Ultrafine particles: Sources, toxicity, and deposition dynamics in the human respiratory tract —— experimental and computational approaches

Ultrafine particles (UFPs ≤ 100 nm) pose significant health risks, including respiratory and cardiovascular diseases, and cancer. This review consolidates main sources, toxicity, and exposure assessment approaches to elucidate the deposition dynamics of UFPswithin the human respiratory tract. Key factors influencing the deposition fraction (DF) are highlighted. Our findings indicate that the DF surpasses 50% for particles ≤50 nm and reaches up to 70% for particles ≤30 nm, impacting both adults and children. Vulnerable populations, such as children and individuals with pre-existing health conditions, are disproportionately affected, yet research focusing on these groups remains scarce. Methodological deficiencies, including high costs, simplifying assumptions, and computational constraints, challenge prediction accuracy. Experimental methods struggle to capture temporal fluctuations, while computational models fail to account for complex phenomena. Addressing these gaps is crucial for refining public health regulations and advancing nanomedicine. An improved understanding of UFPs dynamics will enhance protective measures and nanomedicine applications, particularly in targeted drug delivery and diagnostics. This review emphasizes the need for innovative experimental and computational methods to study UFPs deposition dynamics, ultimately advancing our understanding of UFPs' impact on human health.