Bull. Environ. Contain. Toxicol. (1990) 45:399-407 9 1990 Springer-Verlag New York Inc, Environmental =.Contamination land Toxicology Toxicity Evaluation of the Proposed Secondary and the Primary Effluents Discharged to Massachusetts Bay Krzysztof M. Jop, 1 John W. Williams, 2 and Robert B. Foster1 lSpringborn Laboratories, Inc., 790 Main Street, Wareham, Massachusetts 02571, USA and 2Cosper Environmental Services, Inc., Eaton's Neck Rd., Northport, New York 11768, USA The discharge of industrial and municipal effluents into the nation's surface waters is regulated by the National Pollutant Discharge Elimination System (NPDES). The U.S. Environmental Protection Agency (EPA) released its "Policy for the Development of Water Quality-Based Permit Limitations for Toxic Pollutants" (EPA 1984) in which EPA addresses the control of toxic pollutants beyond technology-based requirements in order to meet water quality standards. To implement this policy, guidance was provided to the respective state and regional permit personnel in the EPA's "Technical Support Document for Water Quality-Based Toxics Control" (EPA, 1985). Both documents recommended that, where appropriate, permit limits based on effluent toxicity should be developed. An important aspect of EPA's policy is the use of effluent toxicity tests to determine if a discharge will likely have any adverse effect on representative species in aquatic environment. In 1986 EPA Region I issued a State Permit for the toxicity evaluation of effluents .discharged from Publicly Owned Treatment Works (PO-rW) and Combined Sewer Overflow (CSO) outfalls to Massachusetts Bay. MATERIALS AND METHODS The experimental pilot wastewater treatment pilot unit consisted of a bench- scale sequencing batch reactor in which both biological treatment and solid- liquid separation occured was constructed and operated in laboratory. The secondary effluent produced during the pilot plant operation was used for testing. Chlorination of the secondary effluent was completed by adding sufficient amounts of sodium hypochlorite 1000 parts per million (ppm) solution to obtain 1 mg/L total residual chlorine (TRC) concentration after the 40-minute contact period. Dechlorination of the secondary effluent was completed by adding sufficient amounts of metabisulfite solution that reduced TRC concentration to bellow detection limit. The effluent samples were collected from the Deer Island and the Nut Island wastewater treatment facilities. Two sets of 7-day samples were collected placed on ice and delivered to the Battelle Ocean Sciences laboratory in September 1987 (first set of effluent samples) and in October 1987 (second set of effluent samples). Each effluent sample was a 24-h composite, collected each day for 7 days either prior to or after chlorination at each treatment plant. A combined sample was prepared each day by combining a Send reprint requests to Krzysztof M. Jop at the above adress. 399