Short-Cut Chronic Toxicity Estimates Using Daphnia magna

The use of a partial life cycle test together with an application factor (AF) is a reliable way to estimate the traditional Daphnia magna 21-day GM-MATC. Application factors were determined for twelve different endpoints from 20 D. magna 21-day chronic tests by dividing the respective endpoints by the 21-day GM-MATC for each chemical. The data indicate that the 48-h no-effect concentration, the 7-, 14-, and 21-day EC50 values, and the 7- and 14-day geometric mean no-effect/effect concentrations can be used with small AFs to reliably estimate the 21-day GM-MATC. The respective AFs are 2.9, 6.0, 2.0, 4.2, and 2.7. The cost associated with obtaining an estimate of the 21-day GM-MATC from a 2-, 7-, 14-, or 21-day study is $800, $5000, $10 000, and $15 000, respectively. The 48-h no-effect concentration provides the shortest and most effective test and does so without sacrificing accuracy. For purposes of ranking chemicals and obtaining preliminary estimates of environmental safety margins, the use of a 48-h no-effect concentration from an acute toxicity test and an AF (33) is recommended as a cost effective way to estimate the chronic geometric mean maximum acceptable toxicant concentration (GM-MATC) for D. magna. The results of this study indicate that there are only minor differences between 14- and 21-day GM-MATCs. Therefore we recommend that standard protocols for testing D. magna be changed to require only a 14-day period of exposure instead of 21 days. The results of this study also provide evidence that a chronic test as short as 7 days could be conducted without significant loss of accuracy.