Bioremediation of Lead, Cadmium and Zinc in Industrially Contaminated Soils of the Al-Ma’amal Area, Baghdad, Iraq, Using Indigenous Pseudomonas and Bacillus Isolates

Abstract

Rapid and poorly regulated industrialisation has resulted in the accumulation of potentially toxic elements (PTEs) in soils within the peri-urban industrial zones of Baghdad. This study quantified lead (Pb), cadmium (Cd), and zinc (Zn) contamination in surface soils from the Al-Ma’amal industrial area, located near brick kilns and open waste-burning sites, and evaluated the ability of indigenous Pseudomonas sp. and Bacillus sp. isolates to reduce metal concentrations under controlled microcosm conditions. Surface soil samples were collected at a depth of 0–20 cm from two contaminated sites and one reference site and analysed using flame atomic absorption spectrometry (FAAS). Soil contamination was assessed using the geoaccumulation index (I_geo), contamination factor (CF), and pollution load index (PLI). A 60-day laboratory-scale microcosm experiment was conducted to evaluate metal removal by a two-strain bacterial consortium. Superoxide dismutase (SOD) and catalase (CAT) activities were measured as indicators of bacterial adaptation to metal-induced oxidative stress. At the most contaminated site, mean concentrations reached 210 mg kg⁻¹ for Pb, 16 mg kg⁻¹ for Cd, and 117 mg kg⁻¹ for Zn. Pb and Cd concentrations exceeded the commonly cited WHO/FAO guideline values by approximately 2.5- and 5-fold, respectively. The calculated I_geo values indicated strong-to-extreme Cd enrichment, while the PLI was approximately 9, confirming substantial overall contamination. The bacterial consortium reduced soil metal concentrations by approximately 62–70% after 60 days. SOD and CAT activities increased markedly under metal-stress conditions compared with the controls, reaching approximately 3.3-fold higher levels. Metal concentrations were strongly and positively correlated with antioxidant enzyme activities, with Pearson correlation coefficients exceeding 0.90. These findings demonstrate substantial anthropogenic Pb and Cd contamination in the soils of the Al-Ma’amal industrial area and support the potential application of indigenous Pseudomonas–Bacillus consortia as a cost-effective and environmentally sustainable strategy for the bioremediation of metal-contaminated industrial soils in Iraq.