Studies on the Biochemical Interactions of Chlorine Dioxide: an Alternative Drinking Water Disinfectant (Chloroform).

Abstract

Chlorination of drinking water leads to the formation of trihalomethanes (chloroform, bromodichloromethane, dibromochloromethane and bromoform) and various halogen by-products, that may be carcinogenic. Therefore, chlorine dioxide (ClO(,2)) which can minimize the formation of these by-products is being considered as a very attractive alternative disinfectant. The effect of ClO(,2) and its end products (ClO(,2)('-) and ClO(,3)('-)) on the formation of chloroform was investigated in vivo following one year treatment with the Cl-compounds in drinking water. Chloroform concentration in rat blood was decreased after administration of the Cl-compounds. The effect of ClO(,2) on chloroform formation was further studied using sodium citrate as an organic substance. When citrate was reacted with HOCl, (beta)-ketoglutaric acid, mono-, di- and trichloroacetones were produced as reaction intermediates and chloroform as the final product. When ClO(,2) was substituted for HOCl, neither chloroform was formed nor citrate concentration was changed. Furthermore, chloroform formation was inhibited by ClO(,2) in the presence of HOCl and citrate. This inhibition of chloroform formation by ClO(,2) is related to the reaction between ClO(,2) and (beta)-ketoglutaric acid to form malonic acid. Chlorine dioxide also oxidizes other intermediates such as mono- and dichloroacetones to acetic acid. Chlorine dioxide (100 mg/l) inhibited ('3)H-thymidine incorporation into the DNA of rat testes and small intestine. A decrease in the thymidine incorporation was also observed in the testes of the 100 mg/l ClO(,2)('-) group, whereas the incorporation was increased in liver treated with 10 and 100 mg/l ClO(,2)('-). Teratogenic studies of chlorine dioxide demonstrated that ClO(,2) at 10 mg/l in drinking water is relatively harmless to rats when fed to pregnant dams. At 100 mg/l ClO(,2), however, some types of embryotoxic effects such as decreases in the numbers of implants and live fetuses and an increase in fetal weight were observed. Chloride is a major metabolite of ClO(,2), ClO(,2)('-) and ClO(,3)('-). Therefore, the kinetics of ('36)Cl('-) were studied in rats following the oral administration of Na('36)Cl. The half-life for ('36)Cl('-) absorption was 19.2 hr, while the elimination half-life was 51.9 hr. The distribution study showed that radioactivity was high in blood, kidney and lung, whereas the lowest activity was observed in fat. The excretion of chloride occurred entirely by the kidney.