Fractionation of tropical soilborne heavy metals - Comparison of two sequential extraction procedures
Doelsch, E.; Moussard, G.; Saint-Macary, H.
Geoderma 143(1-2): 168-179
ISSN/ISBN: 0016-7061 DOI: 10.1016/j.geoderma.2007.10.027
We compared Cr, Cu, Ni and Zn fractionation patterns in four typical soils naturally containing high levels of these elements on the tropical volcanic island of Reunion. Two sequential chemical extraction procedures were used: the modified four-stage BCR procedure (subsequently called mBCR) and the modified six-stage Geological Survey of Canada procedure (subsequently called mGSC). The results obtained by these two procedures highlighted some similarities. With both approaches, exchangeable fractions were the smallest fractions with respect to the four heavy metal (HM) distributions (<5% of the total HM quantity), and residual fractions had the highest Cr, Cu, Ni and Zn contents (39.1-97.9%) in the four soils. In contrast, we noted differences in HM fractions bound to organic matter. These differences could be explained by the different reagents and extraction sequences implemented in the two procedures. However, the most marked difference in the results obtained by the two procedures concerned the HM fraction bound to oxyhydroxides, despite the fact that the same reagent was used (hydroxylammonium chloride). Our results revealed that the mBCR procedure underestimated the proportion of HM bound to this fraction. The mGSC procedure therefore seems more suitable for analysing tropical soils which typically contain high levels of Fe and Mn oxyhydroxides.