Partitioning and distribution of dissolved copper, cadmium and organic matter in Mediterranean marine coastal areas: The case of a mucilage event Michael Scoullos a, * , Marta Plavs ˇic ´ b , Sotiris Karavoltsos a , Aikaterini Sakellari a a University of Athens, Department of Chemistry, Div. III, Laboratory of Environmental Chemistry, Zografou, Panepistimiopolis 157 71, Athens, Greece b RuCer Bos ˇkovic ´ Institute, Center for Marine and Environmental Research, P.O. Box 180, 10002 Zagreb, Croatia Received 10 December 2005; accepted 12 December 2005 Abstract Dissolved copper and cadmium partitioning and their interaction with organic matter were investigated in shallow coastal areas of the Aegean Sea (Eastern Mediterranean). The percentage of DGT-labile copper as for total dissolved copper ranged from 13 to 34% during summer and from 23 to 36% during winter, whereas the corresponding percentage for DGT-labile cadmium was higher in summer (38e68%), in comparison to winter (29e44%). The CCu was found to be 100e260 nM during summer while in winter the range was 42e430 nM. The corresponding CCd reached 27 and 45 nM, re- spectively. The mean TEP value in summer was high (208 mg/L xanthan equiv.), while in winter it reached 441 mg/L xanthan equiv., which indicates significant phytoplankton activity in winter, a feature occasionally observed in the stratified study areas after the breaking down of the thermo- cline/pycnocline, followed by consequent nutrient enrichment of the surface layers by nutrients accumulated in the sea bottom. A significant fraction of dissolved organic carbon (DOC) exhibited surface active properties and was determined as surface active substances (SAS) in mg/L eq. of nonionic surfactant Triton-X-100. Carbohydrates were also determined and they represented up to 33% of the DOC. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: copper; cadmium; complexation; organic ligands; TEP; mucilage; Aegean 1. Introduction The excretion of extracellular mucilage (mostly mono- and polysaccharides) by algae and bacteria may regulate nutrient and trace metal speciation and bioavailability (Leppard, 1997). The amount and composition of DOM could change rapidly in the case of phytoplankton blooms which may last only for a few days, but could influence the overall conditions for longer periods since DOC formation and accumulation can be substantial (Carlson et al., 1998). Concentrations of dis- solved carbohydrates are considerably higher during the peak of blooms (Baldi et al., 1997; Ciglene cki et al., 2003). Hydroxyl, carboxyl and sulfate groups in polysaccharides are strong ion-exchangers and therefore important metal com- plexing sites (Crist et al., 1990). Furthermore, organic matter in a gel phase is abundant and important in sedimentation processes and marine carbohydrate chemistry (Passow, 2002). Verdugo et al. (2004) suggest that the investigation of gels in the marine environment represents an important area of research due to their role in biogeochem- ical metal cycling. The present study concerns the chemical speciation and fractionation of copper and cadmium as well as of dissolved organic carbon (DOC), particulate organic carbon (POC), mono- and polysaccharides (MCHOs, PCHOs), surface active substances (SAS), chlorophyll a (Chl a) and transparent exo- polymer particles (TEP) under the conditions of a summer * Corresponding author. E-mail address: esakel@chem.uoa.gr (M. Scoullos). 0272-7714/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecss.2005.12.007 Estuarine, Coastal and Shelf Science 67 (2006) 484e490 www.elsevier.com/locate/ecss