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Risk assessment is in urgent need of more accurate toxic effect endpoints than those currently in use, especially for low concentrations. Often such endpoints are estimated by analysis of variance, linear interpolation, or smoothing. As these statistical methods are not always satisfactory, some authors have proposed to describe the entire dose--response curves by fully formalized parametric regression models whose parameters have toxicological meaning. These models allow a better evaluation of pollutant effects, including inter- and extrapolation to any other than the measured effect values. Following this line, a four-parameter logistic regression model (standard model) was fitted to survival data of Daphnia magna under pesticide (dinoseb) stress. The heterogeneity of the variance was taken into account with a both-sides logarithmic transformation. Besides the standard model, a hormesis and a threshold model were tested too. These two others models have been described in the literature and might better represent the dose--response function we are looking for. All three models showed a good fit to our data, and the statistics gave no hints as to which model is the most appropriate. As no evidence was seen for hormesis or for the existence of a threshold concentration, we used the simplest, namely, the standard model, for most of our calculations. Model calculations allow the quantification of the effects on individuals' longevity as well as on mean survival time of the population. We used them to define a no-effect value, the statistical-no-effect concentration (SNEC). The SNEC is based on the confidence bands of the modeled regression and represents the highest value for which an effect is statistically not different from the control. The SNEC is an alternative to classical endpoints, like the no-observed-effect concentration (NOEC) or the low-effect concentrations (e.g., EC10, EC5, EC1). [ABSTRACT FROM AUTHOR]

Toxicity of sediment from waterways of Ho Chi Minh City (HCMC), VietNam, was assessed in aqueous and organic extracts using the organisms Daphnia magna and Vibrio fischeri. Sediment samples were taken along the main canals of HCMC and in the Saigon river. The results indicate a relatively high potential toxicity of the extracts, especially concerning the aqueous extracts. V. fischeri shows a higher sensitivity than D. magna for both types of extracts. Sediments from the canalsin the urban areas, where the industrial and domestic activities areconcentrated, indicate a higher potential toxicity than sediments from the river. Organic extracts of deep sediments (about 1.3 m) are less toxic than surface sediment. The toxicity of the organic sediment extracts was higher in 1999 than in 1996, except for one site, where dredging operations have been carried out since 1997. The dredging operations thus have a positive local effect on the sediment quality, but further consequences on water and sediment quality of HCMC canals and rivers still have to be evaluated. [ABSTRACT FROM AUTHOR]

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., (Copyright 2004 Wiley Periodicals, Inc.)

The heat shock protein Hsp70 has been shown to be a promising biomarker in aquatic and terrestrial organisms. However, its analysis in the soil insect Folsomia candida (Collembola) poses many problems as the protein is particularly unstable in this species. Western blotting has shown that the principal degradation fragment has a size of 48 kDa. We have developed a Western blot method that avoids the degradation of Hsp70 and was successful in detecting the protein in the springtail F. candida after a heat shock (12, 18 and 24 h at 32 degrees C). In the second part of the study the organisms were exposed to artificial compressed soil contaminated with the dinitrophenol dinoseb (10, 15 and 20 micrograms g-1 dry weight [DW]). Hsp70 was analysed in pooled samples (40 to 150 collembola according to age) after 1, 2, 3, 4, 5, 6, 7, 11 and 14 days. The only significant induction was observed after 5 days at 20 micrograms g-1 DW of dinoseb. The induction patterns over time were dissimilar for the different concentrations and a relatively high variability between the replicates was observed. Our results show that we must be cautious when interpreting biomarker results, especially those for Hsp70.