A COMPARISON OF THE RESULTS OF FRESH-WATER AQUATIC TOXICITY TESTING OF PULP AND PAPER-MILL EFFLUENTS

Freshwater short-term chronic toxicity tests were conducted quarterly on samples from pulp and paper mills under Cycle I of Canada's Environ mental Effects Monitoring program. The toxicity tests included the 7-d ay Ceriodaphnia dubia partial life-cycle test for survival and reprodu ction, the 7-day rainbow trout (Oncorhynchus mykiss) embryo viability test, and the 72-hr Selenastrum capricornutum algal growth inhibition test. All three tests were performed on a routine basis with few failu res. The responses of the different species were generally not correla ted, suggesting that they responded to different constituents in the e ffluents. On a statistical basis, the algal test exhibited the greates t sensitivity, followed by the trout embryo and Ceriodaphnia tests. In general, the no-observable effect concentrations (NOECs) were lower t han the corresponding IC25 estimates. Due to variability between sampl es from each mill, it was not possible to distinguish between differen t mill production processes with respect to their effect on toxicity. In general, mills that treated their effluent using aerated stabilizat ion basins exhibited less toxicity than other treatment types. However , this observation is preliminary and also affected by variability in test results and limited sample size. Overall, the results suggest tha t toxicity tests have a useful role in identifying toxicity in these e ffluents and that Toxicity Identification Evaluations should be conduc ted to identify the cause of toxicity so that treatment and/or source control can be initiated as appropriate. (C) 1997 IAWQ.