The importance of TOC as an indicator of organic compounds in public waters

COD ( Mn ) is used as an indicator of organic compounds in public waters. Analytical methods for evaluating COD ( Mn ) are simple but entail several problems, such as oxidation rate, and are therefore doubted as appropriate indicators of organic compounds in public waters. In this research, we prepared various aqueous solutions of saccharides and/or amino acids and measured COD and TOC simultaneously. The measured values of TOC were close to the theoretical value for both compounds, and almost all organic carbons in each solution were detectable by TOC equipment. On the other hand, the COD oxidation rate in both the saccharide and amino acid solutions decreased according to the increase in the solutions ’ concentration, and there were also significant differences in the decomposition rate in each compound. The relationship between field data on COD and TOC in Shinji and Nakaumi lakes may be approximated by a quadratic expression, but the approximated curve did not pass the original point. This result indicates that there are some organic compounds that can be decomposed by TOC equipment but not by COD analytical methods, and the decomposition of COD was insufficient in high concentrations in environmental water. Therefore, we consider COD not to be an appropriate indicator of the organic compounds in public waters; instead, TOC should be used.