Elsevier

Journal of Hazardous Materials

Volume 364, 15 February 2019, Pages 108-116
Journal of Hazardous Materials

Improving risk management by using the spatial interaction relationship of heavy metals and PAHs in urban soil

https://doi.org/10.1016/j.jhazmat.2018.09.094Get rights and content

Highlights

  • urban soil is the pool of organic and inorganic pollution.

  • The spatial interaction of heavy metals and PAHs are complex.

  • Bivariate LISA mapping is a good tool to reveal spatial interaction of combined pollution.

  • Source-sink of pollutants were responsible for the spatial interactions pattern of combined pollution.

  • Spatial interactions as the auxiliary variable was use to decision support for urban soil risk management.

Abstract

Identifying combined pollution risk areas is difficult because of the complex pollutant sources and heterogeneous soil properties in urban systems. This study used bivariate local Moran’s I to analyze the spatial interaction between heavy metals and PAHs, revealed the causes of spatial interaction patterns through PMF, and proposed a risk zoning approach for combined pollution in urban areas. The results showed that both heavy metals and PAHs had high spatial heterogeneity in urban soil. Bivariate LISA maps revealed the spatial interactions between heavy metals and PAHs. The historical area was the hotspot of combined pollution. The overlay of pollutant sources and sinks was responsible for the spatial interaction patterns of combined organic and inorganic pollution. Coal consumption was the main emission source for heavy metal and PAHs pollution, accounting for 31% and 21%, respectively. We used bivariate LISA as the auxiliary variable to reduce the uncertainty of identification combined pollution risk zones. More than 11% of the total area clustered significantly where concentration of both heavy metals and PAHs ware in excess of the risk threshold. This study indicates that we can provide better decision-making support for soil risk management based on the knowledge derived from spatial interaction analysis.

Introduction

Urbanization is one of the important driving factors of global environmental change, especially in developing countries where there is ongoing rapid urbanization [1]. Urbanization is always accompanied by industrialization, as a result of which energy consumption and pollution emissions are highly concentrated in urban areas [2,3]. Pollutants such as heavy metals and persistent organic pollutants (POPs) accumulate continuously in urban ecosystems [[4], [5], [6]]. It is inevitable that urban areas carry more containments than other areas. Pollutants enter into the urban system, affecting the ecosystem and human health [7,8]. Therefore, the assessment of different types of pollutants in urban areas and the mitigation of their negative effects are critical issues at the cutting edge of environmental science [9,10].

Heavy metals and polycyclic aromatic hydrocarbons (PAHs) are toxic chemicals that lead to carcinogenic and chronic diseases [11]. They are the most common pollutants in urban air, soil and water. Their sources include traffic, wastes, fuel consumption, etc. [[12], [13], [14]]. Soil is an important sink of heavy metals and PAHs. The compounds are deposited from different emission sources and adhere to organic matter and minerals in the soil [15]. Such pollutants remain persistent in soil for a long time. If pollutants in urban soil exceed environmental standards, they may pose threats to the urban ecosystem and human health [[16], [17], [18]]. They will damage plant growth and lead to secondary pollution of water, as well as threatening human health by exposure to polluted soil through the pathways of dermal contact, breathing and ingestion of soil [19,20].

We analyzed more than 1700 papers focusing on heavy metals or PAHs in urban soil retrieved from the Web of Science with publication dates from 2000 to 2017 (Fig. S1). We have found that spatial distribution, source apportionment, and risk assessment are the most popular keywords in recent research [21,22]. However, there are still some shortages in urban soil pollution research. Urban soil is strongly disturbed by human activities. It is difficult to determine the exact spatial distribution of pollutants because urban soils are more heterogeneous than any other soils [[23], [24], [25]]. Kriging spatial interpolation is usually used to analyze the distribution of pollutants in urban soil. Kriging may smooth the spatial variation of pollutants. In fact, anomalous distributions are very common in urban soil. Contaminants may aggregate in certain areas due to point or line pollution because industries and population are aggregated in certain areas [26,27]. Therefore, we need to pay more attention to cluster distribution patterns in urban areas.

There are numerous studies focusing on pollution in urban soil [[28], [29], [30]]. However, most research is only focused on organic pollution or inorganic pollutants in urban areas; few studies have integrated heavy-metal and PAH pollution [31,32]. Although heavy metals and PAHs have different environmental fates and toxicities, they might come from the same source, such as traffic and fuel consumption, and have the same adsorption mechanisms to soil organic matter and clay [33,34]. These reasons would lead to synergic and antagonistic effects of PAHs and heavy metals in urban soil. Usually, the synergic effects of combined pollution overlaid on high-density-population areas result in environmental risks involving a large number of people. However, we know little about the spatial interaction of organic and inorganic pollutants in urban areas due to the complex mechanisms involved. The lack of such knowledge limits us to risk management of urban soil pollution.

The determination of the spatial interaction of combined pollution and the identification of risk areas are the foundations of soil pollution risk management. An efficient method is needed that can delineate comprehensive risk zones of combined pollution in urban areas. Therefore, we hope to use high-density soil field investigation data and spatial analysis methods to improve the risk assessment of urban soil. The objectives of this research are to (1) demonstrate the spatial distribution of heavy metals and PAHs in urban soil, (2) reveal the mechanism of spatial interaction of heavy metals and PAHs, and (3) propose an efficient risk zoning approach for combined pollutants in urban soil, to improve soil risk management.

