Characterization of binding between 17β-estradiol and estriol with humic acid via NMR and biochemical analysis.

Endocrine disruptors, such as 17β-estradiol (E2) and estriol (E3), are ubiquitously found in the environment and their presence has gained recognition as a significant health risk. Sorption of estrogens by dissolved organic matter (DOM) influences their concentration and effects. Although there is some experimental evidence suggesting that sorption occurs through hydrophobic interactions, there is not a complete understanding of this association. Therefore, we sought to more extensively characterize binding between humic acid (HA), a major component of DOM, with E2 and E3 using nuclear magnetic resonance spectroscopy (NMR). Our results indicate that binding between these estrogens and HA occurs primarily at the aromatic ring, and takes place even at relatively low HA concentration. Specific interactions between E2 and HA were confirmed by assessing binding via ELISA assay, and the effect of binding on estrogenic activity was studied via a yeast bioassay. Together, these studies build upon previously theorized interactions, yielding a more comprehensive model of binding between estrogens and HA, as well as demonstrate the value of the confluence of biochemical assay methods with analytical NMR techniques.