Impact of artificial sunlight aging on the respiratory effects of polyethylene terephthalate microplastics through degradation-mediated terephthalic acid release in male mice

Microplastics are ubiquitous in the atmosphere, leading to human exposure through inhalation. Airborne microplastics undergo degradation due to sunlight irradiation, yet the respiratory risks associated with degraded microplastics remain poorly understood. In this study, we investigated the respiratory effects of polyethylene terephthalate (PET) degraded by artificial sunlight and created a transport and degradation model of PET for risk assessment. PET fibers were cut and subjected to artificial sunlight irradiation. Mice exposed to aged PET showed increased airway resistance induced by methacholine (MCh) inhalation, along with lung inflammation and neutrophil infiltration. Terephthalic acid (TPA) was continuously released from PET aged by artificial sunlight. Exposure to TPA also caused lung inflammation and enhanced airway resistance induced by MCh in mice. These findings indicate that aged PET can cause respiratory impairment via TPA release. A simple transport and degradation model was developed to quantitatively relate the abundance of aged PET produced in this study (i.e. 4,000 × 96 W m-2 h) and aged fractions of PET that can be generated in the atmosphere. Our results suggested 10% to 60% of PET was degraded as that produced in this study over sunny regions in summer, whereas only lower than 1% in high-latitude cities in Europe in winter. This study demonstrates the importance of considering the abundance of aged PET and further development of a transport and degradation model of PET to assess the risk of degraded PET in the atmosphere.