Photodegradation of the steroid hormones 17β-estradiol (E2) and 17α-ethinylestradiol (EE2) in dilute aqueous solution

The photochemical transformation of natural estrogenic steroid 17β-estradiol (E2) and the synthetic oral contraceptive 17α-ethinylestradiol (EE2) has been studied in dilute non buffered aqueous solution (pH 5.5–6.0) upon monochromatic (254 nm) and polychromatic (λ > 290 nm) irradiation. Upon irradiation at 254 nm, the quantum yields of E2 and EE2 photolysis were similar and evaluated to be 0.067 ± 0.007 and 0.062 ± 0.007, respectively. Upon polychromatic excitation, and by using phenol as chemical actinometer, the photolysis efficiencies have been determined to be 0.07 ± 0.01 and 0.08 ± 0.01 for E2 and EE2, respectively.For both estrogens, photodegradation by-products were identified with GC/MS and LC/MS. In a first step, a model compound – 5,6,7,8-tetrahydro-2-naphthol (THN) –, which represents the photoactive phenolic group, was used to obtain basic photoproduct structural informations. Numerous primary and secondary products were observed, corresponding to hydroxylated phenolic- or quinone-type compounds.