Study proposes a preliminary physiologically-based toxicokinetic (PBTK) model for micro- and nanoplastics (MNPs); polymer type, size, shape, surface chemistry, surface biofilms, and biocorona determine toxicokinetic rates; models for engineered nanoparticles are not appropriate due to heterogeneity of MNPs; uptake via inhalation and effects of absorbed chemicals need more investigation