Morphology and particle size distribution in the indoor dust: A hidden threat to human health?

Indoor house dust is emerging as a key contributor to human health issues. Particle size distribution and morphology represent risk factors that have been scarcely studied. In this study, indoor dust samples were collected from homes across two Mexican cities (Hermosillo and Mexico City) through a citizen science approach. Fourteen trace elements were analyzed using portable X-ray fluorescence. The particle size of coarse dust fractions and particle morphology were determined by resuspending the dust in an air chamber and examining it with scanning electron microscopy. At the same time, submicron particle distribution was characterized by dynamic light scattering. Trace metal concentrations were similar between the two cities, except for K, Mn, Rb, Sr, V, and Zr. Univariate comparisons confirm intercity differences for aspect ratio, circle equivalent diameter, and circularity. Mexico City contains large and smoother particles linked to combustion, whereas Hermosillo´s particles are small and angular, reflecting geogenic sources. Dynamic light scattering analysis confirmed the presence of nanoparticles in indoor dust, with mean particle sizes of 126.2 nm in Hermosillo and 142.7 nm in Mexico City, and polydispersity indices of 0.158 and 0.132, respectively. Crystalline particles smaller than 2.5 µm and nanoparticles may be considered emerging indoor pollutants, as chronic exposure could compromise the first line of defense of the human immune system and lung homeostasis. These findings underscore the potential health risks posed by indoor dust particles, highlighting the need for characterization of household dust fractions.