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Airborne Microplastics in indoor environments: current knowledge, methodological challenges, and future directions
Summary
A review of 57 studies found indoor microplastic concentrations ranging up to 14,088 particles per cubic meter—exceeding outdoor levels by one to two orders of magnitude—with synthetic textile fibers as the dominant source and polyester, polyethylene, and polypropylene as the most common polymers. Given that humans spend most time indoors, indoor air represents a primary daily microplastic exposure pathway, with children potentially receiving higher doses relative to body weight.
Indoor environments are increasingly recognized as notable reservoirs and exposure pathways for airborne microplastics (AMPs). This narrative review shows the outcomes from 57 observational studies published between 2017 and 2025, focusing on the occurrence, abundance, and characteristics of MPs in residential and collective indoor spaces. Methodological variability strongly affects the comparability of results. In sampling, 56% of studies used active air collection, 37% passive techniques, and 5% combined strategies. Different pretreatment and analytical approaches were employed, including microscopy, µ-FTIR, µ-Raman, and Py-GC-MS. Reported concentrations range from 0.5 to 14,088 MPs/m³ in residential settings and from 2 to 8,305 MPs/m³ in collective environments, exceeding outdoor control levels (mean ∼260 MPs/m³) by 1 to 2 orders of magnitude. Temporal and spatial variability is a key factor influencing concentrations, along with synthetic textiles, limited ventilation, finishing materials, the number of occupants, and seasonal effects. Fibers dominate in most indoor spaces, with polyester, polyethylene, polypropylene, and nylon as the most frequently identified polymers. The human exposure assessment suggests AMP intake ranging from hundreds to several thousand particles per day, with children potentially assuming higher doses per body weight. However, variability in dose metrics limits comparability across studies. Overall, the findings underscore indoor air as a critical but underexplored exposure pathway, with significant knowledge gaps regarding methodologies and toxicological implications. This review outlines unmet needs and proposes a roadmap to move towards harmonized protocols integrating toxicological assays as priorities to strengthen risk assessment and inform mitigation strategies for AMPs in indoor environments.