Microplastics in the air and potential health risks - a narrative review.

Abstract

Aim: Microplastics, defined as plastic particles smaller than 5 mm and larger than 1 micrometer, along with nanoplastics (in the 1-1000 nm range), are ubiquitous environmental contaminants originating from both primary production and secondary fragmentation. Little is known about exposure to microplastics in ambient air and their health effects. This review summarises current knowledge regarding microplastics in ambient air and their potential health effects.

Methods: To capture the limited available evidence on airborne microplastics exposure and human health, a search strategy using five complementary approaches was designed and implemented across multiple databases and timeframes through September 2024.

Results and discussion: In Switzerland and globally, major sources of airborne microplastics include tyre wear, textile fibres, and the degradation of plastics from various sectors. Exposure measurements reveal that microplastics are present in both indoor and outdoor air, with indoor exposure generally exceeding outdoor exposure. Exposure in cities is higher than in rural areas, thus depending on proximity to human activity. Based on calculations derived from various studies, an adult might inhale from 1,200 microplastic particles per year in remote locations to over 1.5 million particles per year in highly polluted urban areas. Human biomonitoring confirms the presence of microplastics across multiple tissues and bodily fluids, including the lungs, blood, placenta, breast milk, faeces, and, more recently, brain tissue, with evidence suggesting that microplastics can cross biological barriers, including the blood-brain barrier. While epidemiological studies specifically addressing airborne microplastic exposure are lacking, occupational health studies from textile and rubber industries report respiratory symptoms, impaired lung function, and an increased risk of respiratory diseases. Studies examining non-exhaust traffic emissions (as proxies for tyre wear particles) suggest associations with respiratory effects, increased mortality risk, cardiovascular impacts, and potential links to cancer and neurodevelopmental disorders. However, both approaches to understanding and deriving health effects from airborne microplastics have limitations. Additional research challenges include non-standardised measurement methods, a limited understanding of biokinetics, and difficulty differentiating microplastic effects from general particulate matter exposure.

Conclusion: Despite these limitations, microplastics likely contribute to health effects similar to those of particulate matter pollution, with potential additional concerns related to their specific composition and chemical additives. The proportion of microplastics in ambient particulate matter may increase with decreasing exhaust emissions and increasing use of plastic products, emphasising the need for interdisciplinary research on exposure assessment and health implications.