Determination of some heavy metals in soil and edible vegetables grown in two different farms in Damaturu Metropolis, Yobe State, Nigeria

Abstract

Vegetables comprise an important part of our daily foods that contribute some minerals and other nutrients to human body. Consumption of contaminated vegetables by heavy metals results in bioaccumulation of these harmful elements in the body. Therefore, this study is designed to examine the amount of heavy metal concentrations (Nickel, Copper, Cadmium and Zinc) in soil and edible parts of four vegetables namely Amaranthus hybridus (spinach), Hibiscus sabdariffa (roselle), Urena lobata (caesar weed) and Ceratotheca sesamoides (false sesame) grown in two farms. Transfer factor of heavy metals from soil to the plants was also evaluated. Samples were prepared and analysed using Atomic Absorption Spectrophotometry (AAS). The mean concentrations of all the vegetables in the both farms for Ni, Cu, Cd and Zn were obtained as 0.215, 2.341, 0.023 and 2.251 mg/Kg respectively. Whereas, the mean concentrations in the soils were 0.317, 7.560, 0.071 and 9.910 mg/Kg for Ni, Cu, Cd and Zn respectively. The levels of the above heavy metals in almost all the samples from those farms were below the maximum allowable limits recommended by WHO/FAO and therefore, they had acceptable conditions for human consumption. The exception was Ni which was slightly above the (0.1 mg/Kg) WHO/FAO permissible limit in the samples of both farms excluding Urena lobata of Custom Farm. In Bin Bukar, the trend of the transfer factor was in rank of Ni > Cd > Cu > Zn, whereas, in Custom Farm the transfer factor was sort as Cu > Ni > Cd. The highest Transfer Factor (TF) value was 1.464 found in Ceratotheca sesamoides for Ni in Bin Bukar Farm and 0.627 in Urena lobata for Cu in Custom Farm. The Transfer Factor values for Cd, Cu and Zn for the range of vegetables were not substantially high, except for Ni which the ratio was greater than one indicating that the plants have accumulated elements.