PARENT SESSION
PT1 - Aquatic Toxicology
Tuesday, 19 November 2002
8:00 AM to 6:30 PM
Exhibit Hall

(P486) Development of a pH Dependent Toxicity Curve for Ammonia using Pimephales promelas and Ceriodaphnia dubia.

Baummer, John^*,1, McCulloch, Wayne¹, Ruiter, J.², Hoke, Robert², ¹ EA Engineering Science and Technology, Sparks, MD² DuPont USA, Newark, DE

ABSTRACT- In some wastewater discharges, ammonia is a potential source of toxicity, and compliance with whole effluent toxicity can often depend on pH control, either at the end of pipe or during toxicity testing. The toxicity of ammonia in laboratory dilution water, administered as ammonium chloride, was investigated at pH 6.5, pH 6.7, pH 7.0, pH 7.3, pH 7.5 and pH 8.5. Ceriodaphnia dubia (water flea) and Pimephalespromelas (fathead minnow) were used as the test species. Acute toxicity tests with P. promelas were conducted using two different ages of fish (15-day and 30-day old). The pH was controlled during the study by the addition of the hydrogen ion buffers MES (2-[N-morpholino] ethanesulfonic acid) (pKa=6.15), MOPS (3-[N-Morpholino] propanesulfonic acid) (pKa=7.15), and POPSO (Piperazine-N, N'-bis-[2-hydroxypropanesulfonic acid]) (pKa=7.8). Ammonia was measured on individual test concentrations to develop both nominal and measured test end points as total ammonia. The toxicity of ammonia increased approximately 10 fold per pH unit in tests with both species. At pH 7.5 the 48-hour LC50 C. dubia was similar to the 96-hour LC50 for the 15-day old P. promelas. Test results were fairly consistent among the different ages of fish at pH 6.5 and pH 8.5. In contrast, at pH 7.5 the 30-day old fish were almost one half as sensitive as the 15-day old fish or Ceriodaphnia dubia.

Key words: Ammonia, pH, Pimephales promelas, Ceriodaphnia dubia