GENOTOXICITY OF KRAFT PULP SPENT LIQUORS FROM DIFFERENT TYPES OF CHLORINATION PROCEDURES

The genotoxicity of spent liquors from kraft softwood and hardwood pul p bleaching processes was studied using the Ames Salmonella test and t he SOS chromotest. The induction of micronuclei, in vivo, was assayed in bone marrow erythrocytes of B6 mice treated with softwood first chl orination stage spent liquor. The softwood bleaching process used a co mbination of Cl-2 and ClO2 at the first chlorination stage. During the study the amount of free chlorine at the first chlorination stage in the softwood bleachery was gradually decreased, although the amount of active chlorine remained the same. Enzymatic bleaching was also used in a softwood process together with chlorine (Cl-2 + ClO2). The hardwo od bleaching plant used only ClO2 at the first chlorination stage. A d ecrease in genotoxicity, corresponding to the decrease in Cl-2, was ob served in the Ames Salmonella assays of the softwood bleaching plant e ffluents. A similar decrease was observed in the SOS chromotest. The h ighest decrease in mutagenic activity was observed when enzymatic blea ching was used together with chlorine.