CHRONIC TOXICITY OF AMMONIA TO THE AMPHIPOD HYALELLA-AZTECA - IMPORTANCE OF AMMONIUM ION AND WATER HARDNESS

Ammonia toxicity, resulted in the continuous mortality of Hyalella azt eca for up to 10 weeks with similar mortality rates for adults and you ng. Growth was not reduced at concentrations below those causing chron ic mortality (1 mM total ammonia in Lake Ontario water), but reproduct ion was reduced at concentrations as low as 0.32 mM. Chronic mortality , was a function of total ammonia (or ammonium ion), and not un-ionize d ammonia, when the pH was adjusted by addition of acid. However, a 1 in 10 dilution of Lake Ontario water in distilled water resulted in a 10-fold reduction in the 4 week LC50. In contrast to common practice, ammonia toxicity to Hyalella is best defined on a total ammonia basis, but variations in hardness and other ions must be taken into account.