Microplastics and nanoplastics in indoor environments: Current knowledge and future research

Microplastics and nanoplastics (MNPs) are emerging contaminants detected ubiquitously in ecosystems and human populations, with their presence indoors posing potential health risks to building occupants. This paper synthesizes the published studies, up to June 2024, on measurement techniques, indoor levels, and human exposure related to MNPs. In total, 31 original research articles providing quantitative data on indoor MNPs across 46 countries were analyzed. Most studies were conducted in residential settings, with additional investigations in universities, schools, offices, and other indoor spaces. Mass concentrations of indoor MNPs were determined by Py-GC-MS, LC-MS and gravimetric determination, while the number concentrations were determined by microscopy, infrared spectroscopy, or Raman spectroscopy. Reported MNP concentrations in indoor settled dust, fallout particles, and airborne particles in residences ranged from 1000 to 33,000 μg/g, 526 to 9981 items/m²/day, and 0.47 to 2700 items/m³, respectively. The predominant polymers identified were polyethylene terephthalate, polycarbonate, polyethylene, polypropylene, polyvinyl chloride, polystyrene, and polyester, exhibiting diverse shape, size and color. This review consolidates current knowledge on the measurement techniques and levels of MNPs in indoor environments and identified four priority areas for future research: (1) standardization of measurement protocols, (2) characterization of spatiotemporal variation, (3) epidemiological studies on health impacts in building occupants, and (4) development of mitigation strategies.