■

EC20の使用についての記述。

U. S. Environmental Protection Agency (1999) 1999 Update of ambient water quality criteria for ammonia. pp. 160. U. S. Environmental Protection Agency, Washington, DC.

To make CVs reflect a uniform level of effect, regression analysis was used here both to demonstrate that a significant concentration-effect relationship was present and to estimate CVs with a consistent level of effect. Use of regression analysis is provided for on page 39 of the 1985 Guidelines (U.S. EPA 1985b). The most precise estimates of effect concentrations can generally be made for 50 percent reduction (EC50);however, such a major reduction is not necessarily consistent with criteria providing adequate protection. In contrast, a concentration that caused a low level of reduction, such as an EC5 or EC10, is rarely statistically significantly different from the control treatment. As a compromise, the EC20 is used here as representing a low level of effect that is generally significantly different from the control treatment across the usefulchronic datasets that are available for ammonia.