PHYTOREMEDIATION OF LEAD AND CHROMIUM CONTAMINATED SOILS USING SUNFLOWER (Helianthus annuus L.) IN THE MAIGANGA COAL MINING AREA, GOMBE STATE, NORTHEASTERN NIGERIA

Abstract

This study evaluated the phytoremediation potential of sunflower (Helianthus annuus L.) for the management of Pb- and Cr-contaminated soils from the Maiganga coal-mining area in Gombe State, northeastern Nigeria. A greenhouse experiment was conducted using a completely randomized design comprising four soil treatments with five replicates each: uncontaminated control soil (T₀), mine spoil (T₁), agricultural soil adjacent to the mine (T₂), and mine tailings (T₃). Sunflower was cultivated for 12 weeks, after which Pb and Cr concentrations in soil, roots and shoots were quantified using atomic absorption spectrophotometry (AAS). The result revealed that, initial Pb and Cr concentrations were significantly higher (P < 0.05) in contaminated soils, reaching 110.4 ± 5.3 and 88.7 ± 4.2 mg kg⁻¹, respectively. Despite moderate reductions in plant height and biomass under metal stress, H. annuus established successfully across all treatments and maintained substantial biomass production. Metal accumulation was significantly greater in roots than shoots, with maximum root concentrations of 158.9 ± 7.3 mg kg⁻¹ Pb and 102.4 ± 5.3 mg kg⁻¹ Cr, indicating preferential below-ground metal retention. Bioconcentration factors exceeded unity (BCF > 1), whereas translocation factors remained below unity (TF < 1) for both metals, indicating effective root accumulation with restricted root-to-shoot translocation. After 12 weeks of cultivation, bioavailable Pb and Cr in the soil declined by 42.8–58.3% and 35.7–49.2%, respectively. Collectively, the combination of metal tolerance, root accumulation, restricted translocation and reduced soil metal bioavailability indicates that H. annuus has considerable potential for phytostabilization and ecological restoration of Pb- and Cr-contaminated mine soils. Field-scale studies incorporating appropriate organic amendments and longer monitoring periods are recommended to validate and optimize its remediation performance under natural conditions.