Atmospheric microplastics: A review of pollution characteristics, human exposure pathways, and emerging health risks

Microplastics (MPs) pollution is a growing environmental issue due to excessive plastic use and improper waste disposal. While early studies focused on MPs in aquatic and terrestrial ecosystems, recent research has expanded to include air quality. This comprehensive narrative review examines MP concentrations in both indoor and outdoor air, highlighting that poorly ventilated indoor spaces have the highest levels of MPs, while good ventilation helps reduce pollution. Factors such as humidity and precipitation decrease MP concentrations through particle deposition, while temperature, wind, and environmental conditions influence their dispersion and persistence. Effective management of environmental conditions and ventilation design is essential to reduce human exposure to MPs. MPs in indoor and outdoor environments show distinct characteristics. Indoor MPs are mostly small (<30 μm), transparent or black, and mainly appear as fibers, originating from textiles, carpets, and furniture. Outdoor MPs are more diverse, often found as fragments and composed of polymers like polystyrene (PS), polyethylene (PE), and polyethylene terephthalate (PET). Human exposure to MPs occurs primarily through inhalation and ingestion, with indoor environments posing higher risks due to particle accumulation and prolonged human presence. Fine MPs (<10 μm, especially ≤2.5 μm) can penetrate deep into the lungs, causing inflammation, oxidative stress, and systemic toxicity. Ingestion through dust is particularly concerning for infants and toddlers. Despite increasing evidence of health risks, the lack of standardized methods and regulatory limits highlights the urgent need for harmonized exposure assessment and targeted public health interventions. By synthesizing existing literature, this review provides a qualitative assessment of the current state of knowledge, identifies key research gaps, and discusses implications for future policy and exposure mitigation strategies.