Key Takeaways & Executive Findings
- •• • Groundwater in Guyuan is Class IV per GB/T 14848—2017, with TDS averaging 1350.9 mg·L−1, rendering it unsuitable for direct drinking but usable for irrigation after treatment; As requires special attention. • • Nemerow index classifies overall pollution as moderate, with Cr, As, and Mn as key contributors; HPI averages 10.56 but reaches 36.15 at sample PS1-51-下, indicating severe local contamination. • • Carcinogenic risk from Cr and As is 8.037×10−6 a−1 for adults and 3.863×10−6 a−1 for children, below US EPA limits but above stricter international guidelines, emphasizing the need for risk management, especially for children. • • Isotopic and statistical analyses indicate atmospheric precipitation as the primary recharge source; Cr, As, and Mn derive from copper mining, coal extraction, and agricultural activities, highlighting anthropogenic impacts in populated loess areas.
Abstract
Groundwater is a vital drinking and irrigation source in the loess regions of northwestern China. In Guyuan, a densely populated area in southern Ningxia, systematic assessments of groundwater pollution risks are lacking. This study collected 60 groundwater samples and employed the Nemerow index, heavy metal pollution index (HPI), and health risk assessment models to evaluate pollution levels and health risks of eight elements including Cr, As, and Hg. Results show that the groundwater is generally Class IV quality, with a mean TDS of 1350.9 mg·L−1. Average concentrations of As, Cr, and Mn are 4.39, 29.87, and 45.77 μg·L−1, respectively. The Nemerow index indicates moderate pollution. The mean HPI is 10.56, but a local sample (PS1-51-下) reaches 36.15, indicating severe pollution. Health risk assessment reveals that carcinogenic risks from Cr and As for adults and children are 8.037×10−6 a−1 and 3.863×10−6 a−1, respectively, below US EPA limits but above recommended levels by Swedish and Dutch agencies, with children at higher risk. Hydrogen and oxygen isotopes and principal component analysis suggest that groundwater is primarily recharged by atmospheric precipitation. Cr, Zn, and Mn mainly originate from regional copper ore belts, coal mining, and agricultural activities. This study fills a gap in multidimensional groundwater assessment in populated loess areas, identifies pollution characteristics distinct from typical loess regions, and provides a scientific basis for regional water resource risk management and sustainable development.
1. Introduction
Groundwater contamination by heavy metals poses a significant threat to public health and environmental sustainability, particularly in arid and semi-arid regions where groundwater is the primary water source. In China, groundwater supplies drinking water for 70% of the population and irrigation for 40% of farmland. However, industrial activities, mining, and agriculture have led to elevated levels of toxic elements such as Cr, As, and Mn in aquifers. Existing water quality assessments in Ningxia have predominantly focused on the northern Yellow River region, leaving the southern loess areas, including Guyuan, understudied. This lack of data hampers effective risk management and leaves local communities vulnerable to potential contamination.
This study addresses this gap by conducting a comprehensive, multidimensional assessment of groundwater quality in Guyuan, a densely populated loess region. Unlike previous studies that relied on single evaluation methods, this research integrates the Nemerow index, heavy metal pollution index (HPI), and health risk assessment models to simultaneously identify priority pollutants, delineate contamination extent, and quantify human health risks. Furthermore, hydrogen and oxygen isotopes, correlation analysis, and principal component analysis are employed to trace the sources of contaminants. This integrated approach provides a robust framework for understanding the complex interactions between natural geogenic processes and anthropogenic activities, thereby offering actionable insights for water resource management and pollution mitigation in similar loess regions.
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LIU Yuxi, HUANG Yong, LIU Hong, SU Yue, LIU Hui, MA Yuxue, ZHANG Jinghua, YUAN Jianfei, YI Chengtai (2026). Multidimensional Groundwater Quality Assessment and Source Apportionment in the Guyuan Region, Ningxia. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202506084
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Frequently Asked Questions
What are the dominant pollution sources and their relative contributions to groundwater contamination in the Guyuan region?
Isotopic and statistical analyses indicate that groundwater is primarily recharged by atmospheric precipitation, with limited surface water influence. Principal component analysis suggests that Cr, Zn, and Mn are mainly derived from regional copper ore belts, coal mining activities, and agricultural practices. The study does not provide quantitative source apportionment percentages, but these anthropogenic sources are identified as the primary contributors to the observed contamination.
How does the health risk from groundwater contaminants compare between adults and children, and what are the implications for regulatory limits?
The carcinogenic risk from Cr and As is 8.037×10−6 a−1 for adults and 3.863×10−6 a−1 for children. While these values are below the US EPA's maximum acceptable risk of 1×10−4, they exceed the stricter guidelines of 1×10−6 recommended by agencies such as the Swedish and Dutch environmental protection agencies. Children are at higher risk due to their lower body weight and higher water consumption per unit body weight, necessitating stricter protective measures.
What are the limitations of using the Nemerow index and HPI in this context, and how do they complement each other?
The Nemerow index emphasizes the maximum pollution factor, providing a conservative estimate of overall pollution, while HPI aggregates the cumulative load of multiple heavy metals, offering a broader spatial perspective. In this study, the Nemerow index indicated moderate pollution, whereas HPI revealed severe local contamination at specific points (e.g., PS1-51-下 with HPI=36.15). Their combined use allows for both single-element and multi-element assessments, but neither accounts for synergistic toxic effects, which may underestimate actual risks.
How does the groundwater quality in Guyuan compare to other loess regions, and what factors explain the differences?
Compared to other loess regions, groundwater in Guyuan shows greater anthropogenic influence, likely due to higher population density and coal mining activities. The study notes that in loess areas with precipitation-dominated recharge and weak surface water interaction, contaminants are less easily diluted or dispersed, leading to localized accumulation. This contrasts with regions where surface water recharge is more significant, potentially diluting contaminants.
What specific measures are recommended to mitigate the identified health risks and prevent further contamination?
The study recommends controlling the extent of coal mining and regulating agricultural activities to reduce inputs of Cr, As, and Mn. Additionally, it suggests that groundwater should not be consumed directly without treatment, particularly for children, and that appropriate treatment processes, such as arsenic removal, should be implemented. Long-term monitoring and comprehensive management strategies are essential to safeguard public health and ensure sustainable water use.
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