A Daphnia magna first-brood chronic test: An alternative to the conventional 21-day chronic bioassay?

In this study a comparison was made of the results obtained in Daphnia magn a chronic bioassays after first-brood release and after 21 days of exposure , using inhibition of normal reproduction and growth as effect criteria and EC10, EC20, EC50, no-observed-effect concentration (NOEC), and lowest-obse rved effect concentration (LOEC) as statistical parameters. Test substances were sodium bromide (NaBr), 3,4-dichloroaniline (DCA), cadmium, and parath ion, For NaBr, DCA, and cadmium, toxicity evaluated after the first-brood r elease was similar to toxicity evaluated after 21 days, using reproduction as endpoint. Parathion did not affect either reproduction or growth. Thus, LC50, NOEC, and LOEC were calculated using mortality as the endpoint for pa rathion, Results indicate that the period until release of the first brood is sufficient to predict the toxicity of some chemicals to D. magna. Values estimated on the basis of a logistic model (EC10, EC20, and EC50) were mor e appropriate than NOECs and LOECs for evaluating toxicity of the test subs tances, Furthermore, classic endpoints used for the evaluation of chronic t oxicity (inhibition of normal reproduction and growth) may not be adequate to evaluate the sublethal toxicity of compounds that induce cumulative effe cts leading to mortality within the test period and causing no observable e ffects on the reproduction and growth of the species. Endpoints indicative of biochemical stress or effects on specific targets of the test compound m ay be useful in sublethal toxicity evaluation. (C) 1999 Academic Press.