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PM05 Aquatic Vertebrate/Invertebrate Toxicology
(PM098) Influence of temperature and pH on the toxicity of ammonia to the endangered Colorado pikeminnow.
Fairchild, J.1, Allert, A.1, Waddell, B.2, 1 U.S. Geological Survey, Columbia, MO, USA2 U.S. Fish and Wildlife Service, Salt Lake City, UT, USA
ABSTRACT- The USEPA revised the National Water Quality Criteria for Ammonia in 1999. The revised criteria recognize that total ammonia toxicity is pH dependant but that temperature effects vary by species. Therefore, it is recommended that site-specific testing be conducted in cases where endangered species are exposed to ammonia under differing temperature conditions. We conducted a series of toxicity tests with the endangered Colorado pikeminnow (Ptychocheilus lucius) to determine the effect of pH and temperature on the toxicity of ammonia. Studies were conducted as part of a site-specific risk assessment of the effects of ammonia-contaminated groundwater entering the Colorado River from beneath an abandoned uranium tailings pile near Moab, Utah. Laboratory static renewal tests (96-hr) were conducted with juvenile Colorado pikeminnow and well water adjusted for variations in pH and temperature. Water quality (pH, temperature, unionized ammonia, dissolved oxygen, conductivity) and mortality were measured daily. Results indicated that Colorado pikeminnow were two-fold more sensitive to unionized ammonia at 8 °C than 18 °C or 28 °C. Changes in pH had no effect on sensitivity based on unionized ammonia concentrations. Highest exposures of Colorado pikeminnow in the Upper Colorado River occurred during winter conditions and exceeded water quality criteria by over two orders of magnitude. These studies demonstrate the importance of considering site-specific conditions when conducting risk assessments for ammonia and endangered species where seasonal variations in temperature conditions occur. However, the existing water quality criteria for ammonia, if enforced, is protective of Colorado pikeminnow in spite of the increased cold-water sensitivity of the species.
Key words: ammonia, temperature, toxicity, fish
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