From Polluted Banks to Restored Soils: Plant-Microbe Synergy for Heavy Metal Remediation Across Raipur's Industrial-Riparian Gradient

Abstract

Heavy metal contamination of agricultural and riparian soils in rapidly industrialising tropical cities constitutes one of the foremost contemporary threats to soil ecosystem function and public health. The present investigation evaluates a synergistic phytoremediation–microbial consortium strategy for the bioremediation of soils contaminated with lead (Pb), cadmium (Cd), chromium (Cr), nickel (Ni), copper (Cu), and zinc (Zn) at four ecologically distinct sites within the Raipur district of Chhattisgarh, India, namely: the MahadevGhat riverbank on the Kharoon River, the Urla Industrial Estate, the Telibandha Lake drain outfall, and the Siltara Industrial Development Corporation (SIDC) Phase-II zone — a transect spanning a pronounced riparian-to-industrial contamination gradient, with pollution load indices rising from 2.18 at the Kharoon riverbank to 6.84 at the industrial core. Greenhouse microcosm experiments conducted over 60 days employed three plant species — Vetiveriazizanioides (L.) Nash, Helianthus annuus L., and Brassica juncea (L.) Czern. — inoculated with a consortia of metal-tolerant plant-growth-promoting rhizobacteria comprising Bacillus subtilis strain RS-07, Pseudomonas putida strain RS-14, and Arthrobacterchlorophenolicus strain RS-22. Combined treatment achieved statistically superior heavy metal removal efficiencies of 68.4% (Pb), 73.8% (Cd), 60.7% (Cr), and 63.1% (Ni) relative to all single-component controls (p < 0.05). Bioaccumulation factor (BCF) values for Cd in consortium-inoculated B. juncea reached 1.70, confirming genuine hyperaccumulation potential. Temporal recovery of soil enzyme activities — urease, dehydrogenase, alkaline phosphatase, and catalase — confirmed progressive restoration of soil microbial ecosystem function. Pearson correlation analysis revealed strong negative associations between residual soil metal concentration and enzyme activity (r = −0.82 to −0.91, p < 0.001), corroborating that microbial functional recovery co-varies with metal removal. Taken together, the results trace a coherent trajectory from polluted riparian and industrial banks to a demonstrably restorable soil state, and provide a regionally grounded evidence base for the design of integrated plant-microbe bioremediation systems across the industrial-riparian gradient of the central Indian industrial corridor.