Trihalomethanes carcinogenicity

Free chlorine is highly reactive and relatively unstable. Utilities using free chlorine for disinfection have been known to use secondary chlorination stations to maintain residual chlorine concentrations in the potable water distribution system as regulated by the Clean Water Act (CWA). One of the key concerns in using free chlorine for disinfection is that, under certain conditions, free chlorine may react with organic substances in water to form carcinogenic trihalomethanes (THMs) (1,2). 

A disadvantage of chlorine is that reactions with organic matter, particnlarly hnmic materials, produce carcinogenic trihalomethanes snch as chloroform and bro-moform. Advantages of chlorine are that the compound... 

Chlorine dioxide is fast replacing aqueous CI2, particularly in pulp and paper manufacture, because the reaction of CIO2 with organic materials does not appear to form carcinogenic trihalomethanes (THMs) as side-products and because CIO2 is 10... 

Chlorine dioxide has been used widely in Europe since the early 1940 s as a drinking water disinfectant. More recently the USA has suggested the use of chlorine dioxide to reduce the formation of chloro-organic compounds particularly chloroform and other trihalomethanes (THM s) which are known carcinogens(7). 

Dunnick JK, Melnick RL. 1993. Assessment of the carcinogenic potential of chlorinated water experimental studies of chlorine, chloramine, and trihalomethanes. J Nad Cancer Inst 85(10) 817-822. 

There is no clear epidemiological evidence for the carcinogenicity of chlorodibromomethane in humans. However, a number of studies suggest an association between chronic ingestion of trihalomethanes in chlorinated drinking water and increased risk of bladder or colon cancer. These smdies cannot provide information on whether any observed effects are due to chlorodibromomethane or to one or more of the hundreds of other by-products that also are present in chlorinated drinking water. 

Khudoley, V.V., Gvildis, V.Y. Pliss, GB. (1989) Identification of some trihalomethanes in drinking water and assessment of their toxicity, mutagenicity, and carcinogenicity. Vopr. Onkol., 35, 837-842 (in Russian)... 

Reactions between aquatic HS and halogen-based oxidants, during water chlorination process, can lead to the formation of trihalomethanes, with potential carcinogenic effects. Carvalho et al. (2004) investigated reactions of tropical aquatic fulvic acids (AFA) with chlorine and formation of trihalomethanes through fluorescence spectroscopy. 

Formation of trihalomethanes. Reactions of chlorine with organic compounds such as fulvic and humic acids and humin produce undesirable by-products. These by-products are known as disinfection by-products, DBFs. Examples of DBFs are chloroform and bromochloromethane these DBFs are suspected carcinogens. Snoeyink and Jenkins (1980) wrote a series of reactions that demonstrate the basic steps by which chloroform may be formed from an acetyl-group containing organic compounds. These reactions are shown in Figure 17.4. 

Tiihalomethane Formation, Trihalomethanes have the general form CHXa where X can be Cl, Br, or I. CHCI3, chloroform, is of particular interest because it is a suspected carcinogen. The health effects of the other species are unknown. A series of reactions demonstrating the basic steps by which chloroform may be produced during water treatment is as follows ... 

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