Marine Chemistry, 14 (1984) 201--212 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands 201 ORGANIC AND INORGANIC SPECIATION OF COPPER IN THE IRISH SEA CONSTANT M.G. VAN DEN BERG Department of Oceanography, University of Liverpool, Liverpool L69 3BX (Gt. Britain) (Received January 17, 1983 ; revision accepted August 22, 1983) ABSTRACT Van den Berg, C.M.G., 1984. Organic and inorganic speciation of copper in the Irish Sea. Mar. Chem., 14: 201--212. The metal complexing ability of surface water of the Irish Sea has been measured by the MnO2 adsorption method. In all samples strong copper-chelating compounds are present at concentrations of 60--150 nM, with conditional stability constants (log values) of 10.0--10.4. The concentrations of Cu, Pb and Cd in the samples are 16--39 nM, 1--7nM and 0.1--2nM, respectively; much less than the ligand concentrations. The organic compounds form complexes with 94--98% of dissolved copper, and therefore constitute the major form of copper in surface water of the Irish Sea. Recalculation of speciation of the inorganic fraction of copper in seawater reveals that the major complex ion is that of CuCO ° (60%), followed by CuOH + (16%) and Cu(OH) ° (16%). Complexes with borate ions form a small and rather insignificant fraction of 1%. INTRODUCTION The concentrations of trace metals in oceanic seawater are normally extremely low and can be determined directly only by electrochemical techniques unless some form of preconcentration is used. It is important, nevertheless, to investigate their speciation, as several trace metals are known to form complexes with inorganic and organic components of seawater. It is likely that complexation affects strongly the bioavailability of metal ions (Jackson and Morgan, 1978; van den Berg et al., 1979) as well as the removal of trace metals from the seawater column by adsorption on settling particles. Adsorption processes may be expected to suffer from competition from dissolved complexing agents, although in some cases surface adsorption may be enhanced by the presence of complexing material (Davis and Leckie, 1978). Seawater is a medium of very complex composition, but the concentration ratios of the major ions are constant. The concentrations of organic complexing ligands are very low, but their complexing ability should never- theless be investigated in this medium, without any alteration to the concentrations of either complexing ligands or competing ions as this may affect the distribution of metal ions over the various competing ligands in soriition. The separation of copper into organic and inorganic fractions has been 0304-4203/84/$03.00 © 1984 Elsevier Science Publishers B.V.