Phytoremediation Efficiency and Rhizosphere Geochemistry of Selected Hyperaccumulator Plants in Heavy Metal Contaminated Farmlands of the Zamfara Lead-Zinc Mining Belt

Lead poisoning in Zamfara State associated with artisanal gold mining activities represents one of the most severe environmental health emergencies documented in sub-Saharan Africa in recent decades, and phytoremediation using metal-hyperaccumulating plant species offers a potentially cost-effective, socially acceptable, and ecologically restorative approach to managing the expansive soil contamination footprint that chemical and physical remediation technologies cannot practically address at this scale. This study investigates the phytoremediation efficiency and rhizosphere geochemistry of three candidate plant species, specifically Thlaspi caerulescens, Pteris vittata, and a locally identified hyperaccumulator grass species, cultivated on highly lead and arsenic-contaminated soils from three legacy mining village sites in the Zamfara lead-zinc mining belt. Field-scale phytoextraction plots are established with and without soil amendments (EDTA, citric acid, and elemental sulphur) to assess chelant-assisted phytoextraction enhancement. Shoot and root metal concentrations are measured by inductively coupled plasma mass spectrometry following microwave digestion across three sequential growing seasons. Bioconcentration factors and translocation factors are calculated for each species and metal. Rhizosphere geochemistry is characterised through measurement of soil solution metal speciation by diffusive gradients in thin-films technique, rhizosphere pH mapping by microelectrode planar optodes, and exudate organic acid composition by ion chromatography. Microbial community composition in bulk versus rhizosphere soil is analysed by 16S rRNA gene amplicon sequencing, revealing plant-microbiome interactions that modulate metal bioavailability. An original rhizosphere biogeochemical model integrating chemical speciation, organic acid exudation, and microbial transformation is developed as the primary theoretical contribution. Keywords: phytoremediation, lead contamination, Zamfara, rhizosphere geochemistry, hyperaccumulator plants