Microplastics in indoor air from Birmingham, UK: Implications for inhalation exposure

Microplastics (MPs) are a group of emerging contaminants that attracted increasing scientific and societal attention over the past decade. So far, most studies on MPs focus on characterizing their occurrence, fate, and impact in the aquatic environment. In contrast, very little is known about the magnitude, patterns, and associated risks of human exposure to MPs, particularly indoors, despite people spending most of their time indoors. This paper provides the first study hitherto of MPs in indoor air via both active and passive sampling from 30 homes and 30 workplaces in Birmingham, UK. The average concentration of MPs in the active air samples was 15.6 ± 5.4 MP/m³ in homes and 13.1 ± 6.5 MP/m³ in workplaces. For atmospheric deposition samples (passive sampling), the average MPs concentrations were 3735 ± 1343 MP/m²/day in homes and 3177 ± 1860 MP/m²/day in workplaces. Mean concentrations of MPs in UK homes were significantly higher (P<0.05) than those in workplaces for both active and passive air samples. This was mainly driven by carpeted floors in all the studied homes, while 13 of the sampled workplaces were uncarpeted. MPs concentrations in atmospheric deposition (passive) samples were significantly higher (P < 0.05) than airborne (active) MPs samples in the studied microenvironments. Nonetheless, a strong correlation (P < 0.01) was observed between the concentrations of MPs measured by active and passive sampling, indicating common sources of MPs to both active and passive samples collected from the same microenvironments. In terms of morphology, fibres were the dominant shape of MPs, followed by fragments, constituting together ≥90% of the identified MPs in all samples, with the remaining minor percent made up by foams. Airborne MPs were dominated by particles in the size range (10-25 μm), and the particles abundance decreased with increasing particle size. MPs in atmospheric fallout particles, were dominated by larger particles (50-100 μm) with lower contribution from smaller particles (10-25 μm) compared to airborne particles. Nonetheless, combined with the predominance of fibres, this raises concern over the risk from inhalation exposure because MPs fibres in the detected size ranges were observed to penetrate into human lung tissue. PET and PVC were the most abundant polymer types in the studied samples followed by PP and PE. The average daily inhalation exposure of UK adults and toddlers was estimated at 3.0 and 6.3 MP/kg body weight/day, respectively. The higher inhalation exposure of UK toddlers raises concern due to their incompletely developed immune and nervous systems.