sodium-bromide and 3-4-dichloroaniline

When considering joint toxic apical effects at higher levels of biological organization, such as the growth of populations, the so-called pharmacological mode of action that relies on toxicological mechanistic effects on molecular target sites may not be relevant. Such effects on population growth rate will depend on the extent to which juvenile and adult survival rates and production rates (juvenile developmental rates and reproduction) are affected by toxic exposure and also by the sensitivity of population growth rates to life-history changes. In such cases, the ecotoxicological mode of action, defined as the crucial life-history trait processes and/or xenobiotic-life-history trait interactions underlying a toxicological effect on population growth rate, should be considered. Life-table response experiments with the crustacean Ceriodaphnia dubia exposed to single and ternary mixtures of nine compounds were conducted to test the hypothesis that joint effects on population growth rates could be predicted from the mixture constituent ecotoxicological mode of action. Joint effects of mixtures containing pharmacologically dissimilar compounds (cadmium, λ-cyhalothrin, and chlorpyrifos) that differentially affected life-history traits contributing to population growth rates were accurately predicted by the independent-action concept. Conversely, the concentration-addition concept accurately predicted joint effects of two different mixtures: one containing pharmacologically similar acting pyrethroids that also affected similarly life-history traits, the other one that included pharmacologically dissimilar compounds (3,4-dichloroaniline, sodium bromide, and fenoxycarb) acting mainly on reproduction rates. These results indicate that when assessing combined effects on population growth rate responses, selection of mixture toxicity conceptual models based on the ecotoxicological mode of action of mixture constituents provided more accurate predictions than those based on the pharmacological mode of action.

Topics: Aniline Compounds; Animals; Bromides; Cadmium; Chlorpyrifos; Daphnia; Insecticides; Nitriles; Phenylcarbamates; Pyrethrins; Sodium Compounds; Water Pollutants, Chemical

In this study a comparison was made of the results obtained in Daphnia magna 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-observed-effect concentration (LOEC) as statistical parameters. Test substances were sodium bromide (NaBr), 3,4-dichloroaniline (DCA), cadmium, and parathion. For NaBr, DCA, and cadmium, toxicity evaluated after the first-brood release was similar to toxicity evaluated after 21 days, using reproduction as end point. Parathion did not affect either reproduction or growth. Thus, LC50, NOEC, and LOEC were calculated using mortality as the endpoint for parathion. 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 more appropriate than NOECs and LOECs for evaluating toxicity of the test substances. Furthermore, classic endpoints used for the evaluation of chronic toxicity (inhibition of normal reproduction and growth) may not be adequate to evaluate the sublethal toxicity of compounds that induce cumulative effects leading to mortality within the test period and causing no observable effects on the reproduction and growth of the species. Endpoints indicative of biochemical stress or effects on specific targets of the test compound may be useful in sublethal toxicity evaluation.

Topics: Aniline Compounds; Animals; Bromides; Cadmium Chloride; Daphnia; Parathion; Reproduction; Sodium Compounds; Toxicity Tests; Water Pollutants, Chemical

Chronic life-cycle tests using the freshwater cladoceran Daphnia magna aim to measure the effect of toxic chemicals on adult reproduction, in terms of the number of viable offspring produced. A tacit assumption is made that the primary effect of toxicants in these tests is a sublethal effect on the parent, reducing egg production and hence fecundity. The authors' observations on two chemicals, sodium bromide and 3,4-dichloroaniline, demonstrate that this assumption is at least partly false. In these experiments, the primary toxic effect of these compounds was to kill developing eggs in the brood chamber. Total egg output was unaffected, whereas output of viable eggs was severely impaired--an acute lethal effect. A further experiment demonstrated that the effect was limited to those eggs developing in the brood chamber, with eggs in the ovary remaining unaffected. It was suggested that these observations may provide the basis for the development of a short, sensitive early life-stage test with this species.

Topics: Aniline Compounds; Animals; Bromides; Daphnia; Embryo, Nonmammalian; Female; Ovum; Sodium; Sodium Compounds