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Revealing Hidden Interrelationships of PFAS-Pesticides-Microplastics in Urban Waters: Integrating Target and Non-Target Chemical Analyses Across Mexico
Summary
Researchers found that Mexican urban water sources contain a dangerous cocktail of chemicals including pesticides, "forever chemicals" (PFAS), and microplastics that work together in ways we don't fully understand. The highest contamination levels were found near farming areas where irrigation water mixes with city sewage, and many of these pollutants aren't removed by current water treatment methods. This matters because millions of people rely on these water sources for drinking water, but we're not monitoring most of these chemical mixtures that could harm human health.
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 (