IN-VIVO GENOTOXICITY OF DICHLOROACETIC ACID - EVALUATION WITH THE MOUSE PERIPHERAL-BLOOD MICRONUCLEUS ASSAY AND THE SINGLE-CELL GEL ASSAY

Chlorination is a widely used method for disinfection of drinking wate r supplies. Reaction of chlorine with naturally present organic compou nds con result in toxic by-products. One major disinfection byproduct from the chlorination of drinking water is dichloroacetic acid (DCA). This chemical has been shown to be carcinogenic in rodents, yet little genotoxicity data are available to assess the possible role of DNA an d/or chromosomol damage in this process. We have used the peripheral b lood erythrocyte micronucleus (MN) assay and the alkaline single cell gel electrophoresis (SCG) technique to investigate the in vivo genotox icity of DCA in bone marrow and blood leukocytes, respectively. The MN assay detects chromosome breakage and/or malsegregation, while the SC G assay detects DNA damage (e.g., single strand breaks, alkali-labile sites, crosslinking). Mice were exposed to this compound in drinking w ater, available ad libitum, for vp to 31 weeks. Our results show a sme ll but statistically significant dose-related increase in the frequenc y of micronucleated polychromatic erythrocytes (PCEs) after subchronic exposure to DCA for 9 days. In addition, at the highest dose of DCA t ested (3.5 g/l), a small but significant increase in the frequency of micronucleated normochromatic erythrocytes (NCE) was detected followin g exposure for greater than or equal to 10 weeks. Coadministration of the antioxidant vitamin E did not affect the ability of DCA to induce this damage, indicating that the small induction of MN by DCA was prob ably not due to oxidative damage. Based on the lock of any difference observed in the proportion of kinetochore-positive micronuclei between the treated and control animals, we interpret the induced MN as arisi ng from clastogenic events. The SCG technique suggested the presence o f DNA crosslinking in blood leukocytes in mice exposed to 3.5 g/l DCA for 28 days. These data provide evidence that DCA may be an extremely weak inducer of chromosome damage when provided to mice in drinking wa ter under conditions which lead to increased levels of tumors. (C) 199 6 Wiley-Liss, Inc.