Determination of Zn, Mn, Fe and Cu in spinach and lettuce cultivated in Potiskum, Yobe State, Nigeria

Full Length Research Paper

Determination of Zn, Mn, Fe and Cu in spinach and lettuce cultivated in Potiskum, Yobe State, Nigeria

E. I. Uwah¹, M. S. B. Gimba¹ and P. A. Gwaski²

¹Department of Chemistry, University of Maiduguri, P. M. B. 1069, Maiduguri, Nigeria

²Department of Science Laboratory Technology, Ramat Polytechnic, Maiduguri, Nigeria

*Corresponding author. E-mail: uwahemmai@yahoo.com.

Accepted 19 October, 2012

Abstract

The concentrations of four heavy metals, Zn, Mn, Fe and Cu were determined in the roots and leaves of lettuce (Lactuca sativa) and spinach (Amaranthus caudatus) cultivated in Potiskum, Yobe State, Nigeria. The heavy metals were also determined in soil where the vegetables were cultivated. The determination processes were done by Atomic Absorption Spectrophotometer (AAS) techniques. The results show that the heavy metals contents were higher in the soil than the vegetables and also higher in the roots than the leaves in the two vegetables. The levels of Fe obtained in the leaves and roots of spinach were 0.11±0.01 and 0.21±0.05, respectively. The Fe content in the soil was 0.28±0.01. It could be concluded that lettuce and spinach cultivated in Potiskum, Yobe state, Nigeria contained Zn, Mn, Fe and Cu in variable concentrations which may be due to different farming practices adopted in the area to boost productivity. However, the results obtained in this study were lower than the published threshold values (10 to 20.00 mg/kg for Fe and 30 to 300 mg/kg for Pb) considered toxic for plant tissues as well as the critical values or values (Fe: >200-500 mg/kg and Pb: >4 to 30 mg/kg) regarded as excessive. The results were equally lower than the WHO maximum limit (ML) (Pb, 0.3 mg/kg; Zn, 100 mg/kg; Cd, 0.1mg/kg; Mn, 500 mg/kg; Fe, 425 mg/kg; Cu, 73mg/kg; Ni, 67mg/kg and Co, 50 mg/kg) in vegetables. Consumption of these vegetables may not pose health hazards.

Key words: AAS, farming practices, heavy metals, productivity, Potiskum, vegetables.