Photosensitized Degradation of 17β-estradiol and 17α-ethinylestradiol: Role of Humic Substances Fractions

Photodegradation of 17 alpha-ethinylestradiol (EE2) and 17 beta-estradiol (E2) was investigated under simulated solar radiation. Photodegradation kinetics in the absence and presence of humic substances (HSs) fractions (humic acids [HAs], fulvic acids [FAs], and XAD-4), were compared. Although all three fractions were responsible for a noticeable increase on photodegradation rates, the effects were greater for FA and XAD-4. Half-life time decreased from 46 and 94 h (direct photodegradation) for EE2 and E2, respectively, to 6.4, 2.1, and 2.7 h (for EE2) and 5.7, 2.9, and 3.1 h (for E2) in the presence of HAs, FAs, and XAD-4, respectively. The XAD-4 fraction results were similar to those of FAs, which is considered the most photochemically active fraction of HSs. Studies were also conducted in organic matter-rich environmental water matrices. After 5 h, photodegradation ranged from 44 to 94% for EE2 and from 27 to 95% for E2, compared with 16% for EE2 and 6% for E2 in ultrapure water. The maximum photodegradation was obtained in an estuarine water sample, known to be rich in FAs and XAD-4 fractions and poor in HAs, showing that not only is the presence of organic matter an important factor for the photodegradation increase, as also the type of organic matter is determinant.