Heavy metal(loid)s and organic contaminants in groundwater in the Pearl River Delta that has undergone three decades of urbanization and industrialization: Distributions, sources, and driving forces
Graphical abstract
Introduction
The wholesale transformation of agricultural and natural ecosystems to more intensive uses of urbanization and industrialization is among the biggest anthropogenic impacts on earth (Vitousek et al., 1997). In the past few decades, urbanization and industrialization are two of the most widespread environmental changes in China. For instance, the Pearl River Delta (PRD) in the Guangdong Province is one of the fastest developing regions in China. It has undergone a rapid urbanization and industrialization since the late 1970s. Most of the land-use change in the PRD is converted from agricultural land to urban areas, and large-scale investments in industrial development play the major role in urban land conversion (Seto et al., 2002). In addition, the deterioration of surface water quality in this area occurred in the past three decades due to urbanization and industrialization (Cheung et al., 2003; Huang et al., 2013; Ouyang et al., 2006). As a result, groundwater becomes an alternative water resource for drinking, irrigation, and industrial purposes in the PRD. However, the contamination of heavy metal(loid)s and organic chemicals in groundwater often occurs in a rapidly urbanized and industrialized area (Huang et al., 2012; Huang et al., 2013; Leung and Jiao, 2006). Moreover, groundwater with high concentrations of heavy metal(loid)s and/or organic chemicals is harmful to human health and crop growth when it is used for drinking and irrigation (Agency for Toxic Substances and Disease Registry (ATSDR), 2015). Therefore, to improve the groundwater resource management in this area, a comprehensive understanding of the distributions and sources of heavy metal(loid)s and organic chemicals in groundwater in the PRD is necessary.
To date, a couple of studies have already confirmed that heavy metal(loid)s contamination occurred not only in surface water but also in groundwater in some areas within the PRD due to the urbanization and industrialization (Huang et al., 2013; Huang et al., 2014a). Moreover, a previous study has also found the natural source of some metalloids, such as arsenic (As), with high concentrations in a granular aquifer within the PRD (Wang et al., 2012). In addition, the effects of expansion of construction land on some aspects of hydrogeochemical conditions in the PRD have also been well documented in a previous study (Huang et al., 2018). However, a regional scale survey on the distributions, sources, and driving forces of heavy metal(loid)s and organic contaminants in groundwater in the PRD has received little attention.
This study aimed to investigate the distributions of heavy metal(loid)s and organic contaminants in groundwater in the PRD at a regional scale, and to discuss sources and driving forces for heavy metal(loid)s and organic contaminants in groundwater. Among them, the impacts of urbanization and industrialization on the distributions of heavy metal(loid)s and organic contaminants in groundwater in the PRD have been highlighted. The results will benefit groundwater resource management for a sustainable development in the rapidly urbanized areas in China and other countries.
Section snippets
Geographical, geological and hydrogeological conditions
The PRD was formed as a result of the Tibetan Plateau uplift during the Tertiary and Quaternary Periods and is located in southern China (Fig. 1). It has a total area of 41,698 km2 with a population of over 57 million in 2016. The East River, West River, and North River merge in the south of the area and form the Pearl River, which finally discharges into the South China Sea. The central and southern parts of the PRD are mostly covered by Quaternary sediments. Quaternary sediments consist of
Heavy metal(loid)s and organic contaminants in groundwater in the PRD
The heavy metal(loid)s measured in 399 groundwater samples across the PRD in Table 1 are sorted by their mean concentrations (median and interquartile values in Table S2). Fe showed the highest mean concentration, followed by Ba, As, Cr, Ni, Co, Se, and Hg. It is known that the groundwater with high concentrations of heavy metal(loid)s is undrinkable. In the PRD, according to the standard for groundwater quality of China (General administration of quality supervision inspection and quarantine
Conclusions
The results of this study show that undrinkable groundwater related to heavy metal(loid)s in the PRD was mainly due to the high concentrations of Fe (19.3%), followed by As (6.77%), Ni (0.5%), Ba (0.25%), Se (0.25%), and Hg (0.25%), while the concentrations of Cr and Co in groundwater were below allowable limits of China. In total 55 analyzed organic chemicals, 18 of them were detected in groundwater in the PRD. The most frequently detected organic contaminant was naphthalene, and its detection
Acknowledgements
This research was supported by the Fundamental Research Funds for Central Public Welfare Research Institutes, CAGS (SK201611, SK201410), China Geological Survey Grant (DD20160309, DD20179609) and the Natural Science Foundation of Hebei Province of China (D2015504004).
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