Effects of pH and hardness on chronic toxicity of ammonia to Ceriodaphnia dubia
- Univ. of Wisconsin, Stevens Point, WI (United States)
Ammonia is one of the most common toxicants encountered in municipal and industrial discharges. There is limited information on how changes in water chemistry affect toxicity of ammonia to invertebrates. This study assessed effects of pH and hardness on chronic toxicity of unionized ammonia to Ceriodaphnia dubia. Three-brood life cycle tests were run at four pH levels in combination with three hardness levels to determine effects on reproduction. Hardness levels ranged from 40 mg/L CaCO{sub 3} to 180 mg/L CaCO{sub 3}, while pH levels ranged from 6.5 to 9.0. Hardness and pH in combination yielded the lowest toxicity at pH 9.0 in hard water, with a LOEC of 1.31 mg/L unionized ammonia-nitrogen (UIA-N). The highest toxicity was at pH 6.5 in medium water, with a LOEC of 0.04 mg/L UIA-N. Toxicity of unionized ammonia (UIA) generally decreased as hardness increased. Average LOECs ranged from 0.33 mg/L UIA-N in soft water to 0.77 mg/L UIA-N in hard water. Unionized ammonia was least toxic in hard water at pH 7.0, 8.0, and 9.0. At pH 6.5 UIA was least toxic in soft water. Toxicity of UIA generally decreased as pH increased. Average LOECs ranged from 0.08 mg/L UIA-N at pH 6.5 to 0.77 mg/L UIA-N at pH 9.0. Unionized ammonia was most toxic at pH 6.5 at all hardness levels. In both soft and hard water UIA was least toxic at pH 9.0, while in medium water it was least toxic at pH 8.0.
- OSTI ID:
- 37433
- Report Number(s):
- CONF-9410273--
- Country of Publication:
- United States
- Language:
- English
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