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 LC 50 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 LC 50 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 NH 3 > malathion. B. rubens was at least twice as sensitive as Brachionus plicatilis to all toxicants tested 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 yr. 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.