表观分子量和腐殖酸或富里酸的存在是有机前体的性质之一，这些前体可能是在爱荷华河水样中观察到的三卤甲烷水平的季节性模式的原因。pH值和温度等环境条件似乎不是那么重要的因素。该研究还涵盖了科拉维尔油井，改变了氯化点，以及THM的太阳效应。包括23个参考表格和图表。

Apparent molecular weight and the presence of humic or fulvic acids are among the properties of organic precursors that may be responsible for seasonal patterns in trihalomethane levels observed in Iowa River water samples. Such environmental conditions as pH and temperature appear to be less important factors. The study also covers the Coraville well, altering the point of chlorination, and solar effect of THM. Includes 23 references tables, graphs.