COMPARISON OF CHEMICAL SPECIATION OF COPPER IN THE OOSTERSCHELDE AND WESTERSCHELDE ESTUARIES, THE NETHERLANDS

The aim of this investigation was to assess the chemical speciation of copper. Although the Cu concentrations in both the dissolved and part iculate phases differ strongly between the Oosterschelde (OS) and West erschelde (WS) estuaries, The Netherlands, the Cu content of the bival ve Macoma balthica from both sea arms is comparable. Therefore, chemic al speciation of Cu was examined during 1 year at Mo sites, one in eac h sea arm. Two dissolved organic ligand groups could be distinguished. For both sea arms, a relatively weak ligand group with logK'=9.27 and a mean ligand concentration of 250 neq Cu l(-1) was determined. Moreo ver, a relatively strong group was detected with logK'=13.04 and a mea n ligand concentration of 180 neq Cu l(-1) in the WS, and with logK'=1 3.7 and a mean ligand concentration of 48 neq Cu l(-1) in the OS. In b oth sea arms, the calculated free concentration of CU2+ is extremely l ow (<10(-14) M). The strong ligand group is related to salinity and to dissolved organic carbon (DOG) indicating that the river Scheldt and estuarine/marine DOC supply this material. The weak ligand group is re lated to salinity and marine chlorophyll a in the WS, and to DOC in th e OS. The regulating mechanisms of the distribution of Cu over the che mical species are different for the two sea arms. In the WS, there see ms to be no equilibrium between dissolved and particulate Cu. Hence th e free Cu concentration is determined by complexation with dissolved o rganic ligands. In the OS, adsorption on particulate organic matter is the key factor. It is even possible to make a good estimate of free C u in the OS if only dissolved and particulate Cu and POC are known. It is concluded that Macoma does not accumulate Cu from the dissolved ph ase since the free Cu concentration is too low; food must be the sourc e. Since desorption of Cu from particulate matter in the polluted WS i s slow in contrast to desorption in the relatively clean OS, kinetics of particulate Cu seem to be the reason for the relatively high Cu con tent of Macoma in the OS. (C) 1996 Academic Press Limited