Sources Identification and Health Risk Evaluation of 10 Heavy Metals (Metalloids) in Soils of the Aibi Lake Basin, Northwest China

Recently, soils heavy metals pollution and health risks researches in oasis are few, and in this study, the Aibi lake basin—a typical oasis—was chosen as the research area, and then, we evaluated the pollution status and sources identification and analyzed the health risks of ten heavy metals in the soils. Results showed that (1) the average (range) values for As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, and Zn were (6.500–48.040) 20.011, (0.0002–0.088) 0.035, (0.060–18.150) 5.994, (24.160–106.400) 53.557, (3.460–58.760) 16.981, (0.0002–0.099) 0.042, (195.310–842.850) 483.311, (0.960–70.100) 14.235, (0.180–25.390) 8.086, and (22.340–156.250) 61.334 mg/kg, respectively, and we can get except for As, the maximum values of other nine elements all within the limited values provided by the soil environmental quality risk control standard of China. (2) Health risk evaluation showed that the total exposure amount for ADIing for children and adults was 0.001067998 and 0.000344707, ADIinh for children and adults was 9.69977E-08 and 7.95869E-08, ADIderm for children and adults was 8.52275E-06 and 2.09927E-06, and the order of exploring ways is ADIing > ADIinh > ADIderm. (3) The multivariate statistical analysis and PMF results showed that Cr, Cu, Co, Mn, Ni, Pb, and Zn primarily come from the natural background and man-made sources; Cd primarily comes from man-made sources; As and Hg come from natural background sources and industry sources. The results can provide reference values for heavy metals pollution prevention and the protection of the environment in the Aibi lake basin and as well as central Asia.

1. Introduction
Heavy metals are persistent toxic pollutants in the environment and have bio-accumulative and nondegradable characteristics [1–3]. Recently, the pollution of the environment by heavy metals has received the attention of many scholars worldwide. Additionally, they can directly or indirectly affect human health. Thus, research regarding the content of heavy metals in farmland soil has been widely conducted worldwide [4, 5]. The heavy metals found in soils primarily come from urban construction, urban lives, industrialization, wastewaters, dust, and solid wastes from smelt plants, and oil and mining explorations and exceed the amount of heavy metals present from the use of pesticide chemical fertilizers [6, 7].

Previous studies have focused on the spatial distribution, source identification [8], pollution assessment, evaluation of the health risks [9], and environmental risks [10]. Methods used include GIS technology, the enrichment factor method [11], the geo-accumulation index [12], the Hakanson potential risks index [9], the health risks evaluation model [13], multivariate statistical analysis, positive matrix factorization (PMF) [14], and risk assessment coding (RAC) [10].

Initial health risk models by USEPA were carried out using soils, dust, waterbody, and the fruit of plants and evaluated the carcinogenic and noncarcinogenic risks of heavy metals [2, 15]. There are now relevant researches about soil heavy metals health risks evaluation in the world, such as in the study by Li et al. [16], a human risk assessment was carried out for heavy metals in the abandoned metal mine areas of Korea, and the calculated hazard index value for As in the Songchun mine area (3.625) exceeded 1.0. In a study by Harmanescu et al. [17], they carried out a heavy metal health risk assessment for a population via the consumption of vegetables grown in an old mining area in Romania. Al-Hwaiti and Al-Khashman [9] carried out a health risk assessment of heavy metal contamination for the following metals: Cd, Cr, Cu, Pb, V, and Zn in tomato and green pepper plants grown in soils amended with phosphogypsum (PG) waste materials and found that the daily intake of metals (DIM) and the health risk index (HRI) values were <1. According to the first national soil pollution survey of China in 2014, the soil in China currently faces a serious threat from heavy metals pollution [18]. The survey showed that the point exceeding the rate of soil in China was 19.4%, with a slight proportion, mild, moderate, and severe pollution points of 13, 7%, 2.8%, 1.8%, and 1.1%, respectively. The majority of the polluted elements were identified to be Cd, Ni, Cu, As, Hg, and Pb [18].