Synergistic Heavy Metal Remediation through a Novel Black Soldier Fly–Brassica juncea Cascade in Mining-Impacted Soils

Heavy metal contamination represents a critical hazard to environmental and human health. This study assesses cadmium (Cd), lead (Pb), and zinc (Zn) remediation in phosphate-mining soils via entomoremediation with Hermetia illucens (Black Soldier Fly, BSF) larvae, phytoremediation with Brassica juncea, and to our knowledge, this is the first demonstration of their sequential integration. The soils exhibited moderate acidity (pH 5.4), low in organic matter (1.6%), and significantly enriched with Cd (12.4 mg kg ^− 1 ), Pb (285.7 mg kg ^− 1 ), and Zn (412.3 mg kg ^− 1 ).BSF larvae immobilized Cd, Pb, and Zn by 63%, 57%, and 49% within 14 days through gut sequestration, chitin-associated binding, and Ca–P stabilization in alkaline frass. Brassica juncea achieved sustained uptake of Cd (50%), Pb (44%), and Zn (41%) over 30 days mediated by rhizosphere mobilization and vacuolar compartmentalization. Kinetic modeling revealed pseudo-second-order behavior for Cd and Pb under BSF, while Zn uptake within the BSF → BJ cascade shifted from pseudo-first- to pseudo-second-order with improved equilibrium capacity.Bioaccumulation (BAF > 2.4) demonstrated strong larval sequestration of Cd and Pb, while translocation (TF > 1.0) showed substantial phytoextraction of Cd and Zn. Sequential treatment achieved enhanced removal efficiencies (Cd 78%, Pb 70%, Zn 65%) and markedly improved soil quality, including a 35% enhancement in the Soil Quality Index.Mechanistic assays confirmed that BSF preconditioning decreased exchangeable fractions and enhanced BJ antioxidant responses, establishing a synergistic bio-integrated remediation pathway. This insect–plant synergy constitutes a novel eco-engineered remediation strategy combining rapid detoxification with durable stabilization, aligned with circular economy principles.