Formation of estrogenic brominated ethinylestradiol in drinking water: implications for aquatic toxicity testing

17alpha-Ethinylestradiol (EE2) is a synthetic estrogen which is thought to contribute the feminisation of fish exposed to wastewater effluents. During laboratory exposure studies of fish to EE2, it was observed that the estrogen in the aquarium water was rapidly transformed (within 10 min) to mono- and di-brominated A-ring products. Exposure of roach (Rutilis rutilus) to 30 ng L(-1) EE2 resulted in accumulation of dibrominated EE2 in ovaries (apparent bioconcentration factor, BCF 130) and liver (apparent BCF 7894) at concentrations which were 18-67-fold greater than the test EE2 compound. The estrogenic activities of brominated EE2 compounds were tested in an in vitro yeast recombinant estrogen receptor transcription screen (YES). All the brominated products of EE2 were estrogenic, however monobrominated isomers of EE2 were 18-105-fold less estrogenic, and dibrominated EE2 2058-fold less active in the YES than EE2 itself. This study reveals the importance of using chemical methods to verify exposure concentrations of waterborne test chemicals and suggests that bromination of estrogens may occur during water treatment, potentially resulting in the formation of bioavailable estrogenic environmental contaminants.