This study aimed to assess the ecological and human health risks associated with heavy metals in dust samples collected from a densely populated urban area in Tehran, Iran. We measured the concentrations of arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), and lead (Pb) in 12 dust samples (triplicate) from both indoor and outdoor environments in two different seasons using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Human health risk and ecological risk indices were then calculated based on the measured metal concentrations. The average concentrations of As, Cd, Cr, Cu, and Pb were 3.39 ± 1.33, 0.37 ± 0.54, 19.22 ± 15.46, 69.5 ± 34.5, and 70.6 ± 65.03 mg/kg for indoor samples, and 22.16 ± 15.59, 9.21 ± 6.67, 114.57 ± 69.96, 461.81 ± 284.71, and 481.7 ± 219.98 mg/kg for outdoor samples, respectively. Metal concentrations were significantly higher in outdoor samples and showed seasonal variation, with peak levels observed during the warm season. The geoaccumulation index (Igeo) indicated contamination levels ranging from unpolluted to moderately to severely polluted. Cu showed the highest enrichment factor (EF), with values of 5.42 indoors and 4.22 outdoors. The pollution load index (PLI) suggested contamination in most months, excluding August, January, February, and March. In September, indoor levels of Cr and Pb posed non-carcinogenic risks to children, while outdoor levels of As, Cr, and Pb were elevated in July and August, with Cd also contributing in September. Although the total carcinogenic risk (TCR) was generally below 1, Cr exposure outdoors in September exceeded acceptable limits for children. These findings underscore the substantial ecological and health risks posed by heavy metal-contaminated urban dust, particularly during warmer months, and highlight the urgent need for targeted monitoring and mitigation strategies in highly polluted urban environments.
