Development of the method for environmental assessments based on the recognition of the correlation between the speciation of trace metals and the response by living organisms

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At the early stage of this project fundamentals of the trace metal speciation were investigated and the method for adsorptive collection with Calcein-Blue has been established . Using this method, metal ions were determined sensitively and the limit of detection for cadmium and lead ion were 0.05 and 0.04nM,respectively. For various fresh water samples, the concentrations for above metal ions were directly determined to be 0.2-4 nM with great ease. Secondly, to know each concentration for labile and inert complexes, dissolved organic compounds have to be decomposed before measurements. When the concentrations of metal ions are very low, the decomposition process have to be done under non-contaminated condition. We developed the decomposition method of UV-irradiation with low pressure mercury lamp. With this method , interfering compounds for electrochemical measurements, such as aromatic compounds, humic acids, amino acids, etc, could be decomposed successfully under non-contaminated c … More ondition. Further, we tried to investigate to make the physico-chemical standard to understand the response of living organisms to various metal complexes. Humic acid was represented as the ligand in natural waters. To know the complexing capacity, c_<L1>, and the conditional stability constant, K'_<ML1>, using adsorptive voltammetry, various c_<L1> could be obtained under various values for detection window, logalpha_<ML2>, depends on the ligand for adsorptive collection and its concentraion. For nickle ion, when logalpha_<ML2> was 4.73,5.93 and 6.73 at pH 8.5, c_<L1> was determined to be 14.1,8.7 and 8.3 nM/ppm, and logK'_<ML1>, was 12.2,13.6 and 14.5, respectively. As increasing logalpha_<ML2>, c_<L1> was decreased and logK'_<ML1> was increased. This indicates the functinal groups in humic acids have wide range of ability for coodination. At this stage it has been suggested the possibility that, with logalpha_<ML2>, the response of living organisms to metal ion could be recognized by generalized numerical values. Less