Leveraging algal-derived biopolymers to alleviate multi-metal phytotoxicity and enhance maize growth in industrially contaminated soils.

Heavy metal contamination of industrial soils severely constrains crop productivity and environmental sustainability. This study evaluated effectiveness of algal-derived biopolymer carrageenan in mitigating multi-metal (Cd, Pb, Zn, Cu) toxicity and improving maize performance in naturally contaminated soils from four industrial zones of Pakistan (Kasur, Faisalabad, Sialkot, and Korangi). A pot experiment with graded carrageenan levels (0-200 mg kg-1) revealed significant improvements in soil physicochemical properties, including increases in pH (≈10-11%) and electrical conductivity (61-94%), alongside enhanced enzymatic activities. Carrageenan application markedly reduced DTPA-extractable metals, with maximum declines of up to 83% (Cd), 70% (Zn), 69% (Pb), and 62% (Cu), thereby limiting their bioavailability. Consequently, metal accumulation in maize roots and shoots decreased substantially, with reductions reaching 90% for Cd and 74% for Pb in shoots. These changes were accompanied by improved plant tolerance indices and significant biomass enhancement. Carrageenan also stimulated antioxidant defense systems, increasing SOD (66-79%), POD (74-150%), and CAT (56-74%) activities, along with glyoxalase function (up to 160%), while elevating non-enzymatic antioxidants such as ascorbate (up to 140%), glutathione (110%), and phytochelatins (179%). Photosynthetic pigments were significantly improved, with total chlorophyll and carotenoids increasing by up to 65% and 168%, respectively. Overall, carrageenan effectively immobilized toxic metals, reduced their translocation, and enhanced physiological and biochemical resilience in maize, demonstrating strong potential as a sustainable amendment for phytoremediation and crop production in metal contaminated soils.