Abstract
Surface soil samples from 467 sample sites were collected in urban area of Wuhan City in 2013, and total concentrations of five trace metals (Pb, Zn, Cu, Cr, and Cd) were measured. Multivariate and geostatistical analyses showed that concentrations of Pb, Zn, and Cu are higher along Yangtze River in the northern area of Wuhan, gradually decrease from city center to suburbs, and are mainly controlled by anthropogenic activities, while those of Cr and Cd are relatively spatially homogenous and mainly controlled by soil parent materials. Pb, Zn, Cu, and Cd have generally higher concentrations in roadsides, industrial areas, and residential areas than in school areas, greenbelts, and agricultural areas. Areas with higher road and population densities and longer urban construction history usually have higher trace metal concentrations. According to estimated results of the potential ecological risk index and Nemero synthesis pollution index, almost the whole urban area of Wuhan is facing considerable potential ecological risk caused by soil trace metals. These results reveal obvious trends of trace metal pollution, and an important impact of anthropogenic activities on the accumulation of trace metals in soil in Wuhan. Vehicular emission, industrial activities, and household wastes may be the three main sources for trace metal accumulation. Increasing vegetation cover may reduce this threat. It should be pointed out that Cd, which is strongly accumulated in soil, could be the largest soil pollution factor in Wuhan. Effective measures should be taken as soon as possible to deal with Cd enrichment, and other trace metals in soil should also be reduced, so as to protect human health in this important large city.
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Acknowledgments
The research was supported by National Natural Science Foundation of China (Grant No. 41101193), and the Fundamental Research Funds for National Universities (Grant No. 2662014PY062). Opinions in the paper do not constitute an endorsement or approval by the funding agencies and only reflect the personal views of the authors.
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Appendices
Appendix 1:Data quality verification
A dataset of a previous study (Qu et al. 2014), kindly provided by Qu et al., was used for data quality verification of ICP-AES and XRF measurements in this paper. Considering the high spatial variability of trace metals, data points located within the Wuhan Donghu High-tech Development Park, which was the region of the previous study, were extracted. Concentrations of Pb, Zn, Cu, Cr, and Cd by ICP-AES and XRF in this paper were compared to the previous study based on the independent sample t test method. Results listed in Table 5 show that concentrations of Pb, Zn, and Cr by ICP-AES and Pb and Zn by XRF in this study well match those in the previous study (p > 0.05), while concentrations of Cu and Cd by ICP-AES and Cr by XRF are significantly different from those in the previous study (p < 0.05). But, the range of Cd contents is comparable with results by Qu et al. (2013) and Yang et al. (2009). The above results indicate that concentrations of Pb, Zn, Cr, and Cd in this study could be trusted, while the significant difference between Cu contents in this study and the previous study may be caused by the high coefficient of variation of Cu (see the “Trace metal concentrations in urban soils” section).
Appendix 2: XRF data transformation
To integrate trace metal data obtained by ICP-AES and XRF, regression models were established based on the pairwise concentrations of Pb, Zn, Cu, and Cr in the training samples (no Cd data by XRF).
Shown as Fig. 8, concentrations of Pb, Zn, and Cu obtained by XRF had significantly positive relationship with the corresponding ICP-AES measurements; the coefficient of correlation were 0.915, 0.946, and 0.808 for Pb, Zn, and Cu, respectively. XRF measurements fitted fairly well with the ICP-AES measurements for Pb, Zn, and Cu, and the R 2 values were 0.842, 0.895, and 0.675, respectively. On the contrary, Cr by XRF showed no significant relationship with that by ICP-AES, with a quite low R 2 value of 0.027. Wu et al. (2012) also found that XRF measurements of Pb, Zn, Ni, and Cu are highly reliable and agrees well with the ICP-AES experiments, while Cr and Cd by XRF show poor accuracy. Before transformation, BDLs of XRF were examined. A total of 107 BDLs for Pb, 2 BDLs for Zn, and 151 BDLs for Cu were excluded from the dataset. Since XRF-measured Cr was not accurate and no XRF measurement of Cd was higher than the detection limit, XRF measurements of Cr and Cd were abandoned and only ICP measurements of these two elements were used in further analysis. Although 50 % of the detection limit may be used as the substitution in cases where concentrations were BDLs (Zibret 2012), taking this substitution into account would bring about big errors when establishing regression models and performing the transformations. Therefore, in the data transformation stage, ICP measurements of Pb, Zn, Cu, Cr, and Cd were reserved at the training sample points, and XRF measurements of Pb, Zn, and Cu that were higher than detection limit were transformed using the regression models at other data points. The distributions of available data points for Pb, Zn, Cu, Cr, and Cd can be found in Fig. 9.
Quantitative relationships between concentrations of Pb, Zn, Cu, and Cr (mg/kg) obtained by ICP-AES and XRF. Dash lines represent the 1:1 line and the solid lines represent the regression lines. Regression models, corresponding R 2 values, and coefficient of correlation are also presented in this figure
Sampling sites used for analysis of Pb, Zn, Cu, Cr, and Cd. IZ, RS, RA, SA, AA, and GB refer to industrial zone, roadside, residential area, school area, agricultural area, and greenbelt, respectively. The two black ring lines represent the 1st Ring Road and the 3rd Ring Road of Wuhan City, respectively
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Zhang, C., Yang, Y., Li, W. et al. Spatial distribution and ecological risk assessment of trace metals in urban soils in Wuhan, central China. Environ Monit Assess 187, 556 (2015). https://doi.org/10.1007/s10661-015-4762-5
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DOI: https://doi.org/10.1007/s10661-015-4762-5