life among all land use types. The aim of this study is to determine the influence of urbanization and landscape attributes on heavy metal accumulation in urban residential areas.Materials and methodsSoil samples under different vegetative cover types were collected from 115 residential areas of Beijing. Samples were digested using a four-acid mixture (HCl, HNO3, HF, and HClO4). We analyzed contents of nine elements, including Cd, Co, Cr, Cu, Mn, Ni, Pb, V, and Zn. Meanwhile, urbanization and landscape information, including age of residential community, distance to the city center, population density, distance to the nearest building, height of the building, and green space area, were recorded at each sampling site. Statistical analytic tools and geospatial analysis techniques were employed to further examine the relationship between urbanization and landscape indicators and accumulation of heavy metals in urban residential soils.Results and discussionOur results revealed that Cu, Cd, Pb, and Zn were the most accumulated heavy metals in the study area. Their mean concentrations were 23.5, 0.139, 27.3, and 96.2mg/kg, respectively. The spatial distribution of heavy metal accumulation was also analyzed. Urbanization indicators, including age of residential community, distance to the city center, population density, and distance from sampling point to the nearest residential building, were found significantly correlated with the contents of Cu, Cd, Pb, and Zn in residential soils. However, height of the residential building and green space area had little impact on intercepting air pollutants and lowering the heavy metal concentration in residential soils. Moreover, different vegetative types were found to have significant influence on the heavy metal accumulation. Arbor was more efficient than other types in capturing atmospheric suspended particulates which contain heavy metals.ConclusionsIn this study, we identified Cu, Cd, Pb, and Zn as the most accumulated heavy metals, illustrated the spatial distribution characteristics of heavy metal accumulation, and further elaborated the influence of urbanization and landscape patterns, as well as the vegetative cover types on the heavy metal accumulation. The accumulations of Cu, Pb, and Zn in urban residential soils were probably dependent on atmospheric deposition.