Assessing Heavy Metal Contamination Risk in Soil and Water in the Core Water Source Area of the Middle Route of the South-to-North Water Diversion Project, China

Li Tan,Zhanqi Wang,Bin Yang,Zhibin Xue

doi:10.3390/land10090934

Abstract

The Middle Route Project of China’s South-to-North Water Diversion Project (SNWDP) is a national-level water source protection zone and the ecological safety of its water quality and surrounding soil is of great significance. In this study, heavy metals in the surface water and topsoil in the core water source area were quantitatively analyzed using a geographic information system (GIS) and geostatistical techniques combined with environmental pollution and ecological risk assessment models to determine their environmental contamination levels, ecological risk levels, and spatial distribution patterns. Cd was identified as an essential factor responsible for the overall slight heavy metal pollution in the topsoil layer. Heavy metal contamination in surface water was primarily driven by alert-level concentrations of Hg and was consistently distributed in areas with high concentrations of Hg in the topsoil. Applying the potential ecological risk index (RI) revealed two key results. First, surface water showed no ecological risk. The concentrations of heavy metals in surface water met the goals set by relevant authorities in China. Second, overall, the topsoil was at low ecological risk, with a spatial pattern primarily influenced by Cd and Hg. Some heavy metals might have similar pollution sources and originate from human activities such as industrial activities, mining and smelting, and pesticide and chemical fertilizer applications. The study is important for improving the soil and water ecology in the reservoir area and ensuring the northward diversion of high-quality water. In addition, it provides a sound basis for making decisions about local heavy-metal remediation and treatment projects.

Highlights

Heavy metals are the most common pollutants incorporated into indices that characterize various types of environmental quality
The average value of each heavy metal did not exceed the class II standards stipulated in China’s Environmental Quality Standards for Surface Water (EQSSW) (GB 3838-2002) [62] or the standards stipulated in China’s Standard for Drinking Water (SDW) (GB 5749-2006) [63]. This result suggests that the surface-water quality in the study area met the goal set by relevant authorities in China and reached the level required for water-supply purposes
Significant positive correlations were found between CCd and CZn, between CCr and CCu, and between CCu and CZn, with correlation coefficients of 0.452, 0.561, and 0.639, respectively (Table 9). These results suggest that Cd, Zn, Cr, and Cu might have originated from similar sources in the topsoil

Summary

Introduction

Heavy metals are the most common pollutants incorporated into indices that characterize various types of environmental quality. The expansion of industrial and agricultural sectors, and advancing urbanization, large quantities of dangerous chemical substances, heavy metals, are released in various forms into water bodies [9,10,11], causing pollution in aquatic environments which directly or indirectly threatens the safety of humans and other organisms [12,13,14] Characterized by their long-term hazardous effects, high invisibility, high toxicity, non-biodegradability, and ease of accumulation, circulation, and migration, heavy metals in soils can have a significant adverse impact on regional ecological conditions [15,16]. Most published studies tend to focus on heavy metal pollution in either water bodies or soils, while relatively few have simultaneously investigated it in both, and more comprehensive assessments are still lacking [25,26,27,28]

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Discussion

Conclusion