Heavy Metal Uptake and Accumulation by Edible Leafy Vegetable (Amaranthus Hybridus L.) Grown on Urban Valley Bottom Soils in Southwestern Nigeria

Heavy metals, such as cadmium (Cd), lead (Pb) and zinc (Zn), are important environmental pollutants, particularly in urban areas with high anthropogenic pressure. The uptake and accumulation of Cd, Pb and Zn in vegetables (Amaranthus hybridus L.) grown in the valley bottom soils of some cities in southwestern Nigeria were investigated. The concentration of heavy metals in vegetable leaves ranged from 0.4 to 2.0 for Pb (CV, 33), 0.38 to 1.20 for Cd (CV, 25) and 8.2 to 30.4 for Zn (CV, 33). In the vegetable stems, the concentration ranged from 0.8 to 2.6 for Pb (CV = 33), 0.6 to 2.5for Cd (CV, 22) and 11.4 to 18.9 for Zn (CV, 35). Concentration of metals in vegetable roots ranged from 2.2 to 5.1 for Pb (CV, 33), 1.4 to 4.9 for Cd (CV, 22) and 10.2 to 29.0 for Zn (CV, 35). Transfer factors (TF) were in the range of 0.22 and 3.00, with Cd having the highest TF of 3.00. Estimated intake vegetables in mu g day(-1) ranged from 72 to 82 for Cd, 69 to 120 for Pb and 105 to 200 for Zn. The intakes were above the recommended minimum risks levels. Potential risks, particularly for Cd and Pb intake, exceed the daily requirement for consumers of the leafy vegetable at all the sites. The apparent influence of anthropogenic inputs from the cities to these valleys was reflected by the higher concentrations than the reference location. Food quality assurance systems in vegetables grown in urban valley bottoms need to comply with the world standard on heavy metal concentration.