Organic complexation of copper in surface waters of Galveston Bay

The importance of colloidal ligands in the organic complexation of Cu was e lucidated in the estuarine waters of Galveston Bay by use of a number of in strumental techniques. Ultrafiltration was conducted to isolate the ultrape rmeate fraction from the filter-passing fraction and competitive ligand equ ilibration/adsorptive cathodic stripping voltammetry measurements were cond ucted by use of varying amounts of catechol as the competitive ligand. Grea ter than 99.9% of Cu was bound by strong organic ligands with log[K' (M-1)] values of 12.3 +/- 0.15 and 11.1 +/- 0.29 in the filter-passing and ultrap ermeate fractions, respectively. The concentrations of Cu complexing ligand s were lower in the ultrapermeate than in the filter-passing fraction, and the calculated K' values for the colloidal ligands (log K' = 12.9) were 60 times greater than those for the ultrapermeate fraction, suggesting that go od separation of the colloidal fraction during ultrafiltration was achieved . Total Cu concentrations in the filter-passing fraction ranged from 2.27 t o 12.9 nM and were fairly constant at salinity <20 but decreased at salinit y >20. The calculated free Cu concentrations (0.05-0.49 pM) showed an overa ll increasing trend with salinity, possibly resulting from decreasing conce ntrations of Cu complexing ligands toward the seawater endmember. The conce ntration of Cu complexing ligands (21-54 nM) in the estuarine regions of Ga lveston Bay was approximately equal to the concentration of total reduced s ulfur species (20-60 nM) in the filter-passing fraction, suggesting that re duced sulfur species could account for most of the Cu-complexing ligands in these waters.