ABSTRACT
The total effluent from all 15 Finnish pulp mills was biotested with five laboratory-scale sublethal and lethal toxicity tests. The biotests were chosen so as to represent different types of organisms and impact mechanisms: immobilization of the water flea Daphnia magna (24-h EC50), inhibition of light emission of the luminescent bacterium Vibrio fischeri (15-min EC50), growth inhibition/stimulation of the green alga Selenastrum capricornutum (96-h EC50), early life stage development of the zebra fish Brachydanio rerio and MFO activity (EROD) in isolated hepatocytes from rainbow trout (Oncorhynchus mykiss). The effluent samples were collected during normal production periods (1 to 30-d pooled samples) and frozen daily. Thirteen mills had biological effluent treatment (activated sludge or aerated lagoon) and two mechanical treatment systems.
In general the biologically treated bleached kraft mill effluents showed little or no toxic impact on test organisms regardless of mill technology. None of the effluents was toxic to Daphnia even at a 100% concentration. Three effluents were clearly toxic to bacteria and two showed some toxic effects which may have been due to the interfering effect of effluent color. All the effluents stimulated algal growth in some of the test concentrations, and three also caused growth inhibition at rather high concentrations. None of the secondary treated effluents at 100% concentration affected the survival of zebra fish embryos and larvae, whereas the mechanically treated effluents were toxic. Six of the secondary treated effluents had a slight effect on zebra fish hatching by shortening the hatching time, while the mechanically treated effluents prolonged the hatching time. Only two of the effluents exhibited a slight induction in EROD activity, but seven effluents inhibited the activity.
