Mobility of Cd and Cu in formulated sediments coated with iron hydroxides and/or humic acids: A DGT and DGT-PROFS modeling approach Y. Nia a,b , J.-M. Garnier c,⇑ , S. Rigaud c , K. Hanna d , P. Ciffroy a a EDF, R&D Division, Département Laboratoire National d’Hydraulique et Environnement, 6 Quai Watier, 78401 Chatou, France b Cemagref, UR MALY, 3bis quai Chauveau, CP220, F 69336 Lyon Cedex 09, France c CEREGE, Université Paul Cézanne, UMR 6635 CNRS, BP 80, F 13545 Aix en Provence, France d Ecole Nationale Supérieure de Chimie de Rennes, UMR 6226 CNRS, Avenue du Général Leclerc, 35708 Rennes Cedex 7, France article info Article history: Received 28 March 2011 Received in revised form 25 August 2011 Accepted 25 August 2011 Available online 10 October 2011 Keywords: Formulated sediments Metal mobility DGT-PROFS and DIFS model Humic acids Iron hydroxides Aging effects abstract The diffusive gradients technique in thin films (DGT) was used to investigate the kinetic resupply of Cd and Cu to pore water from the solid phase. For the sake of simplification, experiments were performed using formulated sediments that differed in the presence or absence of humic acids (HA) and/or of iron hydroxides (i.e., goethite and ferrihydrite). The effects of the time after the contamination of the solid phase (aging effect) on formulated sediments that were coated with goethite and HA and spiked with Cd were also evaluated. Kinetic DGT results were interpreted using the newly developed, multi-compart- mental model DGT-PROFS. Due to Cu humate formation, the addition of HA slightly increased the Cu concentration in the pore water independent of the effect of the iron hydroxide coating on the formulated sediments and slightly decreased that of Cd. The impact of 8–190 d of aging resulted in a significant decrease in the Cd concen- tration of the pore water over an increasing incubation time. Modeling our results with DGT-PROFS led to the following conclusions concerning the impact of HA and iron hydroxides on Cd and Cu availability. First, in the presence of HA and absence of iron hydroxides, Cd is associated mainly with weak sites, while Cu is bound to strong sites. Similarly, in the presence of both iron hydroxides and HA, Cu appeared to be more heavily associated with the strong sites than did Cd. When the incubation time increased from 8 to 190 d, a proportion of Cd initially adsorbed onto weak sites transferred to the strong sites, suggesting that the adsorption of Cd on sediments is controlled partially by slow kinetic processes. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Predicting the dynamics of metals in the particle/pore water interface of sediments is an important task, as this interaction partly controls their subsequent bioavailability to detrital and de- posit-feeding benthic organisms. These dynamics are governed by surface adsorption–desorption reactions in the particulate phase and are influenced by several physico-chemical properties of the sediment, including the redox conditions. Working with natural sediment makes it difficult to identify and quantify the controlling factors of these adsorption–desorption reactions. Indeed, natural sediments of appropriate quality may not be avail- able throughout the period of experimental tests at all. In addition, indigenous organisms and the possible presence of trace elements that are not targeted in our study might influence the experimental results. Instead, working on formulated sediments can help to overcome the limitations that are generally encountered when investigating natural systems, as it is easier to control the physico-chemical characteristics during experimental procedures. Obviously, it must be kept in mind that the spectrum of compo- nents in formulated sediments is not as comprehensive as those found in natural sediments. Therefore, this work investigated three of the predominant controlling factors on formulated sediments spiked with our desired metals. Iron oxides and hydroxides are ubiquitous in soils and sedi- ments, and they are important components that influence the mobility of various elements. In subsurface soils and sediments, iron oxides generally do not occur as homogeneous assemblages or individual phases. Frequently, the iron hydroxides are present as coatings (i.e., ferrihydrite, goethite and lepidocrocite) on silica sand or silicate clay (Nachtegaal and Sparks, 2004). These compo- nents have a high specific surface area and are able to sorb both metals and organic compounds (Dzombak and Morel, 1990, Randall et al., 1999; Weng et al., 2006). The iron oxides have dif- ferent adsorption capacities according to differences in their 0045-6535/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2011.08.045 ⇑ Corresponding author. Tel./fax: +33 442971539. E-mail address: garnier@cerege.fr (J.-M. Garnier). Chemosphere 85 (2011) 1496–1504 Contents lists available at SciVerse ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere