Abstract:In this study, we attempted to verify the hypothesis that total metals bound to dust of different particle sizes may reflect pollution levels, but cannot predict its bioavailability and risks in human health assessments. Dust samples were collected using active sampling method; during the dry season months of November, 2014 to March, 2015 at different locations in Akure (7˚10ʹN and 5˚15ʹE). The samples were sorted into different particle sizes (< 10µm, 10 -50 µm, >50µm), analyzed for some physicochemical properties and assessed for metals bioavailability using two-step physiological extraction method. The amount of metals (Cd, Cu, Cr, Ni, Pb, Zn and Mn) released in each particle sizes were determined using Perkin-Elmer 6000 Inductively Coupled Plasma -Atomic Emission Spectrometry (ICP-AES) analysis. The results showed that bioavailability of some metals (Cd, Ni, Pb, and Zn) decreases with increasing particle sizes, however, the reverse trend was observed for Mn, Cu and Fe concentrations. This may be attributed to some combination of physicochemical characteristics of the dust and metal speciation. Hence, it was concluded that metal bioaccessibility in dust can best be described by the knowledge of physicochemical characteristics. The exposure dose of the metals showed that cancer risks due to inhalation were very high when compared to other exposure routes (ingestion and dermal contact). The calculated non-cancer (HQ) and cancer risk (HI) for humans in the area showed values higher than unity, indicating possibility of the metals' body burden. Key Words: dust; bioavailability; particle sizes; heavy metals; health risk; exposure IntroductionDusts are finely divided particulate matters that are generated during human activities; sweeping, quarrying, metal fabrication, etc and are readily lifted by wind. Once generated and released to the atmosphere, they travel long distances from emission point source by turbulent atmospheric currents and finally settles either by gravity under condition of calm or brought to the surface by precipitation [1]. In the course of transportation, the suspended metals are loaded to particulates; hence the dust creates a reserve pool of metals in urban atmosphere [2]. In recent time, nonoccupational exposures to dusts in urban atmosphere worldwide have aroused much attention due to its associated health effects. For example, on breathing air containing metal laden particles, the smaller particles can reach the wind-pipe (trachea) and eventually dissolve in the blood stream. According to TUC [3], the two most serious health problems associated with dust are; cancers of the lungs, throat and nose, and other lung conditions called chronic obstructive pulmonary diseases (COPD) which include chronic bronchitis and emphysema. A report in 2007 gave a likely figure of between 7,000 and 8,000 for cancers of the lung and the nose due to exposure dust at work [2].