Occurrence and removal of free and conjugated estrogens in wastewater and sludge in five sewage treatment plants

The occurrence and fate of free and conjugated estrogens were investigated in wastewater and sludge from five sewage treatment plants (STPs) in Guangdong Province, China. Estrone (El) and 17 beta-estradiol (E2) were found in all influent samples at concentrations of 69.3-280 ng L-1 and 1.3-30 ng L-1, respectively. The concentrations of conjugated estrogens were from ND (not detected) to 7.6 ng L-1. High concentrations (27.6-235 ng g(-1)) of E1 were found in sludge of some STPs indicating that sorption was an important estrogen removal mechanism. According to the mass flux analyses for estrogens in STP-A, E2 was mainly removed in the anaerobic process and E1 removal was the combined efforts of biodegradation and sorption. Abnormally high concentrations of EE2 (42.6-246 ng L-1), detected with gas chromatography-mass spectrometry, were found in all influent samples of the STPs, therefore interlaboratory analysis with liquid chromatography-tandem mass spectrometry was conducted for confirmation, which detected no EE2 at all. In consideration of the rather lower estimated EE2 concentration than the measured value, it was speculated that the presence of interfering substances like tetracosanic acid in the matrix could lead to overestimation of EE2 concentration. Overall, the effluents still pose potential estrogenic effect to the downstream aquatic organisms.