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Background: Physical and biological properties of dust particles might affect the availability and distribution of chemicals associated to indoor dust; however it has not been adequately examined. In this study, household dust from Shanghai was fractionated into five particle sizes and size distribution, morphology, surface area, organic matter, microorganisms, elemental composition, metals and organophosphorus flame retardants (OPFRs) compositions were characterized. Also, household dust samples from Stockholm that has previously been characterized were included in the analysis of OPFRs for comparison. Results: The respirable fraction had a yield of 3.3% in mass percentage, with a particle size of 2.22 ± 2.04 µm. As expected, both metals and OPFRs concentrations increased with decreased particle size. Al and Fe dominated (66–87%) followed by the concentrations of Zn (5–14%) and Ga (1.8–5%) of the sum of 16 metals in the dust. The concentrations of OPFRs in Shanghai dust ranged from 5.34 to 13.7 µg/g (median: 7.21 µg/g), compared to household dust from Stockholm that ranged from 16.0 to 28.3 µg/g (median: 26.6 µg/g). Tris(2-chloroisopropyl) phosphate (TCIPP) and tris(2-chloroethyl) phosphate (TCEP) dominated in Shanghai dust samples while tris(2-butoxyethyl) phosphate (TBOEP) dominated in dust from Stockholm homes. Conclusion: The results showed that mass percentage for each particle size fraction was not evenly distributed. Furthermore, the particle-bound microorganisms and OPFRs increased with decreased particle size, whereas metals had the highest concentrations at specific dust sizes. Therefore, it is essential to select the proper particle size in order to assess any specific human exposure study to indoor pollutants. [ABSTRACT FROM AUTHOR]