Children's exposure to airborne microplastics in school classrooms: linking indoor concentrations with respiratory deposition modelling

Ensuring good indoor air quality in schools is essential for healthy child development. Microplastics (MP) pollution in the air has attracted increasing attention in recent years due to the potential negative impact on human health, especially in indoor environments where people spend approximately 90% of their time. The present study is one of the first to combine real classroom airborne microplastic measurements with respiratory deposition and clearance modelling, enabling a health-relevant evaluation of lung-deposited dose in children. We collected total suspended particles from indoor air in 5 primary schools (n = 25) across the urban area of Barcelona to assess MP concentrations and composition. Quantitative analysis was performed by pyrolysis coupled to gas chromatography high-resolution mass spectrometry, a size-unrestricted technique targeting ten polymer types. Total MP concentrations ranged from 64.9 ± 24.3 to 178.7 ± 47.7 ng/m 3 with a mean value of 99.7 ± 44.4 ng/m 3 . Nylon, 6,6 and nitrile butadiene rubber (NBR) were detected in all the samples, with NBR showing the highest concentrations (36.8 ± 14.1 to 109.6 ± 23.6 ng/m 3 ). To evaluate potential health implications, the ExDoM2 dosimetry model based on the International Commission on Radiological Protection framework was applied to estimate respiratory deposition and clearance in children. On average, 32 ± 8 particles were deposited during an 8-hour school day, corresponding to a mass dose of 254 ± 68 ng. After 24 hours, 60–67% of the deposited mass was cleared to the gastrointestinal tract via mucociliary transport, and less than 1% was estimated to reach the bloodstream. These results highlight the relevance of inhalation exposure to MP in school environments and the necessity of additional research during critical developmental stages.