CONTROL OF AMMONIA TOXICITY TO HYALELLA-AZTECA BY SODIUM, POTASSIUM AND PH

The toxicity of ammonia to Hyalella azteca at constant pH in artificia l media was controlled by sodium and potassium, and not by calcium, ma gnesium, or anions. Small increases in the LC50 for total ammonia (fro m 0.15 to 0.5 mM) occurred as sodium was increased from 0.1 to 1 mM an d above, but major increases in the LC50 (to over 10 mM total ammonia) required the addition of potassium. Potassium was, however, more effe ctive at reducing ammonia toxicity at high (1 mM) sodium than at low ( 0.1 mM) sodium. Ammonia toxicity was independent of pH at low sodium a nd potassium concentrations, when ammonia toxicity appeared to be asso ciated primarily with aqueous ammonium ion concentrations. At high sod ium and potassium concentrations, the toxicity of ammonia was reduced to the point where un-ionized ammonia concentrations also affected tox icity, and the LC50 became pH dependent. A mathematical model was prod uced for predicting ammonia toxicity from sodium and potassium concent rations and pH. (C) 1997 Elsevier Science Ltd.