Acute Toxicity Bioassays using Rotifers. - II. A Freshwater Test with Brachionus rubens
Abstract : A 24 h acute toxicity test for freshwater is described using the rotifer Brachionus rubens hatched from cysts. Hatchlings are used in a simple protocol that provides for LC50 calculation and yields highly repeatable results. Hatching is initiated by transferring cysts to warmer temperatures and light. At 25 °C, hatching commences after 17 h and by 25 h, 40% of cysts have hatched. The average hatching percentage for B. rubens cysts was 53%. A reference test using sodium pentachlorophenate (NaPCP) yielded an 24hLC50 of 0.62 mg/l, with a coefficient of variation of 9.7%. The no observed effect concentration (NOEC) for NaPCP was 0.28 mg/l. Protocols for range-finding and definitive tests of unknown toxicants are also described. Six compounds were assayed and had the following toxicity rankings : copper > NaPCP > cadmium > SDS > free NH3 > malathion. B. rubens was at least twice as sensitive as Brachionus plicatilis to all toxicants except malathion. The precision of the B. rubens acute toxicity test is about 3 times better than that of Daphnia. Like its marine counterpart with B. plicatilis, the B. rubens test for fresh water has a major advantage over current aquatic tests in that it eliminates culturing and maintenance of live stocks. Test animals are obtained from dormant eggs which have a shelf life of at least 1 year. Moreover, the rotifer test proposed is fast, convenient, sensitive and repeatable, making it a useful new tool for routine assessment of aquatic toxicity of chemicals and effluents.
N.B.It was eventually found out that the controlled production of cysts of the species Brachionus calyciflorus was more easy than that of Brachionus rubens. For reasons of convenience the former rotifer species hence been given preference as the the test species for the Rotoxkit F microbiotest.