Leaching of Potentially Toxic Metals (PTMs) from Two Nigerian Clays and Related Clay Pottery Used Locally as Foodwares

Abstract

There is presently lack of data on composition of potentially toxic metals and their leaching from clay based foodwares into food. Therefore, in present study we evaluated the leaching of cadmium, chromium, copper, manganese, nickel, lead and zinc from raw clays and traditional clay pots from two locations, Ara-Ekiti, Ekiti State and Kono-Boue, Rivers State in Nigeria. Samples were digested with aqua regia and analysed using atomic absorption spectrometry and also with energy dispersive X-ray fluorescence. Tap water set at different temperatures (27°C and 100°C) and pH values (4.2 and 9.2) were used to leach the pots. The pH of the raw clays ranges from 2.08-6.50. The order of concentrations is Fe>Mn>Pb>Zn>Ni>Cr>Cu>Cd for both clays and this was consistent with the XRF data. The results from this study indicate that Cd, Cr, Cu and Pb were not in leachable forms in clay pots. The clay pots indicated varying leachability for Fe and Mn. The concentration ranges of Fe and Mn leached were 0.16-8.37 ppm and 0.08-10.00 ppm, respectively. In all cases the Kono-Boue pots indicated more leached concentrations of metals than Ara-Ekiti pots. It is essential to assess traditional clay pots for leachability of xenobiotics.

Effect of pH on the Leaching of Potentially Toxic Metals from Different Types of Used Cooking Pots

“…Aleksanyan et al, [32] reported the tendency of Fe to leach at near neutral to neutral pH conditions. The Concentration of Zn was higher at pH 5 than at pH 7, this varying trend in concentration of Zn leached at the different pH conditions was also recorded by Boisa et al [31]. Pb was not detected at all pH conditions.…”

“…The concentration of Fe gradually increased from pH 3 to 5 and at pH 6 it decreased and increased at pH 7. Boisa et al, [31] observed that the concentration of Fe leached upon exposure of Ara-Ekiti clay pot to water of Acidic pH, Neutral pH, alkaline pH were (1.15 mg/L 0.16 mg/L, and 0.08 mg/L respectively). Aleksanyan et al, [32] reported the tendency of Fe to leach at near neutral to neutral pH conditions.…”

“…The high level of Fe recorded in this study may be attributed to the availability of the metal in the earth's crust. Soils from Nigeria are known to be rich in iron [31,33] and the pot used was made in Nigeria.…”