A comprehensive study was conducted at two wastewater treatment plants (WWTPs) and one water treatment plant (WTP) in Windsor, Ontario, Canada. The occurrence of 220 emerging and legacy compounds, their removal efficiencies by the existing treatment processes, and their potential environmental impacts were studied. The results are reported in a two part paper. In this part (I), the occurrence and removal efficiencies are presented. Three of the 47 target pharmaceutically active compounds (PhACs) and endocrine disrupting compounds (EDCs) contributed 89–96% of the total concentration of PhACs/EDCs in the WWTP influents. They were acetaminophen, ibuprofen, and naproxen. The existing treatment processes successfully removed between 95 and 98% of ‘all’ PhACs/EDCs, primarily due to the high removal rates of these three analgesics. Concentrations of PhACs/EDCs detected at the WTP intake were two to three orders of magnitude lower than those in the effluent of the upstream WWTP. These concentrations remained relatively unchanged in the finished drinking water, indicating the WTP's low removal efficiency for trace amounts of them. Polybrominated diphenyl ethers (PBDEs) were detected at concentrations as high as 150 ng/L (for PBDE-209) in the WWTPs’ influent, and removed at 86–96% efficiency. PDBE effluent concentrations were mostly below 1 ng/L at both WWTPs, with a maximum of 9 ng/L for PBDE-209. Octylphenol, nonylphenol, and nonylphenol ethoxylates concentrations were monitored in one WWTP's effluent, and ranged between undetectable and 286 ng/L (LoDs varied between 1.3 and 15.2 ng/L).

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