LONG-TERM MIGRATION OF METALS AT HISTORICAL SMELTING SITES

The vertical migration of metals in soils and rocks is assessed at 3 h istorical Pb smelters ranging in age from ca. 600 to ca. 1800 a. Core samples were taken through contaminated soils into the underlying rock s and analysed for trace elements by ICP-AES. Surface soils contain hi gh levels of metals, particularly Pb which often exceeds a concentrati on of 1%. Of the total amount of Pb and Zn present in contaminated soi ls, only relatively small amounts appear to be in a readily mobile for m. Lead concentrations in heavily contaminated horizons were too high to be controlled entirely by exchange reactions. It is suggested that the metal is also present occluded in slag particles, precipitated as insoluble compounds and specifically adsorbed to soil constituents. Th e low Pb mobility in soils is also related to the elevation of pH in c ontaminated soils by the release of Ca compounds from the slag wastes during weathering. The rate of vertical migration of Pb varies with ro ck type with sandstone being greater than limestone which is greater t han a clay/sandstone matrix. (C) 1996 Elsevier Science Ltd