ABSTRACT
The soils and leaves of fluted pumpkin (Telfairia occidentalis), African spinach, "Green" (Amaranthus hybridus) and water leaf (Talinum triangulare) were collected as randomly composite samples from four (4) different study locations of two (2) each from Owo Local Government Area and Etsako-West Local Government Area. The samples were examined for heavy metal concentrations, using X-ray fluorescence (XRF) technique. Chromium (Cr), zinc (Zn), manganese (Mn), iron (Fe), titanium (Ti), strontium (Sr) and aluminium (Al) of both soil and vegetable samples were detected at higher proportions than the permissible limits of WHO/FAO and EU for soils and plants. Exceptions were obtained for Cr in SL3 (Talinum triangulare from St. Louis farm), and Zn in WB (soil from Water-Board farm), IY (soil from Iyerekhu farm) and IY3 (Talinum triangulare from Iyerekhu farm). Toxic heavy metals, such as nickel (Ni), lead (Pb), cobalt (Co), cadmium (Cd) and copper (Cu) were not detected in both soil and vegetable samples. Generally, the concentrations of the metals in the soil and vegetable samples followed the same decreasing order: Al>Fe>Ti>Mn>Sr>Cr>Zn. The Cr concentrations varied from 54.72 to 191.52 mg/kg among the soil samples and from 0.00 to 280.44 mg/kg among the vegetable samples. The concentrations of Zn were higher in the vegetable samples than the soil samples, ranging from 0.00 to 184.74 mg/kg for soil samples and from 0.00 to 795.17 mg/kg for vegetable samples. Generally, Mn concentrations were higher in the tissues of the vegetable samples than in the soil samples except for slight deviations observed in SL1 (Telfairia occidentalis from St. Louis farm), SL2 (Amaranthum hybridus from St. Louis farm) and OL2 (Amaranthum hybridus from Osuma Layout farm). Iron (Fe) was the most abundant nutritionally essential metal in both soil and vegetable samples, ranging from 22089.07 to 64282.61 mg/kg in the soil samples and 2354.96 to 29950.57 mg/kg in the vegetable samples. Titanium (Ti) concentrations were more predominant in the soil samples than the vegetable samples. The peak (719.10 mg/kg) and least (118.44 mg/kg) Sr concentrations were observed in the OL (Osuma Layout farm) and WB (Water-Board farm) soils respectively, which bioaccumulated, in the same trend, in their corresponding Telfairia occidentalis samples. The Al concentrations ranged from 48333.29 – 75021.09 mg/kg in the soil samples and 30984.10 – 63407.34 mg/kg in the vegetable samples. All the vegetable samples had significant differences in the transfer factors of metals relative to the availability of same metals in the soil, ranging from 0.00 to 9.47. Manganese (Mn) had the peak transfer factor (9.47) in WB3 (Talinum triangulare from Water-Board farm) followed by 9.33 observed in WB1 (Telfairia occidentalis from Water-Board farm). The vegetable samples were recommended for possible application in phytoremediation of polluted soils.
