Case study 6.9: Targeted ammonia toxicity identification evaluation strategy

Acute toxicity to Pimephales promelas was observed in a municipal effluent. Ammonia was identified as a suspect toxicant based on biomonitoring test results (greater toxicity to P promelas than to Daphnia pulex) and ammonia concentrations typically present in the effluent (20 to 30 mg/L total ammonia). An "ammonia characterization procedure" was applied to remove ammonia toxicity from the sample using 3 different manipulations: stripping, zeolite, reducing ambient pH. Residual toxicity that remained in samples after any manipulation would be interpreted as an indication of toxicants other than ammonia. Phase I TIE and follow-up procedures (e.g., Phase II TIE) would then be applied to manipulated sample that showed residual toxicity not attributable to ammonia. In this case study, each of several series of manipulations of toxic samples showed no residual toxicity in manipulated samples that was attributable to toxicants other than ammonia.