Revealing Hidden Interrelationships of PFAS-Pesticides-Microplastics in Urban Waters: Integrating Target and Non-Target Chemical Analyses Across Mexico

Urban aquatic systems are increasingly burdened by complex mixtures of emerging contaminants whose interactions and cumulative risks are often underestimated by conventional monitoring strategies focused on individual compound classes. The co-occurrence of pesticides, per- and polyfluoroalkyl substances (PFAS), pharmaceuticals, volatile organic compounds (VOCs), and microplastics (MPs) poses significant challenges for water quality management in rapidly urbanizing and agro-industrial regions. Here, an integrated framework combining targeted and non-target analytical approaches was applied to assess emerging contaminants across surface water, groundwater, wastewater, and reservoir systems in multiple Mexican cities. Surface waters influenced by intensive agricultural and peri-urban activities exhibited the highest contaminant burdens. Pesticide concentrations ranged from 0.01 to 92 µg L⁻¹, with peak loads in agro-industrial reaches of the Pesquería basin where irrigation return flows and municipal wastewater converge. Transformation processes unified contaminant behavior along the river–reservoir continuum. The widespread detection of neonicotinoid transformation products and PFCA homologues derived from precursor degradation demonstrates that transformation sustains long-term, low-level contamination rather than eliminating parent compounds. Non-target screening expanded chemical coverage beyond predefined target lists and revealed diverse regulated and previously unmonitored VOCs, including industrial solvents and fragrance-related compounds, many showing limited removal during wastewater treatment. Within the semi-arid Presa de la Boca reservoir, MPs were ubiquitous (4–66 particles L⁻¹; median 21 particles L⁻¹). Alkaline pH (8.09–8.60), elevated temperatures (27.6–34.1 °C), and low dissolved oxygen (2.7–3.7 mg L⁻¹) promoted MP weathering and fragmentation. Small particles (<500 µm ≈ 87%), fragments (57.8%), and fibres (35.6%) dominated, while metal enrichment on MP surfaces highlighted their role as secondary vectors linking particulate and dissolved contaminant pathways. Overall, this study demonstrates that integrated target and non-target approaches are essential for resolving interconnected contaminant behavior and supporting mixture-aware monitoring, risk assessment, and management strategies.