Environmental Micro(nano)plastic Exposure and Associated Human Health Risks: A Comprehensive Review

Micro(nano)plastics (MNPs) represent a pervasive and escalating threat to global ecosystems and human health. This review provides a critical synthesis of MNPs’ exposure risks across marine, atmospheric, and terrestrial compartments, with a distinct emphasis on identifying cross-media linkages and methodological inconsistencies that limit current risk assessments. Within marine environments, pollution hazard indices reveal significant spatial heterogeneity, yet their utility is constrained by the absence of toxicity weighting and particle characteristic integration. Atmospheric exposure profiles show variable risks, and the MNPs’ concentration in indoor air (up to 15.8 particles/m3) is significantly higher than in outdoor environments, posing a greater inhalation risk to infants and children who spend more time indoors. A marked increase in MNPs’ concentrations within agricultural soils is identified, where the MNP content in mulched soils (average: 570.2 particles/kg) is more than twice that of non-mulched soils (259.6 particles/kg). Critically, studies have now detected MNPs within human tissues, including the blood, intestines, liver, kidneys, tonsils, and brain, highlighting an urgent need to elucidate their multi-organ toxicity mechanisms, with a novel synthesis of gut–brain axis disruption and transgenerational effects. By integrating exposure dynamics with mechanistic toxicity data, this review advances a cross-system framework that identifies priority research directions, namely standardized detection methodologies, combined pollutant toxicity, and cross-system toxicity mechanisms, which are essential for informing mitigation strategies amid this escalating public health crisis.