Distribution and partitioning of trace metals (Cd, Cu, Ni, Pb, Zn) in Galveston bay waters
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The distribution of several trace metals has been studied in the surface waters of Galveston Bay, Texas, in order to assess the impact of complexation with organic and reduced sulfur species on the partitioning of trace metals between particulate and aqueous species. The distribution of trace metals in the filter-passing fraction <0.45 m) showed two apparent trends: (1) the carrier phase metals (i.e., Fe and Mn) were largely removed in the Anahuac Channel region, which was dominated by direct Trinity River inputs; (2) the other metals (Cd, Cu, Ni, Pb, and Zn) showed non-conservative mixing behaviour, with midsalinity maxima, within the estuarine regions of Galveston Bay. The average percentage of metal in the filter-passing fraction, as compared to the total metal load, decreased in that region from 95% to 9% in the order Ni > Cu>Cd>Zn>Pb>Mn>Fe, while an increasing trend was found in the same sequence for the acid-leachable fractions. The average values of Kdl, the particle-water partition coefficient, expressed as the ratio of weak acid-leachable paniculate fractions to the filter-passing fractions, increased in the order Ni < Cu < Cd < Zn < Mn < Pb < Fe. This sequence is consistent with the relative importance of particulate transport of these trace metals from estuaries to coastal oceans. The observed decrease of Kdl of Cu with increasing concentrations of suspended particulate matter (SPM), also called the "particle concentration effect" (PCE), can be eliminated when the free ionic, rather than the total concentration of Cu in the filter-passing fraction is used for calculating this ratio. A particle concentration effect would be expected if the binding of these trace metals by particles is mediated by solution (i.e., filterpassing) phase ligands. Complexation of Cd, Cu, Ni, Pb, and Zn with reduced sulfur species could be one of the causes for the observed linear correlations between metals and reduced sulfur species in both the filter-passing and filter-retained fractions. Significant correlations between Cu in the weak acid-leachable fraction and chlorophyll a (Chl a) concentrations suggest biological mediation of Cu uptake into the particulate fraction. 2002 Elsevier Science B.V. All rights reserved.
