Abstarct: This study aimed to investigate the environmental geochemistry of potentially toxic elements (PTEs) in indoor and outdoor dust of Shahroud city, determine their sources, and assess the associated health risks. A total of 30 dust samples (15 indoor and 15 outdoor) were collected from different areas of the city and analyzed for the concentrations of 34 elements using ICP-MS. Both single geochemical indices (enrichment factor, geo-accumulation index, single pollution index) and integrated indices (Nemerow index, pollution load index, comprehensive pollution index, and potential ecological risk index), along with statistical analyses (Pearson correlation, principal component analysis), were employed to evaluate contamination levels and identify potential sources. The results showed that concentrations of Zn, Pb, and As were significantly higher in indoor dust compared to outdoor dust, whereas Cd and Sb exhibited higher concentrations outdoors. Pollution indices indicated severe to very severe contamination in some indoor locations (e.g., residential areas on 22 Bahman Street and Alborz Town) and outdoor locations (e.g., the industrial zone). Health risk assessment revealed that children are more vulnerable, with ingestion identified as the dominant exposure pathway. Notably, Pb showed hazard quotient (HQ) values greater than 1 for children at all stations. Carcinogenic risks associated with As, Cd, Cr, and Ni exceeded the safe threshold (CR > 10⁻⁴) in certain locations, particularly for children, whereas Pb did not show significant carcinogenic potential. Statistical analyses confirmed mixed natural and anthropogenic sources for these contaminants, including traffic emissions, industrial activities, and weathering of construction materials..