Experimental study of cadmium interaction with periphytic biofilms O.S. Pokrovsky a, * , A. Feurtet-Mazel b , R.E. Martinez c , S. Morin d , M. Baudrimont b , T. Duong b,e , M. Coste d a Géochimie et Biogéochimie Experimentale, UMR 5563, CNRS-OMP-Université Toulouse, 14 Avenue Edouard Belin, 31400 Toulouse, France b Université de Bordeaux 1, CNRS, UMR 5805 EPOC, Place du Dr Peyneau, 33120 Arcachon, France c Center for Applied Geosciences, Universitat Tuebingen, Sigwartstrasse 10, Tuebingen 72076, Germany d Unité de Recherche Réseaux, Epuration et Qualité des Eaux REQE, Cemagref, 50 Avenue de Verdun, F-33612 Cestas Cedex, France e Institute of Environmental Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet Road, Cau Giay, Hanoi, Viet Nam article info Article history: Received 31 August 2009 Accepted 24 December 2009 Available online 6 January 2010 Editorial handling by D. Fortin abstract This study addresses the interaction of Cd with natural biofilms of periphytic diatoms grown during dif- ferent seasons in metal-contaminated and metal-non-contaminated streams, along a tributary of the Lot River, France. Specifically, it aims to test whether the biofilms from contaminated sites have developed a protective mechanism due to high Cd exposure. Towards this goal, reversible adsorption experiments on untreated biofilms were performed in 0.01 M NaNO 3 with a pH ranging from 2 to 8, Cd concentration from 0.5 to 10,000 lg/L and exposure time from 1 to 24 h. Two types of experiments, pH-dependent adsorption edge and constant-pH ‘‘Langmuirian”-type isotherms were conducted. Results were ade- quately modeled using a Linear Programming Model. It was found that the adsorption capacities of nat- ural biofilm consortia with respect to Cd do not depend on season and are not directly linked to the growth environment. The biofilms grown in non-contaminated (4.6 ppb Cd in solid) and contaminated (570 ppb Cd in solid) settings exhibit similar adsorption capacities in the Cd concentration range in solu- tion of 100–10,000 lg/L but quite different capacities at low Cd concentration (0.5–100 lg/L); unexpect- edly, the non-contaminated biofilm adsorbs approximately 10 times more Cd than the contaminated one. It is therefore possible that the strong low-abundant ligands (for example, phosphoryl or sulfhydryls) are already metal-saturated on surfaces of biofilm grown in the contaminated site whereas these sites are still available for metal adsorption in samples grown in non-contaminated sites. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Potentially harmful metal pollution in freshwater environments brings about significant accumulation of metals in various compo- nents of trophic chains, among which periphytic biofilm communi- ties attract great attention from researchers due to their ability to serve as good pollution indicators or biomonitors (i.e., Hill et al., 2000; Holding et al., 2003; Fuchs et al., 1997; Lowe et al., 1996; Schorer and Eisele, 1997; Le Faucheur et al., 2005). There is persistent industrial pollution of the French hydrosys- tems (e.g., Lot, Gironde) and estuaries of the Atlantic coast by var- ious toxic elements (Zn, Pb, As, Hg and, in particular, Cd), deriving from the middle part of the Lot River. Therefore, significant research efforts have been devoted to the study of Cd migration, speciation and biouptake along a pollution gradient in a pilot site of the Lot River basin downstream to the Gironde estuary in SW France (e.g., Andrès et al., 1999; Gold et al., 2003; Morin et al., 2007, 2008). The environmental setting of the hydrosystem has allowed the development, along the pollution gradient, of diatom biofilms (Morin et al., 2008). These phototrophic biofilms are likely to exert major control on Cd concentration in the river and its diur- nal pattern (Beck et al., 2009; Tercier-Waeber et al., 2009). Metal adsorption and assimilation by aquatic microorganisms is considered as one of the major process controlling the fate of metal pollutants in the environment. It is known that the first step in metal uptake by biota is the adsorption of aqueous ions or com- plexes on external layers of the cell wall. As a result, numerous studies have been devoted to quantification and thermodynamic modeling of reversible metal adsorption on cell walls of aquatic microorganisms (Fein et al., 1997; Boyanov et al., 2003; Ngwenya et al., 2003; Burnett et al., 2006; Guiné et al., 2006, 2007). Among different groups of plankton and periphyton, bacteria, green algae and diatoms have received significant attention, and today, a comprehensive picture of metal bonding to the cell walls of most model aquatic microorganisms is available (Fein et al., 2001; Martinez et al., 2002, 2004; Borrok et al., 2004, 2005; Gélabert et al., 2006, 2007, and references therein). Of the different metals, Cd has received maximum attention over the last 10 a. However, in natural river bed systems, bacteria and algae rarely occur as 0883-2927/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.apgeochem.2009.12.008 * Corresponding author. Tel.: +33 561332625; fax: +33 561332650. E-mail address: oleg@lmtg.obs-mip.fr (O.S. Pokrovsky). Applied Geochemistry 25 (2010) 418–427 Contents lists available at ScienceDirect Applied Geochemistry journal homepage: www.elsevier.com/locate/apgeochem