In vivo detection of genotoxicity in waste water from a wheat and rye straw paper pulp factory

The genotoxicity of waste water from a wheat and rye straw paper pulp mill was investigated by in vivo genotoxicity tests using micronuclei and sister chromatid exchange as endpoints. Micronuclei were studied in mussels ( Mytilus edulis) and sister chromatid exchange in fish ( Nothobranchius rachowi). The paper mill uses chlorine dioxide for bleaching, and the bleaching effluent as well as the combined effluent, i.e. the mixture of all waste water streams, were both tested. Both effluents induced micronuclei and sister chromatid exchanges, although the presence of toxic substances could mask the expression of genotoxicity in some cases for both test systems. The study revealed that genotoxins are produced in the chlorine dioxide bleaching process as well as in the pulping process, indicating also genotoxic activity of non-chlorinated compounds. In contrast to previous studies in which mutagenicity was determined with bacterial assays, genotoxins were only associated with chlorinated organics from bleaching with chlorine and failed in detecting genotoxins in chlorine dioxide bleaching effluents. Aquatic in vivo genotoxicity tests are sensitive and efficient systems and seem to be a promising tool in effluent testing.