Microplastics and human health: exposure pathways, toxicological evidence and mitigation strategies

Microplastics, typically defined as plastic particles smaller than 5 mm, have emerged as a pervasive class of environmental contaminants with increasing relevance to human health. Their widespread distribution in air, water, food and consumer products has raised concerns regarding chronic human exposure and potential biological effects. This review critically examines current evidence on exposure pathways, biological uptake, toxicological mechanisms, organ-specific health effects and mitigation strategies, with particular emphasis on human biomonitoring findings and challenges in health risk assessment. Microplastics have been detected in human biological matrices, including blood, placental tissue, lung tissue, breast milk and faecal samples, confirming internal exposure. Experimental studies have reported oxidative stress, inflammation, mitochondrial dysfunction, endocrine disruption, immune modulation, and adverse effects on the gastrointestinal, hepatic, pulmonary, cardiovascular, reproductive, renal, and nervous systems. However, most evidence is derived from in vitro and animal studies, while human epidemiological data remain limited. This review further discusses the influence of particle size, morphology, polymer composition, surface chemistry, weathering and contaminant adsorption on bioavailability and toxicity. The role of microplastics as carriers of chemical pollutants, plastic additives and microbial communities is also evaluated. Additionally, limitations in analytical methodologies, biomonitoring interpretation, exposure assessment and dose-response characterization are critically examined. A microplastic-specific risk assessment framework is proposed to support future regulatory and public health decision-making. Future research should prioritize standardized analytical methodologies, environmentally realistic exposure models, longitudinal human studies and integrated biomonitoring approaches to strengthen the evidence base for quantitative risk assessment and effective mitigation strategies.