Identification of the transformation products of 17α-ethinylestradiol and 17β-estradiol by mass spectrometry and other instrumental techniques

While it is now well-documented that the synthetic (17α-ethinylestradiol, EE2) and natural (17β-estradiol, E2) estrogens are among the most potent endocrine-disrupting chemicals found in the environment, many of their transformation products (TPs) have not been identified to date. The scarcity of available environmental data on the TPs of EE2 and E2 can be attributed to the difficulty in analyzing trace amounts of previously unknown compounds in the presence of complex environmental matrices. This article presents an overview of current knowledge on the TPs identified from biotic and abiotic degradation studies for these two estrogens and provides a list of the structures of TPs that have been identified to date, resulting from the biodegradation, ozonation, and oxidation of EE2 and E2. We also present the application of liquid chromatography with mass spectrometry (LC-MS), in conjunction with nuclear magnetic resonance spectroscopy (NMR) and X-ray crystallography, in identifying biotic and abiotic TPs of EE2 formed in pure cultures of Nitrosomonas europaea to illustrate how these instrumental techniques can complement each other to identify TPs of estrogens unambiguously.