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Pulmonary-route-dominant retention and exposure burden of biodegradable PLA microplastics: Radiotracer-based toxicokinetics and development of the TRACE exposure-response framework
Summary
Even "biodegradable" plastics aren't automatically safe. A mouse study found that breathing in PLA microplastics (a common plant-based plastic) causes them to build up in the lungs longer and cause more cell stress than swallowing them does. This suggests inhaling microplastics, like from dust or air pollution, may pose a bigger health risk than eating them.
I radiolabeling and high-resolution SPECT/CT imaging to quantify route-dependent biodistribution and clearance kinetics of PLA MPs in mice. Intratracheal administration produced greater and more persistent tissue burdens than oral administration, with prolonged pulmonary retention, systemic redistribution, and a 2.25-fold higher blood area under the curve. To systematically link organ-level exposure burden with cellular biological response, we developed the TRACE (Toxicological Response And Cellular Exposure) framework, comprising five indices (TRACE-M, -C, -E, -R, -I) spanning mitochondrial injury, oxidative stress, and exposure-linked toxicity. TRACE-based analyses revealed stronger oxidative and ultrastructural stress responses in lung-derived cellular models than in gastrointestinal systems. Human exposure contextualization via allometric scaling and time-dependent mass-balance modeling further indicated that repeated inhalation may drive progressive pulmonary PLA accumulation under environmentally plausible conditions. Together, these findings establish inhalation as the dominant hazard route for PLA MPs and demonstrate that biodegradability does not confer biological safety.