Processes controlling metal transport and retention as metal-contaminated groundwaters efflux through estuarine sediments Stuart L. Simpson a, * , Edward J. Maher a,b , Dianne F. Jolley b a Centre for Environmental Contaminants Research, CSIRO Energy Technology, Private Mailbag 7, Bangor NSW 2234, Australia b Department of Chemistry, GeoQuest, University of Wollongong, NSW 2522, Australia Received 8 March 2004; accepted 27 April 2004 Abstract Factors affecting the transport and retention of Cd, Cr, Cu, Ni, Pb and Zn in acidic groundwaters as they pass through estuarine sediments were investigated using column experiments. Acidic groundwaters caused the rapid dis- solution of iron sulfide (AVS) and other iron and manganese phases from sediments that are important for metal binding and buffering. Metal breakthrough to overlying water occurred in the order of Ni>Zn>Cd  Cu  Cr/Pb. Metal transport increased as the sediment permeability increased, reflecting the low resistance to flow caused by larger sand-sized particles and the decreased abundance of metal adsorption sites on these materials. Metal mobility increased as the groundwater pH decreased, as flow rate or metal concentrations increased, and as the exposure duration in- creased.GroundwaterCrandPbwerepromptlyattenuatedbythesediments,themobilityofCuwaslowanddecreased rapidly as sediment pH increased above 4.5, while Cd, Ni and Zn were the most easily transported to the surface sediments and released to the overlying waters. For groundwaters of pH 3, metal migration velocities through sandy sediments were generally 0.5–2% (Cr, Pb), 1–6% (Cu) and 4–13% (Cd, Ni, Zn) of the total groundwater velocity (9–700 m/yr). The oxidative precipitation of Fe(II) and Mn(II) in the groundwaters did not affect metal mobility through the sediments. The results indicated that the efflux of acidic and metal-contaminated groundwater through estuarine sediments would affect organisms resident in sandy sediments more greatly than organisms resident in fine-grained, silty, sediments. Crown Copyright Ó 2004 Published by Elsevier Ltd. All rights reserved. Keywords: Groundwater; Metals; Transport; Retention; Sediment 1. Introduction The efflux of acidic and metal-contaminated groundwater through surface sediments may threaten the integrity of many productive estuarine environ- ments. In Sydney Harbour, Australia, metal-contami- nated groundwater represents a challenge for sediment quality assessments in estuarine bays adjacent to industrial land. Metal contaminants of concern include chromium leaching from land in-filled with industrial waste, mercury near naval dock yards, and zinc from steel galvanising operations. Groundwater contaminants accumulated in surface sediments are a risk to many sediment-dwelling organisms that ingest sediment and detritus material (Wang and Fisher, 1999). Submarine groundwater discharges may increase the flux of metals from contaminated sediments to overlying waters and * Corresponding author. Tel.: +61-2-97106807; fax: +61-2- 97106837. E-mail address: stuart.simpson@csiro.au (S.L. Simpson). 0045-6535/$ - see front matter Crown Copyright Ó 2004 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2004.04.001 Chemosphere 56 (2004) 821–831 www.elsevier.com/locate/chemosphere