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<p>Arsenic (As), a toxic metalloid, whose release from silicate weathering remains poorly quantified despite significant environmental risks. This study investigates a granite weathering profile (GTC) in the eastern Tibetan Plateau under intense weathering conditions. Eighteen weathered samples and a parent rock are analyzed. The weathered samples exhibit As concentrations of 14.9–19.1&#xa0;mg/kg, with mass transfer coefficients (τ<sub>As</sub>) presenting significant depletion (−&#xa0;84.6 to −&#xa0;55.8%) compared to the parent rock (33.0&#xa0;mg/kg). This profile is vertically divided into distinct redox zones: an oxidized topsoil, a reduced zone (40–120&#xa0;cm), and an oxidized zone (below 150&#xa0;cm). The mobilization and redistribution patterns of As, i.e., the reduced zone from 40 to 120&#xa0;cm with relative As enrichment and the oxidized zone below 150&#xa0;cm with severe As depletion, involve complicated geochemical processes. Fe–Mn (hydr)oxides and clay minerals constitute primary As hosts in the profile, with τ<sub>As</sub> values exhibiting strong positive correlations with τ<sub>Fe</sub>, τ<sub>Mn</sub>, and τ<sub>Al</sub> (R<sup>2</sup> = 0.95, 0.65, and 0.91, respectively). The redox-sensitive dynamics of Fe–Mn (hydr)oxides and As speciation could crucially govern As mobilization and redistribution in the GTC profile. Reductive dissolution and desorption processes from Fe–Mn (hydr)oxides in the upper reduced zone, enhance As release, whereas Fe–Mn–Al (hydr)oxides retain substantial As in the deeper oxidized zone via coprecipitation and adsorption. Near-surface low pH conditions and abundant organic matter collectively enhance As mobility. All these factors cooperatively modify the As cycling during chemical weathering. Based on the As loss during granite weathering, a hypothetical 10,000 km<sup>2</sup> watershed model exhibits approximately 3.88 × 10<sup>6</sup> tons of cumulative As discharge from silicate weathering and migrating into aquatic systems. This study advances the understanding of As geochemical behavior during silicate weathering, identifies silicate weathering as a key natural As source, and provides a framework for assessing As risks in ecologically fragile regions.</p>

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Mobilization and redistribution of Arsenic during intense weathering of granite, eastern Tibetan Plateau, China

  • 期刊论文

  • 发表日期：

    2026年3月13日

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  • Zi-Han Xia,
  • Jun-Wen Zhang,
  • Na Wu,
  • Mei-Li He,
  • Qi Liu,
  • Zhi-Qi Zhao

摘要

Arsenic (As), a toxic metalloid, whose release from silicate weathering remains poorly quantified despite significant environmental risks. This study investigates a granite weathering profile (GTC) in the eastern Tibetan Plateau under intense weathering conditions. Eighteen weathered samples and a parent rock are analyzed. The weathered samples exhibit As concentrations of 14.9–19.1 mg/kg, with mass transfer coefficients (τAs) presenting significant depletion (− 84.6 to − 55.8%) compared to the parent rock (33.0 mg/kg). This profile is vertically divided into distinct redox zones: an oxidized topsoil, a reduced zone (40–120 cm), and an oxidized zone (below 150 cm). The mobilization and redistribution patterns of As, i.e., the reduced zone from 40 to 120 cm with relative As enrichment and the oxidized zone below 150 cm with severe As depletion, involve complicated geochemical processes. Fe–Mn (hydr)oxides and clay minerals constitute primary As hosts in the profile, with τAs values exhibiting strong positive correlations with τFe, τMn, and τAl (R2 = 0.95, 0.65, and 0.91, respectively). The redox-sensitive dynamics of Fe–Mn (hydr)oxides and As speciation could crucially govern As mobilization and redistribution in the GTC profile. Reductive dissolution and desorption processes from Fe–Mn (hydr)oxides in the upper reduced zone, enhance As release, whereas Fe–Mn–Al (hydr)oxides retain substantial As in the deeper oxidized zone via coprecipitation and adsorption. Near-surface low pH conditions and abundant organic matter collectively enhance As mobility. All these factors cooperatively modify the As cycling during chemical weathering. Based on the As loss during granite weathering, a hypothetical 10,000 km2 watershed model exhibits approximately 3.88 × 106 tons of cumulative As discharge from silicate weathering and migrating into aquatic systems. This study advances the understanding of As geochemical behavior during silicate weathering, identifies silicate weathering as a key natural As source, and provides a framework for assessing As risks in ecologically fragile regions.