Section snippets

Research area

Nanjing, with a population of 8 million, is one of largest cities in eastern China (shown in Fig. 1). The area is located on the edge of the north subtropic climate zone, with an average annual temperature of 15.4 °C and an annual precipitation of 1106 mm. The vegetation in the region consists of subtropical evergreen broad-leaf forest and artificial needle-leaved evergreen forest. The original soils in this area are paddy soil and Alfisols [35]. Nanjing is a city with a long history and has

Spatial distribution pattern of heavy metals and PAHs

The basic statistical characteristics of heavy metals and PAHs are shown in Table S3. The ranges of variation of heavy metals and PAHs were high in urban soil, which means that heavy metals and PAHs vary greatly among sample points [37]. We used GIS tools (ESRI, ARCGIS) and four spatial interpolate methods (Inverse Distance Weight, Local polynomial, Sample kriging and Kernel Smoothing) to reduce uncertainty in the spatial interpolation. The lowest prediction error Root-Mean-Square (RMS) of the

Discussion

The characterization of spatial complexity of hazardous materials and source apportionment in urban environments are important issues of environmental research [51]. Geostastic, based on GIS, is the main tool to analyze the spatial distribution patterns of pollutant through sampling sites to geographic surfaces [52,53]. However, it is difficult to explain the interaction of different kinds of pollutant using spatial interpolation. Moran’s I is more strictly statistical than geostastic and it

Conclusion

The interaction between inorganic and organic pollutants in urban systems is complex. It is difficult to detect the synergic and antagonistic effects of inorganic and organic pollutants. Bivariate LISA mapping is a good tool for revealing the spatial interaction of geographic phenomena. Here, we used bivariate LISA to analyze the spatial interaction between heavy metals and PAHs in urban soil. The results indicated that bivariate LISA mapping can explicitly represent the spatial complexity of

Acknowledgments

The research was supported by the National Natural Science Foundation of China (41671085), the National Key Research and Development Program of China (2017YFD0800305) and the Fundamental Research Funds for the Central Universities (020914380046).

References (59)

  • A. Cachada et al.

    Risk assessment of urban soils contamination: the particular case of polycyclic aromatic hydrocarbons

    Sci. Total Environ.

    (2016)
  • Y.G. Gu et al.

    Contamination, bioaccessibility and human health risk of heavy metals in exposed-lawn soils from 28 urban parks in southern China’s largest city, Guangzhou

    Appl. Geochem.

    (2016)
  • Z. Karim et al.

    Geochemical baseline determination and pollution assessment of heavy metals in urban soils of Karachi, Pakistan

    Ecol. Indicat.

    (2015)
  • N. Soltani et al.

    Ecological and human health hazards of heavy metals and polycyclic aromatic hydrocarbons (PAHs) in road dust of Isfahan metropolis, Iran

    Sci. Total Environ.

    (2015)
  • J.M. Stajic et al.

    Exposure of school children to polycyclic aromatic hydrocarbons, heavy metals and radionuclides in the urban soil of Kragujevac city, Central Serbia

    Chemosphere

    (2016)
  • N. Mishra et al.

    Atmospheric polycyclic aromatic hydrocarbons in the urban environment: occurrence, toxicity and source apportionment

    Environ. Pollut.

    (2016)
  • Y.B. Sun et al.

    Spatial, sources and risk assessment of heavy metal contamination of urban soils in typical regions of Shenyang, China

    J. Hazard. Mater.

    (2010)
  • A. Šorša et al.

    Geochemical mapping the urban and industrial legacy of Sisak, Croatia, using discriminant function analysis of topsoil chemical data

    J. Geochem. Explor.

    (2018)
  • R. Liu et al.

    Spatial pattern of heavy metals accumulation risk in urban soils of Beijing and its influencing factors

    Environ. Pollut.

    (2016)
  • C. Zhang et al.

    Use of local Moran’s I and GIS to identify pollution hotspots of Pb in urban soils of Galway, Ireland

    Sci. Total Environ.

    (2008)
  • S. Suman et al.

    Polycyclic aromatic hydrocarbons (PAHs) concentration levels, pattern, source identification and soil toxicity assessment in urban traffic soil of Dhanbad, India

    Sci. Total Environ.

    (2016)
  • T. Tarvainen et al.

    Urban soil geochemistry of two Nordic towns: Hämeenlinna and Karlstad

    J. Geochem. Explor.

    (2018)
  • B.G. Wei et al.

    A review of heavy metal contaminations in urban soils, urban road dusts and agricultural soils from China

    Microchem. J.

    (2010)
  • L. Gulan et al.

    Persistent organic pollutants, heavy metals and radioactivity in the urban soil of Priština City, Kosovo and Metohija

    Chemosphere

    (2017)
  • C. Peng et al.

    Assessing the combined risks of PAHs and metals in urban soils by urbanization indicators

    Environ. Pollut.

    (2013)
  • L. Tang et al.

    Contamination of polycyclic aromatic hydrocarbons (PAHs) in urban soils in Beijing, China

    Environ. Int.

    (2005)
  • E.C. Teixeira et al.

    Contribution of polycyclic aromatic hydrocarbon (PAH) sources to the urban environment: a comparison of receptor models

    Sci. Total Environ.

    (2015)
  • C. Wang et al.

    Polycyclic aromatic hydrocarbons in soils from urban to rural areas in Nanjing: concentration, source, spatial distribution, and potential human health risk

    Sci. Total Environ.

    (2015)
  • X. Hu et al.

    Bioaccessibility and health risk of arsenic, mercury and other metals in urban street dusts from a mega-city, Nanjing, China

    Environ. Pollut.

    (2011)
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