Sublethal effects of Eucalyptus-based pulp mill effluents on Tasmanian native fish

The effects of eucalypt-based pulp mill effluent on organisms in marine receiving waters are relatively unknown. A previous study by Munday et al. (1991) assessed the acute toxicity of the effluent discharged from Australian Paper's Burnie pulp and paper mill. However, at that time the mill was discharging up to 20% pine-based effluent. To obtain an accurate assessment of the current situation at the mill, which is now processing 100% eucalypt pulp, the acute toxicity of the Burnie mill effluent to Vibrio fisheri, Isochrysis galbana, Tetraselmis suecica, Nitzschia closterium and Artemia salina was calculated. The acute toxicity of the effluent to microalgae was determined for two reasons; microalgae form the base of the food chain and has been shown to be sensitive to simulated eucalypt-based pulp mill effluent (Stauber et al. 1994), also, as the microalgae formed the base of the food chain in the experiments discussed in Chapter 3, the sensitivity of the microalgae and the Artemia, which fed on the microalgae, to the effluent needed to be assessed. The results obtained were related to the constituents of the effluents with the main toxic property of the effluents being the pH. After the pH had been modified to that of seawater the effluents were less toxic. The effluents were not acutely toxic to single cell algae at the concentrations discharged into Bass Strait. When evaluating the effects of complex effluents such as eucalypt-based kraft pulp mill effluent the different routes of exposure must be considered. The contribution of dietary exposure as well as waterbome exposure needs to be taken into consideration as there has been much discussion in the literature about the extent of the influence of food chain bioaccumulation. To determine the significance of each route of exposure, and if any additive or synergistic effects of the routes occur, an experiment was designed to simulate effects of Burnie mill effluent in the environment. Common jollytails (Galaxias maculatus) were exposed to low levels (0.5%) of effluent via the food chain or via the water column or both food chain and water column. As biotransformation of toxicants occurs in the liver, this organ was analysed to detect any sublethal effects which may have been caused by exposure to the effluent. Significant increases in EROD ( ethoxyresorufin-0-deethylase) activity in fish exposed to the effluent by the combined routes were detected. However, no significant differences in EROD activity occurred between control fish and fish exposed to the effluent by only one route. The effects of the combined routes of exposure appeared to be synergistic rather than additive as a 3 - 4 fold increase in EROD activity was found in fish exposed to the effluent via both routes. This was supported by the increase in histological changes within the livers of fish exposed by the combined routes. Also, proliferation of rough endoplasmic reticulum within the hepatocytes of these fish as determined by transmission electron microscopy was an additional indicator of a sublethal response in fish receiving the effluent by the combined water column and dietary routes. An indirect ELISA to detect the presence of cytochrome P-4501A1 was performed but this method was not sensitive enough to detect effects of effluent exposure. As exposure to pulp mill effluent can have adverse effects on the livers of fish it follows that the reproduction of the fish may be affected, as this organ is involved in hormone metabolism essential to the reproductive processes. To evaluate this aspect of the sublethal effects of pulp mill effluent, Tasmanian blennies were collected from locations in Emu Bay then transferred to the University and maintained in equivalent concentrations of pulp mill effluent to those found in Emu Bay. The blennies then spawned and the resulting embryos were also maintained in the same effluent concentrations until hatching. The exposed blenny larvae were compared with control larvae and showed a significant decrease in length. The number of larvae per spawn and the quality of eggs was also significantly less in Emu Bay fish than control fish. No significant differences between the Emu Bay sites were found so that the incidence of sublethal effects in blenny larvae was not related to distance of blenny populations from the mill outfall. From the results of this series of experiments, simulating environmental exposure to the Burnie mill effluent, as discharged during 1994 - 96, it can be stated that levels of the effluent equivalent to those occurring in Emu Bay cause fish to exhibit minor changes in liver structure and ultrastructure, a slight increase in detoxification enzyme activity and a decrease in embryo / larval growth. These changes apparently do not severely affect the health of the fish. However, the effect of the effluent on reproduction is appreciable and would have a potential impact on the fish population dynamics.