The organic complexation of trace metals in estuarine waters of Galveston Bay: The importance of reduced sulfur species

A series of laboratory studies and field investigations were carried out to elucidate the importance of organic complexation of trace metals in Galveston Bay Estuary by reduced sulfur species. The estuarine distribution of trace metals appears to be controlled by the cycling of thermodynamically unstable reduced sulfur species, such as glutathione, present in Galveston Bay estuarine waters at nanomolar concentrations.; Sensitive methods were developed for the analysis of dissolved sulfides and thiols by using high performance liquid chromatography (HPLC). Glutathione (GSH) was the most abundant thiolic compound in filter-passing fraction (<0.45 mum). Its concentrations ranged from 0.23 to 6.23 nM. Chlorophyll-normalized concentrations of phytochelatin-2 (PC2) were observed to be as high as 6.3 mumol/g chl a in Galveston Bay. The thiols appeared to be produced in situ by phytoplankton, and total reduced sulfur species in the filter-passing fraction also exhibited a linear relationship with chlorophyll a.; Differential Pulse Cathodic Stripping Voltammetry (DPCSV) employing ligand competition by catechol was used to study the organic complexation of copper. Greater than 99.9% of the filter-passing Cu was bound by organic ligands in the estuarine waters of Galveston Bay. The average value of conditional stability constants, given as log K', for the filter-passing fraction was 12.4 +/- 0.3, and was higher than that obtained (11.2 +/- 0.3) for the ultra-permeate fraction (<1kDa). The concentration of the free ionic Cu species was 4 orders of magnitude lower than that of total Cu (2.27--12.89 nM). Total reduced sulfur can account for almost all of the Cu complexing ligands in Galveston Bay estuarine waters. Reduced sulfur species appeared to be important metal complexing ligands in controlling trace metal speciation of Cu, Zn, Ni, Cd and Pb in estuarine waters of Galveston Bay.