Total concentrations of several known xenobiotic estrogenreceptor (ER) agonists and natural and synthetic estrogenwere measured in water by use of a combination ofinstrumental and bioanalytical approaches. Samples from3 municipal wastewater treatment plants (WWTPs) insouth central Michigan (upstream and effluent); 4 pointsource locations on the
Trenton Channel of the Detroit River,MI; and 5 locations in Lake Mead, NV were analyzed.Organic compounds were extracted from 5 L water samplesusing solid-phase extraction
disks and separated intothree fractions based on polarity. Whole extracts andfractions were tested for ER agonist potency using theMVLN in vitro bioassay. ER agonist potency was characterizedby comparing the magnitude of induction elicited by theextract or fraction to the maximum induction caused by 17
-estra
diol (E2). The greatest concentrations of ER agonistswere associated with the most polar fraction (F3).Instrumental analyses and further fractionation were usedto identify specific ER agonists associated with bioassayresponses. Bioassay data were compared to extractconcentrations in order minimize variability associatedwith the extraction procedure. Concentrations of endogenousestrogen, E2, and the synthetic estrogen ethynylestra
diol(EE2) ranged from nondetectable to 14.6 ng/mL extract(nondetectable to 3.66 ng/L water) and represented from88 to 99.5% of the total estrogen equivalents in the watersamples analyzed. Concentrations of alkylphenols (APs)ranged from nondetectable to 148
g/mL extract (nondetectable to 37 000 ng/L water). In general, alkylphenolscontributed less than 0.5% of the total estrogen equivalentsin the water samples. Both bioassay-
directed fractionationresults and comparison of ER agonist concentrations,adjusted for their known relative potencies, support theconclusion that E2 and EE2 were the dominant environmentalestrogens in water samples from mid-Michigan and LakeMead, NV.