Association between urinary microplastic load and systemic inflammation and oxidative stress markers in adults

Microplastics (MPs), plastic particles smaller than 5 mm, are ubiquitous environmental contaminants, yet human evidence linking internal MP burden to systemic biological responses remains limited. This cross-sectional study aimed to characterize urinary MP burden and evaluate its associations with systemic inflammation, oxidative stress, antioxidant defenses, and coagulation markers in 420 adults in China. Urinary MPs were quantified by micro-Fourier-transform infrared spectroscopy with confirmatory micro-Raman spectroscopy and expressed as particles per milliliter and per gram of creatinine. Associations with a panel of inflammatory, oxidative-stress, antioxidant, and coagulation biomarkers were assessed using multivariable linear regression, with MP load modeled as both continuous and quartile-based exposures. MPs were detected in 384 of 420 participants (91.4%); median concentrations were 8.6 particles/mL and 12.3 particles per gram of creatinine. Fibers and fragments predominated, and polyethylene (32.4%) and polypropylene (24.7%) were the most prevalent polymer types. In fully adjusted models, higher urinary MP concentration was positively associated with high-sensitivity C-reactive protein (β = 0.28; P < 0.001), interleukin-6 (β = 0.13; P = 0.002), tumor necrosis factor-alpha (β = 0.09; P = 0.028), malondialdehyde (β = 0.09; P < 0.001), 8-hydroxy-2'-deoxyguanosine (β = 0.54; P = 0.003), and fibrinogen (β = 0.07; P = 0.004), and inversely associated with total antioxidant capacity (β = -0.03; P = 0.016) and superoxide dismutase activity (β = -1.14; P = 0.031). Nine associations remained significant after Benjamini-Hochberg correction for multiple comparisons. Quartile analyses showed coherent dose-response trends across most biomarkers. Higher urinary MP burden was associated with a consistent profile of low-grade systemic inflammation, oxidative stress, reduced antioxidant capacity, and mild coagulation disturbance among apparently healthy adults, supporting the biological plausibility of subclinical effects associated with internal MP exposure. However, causality cannot be established because of the cross-sectional study design.