ECOTOXICOLOGICAL RISK ASSESSMENT FOR THE SAIGON-DONGNAI RIVER BASIN

Abstract

The Sai Gon - Dong Nai river system in Southern Viet Nam has a great social and economic importance but receives many industrial, domestic and agricultural discharges. Ecotoxicological risk assessment starts being an issue in Viet Nam and it is important to dispose of a test system, which is appropriate for the typical Vietnamese conditions with a species being representative of the invertebrates living in these aquatic ecosystems. The micro crustacean Ceriodaphnia cornuta (Cladocera) was isolated in the Sai Gon river. A protocol was developed for the culturing of the organisms, and satisfactory results were obtained for the long-term reproduction of C. cornuta. Quality control criteria were established. The effect of salinity on the toxicity of diazinon, methyl parathion or mercury salt was assessed with the test organisms. The results obtained for the mixture toxicity of salinity (NaCl) and the different toxicants were evaluated by graphical, algebraic and input/output concepts including isobolographics, Mixture Toxicity Index and the concept of Concentration Addition or Independent Action. The results for the mixture toxicity of NaCl and diazinon, methyl parathion or mercury showed independent action and additivity simultaneously. Acute toxicity test with D. magna, C. cornuta and V. fischeri were developed and the ecotoxicity of different matrices sampled in the Sai Gon - Dong Nai rivers including sediment, rice field water and soil, industrial and domestic wastewater were tested with the different bioassays. Relatively high toxicity was observed in most samples from all matrices. Correlation analysis was performed between the responses of the tests and the analysis of physico-chemical and chemical (pesticides and metals) parameters. In general, the responses of C. cornuta were well correlated with D. magna, V. fischeri but in most cases C. cornuta showed a higher sensitivity. The correlations between the organic and metallic micro pollutants and the response of the ecotoxicity tests were generally quite high. The results showed that an ecotoxicity battery of D. magna, C. cornuta and V. fischeri is suitable for the ecotoxicological risk assessment of tropical aquatic systems such as Sai Gon - Dong Nai river in Vietnam.