<jats:title>Abstract</jats:title> <jats:p>Water samples from seven Matagorda Bay locations were collected in spring, summer, and fall to assess micro- and nano-plastics contamination. Samples were oxidatively digested (30% H2O2), filtered, dried, and analyzed by Fourier Transform Infrared spectroscopy FT-IR ATR, Raman spectroscopy, Differential Scanning Calorimetry DSC, and Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy SEM-EDS. The identification of micro- and nano-plastics in estuarine waters is complicated by high salinity and inorganic matrices that can obscure or mask polymeric signals. To address this challenge, an integrated analytical approach was employed, combining vibrational spectroscopy, thermal analysis, and electron microscopy to compensate for the limitations of individual techniques. While surface-sensitive and element-specific methods were influenced by salt encapsulation, differential scanning calorimetry provided complementary bulk thermal evidence of polymeric materials embedded within the inorganic matrix. The spectra consistently showed peaks at ∼3300, 1630, and 1100 cm−1, indicating amine and hydrocarbon groups associated with synthetic polymers. The thermograms of DSC for fall and summer revealed three melting transitions (∼105–110 °C, ∼150 °C, ∼220 °C), consistent with polyethylene PE, polypropylene PP, polyvinyl chloride PVC, and high-melting polyamides PA or polystyrene PS. By contrast, spring samples showed only two transitions (∼85–95 °C, 140–150 °C), suggesting absence of some micro/nano-plastic materials. The outcomes of SEM-EDS demonstrated that the dried residues were dominated by inorganic salts (sodium Na, magnesium Mg, calcium Ca, sulfur S, chlorine Cl) with little detectable carbon, implying micro- and nano-plastic particles were embedded in a salt matrix. Overall, the data suggests the presence of common plastics (PE, PP, PVC, PA) in Matagorda Bay waters, with possible seasonal variation. The prevalent salt background highlights analytical challenges in detecting plastics in estuarine samples. Combining DSC technique alongside SEM-EDS and FT-IR show micro/nano-plastic particles encapsulation within inorganic salt. These findings underscore the plastic pollution in this coastal system and the need for rigorous monitoring and improved isolation of microplastics from saline matrices.</jats:p>