Key Takeaways & Executive Findings
- •• • Mean concentrations of As, Se, Cd, Sb, Pb, Tl, and Bi exceeded local background values; Cd, Se, Bi, and As showed pronounced enrichment, with Cd contributing 87.49% to the potential ecological risk index (RI), indicating its dominance as a contaminant. • • Sequential extraction showed that Zn, Cd, Pb, and Mn had high extractable fractions (F1+F2+F3) exceeding 50%, while Sb, Bi, Se, Tl, Cu, As, V, Cr, and Ni were predominantly in the residual fraction (F4), implying higher mobility and bioavailability for the former group, especially downstream. • • Geo-accumulation index (Igeo) revealed no contamination by Co, Zn, V, or Cr, but varying contamination by Mn, Ni, As, Se, Cd, Sb, Pb, Tl, Bi, and Cu, with pollution severity order Se>Cd>Bi>As>Sb>Pb>Tl>Ni>Cu>Mn>Zn>Cr>Co>V; Cd showed moderate to strong contamination at some sites. • • Source apportionment via PCA and PMF identified three sources: industrial and traffic mixed source (57.60%), natural source (16.00%), and industrial-natural mixed source (26.40%), providing quantitative basis for targeted pollution control.
Abstract
Sediments from the Hengyang reach of the Xiangjiang River were analyzed for concentrations, chemical fractions, and sources of 14 heavy metals (As, Se, Cd, Sb, Pb, Tl, Bi, Co, Ni, Mn, Zn, V, Cr, Cu). Mean concentrations of As, Se, Cd, Sb, Pb, Tl, and Bi exceeded local background values, with Cd, Se, Bi, and As showing pronounced enrichment. Spatial heterogeneity was marked, with higher levels downstream; overall concentrations were lower than previously reported. Sequential extraction revealed that Sb, Bi, Se, Tl, Cu, As, V, Cr, and Ni were predominantly in the residual fraction (F4), while Zn, Cd, Pb, and Mn had higher extractable fractions (F1+F2+F3), with bioavailable fractions generally elevated downstream. Geo-accumulation index (Igeo) indicated no contamination by Co, Zn, V, or Cr, but varying degrees of contamination by Mn, Ni, As, Se, Cd, Sb, Pb, Tl, Bi, and Cu, with pollution severity order: Se>Cd>Bi>As>Sb>Pb>Tl>Ni>Cu>Mn>Zn>Cr>Co>V. Enrichment factors showed significant enrichment for Cd, Sb, and Bi, moderate for Pb, and low for others. Potential ecological risk index (RI) revealed Cd as the primary contributor (87.49% of total risk), with overall moderate risk at downstream sites and slight risk across the entire section. Source apportionment using PCA and PMF identified three sources: industrial and traffic mixed source (57.60%), natural source (16.00%), and industrial-natural mixed source (26.40%). These findings enhance understanding of heavy metal pollution mechanisms in the Hengyang section and recommend priority control of industrial and traffic emissions, with focus on Cd mobility, to support sediment remediation strategies.
1. Introduction
The Xiang River, a major tributary of the Yangtze, flows through Hunan Province, a region historically rich in non-ferrous metal mining and smelting. The Hengyang section, located upstream, has received substantial anthropogenic inputs from industrial activities, urban runoff, and agricultural practices. Previous studies have documented elevated heavy metal concentrations in sediments, yet the complexity of metal speciation and source contributions has hindered effective remediation. Existing assessments often relied on total metal concentrations, overlooking the bioavailability and geochemical phases that dictate ecological risk. Moreover, source identification was frequently qualitative, lacking robust quantitative apportionment to guide regulatory actions.
This study addresses these gaps by integrating high-resolution geochemical analysis with advanced source apportionment models (PCA and PMF). By quantifying 14 heavy metals in sediments and their chemical fractions, the research provides a comprehensive evaluation of pollution status and ecological risk. The application of multiple indices (EF, Igeo, RI) allows cross-validation of contamination levels, while PMF offers a quantitative breakdown of source contributions. This methodological framework enables identification of priority pollutants and sources, facilitating targeted management strategies for sediment quality in the Hengyang section and similar industrialized river systems.
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FANG Xiaohong, HU Linjie, HAN Xiangyu, PENG Bo, ZHONG Yuru, PENG Qing, SHI Shana (2026). Heavy Metal Pollution Characteristics and Ecological Risk Assessment of Sediments in the Hengyang Section of the Xiang River. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025111403
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Frequently Asked Questions
What are the dominant heavy metals of concern in the Hengyang section and their potential ecological risk contributions?
Cadmium (Cd) is the primary contaminant, contributing 87.49% to the potential ecological risk index (RI). Other metals like Se, Bi, As, and Sb also show enrichment, but their individual risk contributions are lower. The overall ecological risk is moderate at downstream sites, primarily driven by Cd.
How do the chemical fractions of heavy metals influence their bioavailability and potential toxicity?
Metals such as Zn, Cd, Pb, and Mn have high proportions in extractable fractions (F1+F2+F3), indicating higher mobility and bioavailability, which poses greater ecological risk. In contrast, Sb, Bi, Se, Tl, Cu, As, V, Cr, and Ni are predominantly in the residual fraction (F4), suggesting they are tightly bound and less likely to be released under typical environmental conditions.
What are the main sources of heavy metal pollution in the Hengyang section, and what are their percentage contributions?
Source apportionment using PCA and PMF identified three sources: an industrial and traffic mixed source contributing 57.60%, a natural source contributing 16.00%, and an industrial-natural mixed source contributing 26.40%. This indicates that anthropogenic activities, particularly industrial and traffic emissions, are the dominant contributors.
How do the current heavy metal concentrations compare to historical data, and what are the implications for remediation?
Overall heavy metal concentrations have decreased compared to previous studies, suggesting some improvement in environmental quality. However, Cd remains a significant concern due to its high enrichment and risk contribution. This trend implies that past control measures may be effective for some metals, but targeted actions are still needed for Cd and other enriched elements.
What are the limitations of the assessment methods used, and how could they be improved in future studies?
The study relies on sediment sampling at specific points, which may not capture temporal variability. Additionally, the use of background values from local references may introduce uncertainties. Future research could incorporate high-resolution spatial mapping, seasonal sampling, and bioavailability assays to refine risk assessments. Also, integrating sediment quality guidelines with ecological responses would enhance the ecological relevance.
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