UV photoconversion of environmental oestrogen diethylstilbestrol and its persistence in surface water under sunlight

As one of the most oestrogenic synthetic compounds in water environment, diethylstilbestrol (DES) has been studied for decades. Some studies showed that DES can be removed by ultraviolet (UV) irradiation. However, no one has paid attention to the formation of oestrogenic disinfection by-products (DBPs) and the persistence of DES in surface water remains a mystery. In this study, UV was found to be very effective in removing oestrogenic activity regardless of water quality. Three oestrogenic DBPs were specifically isolated by oestrogen receptor-based affinity chromatography and identified as 9,10-diethylphenanthrene-3,6-diol, cis-DES and Z,Z-dienestrol. Among them, 9,10-diethylphenanthrene-3,6-diol was proved to have stronger oestrogenic activity than E2, but it can be further photodegraded. In addition, DES was also demonstrated to be a photochromic compound, whose UV-induced intermediates can be transformed back to DES under sunlight, which significantly slows down the photodegradation of DES. This study solves the question as to why UV-degradable DES is still detectable in the ambient water and provides a deep understanding of DES removal during UV disinfection.