Exploratory ATR-FTIR analysis with spectral deconvolution of polymer-like spectral signatures in suspended matter from the Atoyac River, Mexico

Abstract The Atoyac River is one of the most impacted freshwater systems in central Mexico due to sustained industrial, agricultural, and domestic discharges. Despite increasing concern regarding plastic contamination in rivers, information on polymer-related materials in this system remains limited. In this study, a qualitative and exploratory assessment of polymer-like spectral features in suspended matter was conducted along a 43-km section of the Atoyac River. Water samples were collected at six sites representing contrasting land use influences and analyzed directly by ATR-FTIR spectroscopy without chemical or enzymatic removal of organic matter. To improve interpretation of the complex spectra obtained from this highly polluted matrix, Gaussian deconvolution was applied to overlapping absorption regions. Recurrent infrared bands compatible with aliphatic, aromatic, ester, carbonate, and amide-containing structures were detected, showing spectral similarity to common synthetic polymers such as polyethylene-, polypropylene-, polyethylene terephthalate-, polystyrene-, polycarbonate-, and polyamide-like materials. A prominent absorption near 1121 cm⁻ 1 , consistent with sulfonated functional groups commonly associated with textile dyes and other industrial sulfonated compounds, was observed at sites influenced by textile activity. Given the absence of organic matter digestion, the results are interpreted as indicative of polymer-like spectral signatures rather than definitive microplastic identification. This work demonstrates the potential of ATR-FTIR combined with spectral deconvolution as a rapid screening approach for polymer-related contamination in complex freshwater environments and provides a qualitative baseline for future studies employing standardized microplastic extraction and quantification protocols.