Biotransformation of estrone, 17β-estradiol and 17α-ethynylestradiol by four species of microalgae

Natural and synthetic estrogens have been widely detected in wastewater treatment plant (WWTP) influent and effluent as well as in the corresponding receiving aqueous environment and other ecosystems. Microalgae can be used to remove nitrogen and phosphorus in wastewater, but the species-dependent removal of estrogens needs further investigation. In this study we investigated estrone, 17β-estradiol and 17α-ethynylestradiol removals and transformation products by four common microalgae Haematococcus pluvialis, Selenastrum capricornutum, Scenedesmus quadricauda, and Chlorella vulgaris. It was found that H. pluvialis, S. capricornutum and S. quadricauda could more effectively remove all three estrogens in synthetic wastewater effluent. The estrogenic activities i.e. 17β-estradiol equivalency determined by yeast estrogenic screening assay showed substantial estrogenic activity reductions after biotransformation by H. pluvialis, S. capricornutum, and S. quadricauda. Quadrupole Time-of-flight Mass Spectrometry results identified several possible ring-cleavage metabolites as well as their metabolic pathways, which had not been reported yet, confirming the estrogen degradation rather than mere absorption or uptake by microalgae. The findings demonstrate that not only can some specific bacteria degrade estrogens, but also the widely living microalgae are able to degrade these emerging pollutants, suggesting that microalgae could be an advanced treatment of WWTPs to remove nutrients and estrogens.