Key Takeaways & Executive Findings
- •• • Non-target HRMS screening identified 417 emerging contaminants across 8 categories in metro depot wastewater, with 48 at Level 1 confidence; pesticides dominated in detection frequency and concentration, constituting the primary contaminant load—underscoring the need for pesticide-focused monitoring in urban transport infrastructure. • • Spatial distribution varied significantly: industrial materials concentrated in storeroom S1, pharmaceuticals peaked in office/residential S2, and pesticides were highest at S2 but still present at S3, indicating multi-source inputs and mixed dilution/attenuation—necessitating zone-specific management strategies. • • Semi-quantitative analysis of 24 pesticides revealed distinct concentration gradients; e.g., bifenox concentrations were 515.68 ng/L at S2, 60.07 ng/L at S1, and 35.69 ng/L at S3, demonstrating dilution and attenuation along the drainage path—critical for predicting environmental transport and risk. • • Detection of certain pesticides only at the final discharge outlet (S3) suggests potential transformation products or external inputs, highlighting that terminal effluent may pose unrecognized risks—emphasizing the need for comprehensive monitoring beyond source zones.
Abstract
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.
1. Introduction
Emerging contaminants (ECs) in wastewater from non-traditional sources, such as metro maintenance depots, remain largely unexplored despite their potential ecological and health risks. Existing studies focus on rivers, lakes, and wastewater treatment plants, leaving a critical gap in understanding EC profiles from urban transportation infrastructure. Metro depots harbor diverse pollution sources—lubricants, cleaning agents, pesticides, and pharmaceuticals—that enter drainage systems and may threaten aquatic ecosystems. The complexity and concealment of these sources exacerbate environmental risks, yet systematic data on EC types, concentrations, and distribution in such settings are absent.
Non-targeted high-resolution mass spectrometry (UPLC-HRMS) offers a powerful solution, enabling comprehensive screening without pre-defined targets. This technique identifies unknown contaminants via MS/MS fragmentation and database matching, making it ideal for complex matrices like metro depot wastewater. By applying this approach to three functional zones of a metro depot, this study provides the first systematic characterization of ECs in this context, revealing spatial distribution patterns and highlighting pesticides as a priority concern. The findings offer essential data for source apportionment and environmental risk management in urban water systems.
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PAN Jihao, LIU Zhiying, ZHOU Zailing, WU Rongchu, CHEN Zhenguo, QIU Guanglei (2026). Non-targeted Analysis of Emerging Contaminant Characteristics and Distribution Differences in Wastewater from a Metro Maintenance Depot. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202604003
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Frequently Asked Questions
What is the detection confidence level of the identified contaminants, and how was it established?
Among 417 detected contaminants, 48 were identified with Level 1 confidence, meaning they were confirmed by matching retention time, accurate mass, and MS/MS fragmentation against reference standards. This high-confidence subset was used for detailed spatial analysis, ensuring reliability of the reported concentrations.
How do contaminant concentrations vary across the three functional zones, and what are the implications for treatment design?
Semi-quantitative concentrations of 24 pesticides showed S2 (office/residential) had the highest levels, e.g., bifenox at 515.68 ng/L, while S1 (storeroom) and S3 (outlet) had lower levels (60.07 and 35.69 ng/L, respectively). This gradient indicates dilution and attenuation along the drainage path, but also suggests that source control in residential areas is critical. Treatment systems should account for peak loads from S2 and potential transformation products at S3.
What are the potential mechanisms for the observed spatial distribution of pesticides, and how can they be validated?
The gradient (S2 > S1 > S3) suggests surface runoff, hydraulic transfer, and sorption processes. However, the study did not sample green belts or external runoff, so these mechanisms are inferred. Future research should include multi-source sampling and process tracking to confirm transport pathways and transformation.
Which pesticide concentrations exceeded regulatory or ecotoxicological thresholds, if any?
The paper does not compare concentrations to specific regulatory limits, but the highest detected concentration (bifenox at 515.68 ng/L) is in the ng/L range typical for ECs. While not immediately toxic, such levels may pose chronic risks to aquatic life, emphasizing the need for risk assessment based on ecotoxicological data.
How scalable is the non-targeted HRMS method for routine monitoring in other metro depots?
The method is transferable, but requires high-resolution mass spectrometry and comprehensive databases. For routine application, targeted methods for the identified high-priority pesticides (e.g., bifenox) could be developed for cost-effective monitoring, while non-targeted screening remains valuable for discovering new contaminants.
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