How did NAWQA assess the potential for effects of ammonia concentrations on aquatic life?
NAWQA stream samples were compared with aquatic health criteria for both acute and chronic effects using guidelines established by the U.S. Environmental Protection Agency (USEPA) for protection of aquatic organisms (USEPA, 1999 http://www.epa.gov/waterscience/criteria/ammonia/99update.pdf; USEPA 2009 http://www.epa.gov/waterscience/criteria/ammonia/2009update.pdf). The criteria vary with acidity and water temperature, which affect both the toxicity of ammonia and the form in which it occurs. Acute effects are characterized by sudden and severe exposure to a toxicant, whereas chronic effects are generally characterized by prolonged or repeated exposure over many days, months, or years.
