The<unk>  <unk>  is a value that is calculated through aquatic toxicity tests to help set water quality regulations for the protection of aquatic life. Using the results of a partial life-cycle chronic toxicity test, the<unk>  is reported as the geometric mean between the No Observed Effect<unk>  (NOEC) and the lowest observed effect<unk>  (LOEC). The<unk>  is used to set regulatory standards for priority pollutants under the US federal Clean Water Act. Regulatory guidelines give two<unk><unk> s of pollutants to protect against effects: chronic or acute. Since the<unk>  should only be reported in chronic toxicity tests, there is a widely accepted method to convert the chronic<unk>  to a<unk>  that protects against acute effects. The<unk>  is calculated and reported from the results of a number of standard procedures designed by the United States Environmental Protection Agency (US EPA) and other organizations to maintain high accuracy and precision among all toxicity tests for regulatory purposes.
Maximum acceptable toxicant concentration
Risk of mortality
Measured environmental concentration
Relative biological effectiveness
Effective dose 
Measures of pollutant concentration
Indicative limit value
Mortality rate