Risk Assessment in Soils Developed on Metamorphic and Igneous Rocks Using Heavy Metal Sequential Extraction Procedure

Six areas developed on metamorphic and igneous parent materials were selected in Murcia Province (SE Spain), two from diabases, two from mica schist and two from andesites. Three of them potentially polluted by anthropogenic sources and the other three no polluted. One profile and 6 surface samples were collected from each one in order to identify the Pb and Zn concentrations bounded to different soil phases using sequential extraction and to verify if the existent differences in Pb and Zn concentrations from soils developed on the same parent material are the consequence of the anthropogenic activities, or natural geochemical contributions. The results showed that the soils that present higher total Pb and Zn concentrations that come from anthropogenic sources registered higher percentages of these heavy metals in the most labile phases (exchangeable and organic matter bounded heavy metals). In addition, the carbonate phase is also an important sink of metals, however in soils developed on metamorphic and igneous rocks this constituent is very low due to organic and exchangeable phases that retain these metals. This behaviour increases the risk of mobility to trophic chain to plants and microorganisms that may absorb these metals.