Great Lakes Environmental Center (GLEC) conducted flow-through acute and chronic toxicity tests in support of ambient water quality criteria development for the U.S. Environmental Protection Agency (EPA). The objective of the work was to supply EPA with acute and chronic ammonia toxicity data for Hyalella azteca at six test temperatures and one pH to update the toxicity database in support or ambient water quality criteria. Hyalella azteca were exposed under flow-through conditions to measured concentrations of ammonia in a flow-through system for 96 hours to determine the acute toxicity of ammonia to Hyalella. Secondly, the chronic toxicity of ammonia was determined by exposing Hyalella azteca for 40-days to measured concentrations of ammonia in a flow-through system. Ultimately, the median lethal toxicant concentration (LC50) was estimated from the 96-hour acute toxicity tests, and no-observed-effect-concentration (NOEC), lowest-observed-effect-concentration (LOEC), the maximum-allowable toxicant-concentration (MATC), and 40-day EC20 was estimated for toal ammonia and un ionized ammonia from the 40-day toxicity test. Toxicity test results were used to calculated acute:chronic ratios for ammonia. Results indicated that the toxicity of ammonia to an invertebrate was affected by temperature. The toxicity of ammonia generally decreased with an increase in test temperature.
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