Morphological and chemical characterization of nanoplastics in human tissue

Abstract

Micro- (≤ 5 mm) and nano- (≤ 1 μm) plastics have become ubiquitous resulting in inevitable human exposure. Evidence exists of mass-based accumulation of plastic in human tissues with visualization of micron-sized particles (> 1 μm). To date, there is little evidence to address accumulated nanoplastics. Understanding internalized plastic particle morphological and chemical characteristics is essential to facilitate proper design of future mechanistic and controlled exposure health effects studies to determine whether any health-related risks exist. Here we show microscopic evidence and quantitative dimensional analysis of nanoplastics in human decedent brain, kidney, and liver tissues. Mean particle lengths (nm) across the five decedents were 171.2±4.6 for brain, 124.4±3.6 for kidney, and 147.6±6.6 for liver. Mean particle widths (nm) were 45.9±1.5 for brain, 32.3±0.7 for kidney, and 36.1±1.3 for liver. When examining the aspect ratio, 78-83% consisted mostly of an elongated nanometer sized fiber morphology. The study provides isolation with physical and chemical characterization of nanoplastics in human tissues. Interestingly, differences were greater between tissues of a single decedent than across decedents. Consistently, the nanoplastics were largest in the brain. The observations overall suggest specificity with respect to systemic internalization and subsequent tissue accumulation of plastic particles less than one micron.

Keywords: bioaccumulation; brain; dimensions; kidney; liver; microplastics.

Figure 1

Representative high resolution transmission electron microscopy imaging of nanoparticulates isolated from human brain (frontal cortex), kidney (piece containing cortex and medulla), and liver (right central parenchyma).

Figure 2

A: To confirm their polymer nature, nanoparticulates from the brain were imaged and mapped to enable relocation after exposure to the solvent vapors and heating. The grid was exposed to chloroform vapors for 24 hours as described in Supplemental Figure 7. Following exposure to the chloroform vapors, the grid was placed into an oven at 130°C for 24 hours. The particles were imaged before exposure to chloroform (A1), after 24 hours of exposure to chloroform (A2), and after heating at 130°C for 24 hours (A3). B: A sample for Raman spectroscopy was prepared as described in the methods by using particles from liver dispersed in equal volumes of isopropanol and benzene. Spectra collected included internal high-density polyethylene (HDPE) standard (B1, red), particle sample using 600 second exposure with 10 accumulations and 25 μm hole (B2, blue), and the original isolated pellet sample using 180 second exposure with 3 accumulations and 25 μm hole (B3, green).

Figure 3

Physical dimensional profiling of nanoparticulates isolated from human brain, kidney, and liver. A total of 3251 measurements were made with n=205–231 individual measurements per decedent per tissue sample. Samples used for particle size quantification were prepared using isopropanol, which does not affect the polymer fragment dimensions, without filtration.

Figure 4

(A) Average length and width for nanoparticulates isolated from human brain, kidney, and liver (n=5; #p<0.02 vs all groups). (B) Size-distribution pattern of isolated particles illustrating longer length and width associated with brain accumulation. (C) Table illustrating aspect ratio and percentage of particles meeting the fiber criteria. Additional calculations offer estimated average volume and surface area occupied by a particle.