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- Title
TOXICITY OF AMMONIA TO RIO GRANDE SILVERY MINNOW UNDER VARIABLE EXPOSURE REGIMES.
- Authors
Buhl, K. J.
- Abstract
A portion of the federally endangered Rio Grande silvery minnow's (Hybognathus amarus) current range receives discharges from several wastewater treatment plants. These plants experience periodic upset events, whereby they discharge elevated concentrations of ammonia into the Middle Rio Grande, NM. Acute toxicity tests were conducted to determine the effects of short-term exposures to elevated ammonia concentrations on larvae and young juveniles. Two chronic toxicity tests were then conducted simultaneously in which larvae were exposed for 30 days to either constant ammonia concentrations or 12-hour pulses of ammonia in which the peak concentrations were about 1.0X and the daily average concentrations were about 0.5X those in the constant concentration exposure test. In the acute pulsed ammonia tests, exposures to high ammonia concentrations for only 1.5 hours were nearly as toxic as exposures to the same concentrations for 96 hours and the larvae were twice as sensitive to ammonia as the juveniles. The 96-h median lethal concentrations (LC50s), based on total ammonia as nitrogen (N), were 16-23 mg N/L for larvae and 39-70 mg N/L for juveniles. In both chronic tests, growth (body weight) was a more sensitive endpoint than survival. Intermittent exposures to daily pulses of ammonia for 30 days caused reduced growth of silvery minnow at the same 24-h mean concentration as was observed in the continuous exposure study. In both exposures, the estimated no observed effect concentrations and maximum acceptable toxicant concentrations of total ammonia based on 24-h mean values were 4.6-4.7 and 6.8 mg N/L, respectively.
- Subjects
RIO Grande silvery minnow; TOXICITY testing; AMMONIA
- Publication
Proceedings of the South Dakota Academy of Science, 2015, Vol 94, p373
- ISSN
0096-378X
- Publication type
Article