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Purpose <p>This study aims to quantify the natural versus anthropogenic contributions to cadmium (Cd) pollution in the sediments of the Xitiaoxi River system in Anji County, and identify the dominant sources driving the spatial distribution patterns. Key research questions include: How do bedrock weathering and human activities govern Cd isotopic fractionation? What roles do industrial/agricultural inputs play in hotspot formation? How does the geological background regulate baseline pollution?</p> Methods <p>We analyzed 82 sediment samples using: cadmium isotopic fingerprinting (δ¹¹⁴/¹¹⁰Cd) to trace pollution sources, the geo-accumulation index (Igeo) for pollution assessment and a Bayesian mixing model (MixSIAR) for source apportionment. Samples covered eight sub-areas (A-H) with distinct geological/land-use features. Measurements of isotope ratios were taken using MC-ICP-MS following Cd purification. MixSIAR combined isotopic signatures (-0.2441‰ to + 0.7354‰) and concentration data to calculate the contributions from natural weathering, industrial emissions, and agricultur⁠⁠⁠⁠⁠⁠⁠al inputs.</p> Results <p>Bedrock weathering accounted for 14.7%–88.1% of the Cd through mineral desorption/hydraulic sorting. Industrial Area D showed severe pollution (6.54&#xa0;mg kg<sup>− 1</sup>, 14.5× background) with light-isotope dominance (δ¹¹⁴/¹¹⁰Cd = + 0.2981‰, 34.2% contribution), linked to historical acid-washing. Agricultural Area B exhibited heavy-isotope enrichment (δ¹¹⁴/¹¹⁰Cd = + 0.7354‰) where phosphate fertilizers contributed 82.3%. Geological units controlled the baseline distribution. Siltstone Area C exhibited very low levels of Cd (0.084&#xa0;mg kg<sup>−1</sup>due to leaching. Areas A and E, consisting of mudstone and limestone, showed negative δ¹¹⁴/¹¹⁰Cd resulting from sulfide weathering. Quaternary Areas F-H displayed moderate fractionation (0.46‰–0.52‰) caused by urban emissions.</p> Conclusions <p>Cd pollution reflects dual control by natural baselines (bedrock weathering) and anthropogenic forcing (industry/agriculture). Isotopic fingerprinting coupled with MixSIAR quantitatively resolved industrial (34.2%), agricultural (up to 82.3%), and natural (avg. 46.5%) contributions, proving effective for complex source discrimination. Priority governance targets include: remediation of historical industrial zones (Area D) and agricultural non-point source control (Area B). The coordinated management of geological backgrounds and human activities is essential for regional pollution mitigation.</p>

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Cadmium isotope fingerprinting reveals natural and anthropogenic dual-drivers and spatial-source-specific pollution characteristics in Northern Zhejiang sediments

  • 期刊论文

  • 发表日期：

    2026年4月27日

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  • Enqin Yao,
  • Tiansen Yang,
  • Fei Jia,
  • Chenyang Zhou,
  • Zhouyang Shi,
  • Xinyu Ma,
  • Angliang Zhang,
  • Xing Shen

摘要

Purpose

This study aims to quantify the natural versus anthropogenic contributions to cadmium (Cd) pollution in the sediments of the Xitiaoxi River system in Anji County, and identify the dominant sources driving the spatial distribution patterns. Key research questions include: How do bedrock weathering and human activities govern Cd isotopic fractionation? What roles do industrial/agricultural inputs play in hotspot formation? How does the geological background regulate baseline pollution?

Methods

We analyzed 82 sediment samples using: cadmium isotopic fingerprinting (δ¹¹⁴/¹¹⁰Cd) to trace pollution sources, the geo-accumulation index (Igeo) for pollution assessment and a Bayesian mixing model (MixSIAR) for source apportionment. Samples covered eight sub-areas (A-H) with distinct geological/land-use features. Measurements of isotope ratios were taken using MC-ICP-MS following Cd purification. MixSIAR combined isotopic signatures (-0.2441‰ to + 0.7354‰) and concentration data to calculate the contributions from natural weathering, industrial emissions, and agricultur⁠⁠⁠⁠⁠⁠⁠al inputs.

Results

Bedrock weathering accounted for 14.7%–88.1% of the Cd through mineral desorption/hydraulic sorting. Industrial Area D showed severe pollution (6.54 mg kg− 1, 14.5× background) with light-isotope dominance (δ¹¹⁴/¹¹⁰Cd = + 0.2981‰, 34.2% contribution), linked to historical acid-washing. Agricultural Area B exhibited heavy-isotope enrichment (δ¹¹⁴/¹¹⁰Cd = + 0.7354‰) where phosphate fertilizers contributed 82.3%. Geological units controlled the baseline distribution. Siltstone Area C exhibited very low levels of Cd (0.084 mg kg−1due to leaching. Areas A and E, consisting of mudstone and limestone, showed negative δ¹¹⁴/¹¹⁰Cd resulting from sulfide weathering. Quaternary Areas F-H displayed moderate fractionation (0.46‰–0.52‰) caused by urban emissions.

Conclusions

Cd pollution reflects dual control by natural baselines (bedrock weathering) and anthropogenic forcing (industry/agriculture). Isotopic fingerprinting coupled with MixSIAR quantitatively resolved industrial (34.2%), agricultural (up to 82.3%), and natural (avg. 46.5%) contributions, proving effective for complex source discrimination. Priority governance targets include: remediation of historical industrial zones (Area D) and agricultural non-point source control (Area B). The coordinated management of geological backgrounds and human activities is essential for regional pollution mitigation.