The health of surface water is closely related to human society, because surface water is not only an important source of drinking water for human beings, but also a living environment for aquatic plants and animals, and can also be used as irrigation water for crops [1, 2]. Surface water is an important part of urban ecosystem, mainly rivers and lakes, which play an irreplaceable role in urban development and human life. Urban rivers are an important sink of contaminants, a large number of contaminants, including trace metals, organic and inorganic compounds, etc., have been released into rivers and contaminated water because of the development of industrialization and population growth [3, 4].
Among these contaminants found in rivers, metal contaminants are a significant global concern because of their persistence, environmental toxicity, bioaccumulation, etc [5–8]. Human beings can be threatened by metals in water bodies directly by drinking water, or indirectly, by food chain [9]. There are many sources of metal in water, mainly including nature sources, such as geological erosion, weathering, and precipitation; anthropogenic activities sources, such as mining; metal processing; industrial wastewater; and the application of pesticides and fertilizers [10–12]. Many studies have shown that some toxic trace metals have triple effects (carcinogenesis, teratogenesis and mutagenesis). Among the many metal elements, some elements are necessary for human metabolism, such as Cu, Zn, Fe, and,Mn, but above a certain level has toxic effects. Some elements have no physiological activity, such as As, Cd, Hg, and Pb, which can damage the human's endocrine system and are listed as environmental endocrine disruptors by the U.S. environmental protection agency (EPA) [13–15]. Therefore, it is of great practical significance to investigate and assess the distribution and human health risk of metals in water bodies.
The effect of human beings threatened by metals in water bodies is particularly significant in some developing countries including China. The Xiangjiang River has become one of the most seriously and heavily polluted rivers in China over the past few decades due to the metallurgical industries and wastewater discharge from mining [16]. The Xiangjiang River is the second tributary of the Yangtze River and an important drinking water source in south China. It flows through the Hunan province and supports the major cities, providing service to industry agriculture and population [14, 17]. There are many researchers have studied the distribution and risk assessment of heavy metals in surface water or sediment of the Xiangjiang River [18, 19]. Prevalently, Cd, Cr, Zn, Cu, Ni, As and Pb, were previously studied in the Xiangjiang River, while some unheeded metals such as Mg, Co, V, Mn, Fe, Ba and Sb have been overlooked [20]. Moreover, riverine sediments, as a reservoir of contaminants, accumulates a large amount of metals. In the case of external environmental disturbance, the metals in the sediments will be desorbed and released into the overlying water and then resuspend into the surface water [21, 22]. Thus, there is a lack of research on the vertical distribution of metals in the water and a systematic study is necessary to associate the surface and overlying water bodies with the distribution, characteristics, health risk assessment, and possible sources of metals.
In this work, we collected 60 surface and overlying water samples from the Zhuzhou and Xiangtan Reaches of the Xiangjiang River as a typical area in order to (1) characterize the vertical distributions of 12 metals (Mg, V, Cr, Mn, Fe, Co, Ni, Zn, As, Cd, Sb, and Ba) in the water bodies, (3) identify possible sources of metals pollution from principle component analysis (PCA) and Pearson's correlation analysis, and (3) assess the potential human health risk posed by the target metals in the river water. The results are expected to provide basic data and scientific evidence for the prevention and control of metal pollution in drinking water sources and help in the development of appropriate water quality management strategies in nearby areas and similar riverine systems.