Retinoid X receptor activities of source waters in China and their removal efficiencies during drinking water treatment processes

There is increasing evidence of estrogenic activities of source waters and drinking waters in China based on estrogen receptors (ERs) testing. However, relating such activities to retinoid X receptors (RXRs) in both drinking and source waters are lacking. To rectify this situation, we assessed 23 source water samples from six major river systems in China. We also collected samples at various stages of water processing from three drinking water treatment plants (DWTPs) using a two-hybrid RXR yeast assay with and without metabolism. No RXR agonistic activity was observed, but significant antagonistic activity was detected in all sample extracts. The RXR antagonistic activities of source water sample extracts ranged from 15.2% to 57.8% without metabolism and 11.5% to 68.3% with metabolism, respectively. In the drinking water treatment processes, RXR antagonistic activities without metabolism and with metabolism of up to 31.4% and 37.5% were removed, respectively. Nevertheless, the remaining RXR antagonists in treated drinking water from these source waters could still be harmful to human health. To the best of our knowledge, the occurrence of in vitro RXR disruption activities in source and drinking water has not been previously reported in China. Therefore, an attempt was made to conduct detailed studies investigating RXR disrupting activities and their possible risks in source and drinking water.