PARENT SESSION
PM11 - Sediment Toxicology
Monday, 18 November 2002
8:00 AM to 6:30 PM
Exhibit Hall

(P307) Effects of ammonia on juvenile unionids in laboratory sediment toxicity tests.

Newton, Teresa^*,1, Allran, John², O'Donnell, Jonathan², Bartsch, Michelle¹, Richardson, William¹, ¹ USGS, Upper Midwest Environmental Sciences Center, La Crosse, WI, USA² Universtiy of Wisconsin-La Crosse, La Crosse, WI, USA

ABSTRACT- Ammonia is a relatively toxic compound generated in water and sediments by heterotrophic bacteria and ultimately accumulates in sediments and pore water. Recent data suggests that unionids are sensitive to un-ionized ammonia (NH₃-N), relative to other organisms. Juvenile Lampsilis cardium mussels were exposed to NH₃-N in pore water in replicate 96-h and 10-d sediment toxicity tests. The 96-h LC50s were 127 and 165 g NH₃-N/L and the 10-d LC50s were 93 and 140 g NH₃-N/L. The EC50s (based on the proportion affected, including dead and inactive mussels) were 73 and 119 g NH₃-N/L in the 96-h tests and 71 and 99 g NH₃-N/L in the 10-d tests. Growth rate was substantially reduced at concentrations between 31 and 76 g NH₃-N/L. There were no substantial differences in any of the responses between the two test durations, however, there was considerably less variation associated with the 10-d exposures. The lethality results (when expressed as total ammonia) are about one-half the acute national water quality criterion for total ammonia, suggesting that existing criteria may not be protecting juvenile unionids.

Key words: freshwater mussels, ammonia, toxicity, juveniles