UPTAKE AND ELIMINATION OF RESIN ACIDS AND PHYSIOLOGICAL-RESPONSES IN RAINBOW-TROUT EXPOSED TO TOTAL MILL EFFLUENT FROM AN INTEGRATED NEWSPRINT MILL

The effects of thermomechanical pulping effluents from an integrated n ewsprint mill were tested on rainbow trout (Oncorhynchus mykiss). Cont inuous-flow exposures under laboratory conditions were conducted at th ree dilutions (1:200, 1:400, and 1:1,000) for 8 weeks, followed by a 4 -week recovery period. Sublethal effects were assessed using physiolog ical and biochemical parameters including liver histology, hematology, serum biochemistry, and hepatic enzyme assays. Exposure was verified by analyzing water column, fish bile, and fish tissues for resin-acid concentrations. The effluent was found to be lethally toxic to rainbow trout within 3 to 4 weeks at a dilution of 1:200. Resin-acid concentr ations in bile, muscle, gill, and liver showed a clear-cut positive do se response. However, relatively few responses and changes in the phys iological parameters analyzed were found when comparing exposed and re ference fishes. The small differences in physiological parameters betw een the reference group and an exposure group (1:400) after a 4-week r ecovery period show that the observed responses were reversible. It is note worthy that the difference between the lowest acutely toxic conc entration and the concentration at which only slight physiological res ponses occurred was very narrow for this effluent.