Settleable microplastics in residential buildings in a Middle Eastern area during warm and cool seasons; quantification, characterization, and human exposure assessment

Prolonged daily presence of the general public, combined with the existence of numerous plastic materials in residential buildings, may lead to significant exposure to indoor microplastics (MPs). This may be more heightened for settleable MPs, as they can be inhaled when airborne and ingested after deposition on interior surfaces. To date, such pollution in residential buildings has received limited attention, and the impact of change in season on it has not yet been well explored. Additionally, no information is available about it from the Middle East. In this study, fallout samples were collected over 45 days from residential buildings in Tehran megacity during the warm (spring) and cool (autumn) seasons of 2023. After sample pretreatment, MPs were analyzed by fluorescent microscopy and micro-Raman spectroscopy. The mean indoor MP deposition rate was 2.6 × 10±1.9 × 10 MP/m/day in spring and significantly reduced to 1.3 × 10±1.0 × 10 MP/m/day in autumn. The studied buildings were vacuum cleaned at least "once a week", and no significant difference was observed in MP deposition rates between the buildings with "once a week" and "≥twice a week" cleaning frequencies. Fibers and polyethylene terephthalate (PET) were the predominant identified MPs. The mean daily intakes were estimated to be 1.9 × 10±1.6 × 10 and 8.3 × 10±6.4 × 10 MPs in spring and autumn, respectively. Overall, the deposition and exposure rates of settleable MPs in residential buildings varied significantly between warm and cool seasons. The significant rate of exposure to indoor settleable MPs highlights the urgent need for effective measures to reduce human exposure in residential buildings, particularly during warm months.