Heavy Metal Concentration of Okra (Abelmoschus Esculentus) Grown on Dumpsite Soil in Benin City, Nigeria

Abstract

The study investigates the concentrations of heavy metals in Okra (Abelmoschus esculentus) planted in dumpsite soil obtained from the University of Benin and Ekosodin in Benin City. Soil samples were collected before and after planting and analyzed for pH, total nitrogen (N), total organic carbon (C), phosphorus (P), iron (Fe), zinc (Zn), manganese (Mn), and heavy metal concentrations (Cu, Pb, Cd, and Cr). The study reveals variations in soil acidity levels across different locations before and after planting. In Table 1, soil pH was moderately acidic in Farmland (5.61), neutral in Market (6.79) and Residential (6.76) areas, and slightly acidic in Faculties (6.14). In Table 2, after planting, the pH remained moderately acidic in Market (5.68) and Residential (5.80), while becoming strongly acidic in Farmland (5.42) and Faculties (5.36). Total N and P decreased in most dumpsites after planting, while total organic carbon increased. Fe, Zn, and Mn concentration varied between dumpsites and after planting stages. Particle size distribution remained predominantly sandy across dumpsites and planting stages. The study suggests that Okra plants cultivated in various dumpsite soils showed no toxic levels for the selected heavy metals, with concentrations generally falling within acceptable limits for vegetable consumption. The copper concentration highest uptake observed in Okra plants from Residential Land (36.0 mg/kg) and the lowest in Farmland (23.3 mg/kg). Lead (Pb) uptake varied across dumpsites: Market (0.15 mg/kg), Farmland (0.10 mg/kg), Residential Land (0.12 mg/kg), and Faculties (0.06 mg/kg). Cadmium (Cd) uptake was observed at Market dumpsites (0.05 mg/kg), Farmland (0.02 mg/kg), Residential Area (0.01 mg/kg), and Faculties (0.04 mg/kg). Heavy metal concentrations in the soil and Okra plants were generally below the permissible limits set by the Department of Petroleum Resources (DPR) for soil and World Health Organization (WHO) for vegetables intended for human consumption.