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 indicator for evaluation of bleached kraft mill effluents, we compared this test with the Microtox(R) 15-min acute toxicity test and the Ceriodaphnia dubia 7-d chronic toxicity test. Water samples used in each test were collected from three areas in a bleached kraft pulp and paper mill using a 100% chlorine dioxide bleaching process: 1) river water prior to use in the mill; 2) the combined acid/base waste stream from the pulping process prior to biological treatment in the aerated stabilization 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 toxicity 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 treatment 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% concentrations, slight toxicity at 10%, and acute toxicity at the 100% ASB influent concentration. Tests with biologically-treated ASB effluent indicated a substantial reduction in observed toxicity to Microtox(R) bacteria, 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 relationship was found among any toxicological response and effluent levels 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 organic carbon.