Methodology, characterization, and multiple-path particle dosimetry modeling of laboratory inhalation exposure for...

Plastics are ubiquitous in all trophic environments. Human exposures primarily occur via ingestion, inhalation, and/or injection routes. However, laboratory models of micro- and nanoplastic (MNP) particle exposures replicating the human condition remain inconsistent and uncharacterized, thus limiting study strength and compromising the reliability of results. The purpose of this study was to thoroughly optimize and characterize an established methodology for MNP rodent inhalation exposures, and to model particle respiratory deposition to estimate theoretical in silico exposures in rats and humans for the assessment of MNP health effects. Using our whole-body rodent inhalation facility, we generated MNP aerosols after thorough material characterization of a commercially available food-grade polyamide-12 (PA-12) bulk microparticle powder. PA-12 particulate was thoroughly assessed via pyrolysis-gas chromatography-mass spectrometry (PY-GC-MS), attenuated total reflectance-Fourier-transform infrared (ATR-FTIR) spectroscopy, and helium ion microscopy (HIM) to confirm material chemistry, size, and surface shape. Representative MNP were established and measured at three mass concentrations, low (1.01 mg/m³ ± 0.17), mid- (5.05 mg/m³ ± 0.5), and high (9.98 mg/m³ ± 3.14) levels, representative of environmental and occupational exposure. The aerosol micro- and nanoparticle size distributions were measured and monitored in real-time with a scanning mobility particle sizer (SMPS), an aerodynamic particle sizer (APS), and a high-resolution electrical low-pressure impactor (HR-ELPI+) over a size range of 10 nm - 20 μm. Multi-day studies were conducted to assess intra- and inter-day variability in terms of several size distribution summary statistics. The merged data revealed a bi- and tri- modal distribution of particles with geometric mean diameters within the nano- and micro- size ranges for all concentrations. While commercial characterization reported an average size of 5 μm ±1, aerosol characterization in-house revealed MNP well within the nano-range, with average geometric mean of less than 200 nm and aerodynamic size peak mode values less than 100 nm at all concentrations. These data were entered into multiple-path particle dosimetry (MPPD^©) model software to predict pulmonary anatomical deposition, which identified no significant differences between Sprague-Dawley rats and humans. Overall, we provide a thoroughly characterized methodology for controlled laboratory-based assessments to evaluate MNP toxicity and risk over a range of environmental and occupational doses. MPPD modeling of these exposures identifies pulmonary tract deposition within the human and rodent model, with no physiological differences between the low and high dose. This study provides a foundational methodology to assess the toxicological implications of MNP inhalation. Using our whole-body rodent inhalation facility, we generated MNP aerosols after thorough material characterization of a commercially available food-grade polyamide-12 (PA-12) bulk microparticle powder. PA-12 particulate was thoroughly assessed via pyrolysis-gas chromatography-mass spectrometry (PY-GC-MS), attenuated total reflectance-Fourier-transform infrared (ATR-FTIR) spectroscopy, and helium ion microscopy (HIM) to confirm material chemistry, size, and surface shape. Representative MNP were established and measured at three mass concentrations, low (1.01 mg/m³ ± 0.17), mid- (5.05 mg/m³ ± 0.5), and high (9.98 mg/m³ ± 3.14) levels, representative of environmental and occupational exposure. The aerosol micro- and nanoparticle size distributions were measured and monitored in real-time with a scanning mobility particle sizer (SMPS), an aerodynamic particle sizer (APS), and a high-resolution electrical low-pressure impactor (HR-ELPI+) over a size range of 10 nm - 20 μm. Multi-day studies were conducted to assess intra- and inter-day variability in terms of several size distribution summary statistics. The merged data revealed a bi- and tri- modal distribution of particles with geometric mean diameters within the nano- and micro- size ranges for all concentrations. While commercial characterization reported an average size of 5 μm ± 1, aerosol characterization in-house revealed MNP well within the nano-range, with average geometric mean of less than 200 nm and aerodynamic size peak mode values less than 100nm at all concentrations. These data were entered into multiple-path particle dosimetry (MPPD^©) model software to predict pulmonary anatomical deposition, which identified no significant differences between Sprague-Dawley rats and humans. Overall, we provide a thoroughly characterized methodology for controlled laboratory-based assessments to evaluate MNP toxicity and risk over a range of environmental and occupational doses. MPPD modeling of these exposures identifies pulmonary tract deposition within the human and rodent model, with no physiological differences between the low and high dose. This study provides a foundational methodology to assess the toxicological implications of MNP inhalation.