The determination by atomic absorption spectroscopy of the iron, nickel, copper, zinc and cadmium content of two cultivars of white yam (Dioscorea rotundata Pair) and their source soil from three farms, and also of random samples of the cultivars from five geographical areas in Kaduna and Plateau states of Nigeria, is reported. The analyses show all the metals except Fe to be in trace amounts in the tissues of both cultivars; the barks contain two to four times more. The iron content was found to be about 20 times higher in the bark than in the tissue. Less than 0.7% of the metals present in the soil could be extracted with NH,NO, solution. Yam bark, which contains reasonable amounts of the above metals, could be useful as cattle feed. Yam tissue, having a high content of Z n compared with Cd, could be recommended for the diet of hypertensive patients.
The mineral content of white yam (Dioscorea rotundata Poit), an important staple foodstuff in the tropics, appears to have been little studied. There have been a few reports on the ash, calcium, sodium and potassium contents of yam (Schroeder 1976; Bonire et a1 1990) but none on the Fe, Ni, Cu, Zn and Cd content of any variety of yam.
Many minerals are essential both for the anatomical build-up and the physiological functioning of the human body (