The Formation of Trihalomethanes.

As a result of the trihalomethanes issue, the significance of natural aquatic humus in drinking water has increased considerably. In 1974 Rook1 published an investigation conducted at the Rotterdam water utility which showed haloforms at significant levels immediately following chlorination. Later that year Bellar, Lichtenberg, and Krone2 reported significant levels of organohalides in some US drinking waters. Both discussions argued that the halogenated organics found were the result of action of chlorine on naturally colored waters. Principal among the compounds found were the trihalomethanes, especially chloroform. In 1975 Rook3 gave a more complete presentation of the various factors influencing the formation of trihalomethanes, leaving little doubt that they resulted from the action of chlorine on natural organics. Later that year EPA presented the results of the National Organics Reconnaissance Survey (NORS)4 showing that THMs could be found in almost every finished water but only occasionally in raw water supplies. In 1976 the National Cancer Institute5 published results showing that at high doses chloroform, the most common THM, could cause cancer in rats. This was soon followed by an FDA ban'* on the use of chloroform as an additive in the preparation of food or drugs, and now the water industry faces a proposed EPA regulation7 designed to limit the long-term average exposure of the public to THMs via the drinking water supply. This article summarizes the information presently available on the factors influencing the THM reaction. First, a brief discussion of the character of natural aquatic humus is in order.