As a recently developed disinfection technology, ultraviolet (UV)/chlorine treatment has received much attention. Many studies have evaluated its effects on pathogen inactivation, contaminant removal, and formation of disinfection by-products (DBPs), but its potential for environmental estrogen removal and estrogenic DBP generation, which can also be a risk to both ecosystem and human health, have not been evaluated. In this study, UV/chlorine treatment resulted in a greater removal of estrogenic activity in synthetic effluent samples containing 17 beta-estradiol (E2) than did UV or chlorine treatment alone regardless of the water quality. For both the UV/chlorine and chlorine treatments, there was significant interference from NH3-N, although the UV/chlorine treatment was less affected. Estrogen receptor based affinity chromatography was used to isolate the specific estrogenic DBPs, and a novel product, with high estrogenic activity compared to E2, Delta 9(11)-dehydro-estradiol, was identified. It was generated by all three treatments, and might be previously mistakenly recognized as estrone (E1). This study demonstrated that UV/chlorine is a better treatment for the removal of 17 beta-estradiol than chlorine and UV alone. The new identified estrogenic DBP, Delta 9(11)-dehydro-estradiol, which can be isolated by affinity chromatography, could be an emerging concern in the future. (C) 2016 Elsevier B.V. All rights reserved.