Objective To study the DNA damage induced by dichloroacetic acid(DCA) and trichloroacetic acid(TCA) which are from drinking water disinfection by-products. Methods V79 cells and hepatocytes of mice were treated with DCA and TCA for 1 hour and then were tested by comet assay. After stained by EB, tail length of the cells were observed and counted under the fluorescence microscope. Results Both DCA and TCA could result in the increasing of average tail length of the treated cells whether they were V79 cells or hepatocytes of mice and the dose-response relationships were seen. Conclusion Both DCA and TCA can cause DNA damage of mammalian cells and this may be related to the carcinogenic mechanism. DCA and TCA belong to genetic carcinogens.

Objective To develop an un_fluorescent staining method in Comet Assay. Methods Some special un_fluorescent DNA staining methods, Feulgen, Methyl Green, Stains_all and Silver_Stain were tested in Comet Assay and the comparison studies with EB stain were carried out. Results Among the stain methods tested, just the silver_stain could give a satisfactory effect: legible, ease to judge the stained area of the comets head and tail, permanent, sensitive, could make little segment of DNA be stained, which couldnt be stained by EB stain, the length of comets head and tail, were over 2 times of that of EB stain, safety and economical. Conclusion The silver_stain method discarded the defects of EB stain, so that it could replace EB stain and make comet assay possible to be extended.

Objective To detect DNA lesions induced by complex pollutants existing in environment using the technique of randomized terminal linker,dependent PCR (RDPCR). Methods SD rats were treated with organic concentrate by injection i.p., DNA were extracted from rat's liver, kidney, lung and leucocytes, then RDPCR was used to detect DNA damage of exon 7 of p53 gene. Results Organic concentrate of drinking water could make rat's genomic DNA broken. Hybridization bands were found in liver and kidney tissues after RDPCR, none in blood and lung tissues. Conclusion Organic concentrate of drinking water can cause the DNA lesions of exon 7 of p53 gene and the major target organs are liver and kidney. The technique of RDPCR can be used to detect DNA damage induced by complex environmental pollutants.

Objective To assess the effect of chloramine disinfection on the formation of drinking water disinfection by-products(DBPs )and their mutagenicity.Methods The bacterial indices,chloroform and carbon tetrachloride content in the finished water samples using liquid chlorine and chloramine disinfection respectively were determined in August,2001(plentiful water season)and in March,2002(low water season).The mutagenicities of organic extracts from the water samples were tested using Ames test.The levels of DBPs and the mutagenic activities of water samples treated with different disinfection methods were compared.Results The total count of bateria and coliform bacteria were0/ml and0/L respectively at free chlorine con-centration of about 1mg /L in the chloraminated drinking water,which decreased81%-84%compared with those of the chlori-nated drinking water samples.The carbon tetrachloride concetration were all

Objective To detect the DNA damage of ras gene induced by organic concentrate of drinking water using randomized terminal linker-dependent PCR. Methods The single-stranded probes of exons of rass gene in human were prepared. The TK6 cell was treated with organic concentrate of drinking water, then genomic DNA was amplified by RDPCR and detected by Southern hybridization with the probe. Results The clear hybridized band induced by organic concentrate of tap water could be seen in the position of exon 2 of N-ras gene,but in those of exon 1 of N-ras, exon 1 and 2 of H-ras gene it could not be detected. No hybridized bands induced by organic concentrate of raw water were seen in any position. Conclusion The organic concentrate of drinking water can cause the DNA damage of ras gene and it is considered as a kind of genotoxic substance.

liver cells.Repair test showed that liver cells had the strongest repair ability,spleen cells were the second and kidney cells had no repair ability nearly within 2 h incubation. Conclusion The tissue cells had a big difference to oxidative damage and repair ability and comet assay could be used as detection of DNA oxidative damage and repair ability in exo_chemicals.