Interactions of some heavy metals in soil and effects on their uptake by spinach (Spinacia oleracea)

Abstract

Physico-chemical analysis, total metal concentration and chemical speciation of soil have been studied using standard analytical methods. Determination of heavy metals in soil and spinach were also carried out. The seeds of spinach were planted in pots and nurtured in a glass house for 30 days, after which the plant was harvested. The soil used for the planting was taken from the research farm of the Federal University of Technology, (FUT) Minna, and treated with the metals Pb, Cd, Cu and Zn in single and combined forms. The initial levels of these metals in soil decreased in the order Zn> Cu> Cd while Pb was not detected. Sequential extraction procedure was used to separate the heavy metals in soil into six geochemical forms: Water soluble, exchangeable, carbonate, Fe/Mn Oxide, organic and residual. Among the four heavy metals studied, the mean of the concentration of Zn in the water soluble fraction was the highest (33.00 mg/kg) while the lowest (0.50 mg/kg) was Pb bound to organic and exchangeable fractions. The mean of the heavy metal concentration in soil for single metal treatment was highest (51.33 mg/kg) in Zn treated soil and lowest (0.33 mg/kg) in Pb treated soil. Similarly, the mean of the heavy metal concentration in soil for combined metal treatment was highest (60.00 mg/kg) in Cu/Zn treated soil and lowest (0.55 mg/kg) in Pb/Zn treated soil. The mean of the heavy metal concentration in spinach for single metal treatment was highest at (57.67 mg/kg) and lowest at (0.33 mg/kg). Similarly, the mean of the heavy metal concentration in spinach for combined metal treatment was highest at (56.67 mg/kg) and lowest at (1.00 mg/kg). It was observed that the concentration of Zn both in soil and spinach fell below the maximum permissible level. The result of the transfer factor showed that Cd is the most mobile metal in spinach while Zn is the least. The order of decreased mobility is Cd> Pb > Cu> Zn.

Key words: Interactions, Sequential Extraction, Antagonistic, Synergistic, Transfer Factor