Study finds children inhale 60% more microplastics in classrooms than outdoors

A school in Estarreja, Portugal, sits one kilometer from an industrial complex that has manufactured polyvinyl chloride and other chemicals for decades. Researchers decided to measure what children were actually breathing inside those classrooms. What they found was straightforward and unsettling: the air indoors carried significantly more microplastics than the air outside.

The study, published in Environment International, analyzed seventy air samples collected across four classrooms and the outdoor schoolyard over two seasons—winter and spring. The children ranged from ages three to eleven. Using advanced analytical techniques, the researchers identified six types of polymers in the classroom air: polymethyl methacrylate, polypropylene, nylon-6,6, nitrile butadiene rubber, polystyrene, and polyvinyl chloride. They also detected phthalates, nicotine, and pesticides. The numbers told a clear story. Indoor microplastic concentrations averaged 21.8 nanograms per cubic meter. Outside, the average was 13.4 nanograms per cubic meter. The difference was statistically significant and substantial—roughly sixty percent more plastic particles circulating in the classrooms than in the open air.

Polystyrene emerged as the most consistent indoor pollutant, appearing in every single classroom sample collected. Nitrile butadiene rubber was the most abundant by concentration. Spring measurements showed higher levels than winter, likely because warmer, more humid conditions accelerate the breakdown of plastic materials into smaller fragments. The researchers calculated that children in these classrooms inhaled approximately 1.57 nanograms of plastic per kilogram of body weight each day, with first-graders—ages six and seven—experiencing the highest exposure.

Why this matters hinges on basic biology. Children breathe more air relative to their body weight than adults do. Their immune and respiratory systems are still developing. Microplastics suspended in air can be inhaled deep into the lungs, where they may trigger inflammatory responses. Until now, few studies had actually measured what children breathe inside schools—the places where they spend a substantial portion of their childhood. This research filled that gap, at least for one school near an industrial source.

The authors were careful to note that their exposure estimate is conservative, based on a measure of breathable particulate matter that includes non-respirable fractions. They also acknowledged that while wind-direction analyses suggest the nearby PVC manufacturing complex is a likely contributor, this has not been definitively validated as the source. What remains unknown is the long-term health impact of inhaling this particular mixture of plastics and chemical additives over months and years. The researchers called for routine air quality monitoring in schools and further investigation into those effects. For now, the baseline is set: children in this Portuguese classroom are continuously exposed to a complex cocktail of plastic pollutants, and the air they breathe indoors is measurably dirtier than the air outside.