The presence of chemicals exuded by fish affects the life-history response of Ceriodaphnia cf. dubia to chemicals with different mechanisms of action

The toxicity of chemicals with different mechanisms of action (3,4-dichloroaniline, fenoxycarb, and chlorpyrifos) to the cladoceran Ceriodaphnia cf. dubia was examined in the presence and absence of chemicals exuded by fish, termed fish kairomones. A range of life-history traits were examined, including mean brood sizes, survival, net reproductive rate (Ro) and population growth rate (r). Cladocerans exposed to 3,4-dichloroaniline showed similar sensitivities in the presence and absence of fish kairomones with respect to all of the life-history traits examined. The presence of fish kairomones reduced the sensitivity of cladocerans to fenoxycarb with respect to mean brood sizes and r but increased their sensitivity in terms of Ro. The presence of fish kairomones increased the sensitivity of cladocerans to chlorpyrifos with respect to survival, r, Ro, and mean brood sizes. The general trends observed were similar to those shown when C. cf. dubia was exposed to these chemicals under low food conditions, and it is suggested that the effects of fish kairomones on toxicity may be attributed to the reduction in feeding rates observed when C. cf. dubia is exposed to fish kairomones.

Toxicity of laundry detergent components to a freshwater cladoceran and their contribution to detergent toxicity

The toxicity of 39 laundry detergent components including surfactants, enzymes, builders, fabric brighteners, fillers, and coloring agents to the cladoceran Ceriodaphnia cf. dubia was determined. The difference between the most and the least toxic components was approximately 17,000-fold and 1,000,000-fold for the mg/L and mmol/L EC50 data, respectively. Two of the components had high toxicity (EC50 values < 1 mg/L), 11 moderate toxicity (EC50 values between 1 and 10 mg/L), and the remaining 26 components had low toxicity (EC50 values > 10 mg/L). Analysis revealed that mixtures of the components interacted antagonistically, additively, and synergistically. On a molarity basis the most toxic group of compounds was the surfactants followed by the brighteners. The most toxic individual components included sodium carboxymethyl cellulose, sodium silicate solution, four brighteners, sodium perborate tetrahydrate, and the surfactants. Many of the most toxic components, however, contributed very little to the toxicity of the detergents due to being present in the detergents at low concentrations. The main contributors to the toxicity of detergents were the sodium silicate solution and the surfactants-with the remainder of the components contributing very little to detergent toxicity. The potential for acute aquatic toxic effects due to the release of secondary or tertiary sewage effluents containing the breakdown products of laundry detergents may frequently be low. However, untreated or primary treated effluents containing detergents may pose a problem. Chronic and/or other sublethal effects that were not examined in this study may also pose a problem.

The number of components in a mixture determines whether synergistic and antagonistic or additive toxicity predominate: the funnel hypothesis

A new hypothesis, the funnel hypothesis, was derived to explain the variation in toxicity of equitoxic multicomponent mixtures of nonspecific toxicants (narcotics). The variation is explained in terms of the volumes associated with solute-solute and solute-solvent interactions. The hypothesis predicts that as the number of components in a mixture increases, the range of deviation from toxic additivity decreases. It also predicts that the toxicity of mixtures measured using biological endpoints that require high toxicant concentrations will deviate more from toxic additivity than endpoints that require low concentrations. Aquatic toxicity data for equitoxic mixtures of narcotic toxicants to a range of aquatic organisms compiled from the literature support the predictions of the funnel hypothesis.

Comparison of the critical concentration and critical volume hypotheses to model non-specific toxicity of individual compounds

The critical concentration and critical volume hypotheses for non-specific toxicity require the molar concentration (CC) and volume fraction (VF) of toxicant in target tissue to be constant. Thus these factors should be independent of the octanol-water partition coefficient (Kow) for individual compounds. CC and VF values were calculated based on acute sub-lethal, acute and chronic lethal toxicity data, Kow and pure component molar volume (MV) data. When these values were plotted against log Kow, the slopes of the regression equations were significantly different to zero but were not significantly different from each other. The observed slight increase in CC and VF with increasing log Kow was attributed predominantly, to the use of Kow values which overestimate the target tissue-water partition coefficient (Kow). An additional error associated with the volume fraction calculations was the use of the molar volume instead of partial molar volume. VF and CC values were calculated correcting for both these factors and regressed against log Kow. The resulting equation for VF had a gradient not significantly different from zero, while that for CC was, thus indicating the superiority of the critical volume hypothesis in modelling non-specific toxicity of individual compounds.

Prediction of the toxicity of mixtures of shale oil components

The toxicities of selected oil shale components and of mixtures of these components to a mixed marine bacterial culture have been determined. The toxicities of mixtures whose components were members of the same homologous series were found to be additive. In all other cases, even when the compounds were as closely related as structural isomers, synergism was observed. Simple and multiple linear regression equations utilizing measures of toxicity and molecular descriptors were used successfully to predict the enhancement of toxicity due to interaction of components in mixtures regardless of the mode of interaction.