EVALUATION OF BLEACHED KRAFT MILL PROCESS WATER USING MICROTOX(R), CERIODAPHNIA-DUBIA, AND MENIDIA-BERYLLINA TOXICITY TESTS

To determine whether a 7- to 10-d embryo toxicity/teratogenicity test with the inland silverside fish, Menidia beryllina, is a sensitive ind icator for evaluation of bleached kraft mill effluents, we compared th is test with the Microtox(R) 15-min acute toxicity test and the Ceriod aphnia dubia 7-d chronic toxicity test. Water samples used in each tes t were collected from three areas in a bleached kraft pulp and paper m ill using a 100% chlorine dioxide bleaching process: 1) river water pr ior to use in the mill; 2) the combined acid/base waste stream from th e pulping process prior to biological treatment in the aerated stabili zation basin (ASB); and 3) the effluent from the ASB with a retention time of approximately 11 d. Relative toxicity determined by the three tests for each water sampling location was compared. All three toxicit y tests were predictive indicators of toxicity; however, the C. dubia and M. beryllina tests were the more similar and sensitive indicators of toxicity. Process water (ASB influent) prior to biological treatmen t in the ASB was toxic at all concentrations using the Microtox(R) and C. dubia tests. The fish embryo test showed no toxicity at 1% concent rations, slight toxicity at 10%, and acute toxicity at the 100% ASB in fluent concentration. Tests with biologically-treated ASB effluent ind icated a substantial reduction in observed toxicity to Microtox(R) bac teria, C. dubia, and M. beryllina. No toxic responses were observed in any test at a 1% ASB effluent concentration which was the approximate effluent concentration in the receiving river following mixing. No re lationship was found among any toxicological response and effluent lev els of adsorbable organic halides, polychlorinated phenolic compounds, 2,3,7,8-tetrachlorodibenzo-p-dioxin, 2,3,7,8-tetrachlorodibenzofuran, total suspended solids, color, chemical oxygen demand, or total organ ic carbon.