Site-Specific Water Quality Assessment Utilizing a Water Effects Ratio Approach for Evaluating Ammonia Toxicity in Freshwater Systems

Aquatic toxicological studies were conducted to evaluate the potential toxicity of ammonia introduced into waters of the San Gabriel and Los Angeles Rivers (Los Angeles County, California). These studies were used to ascertain the site-specific Water Effects Ratio (WER) for ammonia in these receiving waters. We performed a series of acute toxicity tests to determine the factors that control the toxicity of ammonia in these environments. 

The results of those tests indicated that an approximate 10-fold increase in ammonia concentrations are required in local waters to achieve the same toxicity observed using standard test waters. This effect on the acute toxicity tests was then extended to evaluate the influence of these waters on the toxicity, growth, and reproductive potential in long-term chronic tests. The results from this extended test indicated that the WER for ammonia with chronic testing may even be larger than observed for the acute tests. 

The data indicated that the controlling factor for these tests under similar hardness values are the concentrations of sodium (Na2+) and potassium (K+) ions in the river waters. A control exposure to match these ion concentrations provided similar protection as observed in the toxicity tests with the San Gabriel River waters that we used. It is likely that the controlling factor for the toxicity testing with Hyalella azteca is not only hardness, but also the Na2+ and K+ content of the river waters.