Heavy metals in urban soils with various types of land use in Beijing, China
Introduction
Urban soils have some specific characteristics such as unpredictable layering, poor structure, and high concentrations of trace elements [1], [2]. Although urban soils are not used for farming, as pollutants in urban soils can be easily transferred into humans through ingestion, inhalation, or dermal routes, etc., they will pose a health risk to urban residents. Due to the high population density and intensive anthropogenic activities, urban soils have been severely disturbed. Consequently, a great number of environmental problems have emerged, among which the heavy metal pollution remains as a major issue. The pollutants can be released in many ways such as vehicle emission, chemical industry, coal combustion, municipal solid waste, the sedimentation of dust and suspended substances in the atmosphere [3]. The concentrations of Cu, Pb and Zn in general are considered to be affected by traffic sources [4], [5], [6], and Cd might be associated with industrial activities [7]. These emissions have continuously added heavy metals to urban soils and they will remain present for many years even after the pollution sources have been removed.
The heavy metals in urban soils have a direct influence on public health [8]. Previous studies have revealed that human exposure to metals such As, Pb and Hg will lead to their accumulation in the fatty tissues and affect the central nervous system [9], [10], [11]. Furthermore, the high concentrations of heavy metals in urban soils have severely disturbed the natural geochemical cycling of the urban ecosystem [5]. Therefore, much attention has been paid to the issues relating to urban soil contamination with heavy metals during the past decades [12], [13], [14], and the researches on heavy metals in urban soils have mainly focused on the level investigation. However, the research on the heavy metal distribution in different types of land use is limited [15], [16]. As the pollutants in soils with different types of land use may exert different impact on public health [17], [18], the study on the heavy metal concentrations in different types of land use of urban soils is desired.
Beijing is the political, economic and cultural center of China, with a history of over 1000 years and the residents of more than 10 million. Several researches have investigated the heavy metal concentrations in the suburban soils [19], [20] and urban park soils [21] of Beijing. These studies showed that contamination of some heavy metals has occurred in suburban soils, and the accumulation was readily apparent in the urban park soils, especially Cu and Pb. However, the heavy metal concentrations in urban soils and those in different types of land use in Beijing remain unknown. In addition, as there is currently no soil quality criteria of heavy metal concentrations in urban soils for different types of land use in China, the investigation on heavy metals in urban soils with various types of land use in Beijing will provide scientific data and basis in this regard.
In this study, the distribution of Cd, Cr, Cu, Ni, Pb and Zn in urban soils of Beijing and the differences of their concentrations in 6 types of land use, including business area (BA), classical garden (CG), culture and education area (CEA), public green space (PGS), residential area (RA) and roadside area (RSA), were investigated. The maps of the 6 observed heavy metals were made to identify their spatial patterns in the region, and the possible sources of these heavy metals were identified through multivariate statistical analysis.
Section snippets
Study area
Beijing, the capital of China, is situated at the northern tip of the roughly triangular North China Plain, with its center located at 39.9N and 116.4E. As one of the four municipalities in China, it consists of 18 administrative districts (counties), among which 8 districts constitute the urban area. The urban area of Beijing is situated in the south-central part of the municipality and occupies an expanding part of the municipality's area. It spreads out of the concentric ring roads, of which
Heavy metal concentrations in urban soils
The descriptive statistics of heavy metal concentrations in urban soils of Beijing are summarized in Table 1. The skewness values of Cd, Cu, Pb and Zn were 2.24, 3.80, 2.39 and 2.57, respectively, revealing the strongly positively skewed distribution. After the logarithmic transformation was applied to the raw data of Cd, Cu, Pb and Zn, the skewness values reduced to 0.68, 1.49. 1.09 and 1.19, respectively. The log-transformed data of Cd, Cu, Pb and Zn passed the Kolmogorov–Smirnov test for
Conclusion
This investigation in different types of land use in Beijing revealed an obvious accumulation of Cd, Cu, Pb and Zn; their concentrations were much higher than the background values of Beijing. The concentrations of Cr and Ni in urban soils of Beijing were comparable to the background values. Pearson's correlation analysis showed that Cd, Cu, Pb and Zn concentrations were significantly positively correlated with BC at the 0.01 level.
The concentrations of Cd, Cu, Pb and Zn in CG were much higher
Acknowledgements
The study was supported by the Major State Basic Research Development Program (No. 2010CB951104) and the Scientific Research Foundation of Beijing Normal University (No. 2009SD-8).
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