PHYTOEXTRACTION POTENTIALS AND EARLY GROWTH PERFORMANCE OF BLACK NIGHTSHADE (Solanum nigrum) SEEDLINGS ON CONTAMINATED SOILS FROM DIFFERENT MECHANIC SITES AROUND WUDIL KANO

Abstract

Heavy metal contamination from indiscriminate disposal of spent engine oil in mechanic workshops poses serious environmental and agricultural challenges in Wudil, Kano, Nigeria. This study evaluated the phytoextraction potential and early growth performance of Solanum nigrum seedlings grown on soils from four mechanic sites compared to uncontaminated farmland soil. A greenhouse pot experiment was conducted under a Completely Randomized Design (CRD) with five soil treatments and four replicates. Growth parameters (emergence, days to emergence, height, canopy width, leaf number, and biomass) were recorded for four weeks, while soil and plant tissues were analyzed for Pb, Cd, Zn, and Ni using atomic absorption spectrophotometry. Results showed significantly (P<0.05) reduced germination (from 90% to 80%), seedling height (16 to 20 cm), and biomass in contaminated soils compared to control (95%, 22.5 cm, 1.80 g shoot DW), with mechanic site C performing worst. Post-harvest soil analysis revealed significant (P<0.05) reductions in heavy metals from 17.9% to11%, confirming active phytoextraction. Metal accumulation was higher in roots than shoots for Pb, Cd, and Ni, indicating phytostabilization, while Zn showed greater shoot translocation (TF>1), highlighting phytoextraction potential. Bioconcentration factors (BCF) for most metals ranged from 0.28–0.41, with Zn showing relatively higher accumulation and mobility. These findings suggest that, S. nigrum tolerates contaminated soils, reduces metal concentrations, and may serve as both a phytostabilizer (Pb, Cd, and Ni) and a phytoextractor (Zn). The study concludes that S. nigrum is a promising, low-cost candidate for phytoremediation of mechanic site soils in northern Nigeria, though multiple cropping cycles may be required for effective decontamination.