Quantification of estrogen concentration in a creek receiving wastewater treatment plant effluent Adebayo O. Adeyeye & Brian G. Laub Received: 26 July 2019 /Accepted: 2 June 2020 # Springer Nature Switzerland AG 2020 Abstract Estrogen in streams threatens aquatic ani- mals, especially where wastewater treatment plant (WWTP) effluent contributes to baseflow. We investi- gated total estrogen (E1+E2+E3) as estradiol equivalent (E2) and ethynylestradiol (EE2) concentration in Cibolo Creek (Cibolo), a groundwater-fed stream near San Antonio, TX, receiving effluent via two WWTP. We collected water samples bi-monthly from late spring to early fall 2018 in Cibolo and WWTP effluent, and used ELISA analysis and discharge measurements to deter- mine concentrations and loads of estrogens. We mea- sured several environmental variables to investigate what factors influenced estrogen concentrations in Cibolo downstream from WWTP inputs. Mean concen- trations of WWTP effluent (E2, 41.43 ± 15.48; EE2, 11.40 ± 2.07 ng L -1 ) were higher compared with con- centrations in Cibolo, both downstream (E2, 30.09 ± 25.85; EE2, 6.33 ± 1.92 ng L -1 ) and upstream (E2, 12.91 ± 11.12; EE2, 4.5 ± 1.38 ng L -1 ) of WWTP in- puts. Both E2 and EE2 concentrations decreased down- stream from WWTP inputs, a section of stream without large quantities of fine sediments for sorption, indicating potential dilution or chemical and biological degrada- tion. Effluent into Cibolo via the first, and older, WWTP contributed the most estrogen load in Cibolo. Median concentrations of E2 and EE2 were 19 and 5 ng L -1 , respectively, downstream of WWTP inputs, concentrations known to affect reproductive processes of aquatic biota and impair human health. Results sug- gest estrogens may pose a risk to aquatic ecosystems wherever WWTP effluent comprises a majority of baseflow, though further studies are required in this stream to verify biological impacts. Keywords Estradiol . Ethynylestradiol . Cibolo Creek . Wastewater treatment plant (WWTP) effluent . Water quality Introduction Water pollution is a global threat to drinking water and aquatic biota (Vorosmarty et al. 2010). Some major sources of pollution include treated industrial and mu- nicipal discharges (Ting and Praveena 2017), organic manures (Adeel, Song, Wang, Francis, and Yang 2017), rising population, rapid industrialization, accelerating urban growth, deforestation, industrial and municipal untreated effluent discharge, use of non-biodegradable pest control, and use of chemical fertilizers instead of organic manures, all frequently exacerbated by the ab- sence of environmental rules and regulations (Dawodu, Aderolu, Elegbede, and Adekunbi 2015). There have also been rising concerns about emerging contaminants such as pharmaceuticals and hormonal drugs, particu- larly natural and synthetic estrogens (Kolpin et al. 2002; Ebele, Abdallah, and Harrad 2017). Estrogens are often present in aquatic environments and drinking water at detectable concentrations, causing potential harm to Environ Monit Assess (2020) 192:426 https://doi.org/10.1007/s10661-020-08394-z A. O. Adeyeye : B. G. Laub (*) Department of Environmental Science & Ecology, College of Sciences, The University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, USA e-mail: brian.laub@utsa.edu