Culturing and Bioassay Testing ofDaphnia magnaUsing Elendt M4, Elendt M7, and COMBO Media

A performance-based, tiered approach was used to evaluate survival, growth, and reproduction ofDaphnia magnain three selected synthetic media: Elendt M4, Elendt M7, and COMBO. Both Elendt M4 and Elendt M7 are high-hardness media currently recommended for Organization for Economic Cooperation and Development (OECD) testing. COMBO is a softer medium similar in total hardness to natural water found in the environment. Tier I consistent of an acclimation phase; Tier II involved a 21-day evaluation of survival, growth, and reproduction; and Tier III used each medium in a 21-day chronic study using a reference toxicant, 3,4-dichloroaniline (3,4-DCA). The evaluation of the performance of each medium was based on acceptance criteria similar to those used by the U.S. Environmental Protection Agency and the European Commission. Tests were run concurrently at three laboratories to assess interlaboratory variability. Daphnids were acclimated to the media for less than 1 month. Daphnid performance in all media exceeded the European Economic Community (EEC) validity criteria; however, reproductive performance and growth were significantly greater in the Elendt media than in COMBO. 3,4-DCA exerted more toxicity to daphnids in COMBO medium [no-observed-effect concentration (NOEC), <3.1μg/liter] compared with those in the Elendt media (NOEC, ≤8.8 μg/liter). Elendt M7 medium provided the most consistent NOECs between laboratories (3.1–8.8 μg/liter). However, results from two of three laboratories indicated decreases in fecundity over time in all media. The use of synthetic media for long-term culturing and bioassay testing ofD. magnais still in question.