A system which enabled the simple exchange of reagents , during the electrochemical determination of chromium(III) or (VI) was developed. This media exchange system was used to investigate the effect of pH on the complexation and pre-concentration of chromium separately from the production of the electrochemical signal. While the complexation and preconcentration of chromium in fresh or sea water was slightly enhanced at pH 5, compared with pH 6.2, the electrochemical signal was markedly increased, being up to 10 times higher at the lower pH. The addition of a column containing basic alumina, into the media exchange system, led to the development of a method for the selective determination of chromium(VI) and total chromium. The system had a detection limit of less than 1 gg 1-1, and was capable of determining chromium(VI) and total chromium in a sample in twenty minutes. The system was used on-board a boat to monitor the chromium levels in the Tees estuary. In this exercise, an unidentified interferent prevented levels from of chromium being measured. However, a procedure for overcoming this was developed, and an approach for investigating the contaminant investigated. Using electrochemical methods for the determination of chromium(III) and (VI), the toxicity of these chromium oxidation states to three aquatic organisms, at varying salinities have been determined. A further study explored the impact of organic chelators on the toxicity of both chromium oxidation states to one of the organisms, Tisbe batagliai. The experiments demonstrated that chromium(III) was initially more toxic than chromium(VI). However with increasing time the toxicity of chromium(VI) increased over that of chromium(III). It was also shown that at increased salinity there was a reduction in the toxicity of chromium(III). The effect of the organic ligands, EDTA, NTA and citric acid, was to reduce substantially the toxicity of chromium(III), but enhance that of chromium(VI) to Tisbe.

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