Portuguese saltpans: therapeutic potential of salts in thalassotherapy

Salts produced in traditional saltpans represent a potentially valuable natural resource for wellness and therapeutic applications. However, their properties must be properly assessed to support their safe and effective use in thalassotherapy and dermatological treatments. This study characterized salt samples from traditional and semi-industrial saltpans located in the Ria Formosa (southern Portugal) and Ria de Aveiro (northwest Portugal) coastal lagoons, aiming to evaluate their potential for thalassotherapy and dermatological applications, with particular attention to the influence of oxygen exposure after collection. Twelve representative salt samples were collected and analyzed for mineralogical identification and chemical composition (major, minor, and trace elements, soluble organic matter), complemented by Raman spectroscopy, SEM-EDS, and GC-MS analyses. All samples revealed halite as the dominant mineral phase, with the presence of accessory evaporite minerals, including gypsum, calcite, kieserite, and anhydrite. Raman and SEM-EDS analyses revealed the occurrence of hydrated Mg-sulfates at crystal surfaces, suggesting secondary crystallization processes during evaporation. Comparative analyses between wet and dried samples showed that atmospheric exposure promotes mineralogical diversification, including dehydration reactions and carbonate precipitation. In contrast, submerged salts preserved simpler assemblages dominated by halite, gypsum, and Mg-sulfates, with an absence of PTEs, reflecting a high purity level. Geochemical analyses confirm Na-Cl-type salts with minor Mg, Ca, K, and S contributions, while trace elements such as Cr, Ni, and Zr occur mainly as detrital impurities. These findings highlighted the mineralogical characteristics of Portuguese saltpan-derived salts and support their potential valorization for thalassotherapy and wellness-related applications, while emphasizing the importance of safety assessment.