Ambient Air Pollution and Biomarkers of Oxidative Stress in a High-Traffic Residential District of Baghdad, Iraq

Abstract

Background: Ambient air pollution is a leading modifiable environmental determinant of non-communicable disease, acting through the induction of systemic oxidative stress and low-grade inflammation. Baghdad, Iraq, experiences ambient particulate matter (PM₂.₅, PM₁₀) and nitrogen dioxide (NO₂) concentrations that substantially exceed World Health Organization (WHO) Global Air Quality Guideline (AQG) 2021 levels. Direct neighbourhood-level evidence linking ambient pollution to circulating oxidative stress biomarkers in Iraqi residential populations remains limited. Objective: To compare ambient concentrations of PM₂.₅, PM₁₀, NO₂, and sulfur dioxide (SO₂), and circulating biomarkers of oxidative stress  — malondialdehyde (MDA) and reduced glutathione (GSH) — between adult residents of the Al-Amil district (a high-traffic mixed residential-industrial area in southwestern Baghdad) and residents near Al-Zawraa Park (a low-traffic green-space reference area), and to evaluate relationships between pollutant concentrations and biomarker levels against WHO AQG 2021 reference values. Methods: A cross-sectional comparative study was conducted in October–November 2023 among adult residents of Al-Amil (exposed group, n = 80) and the Al-Zawraa Park reference area (control group, n = 80). Ambient PM₂.₅, PM₁₀, NO₂, and SO₂ were measured using a calibrated real-time monitoring station over 14 consecutive days at each site. Venous blood samples were collected; serum MDA was quantified by the thiobarbituric acid reactive substances (TBARS) spectrophotometric method and GSH by the Ellman (DTNB) method, each referenced to a freshly prepared calibration curve. Group comparisons used the independent-samples t-test; associations between pollutant concentrations and biomarkers were assessed by Spearman correlation and linear regression (α = 0.05). Results: Mean 14-day PM₂.₅ at the exposed site was 89.8 ± 13.0 µg/m³ versus 30.1 ± 5.4 µg/m³ at the control site (p < 0.0001), exceeding the WHO AQG 2021 24-hour reference of 15 µg/m³ by 5.99-fold and 2.01-fold, respectively. PM₁₀ was 181.2 ± 16.9 versus 69.1 ± 9.6 µg/m³ (p < 0.0001); NO₂ was 56.9 ± 10.5 versus 19.1 ± 5.7 µg/m³ (p < 0.0001); SO₂ was 24.9 ± 5.4 versus 9.2 ± 3.6 µg/m³ (p < 0.0001). Serum MDA was significantly higher in the exposed group (3.76 ± 0.62 nmol/mL vs. 1.88 ± 0.40 nmol/mL; p < 0.001) and GSH significantly lower (18.7 ± 4.1 µg/mL vs. 33.6 ± 4.7 µg/mL; p < 0.001). Strong positive Spearman correlations were observed between PM₂.₅ and MDA (ρ = 0.736, p < 0.0001) and between NO₂ and MDA (ρ = 0.744, p < 0.0001). Linear regression yielded: Serum MDA = 0.031 × PM₂.₅ + 0.929 (R² = 0.749, p < 0.0001). Conclusions: Residential proximity to a high-traffic mixed-use Baghdad district is associated with substantially elevated ambient pollutant concentrations all exceeding WHO AQG 2021 reference values and a concomitant oxidant-antioxidant imbalance characterised by significantly elevated MDA and depleted GSH. These findings support the urgent need for traffic management, industrial emission control, and green-space expansion policies in Baghdad, and provide a neighbourhood-level, WHO-referenced evidence base for Iraqi environmental health policy.