Quantitative human biomonitoring of micro- and nanoplastics: Exposure profiles, mechanistic insights, and health implications.

Micro- and nanoplastic (MnP) pollution has become an escalating environmental and public health concern, supported by increasing human biomonitoring evidence of their presence in the body. We performed a PRISMA-guided quantitative analysis of 70 human-sample studies (2019-2025) spanning multiple organ systems and body fluids. After being standardized by the unit, reported concentrations ranged 0.2-342.55 items/g or 0.43-275.78 μg/g, with relatively higher content in digestive, reproductive, circulatory, and respiratory samples. Polyethylene (PE, n = 84), polypropylene (PP, n = 63), polystyrene (PS, n = 59), polyethylene terephthalate (PET), and polyvinyl chloride (PVC) were predominant, less frequent polymers followed a long-tail distribution. Particle sizes clustered at 10-100 μm, and nanoplastics (<1 μm) were infrequently quantified due to analytical limits, a few studies have reported detections in placental or brain tissues, but these observations remain preliminary and require prudent interpretation. Common digestion protocols included 30 % H2O2 and 10 % KOH. μ-Raman, LDIR, μ-FTIR, and Py-GC/MS produced systematic differences between particle-count and mass-based metrics, underscoring methodological dependence that limits interstudy comparability. Current toxicological evidence and limited epidemiological observations indicate potential associations with oxidative stress, inflammation, immune alterations, and endocrine-related effects, while no causal relationships have been demonstrated in humans. However, prevalence estimates and risk assessments are limited by small sample sizes and uneven age and sex representation. Importantly, this quantitative synthesis of human-sample data integrates multi-matrix MnP concentrations, delineates exposure profiles, identifies critical knowledge gaps, and underscores the need for standardized analytical approaches and longitudinal low-dose studies to support health risk assessment and policy development.