Microplastics in human lung tissue from autopsy samples collected in 1991 and 2024: a comparative post-mortem study

Background Environmental accumulation and human exposure to microplastics MPs are increasing. It is not known whether there is a higher bioaccumulation of microplastics (MPs) in human lungs collected recently and compared with those collected decades ago. We aimed to assess changes in the presence, abundance, size, and types of MPs in human lung tissue collected 33 years apart, and to characterize histological patterns in these samples. Methods We performed a comparative study of paraffin-embedded lung tissues collected post-mortem from two series of autopsy cases deceased either in 1991 (n = 42) or in 2024 (n = 57), both from the same tertiary care medical center. We assessed MPs prevalence, abundance, size, and polymer type using laser-direct infrared (LDIR) imaging. Particle count per gram of tissue was the primary endpoint. As supporting analysis, we evaluated MPs type and concentrations through pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS) in a representative subset of samples. We also assessed collagen I staining to evaluate fibrosis and CD68 infiltration as an index of lung inflammation. Findings MPs were identified by LDIR in lung samples from 8/42 individuals (19%) deceased in 1991 and 44/57 (77%) deceased in 2024. MP burden per gram of tissue (median; Q1-Q3) increased from 12.9 particles (11.3–13.7) to 19.9 (15.5–28.2), with results corroborated by a two-part hurdle model analysis. Particle diameter decreased from 56.2 μm (44.9–73.4) to 22.4 μm (15.4–37.9). When considering the mean ± SD of the relative abundance (%) of each plastic type/total MPs for each individual positive to MPs in the two groups, polymer composition shifted from polyethylene predominance (51.7 ± 2%) in 1991 to a more heterogeneous mix including polyethylene terephthalate (28.4 ± 3.1%), polyvinyl chloride (14.3 ± 2.4%), and polystyrene (14.2 ± 2.6%) in 2024. Py-GC/MS provided similar results in terms of MPs prevalence and relative abundance, while SEM suggested a pervasive presence of particles enriched in Sulphur in the 2024 group. Lung samples with evidence of MPs showed higher CD68 and collagen I abundance compared with those without evidence of MPs, independently of the case series. Interpretation MPs contamination of human lung tissue was more frequently detected, showed greater polymer diversity, and was composed of smaller particles in post-mortem samples collected in 2024 compared with those collected in 1991. These observations are hypothesis-generating and should be interpreted in the context of the observational, cross-sectional, and retrospective nature of the study design. Funding This work has been supported by Italian Ministry of Health through Ricerca Corrente to IRCCS MultiMedica, and by Ricerca Ateneofund for Outcomes Research in Cardiovascular Diseases.