Acute Toxicity Bioassays using Rotifers. I. A Test for Brackish and Marine Environments with Brachionus plicatilis

Abstract :A standardized 24-h acute toxicity test for the marine environment using the rotiferBrachionus plicatilisis described. Test animals are obtained by hatching cysts, thus eliminating the need for stock cultures. Since animals hatching from cysts are of similar age, genotype and physiological condition, test variability is greatly reduced. Controlled cyst hatching is achieved by transferring to lower salinity, warmer temperature and light. After 23h at 25 °C and 15 ppt salinity, hatching begins and proceeds rapidly. By 28 h, 90% of the cysts have hatched. A protocol is outlined to collect the neonates and use them in a simple acute toxicity test to calculate a 24 h LC50. A reference test using sodium pentachlorophenate (NaPCP) is described as well as a range-finding test and a definitive test for unknown toxicants. The toxicity of six compounds toB. plicatiliswas examined with the following decreasing sensitivities : copper > NaPCP > SDS > free NH3> cadmium > malathion. For 3 of the 6 compounds tested, salinity increase from 15 to 30 ppt resulted in higher sensitivity, whereas for the other 3 compounds there was no effect. In comparison with current test organismsB. plicatilisis either more equal or less sensitive depending on the compound, confirming the species-chemical specificity of mode of action of toxicants. The repeatability of the rotifer test is 5-6 times better than reported forDaphniatests and twice as good as theArtemianauplii bioassay. Like the standard brine shrimp nauplii acute test, the cyst-based rotifer test is an important advance in acute toxicity testing since it eliminates stock cultures, is rapid, sensitive, highly repeatable, easy to execute and cost effective.