The use of Daphnia magna neonates hatched from ephippia for toxicity testing

Abstract

The continuous increase in the number of new chemicals as weIl as the discharges of solid and liquid wastes potentially hazardous for the envirornnent has in the past years triggered the need for simple and inexpensive bioassays for routine testing. Although Daphnia magna is a key test species in aquatic toxicology, toxicity testing with this species implies continuous culturing of live stocks of test organisms, in good health and in sufficient numbers. Besides the technological and financial burden, which this represents, "cemventional" tests also often suffer from a poor precision of the test results. The use of resting stages of bioassay species, from which the test organisms can be hatched on demand, is an attractive alternative to the problems posed by the year-round culturing oflive stocks. In this study, the suitability of D. magna neonates hatched from ephippia, for acute tests, was evaluated in comparison to neonates taken from live laboratory stock cultures. The analysis was based on test sensitivity as weIl as on test precision. Twenty four hour and 48-h EC50's for one inorganic and 3 organie ehernicals for both ex-ephippial and live stock neonates were deterrnined according to the OECD Guidelines for Daphnia acute testing. For all the chemicals tested, neonates hatched from ephippia never differed in sensitivity by more than a factor 2 from those taken from live stock cultures. The precision of the EC50's obtained with ex-ephippial neonates was found to be highly comparable to that of the values obtained with live stock neonates. Despite the low number of chemicals tested, the results of this study again confirm that an ephippium-based toxicity test is a valuable alternative to the conventional Daphnia acute test.