Organ-level translocation and tissue-specific accumulation of micro- and nanoplastics in wild birds

Global plastic pollution has introduced microplastics (MPs, < 5 mm) and nanoplastics (NPs, < 1 µm), collectively termed micro(nano)plastics (MNPs), into terrestrial ecosystems, yet their in vivo fate remains unclear. We quantified MNP burdens across six tissues-feathers, lungs, intestinal contents, blood, brain, and pectoral muscle-in ten wild bird species spanning a 55-fold body-mass gradient, using Laser Direct Infrared spectroscopy (LDIR) for MPs (20-500 µm) and Pyrolysis-Gas Chromatography-Mass Spectrometry (Py-GC-MS) for NPs. Six patterns emerged: (1) small-bodied birds carried higher MNP burdens than larger species; (2) exposure interfaces harbored more MNPs than internal compartments; (3) NPs showed greater translocation potential than MPs; (4) particle characteristics shaped abundance-pellet acrylates (ACR), polyvinyl chloride (PVC), and polyethylene terephthalate (PET) dominated internal tissues, while fibers were largely excluded by anatomical filtration; (5) blood MNP levels showed a positive trend with those in internal organs, suggesting potential utility as a proxy for internal burden; (6) hazard index analysis identified high-risk burdens in most organs, with PVC and polyurethane (PU) requiring regulatory attention. This study provides the first organ-level MNP distribution map under natural exposure and positions birds as potential bioindicators for cryptic plastic pollution in terrestrial systems.