Geochemical partitioning of potentially toxic metals in soils and sediments from the Anka area, north-western Nigeria

Abstract

The partitioning of Cr, Cu, Mn, Ni, Pb and Zn between different geochemical phases in soils and sediments from five artisanal mining contaminated villages in the Anka area, north-western Nigeria has been investigated. This is aimed at determining the ease with which these elements can be mobilized into the environment. Twenty five samples were subjected to sequential extraction procedures and the concentration of the elements in the exchangeable, carbonate and Fe/Mn oxides fractions determined using inductively coupled plasma-optical emission spectrometry. Total elemental concentration was measured by x-ray fluorescence spectrometry. The results show that the carbonate phase is the most geochemically significant in terms of the sequestration of majority of the elements, especially, Pb, Cu and Zn. This is followed by the Fe/Mn oxides and the finally the exchangeable fractions in that order. Generally, the lability of the elements was found to decrease in the order Pb > Cu > Zn > Mn > Ni > Cr, mainly controlled by the release of the elements from the carbonate and oxide phases. This indicates possible risk of mobilization of the elements under reducing, slightly acidic environmental conditions. In spite of the high concentration of the elements, especially Pb, Cu and Zn obtained in the carbonate and oxide fractions, less than 50 % of their total concentration is easily mobilisable. The remainder is held within less labile geochemical phase within the matrices. This further confirms that the sequential extraction protocols are better environmental assessment tools compared to determination of total concentrations alone. Remediation technologies aimed at reducing the acid susceptibility of these materials should be pursued in order to minimize the impact of the metals on the environment and health of the local population.