| Summary: | The concentrations of PM10 were measured both indoors and outdoors at 10 roadside residential buildings in Phitsanulok, Thailand during the dry and wet seasons of 2014. Seven trace metals (Zn, Fe, Pb, Cd, Ni, Cu and Cr) were also analysed in PM10. The monthly average concentrations of indoor and outdoor PM10 were 41.5 to 105.3 μg m–3 and 95.2 to 145.1 μg m–3, respectively. PM10 concentrations were significantly higher during the dry season compared to the wet season. The indoor/outdoor (I/O) ratios were less than one indicating that the particulate matter originates from the outdoor environment. Overall, the average concentrations of heavy metals in PM10 ranged from 0.2 to 2.7 μg m–3 and 0.5 to 7.1 μg m–3 for the indoor and outdoor environments, respectively. A strong positive correlation in indoor PM10 was found between Zn and Cu, Zn and Ni, and Cu and Ni. Zn and Ni, Pb and Cu, Cu and Ni, Cd and Ni, and Zn and Cu showed strong positive correlations in the outdoor environment. The enrichment factors of Zn, Cu, Pb, Cr and Ni were less than one suggesting that the metals in indoor PM10 have originated from crustal materials. For the health risk assessment, Cr was found to have the highest excess cancer risk in an evaluation using an Integrated Risk Information System. © 2016 Universidad Nacional Autónoma de México
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