<![CDATA[Graphical Abstract Highlight Research 1. Microplastic abundance and polymer profiles were evaluated in traditional brine and boiled sea salt. 2. A sharp surge in particle concentration was confirmed during the transformation from brine to solid salt crystals. 3. Microscopic analysis revealed that fibre structures were the most dominant shape across all sampling stages. 4. FTIR spectroscopy successfully fingerprints synthetic polymers, including polyethylene and polyacrylonitrile. Abstract Microplastic contamination has emerged as a growing environmental concern in coastal ecosystems and poses potential risks to food safety through its accumulation in sea salt. Traditional salt production systems are particularly vulnerable to contamination by marine debris; however, information on microplastic occurrence in traditionally boiled sea salt produced using saline–soil filtration systems remains limited. Therefore, this study aimed to investigate the abundance, morphological characteristics, and polymer composition of microplastics in brine and crystallised sea salt traditionally produced in Watu Asa Village, Central Sumba, East Nusa Tenggara, Indonesia. A descriptive-exploratory study employing purposive sampling was conducted in a traditional salt production system. Brine samples were collected from saline-soil filtration units prior to boiling, while salt crystal samples were obtained after the brine-boiling process. Microplastics were isolated through density separation and oxidation using 30% H₂O₂, followed by morphological characterisation under an optical microscope at 40× magnification. Polymer identification was performed using Fourier-transform infrared spectroscopy (FTIR). The results revealed a substantial increase in microplastic concentration during the conversion of brine into salt crystals. Microplastic abundance increased from 285 ± 17.32 particles L⁻¹ in the filtered brine to 35,000 ± 2,500 particles kg⁻¹ in the boiled salt crystals. Fibres were the dominant microplastic morphology in all samples, followed by fragments and films. FTIR analysis confirmed the presence of several synthetic polymers, including polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and polyacrylonitrile (PAN). The hydroxyl signal (3328.90 cm-1) previously assigned to poly(vinyl alcohol) (PVA) was reclassified as surface-bound moisture and weathering-induced oxidation products. Polyurethane (PU) was excluded as it was not detected in the confirmed spectral library matching. In conclusion, the traditional brine-boiling process concentrates microplastics in the final salt product, potentially increasing consumer exposure to microplastic contamination. Further research should evaluate practical filtration technologies for reducing microplastic loads during brine processing and assess the long-term implications of microplastic ingestion through traditionally produced sea salt. ]]>
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