Effects of pulp and paper mill effluents on fish immune defence

Abstract

Discharges from pulp and paper mills cause a marked contamination in recipient waters. A variety of biological effects in fish have been associated with exposures to bleached kraft mill effluents (BKMEs). Lately emphasis has been placed on the development of tests in which fish serve as sentinel animals or biomarkers of immunotoxicity in contaminated waters. In order to study the effects of BKMEs on fish immune defence, a panel of assays was developed for roach (Rutilus rutilus). The fish were challenged by immunising and the numbers of antigen-specific antibody-secreting cells (ASC) in lymphoid organs and blood were enumerated, and the levels of the antigenspecific antibodies in the circulation were determinated. In addition, immunoglobulin-secreting cells (ISC), the concentration of immunoglobulin and mitogen driven proliferation of lymphocytes in vitro were assayed. Furthermore, phagocytosis and migration of leukocytes were studied. The antibody-mediated immunity of roach was suppressed after exposure, both on-site in a contaminated lake and in an aquarium, to BKME from a mill with elemental chlorine/ chlorine dioxide (C/D) bleaching. Exposure to diluted untreated bleach liquor from C/D process suppressed immunoreactivity more than liquors from elemental chlorine-free (ECF) or totally chlorine-free (TCP) processes. Primary-treated and also secondary-treated BKME from a mill using ECF /TCF bleaching affected immune parameters of fish. Sex-related differences were evident in certain immune functions. Response to immunisation proved to be a sensitive indicator of effects of BKMEs on fish immune system. The results indicate that BKMEs are potentially immunotoxic in fish. Recent changes in pulping and bleaching processes have resulted in less immunomodulatory effects suggesting lower toxicity.