Site-specific acute and chronic toxicity of ammonia to Daphnia magna straus

The acute and chronic toxicity of ammonia (expressed as un-ionized ammonia nitrogen, NH3-N) to Daphnia magna was determined in support of the development of site-specific water quality standards for ammonia in the Tittabawassee River at Midland, Michigan. The 48-h LC50 value (95% confidence interval) obtained was 2.94 (2.70 to 3.22) mg NH3-N/L. The 21-d chronic value, presented as the maximum acceptable toxicant concentration (MATC), was between 0.42 and 0.87 mg NH3-N/L. Expressing the chronic value as the geometric mean of 0.42 and 0.87 resulted in an MATC of 0.60 mg NH3-N/L. The toxicity values derived during this study were similar to those reported in the literature for D. magna.