Tropical ecotoxicity testing with Ceriodaphnia cornuta

The Sai Gon-Dong Nai river system in southern Vietnam is of great social and economic importance yet receives a large amount of industrial, domestic, and agricultural discharges. Toxicity assessment has started to become an issue in Vietnam, and it is important to employ a test system that is appropriate for typical Vietnamese conditions with a species that is representative of the invertebrates living in its aquatic ecosystems. The aim of this study was to develop and to validate an ecotoxicity test with an autochthonous organism. The microcrustacean Ceriodaphnia cornuta (Cladocera) was isolated from the Sai Gon River. A protocol was developed for the culturing of the organisms, and satisfactory results were obtained for long-term reproduction of C. cornuta. Quality control criteria were established. The toxicity of two relevant pesticides (diazinon and methyl parathion) and two metals (chromium and mercury) to C. cornuta was evaluated and compared to the standard organisms for ecotoxicological testing: Daphnia magna and Vibrio fischeri. Nonlinear regression models were applied to estimate such parameters as EC(50). The results of acute toxicity tests showed that C. cornuta was less tolerant than D. magna and V. fischeri to salinity and that C. cornuta was more sensitive than D. magna and V. fischeri to potassium dichromate, diazinon, methyl parathion, and mercury.