Lung retention, distribution and persistence of polymer particles in rats exposed via inhalation

Microplastics have been repeatedly detected in the human body, yet uncertainties surround their bioavailability and fate due to experimental challenges and limitations, especially regarding their nano-sized counterparts. Knowing that toxicokinetics information is essential for accurate risk assessment and management, this research aimed to (1) evaluate different sample preparation and quantification methods for nanoplastics particles in mammalian tissue, and (2) investigate the lung retention, bioavailability and fate of these particles.

In this study, rats inhaled aerosols with up to 50 mg/m³ of Nile Red-labeled polystyrene (PS-NR) or unlabeled polyamide particles (PA-6) particles for 28 days. The tissues were analyzed for the presence of polymer particles. PS-NR were quantified in formalin-fixed tissue by confocal fluorescence laser microscopy with semi-automatic imaging analysis, and PA-6 particles were quantified in dried tissues by pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS).

PA-6 deposition was detected and quantified in lung and lymph nodes. Deposition of PS-NR was quantified in lungs and lung-draining lymph nodes, but no particles were detected in the liver, spleen, and kidneys. The lung burdens and translocation to the draining lymph nodes were similar for both particles, and particles were still detectable after the end of the exposure periods (five weeks for PS-NR and 13 weeks for PA-6).

This work highlights limitations and applicability of the various methods for sample preparation, detecting and quantifying polymer particles in mammalian tissues. In addition, it provides reliable data on the internal dose of inhaled polymer particles.