Evaluation on trihalomethane formation potentials of dissolved organic matter using the dissolved organic carbon fractionation method.

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A steady increase bas been observed in dissolved organic matter (DOM) in several lakes, such as Lake Biwa ; this may be a new type of lake water pollution. The accumulation of DOM in lake presents a serious challenge for drinking-water management since DOM is a major precursor of trihalomethanes (THMs) produced during chlorination in water treatment. Aquatic humic substances (AHSs) have been reported to be the major THM precursor in natural waters. However, it is rarely the case that AHSs were appropriately isolated from natural waters and subsequently their THM formation potentials were measured. Besides, non-AHS DOM, the remaining after AHSs separation, has never been evaluated for its THM formation potentials. Therefore, evaluation on the characteristics of THM formation potentials of DOM in lake water is urgently needed.The objectives of this study were : to develop a method by which DOM is separated into well-characterized macro-fractions based on the separation conditions of AHSs ; and to measure and evaluate THMFP of DOM, AHSs and non-AHSs fractions in Lake Kasumigaura, the second largest lake in Japan.The major findings in this study were as follows : (1) hydrophilic acids were predominant over AHSs (AHSs are hydrophobic acids) ; and (2) hydrophilic fractions ( = hydrophilic acids + bases + neutrals ) were significantly greater in THM formation potential as μmole THM formed per liter than AHSs, which has been considered the major THM precursor in natural waters. These findings clearly suggest that hydrophilic DOM be more important than AHSs in terms of THM precursors in lake waters.