MOBILIZATION OF HEAVY-METALS AND ARSENIC IN POLLUTED WETLAND SOILS AND ITS DEPENDENCE ON DISSOLVED ORGANIC-MATTER

The wetland soils of the Mulde river in the industrial district of Bit terfeld-Wolfen (Germany) are highly contaminated with heavy metals and arsenic. We studied the mobility of accumulated heavy metals and arse nic and the influence of dissolved organic matter (DOM) on element mob ility. Undisturbed soil cores were taken from five different sites to represent a wide range of heavy-metal contamination, soil properties a nd dissolved organic carbon (DOG) concentrations. The acid-soluble con centrations (mostly equal to the total content) were up to 1100 mg kg( -1) for Zn, 800 mg kg(-1) for Cr, 364 mg kg(-1) for Cu, 265 mg kg(-1) for As and 37 mg kg(-1) for Hg, depending on the sampling site. Percol ation experiments using small lysimeters with undisturbed topsoil core s illustrated a considerable mobilization of Zn, Cd, Cu, Cr and Hg, de pending on soil properties. Up to 80 mu g 1(-1) Cd, 8 mg 1(-1) Zn, 130 mu g 1(-1) Cr, 160 mu g 1(-1) Cu and 7 mu g 1(-1) Hg were detected in the soil percolates. Arsenic mobilization was low. The concentration of Cr, Hg, Cu and As in the soil percolates was positively correlated with DOM. Besides the element content (mobile or acid-soluble), soil p H and soil characteristics describing the soil potential for heavy-met al adsorption (clay, oxides, cation exchange capacity), the DOC concen tration in the soil solution should be known to access the potential m obilization of Hg, Cr, Cu and As. In contrast, Cd and Zn mobilization depends on soil pH and mobile element content, but not on DOM. Additio nal studies on two soil profiles (down to 1.5 m) confirmed the translo cation of heavy metals from the highly contaminated topsoil into deepe r soil horizons and into the groundwater and the influence of DOM as r evealed with the percolation experiment. Our results also showed that DOM is of minor importance on the mobilization of heavy metals in soil s with a low soil pH (< 4.5). (C) 1998 Elsevier Science B.V.