Heavy metals concentration in rhizosphere and tissues of smooth pigweed (A. hybridus) and bush okra (C. olitorius) cultivated on an abandoned dumpsite

Abstract

The study assessed the concentrations of Pb, Cr, and Cd in rhizosphere and tissues of A. hybridus and C. olitorius grown on a dumpsite converted to farmland by plant and 0-15 cm depth soil samples which were air-dried, digested and analysed using Atomic Absorption Spectrophotometry. Some physiochemical parameters that affect transport of soil nutrients into plant tissues were analysed using standard methods. The pH of the rhizosphere soil of C. olitorius was 6.71 and the soil of A. hybridus was slightly alkaline in nature with pH 7.75. The rhizosphere of A. hybridus had the highest concentration of Pb (123.20±90.04 mg/kg) and Cd (0.63±0.63 mg/kg) while Cr was highest in the rhizosphere of C. olitorius (36.57±8.61 mg/kg). The result showed total and bioavailable metal concentrations in the soils were in the order of Pb > Cr > Cd. The order of metal uptake varied with vegetable crop. Metal concentration in tissues of A. hybridus followed the order of Pb > Cr > Cd while C. olitorius was Cr > Pb > Cd. Concentrations of Cd, Pb and Cr exceeded the maximum permissible limit in soil and within allowable limit in the tissue. C. olitorius had transfer factor (TF) < 1 for Cd, Pb and Cr. A. hybridus had similar transfer factor except for Cr with TF > 1. The study concluded that the dumpsite converted to farmland is highly contaminated with Pb, Cr, and Cd and highly accumulated by the vegetables.