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The direct examination of biologically active Cu in seawater

University of British Columbia

An analytical technique for the differentiation of biologically active copper (Cu) in seawater was developed. The procedure involves passing a seawater sample through an ion exchange resin of the sulponate type until complete breakthrough of metal ion is achieved. The sorbed Cu is then eluted and its total concentration is determined by anodic stripping voltammetry. Comparison with Cu adsorption from standard seawater samples of similar composition, pH, and ionic strength yields a Cu equivalent measurement that is related to the free cupric ion activity of the sample. Since the cupric ion is believed to be the toxic form of the metal, the Cu equivalent measurement can be related to the biologically active fraction of Cu. The measurement of biologically active Cu by the resin technique was verified by comparing the analytical results with results from phytoplankton bioassays. Tests were first conducted in artificial seawater that had its chemistry well defined and where model organic ligand (EDTA, NTA, histidine and glutamic acid) were used to control the speciation of the metal. In the experiments using the organic ligands EDTA, NTA, or glutamic acid added to Cu spiked artificial seawater, a strong relationship between the Cu equivalent values and growth rates of the bioassay organism was found (r=0.92). However, in experiments with histidine, this relationship was much weaker and was attributed to the adsorption of positively charged Cu-histidine complexes onto the resin. The adsorption of these complexes results in overestimating the amount of biologically active Cu present in the sample. The few studies on the electrochemical nature of organic complexing agents in seawater suggests, however, that most are negatively charged. Thus the technique would be suitable in many seawater systems. The analytical and bioassay techniques were then applied to natural seawater samples collected from five depths in a local fjord. A discrepancy was found between some of the bioassay and resin test results. However, the discrepancy was attributed to a physiological Cu-Mn interaction in the bioassay organism and not to a problem with the resin technique.

Text

2010-05-03

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http://hdl.handle.net/2429/24386

Oceanography

University of British Columbia

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