Probing the primary mechanisms affecting the environmental distribution of estrogen and androgen isomers.

Land application of animal manure has been identified as a source of natural and synthetic hormone contaminants that are frequently detected down-gradient of agricultural operations. Much research on the environmental fate of hormones has focused on the structural isomers most biologically active in mammals, e.g., the 17β-isomers of the estrogen estradiol (E2) and the synthetic androgen trenbolone (TB). However, recent work has shown that the α- and β-isomers of E2 and TB can cause comparable effects on certain aquatic species. To improve our understanding and ability to predict isomer-specific interactions with environmental sorbents, we measured the association (K(DOC)) of the α- and β-isomers of E2 and TB as well as their primary metabolites (estrone and trendione) with two commercial dissolved organic carbon (DOC) sources by measuring both free and DOC-bound hormone concentrations. We also measured solvent-water partition coefficients partitioning (K(SW)) for the same hormones using hexane, toluene, and octanol. Log K(DOC)(*), log K(OC) (OC-normalized sorption by soils), and K(OW) values are all greater for the β-isomer except between the E2 isomers. Theoretical descriptors reflecting electronic character and solute-solvent interactions were calculated to elucidate isomer-specific behavior. Trends for log K(OW) and log K(DOC) among hormones as well as between isomers are explained reasonably well by computed electrostatic potential and H-bonding parameters.