As a part of a National Pollutant Discharge Elimination System (NPDES) biomonitoring program a series of toxicity tests was conducted with process water from a chemical plant using Ceriodaphniu dubia and Pimephales promelas. There were marked differences among the two tested species. The acute (LC50) values from 96-h static toxicity tests with Pimephulespromelas were always lower (higher toxicity) than the values obtained from the invertebrate tests. The concentration of ammonia in the effluent, particularly its un-ionized form (250 mg NH,-N/L, which represents 0.7 mg NH,-N/L), was above the threshold concentration for most freshwater species and therefore was the primary suspect of the toxicity present in the effluent.Prior to initiation of the toxicity identification evaluation (TIE) program, chemical analyses that included measurements of inorganic and organic parameters were conducted with the effluent. During the TIE fractionation, a portion of the sample was purged with nitrogen to remove volatile organics, and a second portion of the sample was pressure-filtered through a 0.45-1.lm filter. Because toxicity equal to the whole sample was found in these fractions, a portion of the inorganic fraction was subfractionated into zeolite, clinoptilolite, activated carbon, pH-adjustment, aeration, and cation fractions. The results of these tests confirmed that ammonia played a role in the sample's toxicity. However, when ammonia was removed from the effluent sample, toxicity was still present. Next organic chemicals were fractionated as suspected sources of toxicity. At first, organics were removed from the effluent by passing the filtered sample over an XAD-resin column. Because a portion of the reconstituted organic fraction was toxic, the organic fraction was subfractionated further by extracting with dichloromethane at pH > 11, pH < 2, and pH 7.1. The dichloromethane extracts were toxic, whereas the aqueous portions were not toxic. The neutral extract, which was more toxic than the basic and acidic extract, was further fractionated by using HPLC. Seventeen HPLC fractions were isolated and tested for toxicity to determine which constituent(s) were responsible for the observed whole effluent toxicity.

As a part of a National Pollutant Discharge Elimination System (NPDES) biomonitoring program a series of toxicity tests was conducted with process water from a chemical plant using Ceriodaphnia dubia and Pimephales promelas. There were marked differences among the two tested species. The acute (LC50) values from 96‐h static toxicity tests with Pimephales promelas were always lower (higher toxicity) than the values obtained from the invertebrate tests. The concentration of ammonia in the effluent, particularly its un‐ionized form (250 mg NH4‐N/L, which represents 0.7 mg NH3‐N/L), was above the threshold concentration for most freshwater species and therefore was the primary suspect of the toxicity present in the effluent. Prior to initiation of the toxicity identification evaluation (TIE) program, chemical analyses that included measurements of inorganic and organic parameters were conducted with the effluent. During the TIE fractionation, a portion of the sample was purged with nitrogen to remove volatile organics, and a second portion of the sample was pressure‐filtered through a 0.45‐μm filter. Because toxicity equal to the whole sample was found in these fractions, a portion of the inorganic fraction was subfractionated into zeolite, clinoptilolite, activated carbon, pH‐adjustment, aeration, and cation fractions. The results of these tests confirmed that ammonia played a role in the sample's toxicity. However, when ammonia was removed from the effluent sample, toxicity was still present. Next organic chemicals were fractionated as suspected sources of toxicity. At first, organics were removed from the effluent by passing the filtered sample over an XAD‐resin column. Because a portion of the reconstituted organic fraction was toxic, the organic fraction was subfractionated further by extracting with dichloromethane at pH > 11, pH < 2, and pH 7.1. The dichloromethane extracts were toxic, whereas the aqueous portions were not toxic. The neutral extract, which was more toxic than the basic and acidic extract, was further fractionated by using HPLC. Seventeen HPLC fractions were isolated and tested for toxicity to determine which constituent(s) were responsible for the observed whole effluent toxicity.

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