Trihalomethane in Drinking Waters: A Statistical Study
The formation of trihalomethane compounds (T.H.M.C.) in drinking water after chlorination is a cause of considerable health concern. This paper deals with a mathematical-statistical analysis of data obtained from a collaborative T.H.M.C. monitoring programme on several water distribution systems in Italy, carried out jointly by a number of Italian Public Institutions. Levels of T.H.M.C. were determined at different intervals after chlorination treatment. As far as levels of T.H.M.C. determined 1–3 hours after chlorination are concerned, a statistically-significant increase of chloroform (CHCl3), dichlorobromomethane (CHCl2Br), and dibromo-chloromethane (CHClBr2) levels (as an average, respectively ≃300%, ≃200%, ≃30%), was detected. Levels of CHCl3, CHCl2Br and CHClBr2 in chlorinated waters appeared correlated with those of Total Organic Carbon (T.O.C) in water before chlorination as well as with those of water residual chlorine (Fig. 1). Water temperature was positively related to formation of CHCl3 and CHCl2Br. Finally, an increase of water pH also resulted in an increase of CHCl3. The formation of the three above organochlorinated compounds appeared to follow a substantially identically pattern. As far as the levels of T.H.M.C. determined 24 and 72 hours after the chlorination treatment, they were, as an average, 1.5–2.3 and 1.6–2.8 times higher, thus showing that formation of organohalogens takes place to a large extent within a short interval of the water treatment. A mathematical model of the T.H.M.C. formation was carried out (Fig. 2).
Key wordsTrihalomethane Drinking waters Mathematical model T.O.C. Chlorination Statistical analysis
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