Influence of hydrology on heavy metal speciation and mobility in a PbeZn mine tailing Elza Kova ´cs a, * , William E. Dubbin b , Ja ´nos Tama ´s a a Department of Water and Environmental Management, Center of Agricultural Sciences, University of Debrecen, H-4015 Debrecen, P.O. Box 10, Hungary b Department of Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5BD, UK Received 15 December 2004; accepted 8 August 2005 Variable hydrology influences heavy metal speciation and mobility, and the formation of neutralization zones, in a PbeZn mine tailing. Abstract Among the inorganic toxicants of greatest concern in mine tailings, Pb, Zn, Cu, Cd and As figure prominently due to their abundance and potential toxicity. Here we report on their biolability and solid-phase speciation in two sediment cores subject to variable hydrological regimes at an abandoned pyritic mine tailing. The oxic conditions of well-drained sediments induced pyrite oxidation and the subsequent liberation of H C , SO 4 2ÿ and considerable quantities of Fe(III), which precipitated as goethite. Solubility of Pb, Zn, Cu and Cd was closely coupled to pH and goe- thite presence. Metal lability was particularly low in zones of neutralization, formed by the accumulation of calcite, first carried then deposited by percolating waters in both saturated and unsaturated cores. We conclude that differential hydrology induces variable heavy metal speciation and biolability in PbeZn mine tailings, and suggest that site-specific risk assessments must account for past and present hydrological regimes. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Mine tailing; Heavy metal; Speciation; Hydrology; Oxidation 1. Introduction The oxidative weathering of pyrite (FeS 2 ) in pyritic mine wastes contributes to the formation of acid mine drainage waters and is therefore the dominant process controlling heavy metal mobility and speciation (Garcı ´a et al., 1996; Hayes and Traina, 1998; Lacal et al., 2003). Pyrite oxidation is frequently mediated by O 2 dissolved in the waters bathing the mineral surface. The process is complex, as it involves numerous bio- geochemical pathways which vary both temporally and spatially. Factors such as pH, pO 2 , pyrite morphology and spe- cific surface area, presence or absence of sulfide- and iron- oxidizing bacteria (e.g. Leptospirillum ferrooxidans, Thiobacillus ferrooxidans, Thiobacillus thiooxidans) and clay minerals, as well as various hydrological factors, determine the rate and ex- tent of pyrite oxidation (Sengupta, 1993; Evangelou and Zhang, 1995; Jenkins et al., 2000; Johnson, 2003). Oxidative weathering of pyritic ore ultimately releases H C , which, in the absence of buffering agents, increases the solubility of heavy metal- containing minerals, and also increases aqueous Fe 3C , which can facilitate the oxidative dissolution of many heavy metal sulfides (Salomons, 1995; Fowler and Crundwell, 1998, 1999; Puura and Neretnieks, 2000). As pyrite oxidation is a surface- controlled reaction, cubic pyrite, with its smooth and minimal surface, is less reactive than the higher surface area conglomer- itic and framboid forms (Moses et al., 1987; Stro ¨mberg and Banwart, 1999). The acid-buffering capacity of a pyritic mine tailing is largely controlled by its constituent aluminosilicates (e.g. muscovite, illite), carbonates (e.g. calcite, dolomite, Sr-, Fe- and Mn-carbonates), and Al-, Fe- and Mn-hydroxides, which * Corresponding author. Tel.: C36 52 508 456; fax: C36 52 508 455. E-mail address: ekovacs@gisserver1.date.hu (E. Kova ´cs). 0269-7491/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2005.08.043 Environmental Pollution 141 (2006) 310e320 www.elsevier.com/locate/envpol