CYTOGENETIC EFFECTS OF SOFTWOOD KRAFT PULP BLEACHING EFFLUENTS AND METHANESULFONYL CHLORIDE IN CHINESE-HAMSTER OVARY CELLS

The genotoxicity of effluents collected from a conventional 5-stage so ftwood kraft pulp bleaching process was studied in Chinese hamster ova ry (CHO) cells in vitro. Spent liquor from the first chlorination stag e (C/D), where elemental chlorine and chlorine dioxide had been used i n equal proportions, was shown to induce a dose-dependent increase in sister chromatid exchanges (SCEs) without metabolic activation (4-h tr eatment), with a maximum increase of 1.6 times over the control level at 204 mu 1/ml; this dose also induced 15.5- and 20.5-fold increases i n cells with chromatid-type chromosomal aberrations after 4-h and a 20 -h treatment, respectively. Another C/D stage spent liquor from a proc ess where the ratio of elemental chlorine and chlorine dioxide had bee n 9:1 produced a 40.5-fold elevation of cells with chromatid-type aber rations at 204 mu 1/ml (20-h treatment). This sample clearly increased chromosomal aberrations also when tested as a concentrate (4-h treatm ent), which showed that the observed clastogenicity was not unspecific ally due to the relatively large volumes used in the treatments with t he unconcentrated liquors. In general, the use of rat liver S9 mix red uced the genotoxicity of the spent liquors. The results agree with ear lier findings on the Salmonella mutagenicity of the same C/D samples: both the prokaryotic and eukaryotic assays showed a reduction in genot oxicity when the amount of elemental chlorine in the bleaching process was reduced. An effluent sample collected from the alkaline stage of the process was not clastogenic with or without metabolic activation. Methanesulfonyl chloride, a new compound identified in bleaching plant air, was found to be induce chromosomal aberrations in the presence o f S9 mix.