Assessment of the genotoxic potential of pulp mill effluent using bacterial, fish and mammalian assays

Abstract

Extracts of bleached kraft mill effluent (BKME) have been shown to contain mutagenic activity and to induce biochemical responses in fish, such as increased activity of the mixed-function oxygenase (MFO) enzyme system. Recent work has shown that Ames-positive substances in BKME are direct-acting mutagens, and that the majority of mutagenic activity is extracted by XAD-4 and XAD-8 resins and eluted by aqueous solutions of sodium hydroxide (NaOH) or methanol (MeOH). In this study, the genotoxic potency of BKME extracts was further assessed using a bacterial (Umu-C) genotoxicity assay, an in vivo hepatic micronucleus assay with trout, and an in vitro assay for DNA strand breaks with Chinese hamster lung V79 cells and two mouse liver cell lines (TIB 73 and TIB 75). The majority of mutagenic substances from the filtered effluent were adsorbed by XAD-4 and XAD-8 resins and DEAF cellulose, and were effectively removed from these adsorbents by NaOH or McOH. The mutagenic fraction extracted by XAD-4 and eluted by McOH consistently induced DNA strand breaks in the assays with V79, TIB 73, and TIB 75 cells. Activity of these fractions was not altered by the addition of rat liver microsomes or dialysed liver cytosol from various vertebrate species. The fractions extracted by XAD-8 and eluted with NaOH, and extracted by XAD-8 and eluted with McOH did not induce DNA damage in assays with V79 cells. The genotoxic responses indicated direct acting genotoxicity to mammalian and fish cells and correlates with bacterial mutagenicity, and that these bioassays are complementary when applied to screening of BKME samples for genotoxic potential.