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<p>Industrial development in semi-arid regions generates persistent soil contamination requiring baseline geochemical characterization for environmental management. This study presents a geochemical assessment of heavy metal and petroleum hydrocarbon contamination in industrial soils of Erbil, Kurdistan Region of Iraq, integrating pollution indices with spatial analysis and multivariate statistics. Twenty-two composite soil samples (0–15&#xa0;cm depth) collected around refinery facilities were analyzed for heavy metals (Pb, Cd, Ni, Cr, Cu, Zn, Be, Se, As, etc.), total petroleum hydrocarbons (TPH), and physicochemical properties. Geochemical analysis revealed cadmium (0.70–4.92&#xa0;mg&#xa0;kg<sup>−1</sup>), lead (17.31–185.0&#xa0;mg&#xa0;kg<sup>−1</sup>), and beryllium (5.29–126.02&#xa0;mg&#xa0;kg<sup>−1</sup>) exceeded international soil quality guidelines at 31.8, 54.5, and 100% of sites, respectively. The Canadian Soil Quality Index ranged from 41.87 to 81.11, indicating moderate overall contamination based on CSQI. The Geo-accumulation Index (Igeo) revealed spatially differentiated pollution: beryllium was classified as heavily polluted across all sites (mean Igeo = 3.56), while cadmium (1.66) and lead (1.05) showed moderate enrichment; chromium and nickel returned negative Igeo values, confirming their predominantly lithogenic origin. Contaminated soils exhibited strong alkalinity (pH 8.0–9.0), severe salinization (electrical conductivity up to 9.11 dS m<sup>−1</sup>), and depleted organic matter (1.02–4.00%). Total petroleum hydrocarbons reached 151.0&#xa0;mg&#xa0;kg<sup>−1</sup> near refinery infrastructure. Principal Component Analysis identified three geochemical source groups: anthropogenic refinery-vehicular emissions (46.2% variance), mixed geogenic-anthropogenic contributions (21.4% variance), and soil fertility variation (11.8% variance). Spatial interpolation revealed contamination gradients decreasing with distance from industrial sources, consistent with atmospheric deposition patterns. Semi-arid climate processes—limited precipitation (375–450&#xa0;mm&#xa0;year<sup>−1</sup>), high evaporation rates, and alkaline soil conditions—promote surface-horizon accumulation and prolong contaminant residence time. This geochemical baseline establishes essential reference values for Iraq’s Kurdistan Region and demonstrates how semi-arid pedogeochemical conditions influence contaminant distribution and persistence in petroleum-producing regions.</p> Graphical Abstract <p></p>

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Geochemical assessment of heavy metal and petroleum hydrocarbon contamination in semi-arid industrial soils: a case study from Erbil, Iraq

  • 期刊论文

  • 发表日期：

    2026年6月15日

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  • Mehmet Fatih Dilekoğlu,
  • Barzan Omar Azeez,
  • Masoud Hussein Hamed

摘要

Industrial development in semi-arid regions generates persistent soil contamination requiring baseline geochemical characterization for environmental management. This study presents a geochemical assessment of heavy metal and petroleum hydrocarbon contamination in industrial soils of Erbil, Kurdistan Region of Iraq, integrating pollution indices with spatial analysis and multivariate statistics. Twenty-two composite soil samples (0–15 cm depth) collected around refinery facilities were analyzed for heavy metals (Pb, Cd, Ni, Cr, Cu, Zn, Be, Se, As, etc.), total petroleum hydrocarbons (TPH), and physicochemical properties. Geochemical analysis revealed cadmium (0.70–4.92 mg kg−1), lead (17.31–185.0 mg kg−1), and beryllium (5.29–126.02 mg kg−1) exceeded international soil quality guidelines at 31.8, 54.5, and 100% of sites, respectively. The Canadian Soil Quality Index ranged from 41.87 to 81.11, indicating moderate overall contamination based on CSQI. The Geo-accumulation Index (Igeo) revealed spatially differentiated pollution: beryllium was classified as heavily polluted across all sites (mean Igeo = 3.56), while cadmium (1.66) and lead (1.05) showed moderate enrichment; chromium and nickel returned negative Igeo values, confirming their predominantly lithogenic origin. Contaminated soils exhibited strong alkalinity (pH 8.0–9.0), severe salinization (electrical conductivity up to 9.11 dS m−1), and depleted organic matter (1.02–4.00%). Total petroleum hydrocarbons reached 151.0 mg kg−1 near refinery infrastructure. Principal Component Analysis identified three geochemical source groups: anthropogenic refinery-vehicular emissions (46.2% variance), mixed geogenic-anthropogenic contributions (21.4% variance), and soil fertility variation (11.8% variance). Spatial interpolation revealed contamination gradients decreasing with distance from industrial sources, consistent with atmospheric deposition patterns. Semi-arid climate processes—limited precipitation (375–450 mm year−1), high evaporation rates, and alkaline soil conditions—promote surface-horizon accumulation and prolong contaminant residence time. This geochemical baseline establishes essential reference values for Iraq’s Kurdistan Region and demonstrates how semi-arid pedogeochemical conditions influence contaminant distribution and persistence in petroleum-producing regions.

Graphical Abstract