Observations of estrogenicity or toxicity for chemicals screened as potential modulators.

aresults from modulator screening studies were classified as ‘clear negative’ (reduction in effect of REFmix at multiple concentrations showing an approximately sigmoid dose-response), ‘possible negative’ (reduction in effect of REFmix at a single concentration or multiple concentrations with a apparent linear concentration-response relationship) and ‘none’ (no indication of a negative or positive effect).b‘Active’ indicates a positive signal in ESCREEN (estrogenicity), clearly distinguishable from assay variability and noise and usually supported by a dose-response (i.e. not reliant on data from only a single concentration).c‘Possible toxicity’ indicates a decrease in value for treated wells below that of vehicle controls, this signal is small so the assignment of toxicity is not certain; ‘Toxic’ indicates a reduction in signal evoked by increasing concentrations above those at which a chemical showed activity (estrogenicity).