Accumulation pattern of trace metals in Spinacia oleracea harvested from soil treated with urine in comparison with other soil amendments in Pretoria, South Africa

Abstract

Purpose The study assessed trace metal levels in the leaves, stalks and roots of Spinacia oleracea harvested from soil treated with urine in comparison to chemical fertilizers and biosolids. Methods Spinacia oleracea seedlings were planted on soils pretreated with urine, chemical fertilizers and biosolids. Results The soil treated with chemical fertilizers resulted in an increase of Cr, Pb, Cd, Cu, Ni and Sb while there was an increase in the concentrations of Zn and Hg in the soil treated with urine. The soil with no amendments recorded higher mean values of As and Mn, whereas the biosolids treatment did not show any increases of the trace metals in the soil. The concentration of Mn, Pb and Ni in the leaves and stalks of S. oleracea harvested from soil treated with urine were below the recommended limits for trace metals in edible plants as set by WHO even though the urine treatment recorded the highest concentration of Cd in the roots, stalks and leaves. The S. oleracea harvested from the soil treated with chemical fertilizers showed an accumulation Cu and Mn in the stalks and leaves while those harvested from soil treated with biosolids showed an accumulation of Cr, As, Zn and Ni in the stalks and Cr, Pb and Sb in the leaves and all trace metals in the roots except Cd and As. S. oleracea harvested from the soil with no amendments showed an accumulation of Cr, As, Zn and Ni in the stalks and Cr, Pb, Zn and Sb in the leaves. The transfer factor showed that Cd, Zn, Mn and Sn were translocated from the soil to the leaves even though the concentrations were below acceptable limits for human consumption. Conclusions The study demonstrated that the use of urine as a soil amendment may not facilitate or increase the bioavailability of trace metals in the plant tissues.

Keywords

• Agriculture
• Organic waste
• Trace metals
• Urine