Heavy metal content of selected African leafy vegetables planted in urban and peri-urban Nairobi, Kenya

Abstract

African indigenous vegetables planted along Nairobi Rivers are suspected to absorb metals from industrial and domestic effluent. Ten (10) of the commonest vegetables in Kenyan markets grown along these rivers and the soils in their rhizosphere from 25 sites were analyzed for Pb, Cu, Zn, Cd and Cr. Soils were air-dried then leached using 0.05 M EDTA, filtered and analysed in AAS. Vegetables were oven-dried, ground, ashed then analysed in AAS. In both soil and vegetables, the metal concentration was generally in the order Zn > Cu > Pb > Cd >Cr. In soil the concentrations were Pb 0.57 - 20 mg/kg, Cu 3.59 - 75.37 mg/kg, Zn 14.62 - 198.3 mg/kg, Cr 0.03 - 1.4 mg/kg and Cd 0 - 2.6 mg/kg. In vegetables the values were Pb 0 - 2.4 mg/kg, Cu 0.52 - 21.34 mg/kg, Zn 20.13 - 89.85 mg/kg, Cd 0 - 3.02 mg/kg and Cr 0 - 1.24 pp. There were significant differences within vegetables at each site (P<0.05). In most sites, there was a positive correlation of soil metal content with that in vegetables. The metal concentrations in soil were within permissible levels allowable by WHO/FAO except for a few instances in Cd. In vegetables all metals except Cu were in a few sites higher that the recommended limits. Government clean-up activities and monitoring of waste disposal is recommended for potential agricultural land.

Key words: African Indigenous vegetables, heavy metals, pollution, urban and peri - urban agriculture, Nairobi.