Non-targeted Analysis of Emerging Contaminant Characteristics and Distribution Differences in Wastewater from a Metro Maintenance Depot
Emerging contaminants (ECs) in wastewater from urban transportation infrastructure remain poorly characterized. This study employed high-resolution mass spectrometry (HRMS)-based non-target screening to systematically identify the composition and spatial distribution of ECs in wastewater from three functional zones of a metro maintenance depot: storeroom (S1), office/residential area (S2), and final discharge outlet (S3). A total of 417 contaminants were detected, spanning eight categories including industrial materials, pharmaceuticals, pesticides, and natural products. Among these, 48 substances were identified with Level 1 confidence via spectral matching. Pesticides exhibited the highest detection frequency and concentration levels, representing the primary contaminant load. Semi-quantitative concentration heatmaps of 24 pesticides revealed significant spatial variation: S2 showed the highest number and concentration of contaminants, reflecting inputs from landscaping and vector control; S1 and S3 showed lower levels, indicating dilution, migration, and attenuation. Representative pesticide bifenox displayed a clear concentration gradient (S2 > S1 > S3), suggesting transport mechanisms such as surface runoff, hydraulic transfer, and sorption. These findings underscore the complexity and diversity of EC sources in metro depot wastewater, highlight the need to prioritize pesticides in regulatory management, and provide fundamental data for understanding EC environmental behavior and informing water environment risk assessment.