Mixed-function oxygenase enzyme responses and physiological disorders in fish exposed to kraft pulp-mill effluents: a hypothetical model

Three-spined stickleback, Gasterosteus aculeatus L. larvae and immature rainbow trout, Salmo gairdneri (Richardson) were exposed to six different bleached kraft-mill effluents (BKME) from mills using different bleaching sequences. The sticklebacks were exposed from the egg stage to age 5-months and the rainbow trout for 7 weeks. Effects on growth, mortality, liver-tissue structure, and parasite frequency were noted in the stickleback populations. These effects are combined with effects obtained on the mixed function monoogygenase (MFO), 7-ethoxyresorufin-o-deethylase enzyme (EROD) in the rainbow trout into a hypothetical model of BKME effects on fish. BKMEs are extremely complex mixtures of toxic and potentially toxic compounds. The relative concentrations of these compounds in BKMEs may vary and may thus induce different biological responses depending on the length of exposure, time of observation, and the degradability/lipophilic properties of substances. Due to its central role in detoxification of xenobiotic substances as well as in the transformation of endogenous substances such as hormones, the MFO-system is used to determine the effects of exposure to BKMEs. Effects on growth, liver structure, and diseases are described as secondary effects elicited by an affected detoxification system.