EXTRACTION OF CHROMIUM, NICKEL AND IRON AND THE AVAILABILITY OF CHROMIUM AND NICKEL TO PLANTS FROM SOME SERPENTINITE-DERIVED SOILS FROM THE EASTERN TRANSVAAL AS REVEALED BY VARIOUS SINGLE AND SEQUENTIAL EXTRACTION TECHNIQUES

A distinct feature of certain plant species growing on serpentinite derived soils is their ability to hyperaccumulate heavy metals such as nickel (Ni) and chromium (Cr). This study was conducted to determine the availability of these heavy metals and their ease of extraction with various reagents. Various standard chemical reagents were used to extract Cr and Ni from nine different soils originating from two sites in the easter Transvaal, South Africa. In addition, the sequential extraction of Cr, Ni, and iron (Fe) was undertaken. Of all the extractants used 4M nitric acid was the most efficient. Acetic acid appeared to be the best single extractant for estimating plant available Cr on the basis of leaf concentration. Acetic acid, ammonium acetate, copper (II) chloride, EDTA and aluminium chloride appeared to be equally efficient for estimating plant available Ni. Oxidation of organic matter resulted in a higher recovery of Cr and Ni thus highlighting the importance of this fraction in immobilizing these elements. In general, samples with the highest acetate and DCB extractable Fe values coincided with those samples having the highest extractable Cr.