Spatial assessment of the ecological hazards of polycyclic aromatic hydrocarbons (PAHs), total petroleum hydrocarbons (TPHs), and soil thermal footprint. Fallujah, Iraq

Abstract

Post-conflict environments in Iraq, and Fallujah (Anbar Governorate) in particular, have been subjected to repeated high-intensity military operations, widespread building demolition, open burning of infrastructure, and fuel-depot destruction, all of which are known to deposit pyrogenic polycyclic aromatic hydrocarbons (PAHs) and petroleum hydrocarbons (TPH) into adjacent agricultural soils. Despite an internationally recognised legacy of environmental and health concern in Fallujah, comprehensive organic soil contamination datawith spatial resolution, quantitative risk assessment, and soil-quality indexing remain scarce in the peer-reviewed literature. Objectives: To determine the concentrations of the 16 USEPA priority PAHs, total petroleum hydrocarbons (TPH C10–C40), benzo[a]pyrene toxic equivalent quotient (BaP-TEQ), and black carbon (BC) across a twelve-site spatial network in Fallujah; to compute the Pollution-Load Index (PLI), Contamination Factor (CF), and Integrated Soil-Quality Index (SQI); to identify PAH sources using diagnostic ratios and principal component analysis (PCA); to characterise the spatial decay from the conflict epicentre; and to assess ecotoxicological and human-health implications against international soil-screening standards. Methods: Twelve surface soil samples (0–20 cm) were collected from sites spanning 120–2,850 m from the Al-Sarai conflict epicentre in November 2023 dry season to minimise leaching bias. Σ₁₆PAHs and individual congeners were quantified by GC-MS (SIM mode; deuterated surrogate internal standards; seven-point calibration; MDL 0.005 µg/mL); TPH (C10–C40) by GC-FID (ISO 16703; nine-point calibration); black carbon (BC) by thermo-optical analysis (EUSAAR_2 protocol). Physicochemical parameters (pH, EC, TOC, CEC, TN, available P, CaCO₃) were determined by standard methods. Contamination indices (CF, PLI, BaP-TEQ), source fingerprinting (diagnostic ratios; Fla/(Fla+Pyr); Ant/(Ant+Phe); IcdP/(IcdP+BghiP); BaA/(BaA+Chr)), PCA, ordinary-kriging interpolation, and Spearman/Pearson correlations were computed. Spatial decay modelling used nonlinear least-squares exponential fitting. Results: Σ₁₆PAH ranged from 0.24 mg/kg (background, S-12) to 16.56 mg/kg (epicentre, S-01), with extreme contamination (> 10 mg/kg; Maliszewska-Kordybach class IV) at three sites within 220 m of the epicentre. BaP-TEQ peaked at 4.97 mg/kg at S-01, exceeding the 1.0 mg/kg indicative action level at three sites. TPH peaked at 3,079 mg/kg (S-01) versus a background of 105 mg/kg; the Dutch TPH target value (50 mg/kg) was exceeded at nine of twelve sites. The integrated organic PLI reached 14.75 at S-01; ordinary-kriging surfaces show PLI > 3 (highly polluted) persisting to ≈ 400 m and PLI > 2 to ≈ 600 m from the epicentre. Exponential spatial-decay modelling estimated half-distances of 333 m (Σ₁₆PAH) and 276 m (BaP-TEQ). PCA (PC1 = 92.4% variance) and diagnostic ratios (Ant/(Ant+Phe) > 0.10; Fla/(Fla+Pyr) > 0.50) confirmed a dominantly pyrogenic combustion source at epicentre and high-tier sites. SQI was severely impaired at the three extreme sites (SQI ≤ 0.072 vs background 0.90). Conclusions: Fallujah agricultural soils within ≈ 400 m of the Al-Sarai conflict epicentre are severely contaminated with carcinogenic pyrogenic PAHs and petroleum hydrocarbons, with organic PLI values exceeding all published Iraqi and regional benchmarks. The SQI data confirm concurrent biological soil function impairment. These findings provide a spatial, multi-parameter evidence base for prioritised remediation, agricultural land-use restrictions within the extreme tier, and continued environmental health monitoring in Fallujah as mandated by UN Environment Programme principles for post-conflict recovery.