Bioanalytical equivalents and relative potencies for predicting the biological effects of mixtures.

Bioanalytical equivalents (BEQs) of mixtures and environmental samples are widely used to reflect the potential threat of pollutants in the environment and can be obtained by bioassays or using chemical analysis combined with relative potencies (REPs). In this study, the relationships between bioassay-detected BEQs (Bio-BEQs) and chemically analyzed BEQs (Chem-BEQs) were studied. BEQs and REPs are correlated with effect level and the concentration-response curves of the reference standard and sample. Thus, effect level (e.g., EC 10 , EC 25 and EC 50) should be addressed for the BEQ values obtained from bioassays or chemical analyses. The previous prerequisites for REPs application (i.e., curves that are parallel and have the same maximum response) are redundant, and the use of REPs for the calculation of BEQs or in risk assessment should instead be based on the same effect level. For a complex mixture with many components, all active components can be regarded as dilutions of a standard compound for inducing a specific effect. Relative toxicity estimates based on EC 50 ignore the contribution of weak-active components with maximum response below EC 50 of the reference standard, especially in complex mixtures or environmental samples. REPs based on an effect level EC 10 that can be clearly discriminated from background response are recommended for BEQ calculation. As an example, the aryl hydrocarbon receptor (AhR)-mediated activity of US EPA priority polycyclic aromatic hydrocarbons (PAHs) in RTL-W1 cells was used to assess the reliability of REPs for mixture toxicity prediction based on the effect level EC 10. Unlabelled Image • Effect level should be addressed for bioanalytical equivalents. • Components can be viewed as dilutions of a compound for inducing a specific effect. • Toxicity estimates at a high effect level ignore weak-active components. • Relative potencies at EC 10 can be used to calculate bioanalytical equivalents. [ABSTRACT FROM AUTHOR]