Bioremediation of Pb, Cd and Cr by Soil Bacteria from Urban-Industrial Transition Zones

Abstract

Urban–industrial transition zones are dynamic areas where residential, traffic, and industrial activities coexist, often leading to persistent heavy metal contamination. Metals such as lead (Pb), cadmium (Cd), and chromium (Cr) are of particular concern due to their non-biodegradable nature, long-term persistence in soil, and associated ecological and public health risks. Their accumulation alters soil chemistry and disrupts native microbial communities essential for soil health. This study investigated the resilience of indigenous soil bacteria and their potential role in heavy metal bioremediation. Soil samples were collected from urban gardens and textile-influenced industrial sites and analyzed for physicochemical parameters (pH, moisture, texture) and heavy metal concentrations using standard colorimetric methods. Pb and Cd were estimated by the dithizone method at 520 nm, while Cr was quantified at 540 nm following acid digestion. Industrial soils showed comparatively altered physicochemical properties and higher metal loads. To assess microbial adaptation, samples were enriched in metal-supplemented nutrient broth, and distinct bacterial isolates were purified. Minimum inhibitory concentration (MIC) studies under combined metal stress identified three highly tolerant isolates, which were further tested for compatibility and consortium development. Biosorption potential was evaluated in liquid culture, followed by laboratory-scale soil microcosm experiments using metal-spiked sterile soil. Both individual isolates and the consortium were applied, and metal reduction was monitored over time. The consortium demonstrated enhanced remediation efficiency compared to individual strains. Statistical correlation analysis further examined the relationship between pollutant concentration and removal efficiency. Overall, the findings highlight the adaptive capacity of indigenous soil bacteria and support their potential use as bioindicators and eco-friendly agents for sustainable heavy metal bioremediation.