The interaction of heavy metals with urban soils: sorption behaviour of Cd, Cu, Cr, Pb and Zn with a typical mixed brownfield deposit Julita Markiewicz-Patkowska, Andrew Hursthouse * , Hanna Przybyla-Kij Division of Chemistry and Chemical Engineering, School of Engineering and Science, University of Paisley, Paisley, PA1 2BE, UK Received 4 June 2004; accepted 22 September 2004 Available online 27 October 2004 Abstract This study investigated the sorption characteristics and release of selected heavy metals (Cd, Cu, Cr, Pb and Zn) from a typical urban soil material from a derelict brownfield site in Western Scotland, UK. The study aimed to evaluate contaminant interactions with an urban substrate, comprising a mix of mineral soil and residue materials (e.g. brick, concrete, wood). This type of material has received little consideration in the literature to date. Soil samples were subject to a sequence of test involving batch equilibration and dynamic leaching, in single (non-competitive) and multi-element (competitive) solutions. The batch experiments were carried out in unadjusted and close to soil field pH conditions (pH 2 and 7, respectively). The equilibrium adsorption capacity for heavy metals was measured and extrapolated using the Langmuir isotherm. The parameters of the isotherms x m (the maximum amount adsorbed per unit mass of adsorbent (mg/g)) and b (adsorption constant (mce:sup>/ce:sup>/g)) were calculated for Cd, Cu, Cr, Pb as single-element and multi-element solutions. The adsorption from the single-element solution was more effective than adsorption under multi-element conditions, due to competitive effects. For example, the adsorption of copper from a single-element solution was over four times greater than for a multi-element solution. In the case of Cr and Zn, migration of metal from soil to solution was observed. Adsorption capacity at pH 2 followed the order CrNCuNPbNCd and at pH 7 CdNZn, with precipitation affecting Cu and Pb behaviour. During the column leaching experiment, most of the heavy metals were irreversibly bound to the soil, but in the case of Cr some movement from soil into solution was observed. The results also showed that Cd, Cu, Pb and Zn were removed from the solution and adsorbed on the soil. No significant difference in the metal removal from single- and multi-element solutions was observed. Overall, the urban residue behaved in a similar manner to mineral soils despite a significant component of anthropogenic solid materials. D 2004 Elsevier Ltd. All rights reserved. Keywords: Heavy metal mobility; Urban soil; Adsorption; Isotherm model; Groundwater contamination 1. Introduction The ground making up surface deposits in urban environments represents a complex mixture of natural parent materials and residues from the continued use and reuse of sites for human activity (Hollis, 1991). Urban soils have received little attention as a functional medium in the urban ecosystem, beyond the identification of contaminated sites and specific programmes to mitigate risks posed by the contaminants (Hursthouse, 2001; Pollard et al., 2001). As a result of the dynamic nature of human interactions with soil, the redevelopment and reuse of urban space often results in the addition of materials from a wide variety of sources with correspondingly diverse physical and chemical properties (Hollis, 1991). The common result of human activity is to increase the soil pH through the addition of building rubble which includes cement, concrete, brick, structural metallic components, wood and a variety of other wastes (Bridges, 1991; Rosenbaum et al., 2003). This complex substrate continues to support urban development, but in order to devise more sustainable 0160-4120/$ - see front matter D 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.envint.2004.09.004 * Corresponding author. Tel.: +44 141 848 3213; fax: +44 141 848 3204. E-mail address: andrew.hursthouse@paisley.ac.uk (A. Hursthouse). Environment International 31 (2005) 513 – 521 www.elsevier.com/locate/envint