Unveiling N-nitrosomorpholine precursors in wastewater using nontarget, target analysis and transformation mechanism

N -nitrosomorpholine (NMOR), as a highly carcinogenic N -nitrosamine, has been widely detected in urban sewer systems. NMOR ranged from 27.2 to 817 ng/L in winter, follow by summer (2.09–453 ng/L), in raw wastewater collected from pumping stations connected to a Wastewater Treatment Plant (WWTP). Especially in winter, NMOR was detected (200–295 ng/L) in the influent, with residue of 98.0–116 ng/L in the effluent. Therefore, it is necessary to control NMOR before the WWTP. However, the corresponding precursors and transformation mechanisms in sewer systems are not yet fully understood. This study has identified NMOR precursors in sewer systems by nontarget analysis combined with targeted analysis. NMOR formation was confirmed by nitrosation and chloramination through distinct pathways from a known (morpholine, MOR) and two unreported ( N -methylmorpholine, NMM and N -methylmorpholine- N -oxide, NMMO) precursors. In addition, NMM and MOR were detected up to 8.65 and 14.3 μg/L in raw wastewater, as well as up to 0.250 and 1.17 μg/L in the effluent. NMOR formation by chloramine could reach to 73.0 ng/L. This study demonstrated the extensive presence of NMOR precursors in raw and treated wastewater, in which new identified precursor NMM might significantly contribute formation of NMOR.