Microplastics as carriers of environmental contaminants: Implications for human exposure, toxicokinetics, and health risk.

Microplastics have emerged as pervasive environmental contaminants that are widely distributed across aquatic, terrestrial, and atmospheric environments. Beyond their physical presence, growing evidence suggests that microplastics can interact with and adsorb a diverse range of environmental contaminants, including persistent organic pollutants, polycyclic aromatic hydrocarbons, heavy metals, pharmaceuticals, and per- and polyfluoroalkyl substances. These interactions may transform microplastics into potential carriers that facilitate the environmental transport and trophic transfer of hazardous chemicals. As a result, microplastic-mediated contaminant exposure has become an emerging concern in environmental health sciences. This review provides a comprehensive synthesis of current knowledge regarding the role of microplastics as carriers of environmental contaminants and their implications for human exposure, toxicokinetics, and health risk assessment. We first summarize the major sources and environmental distribution of microplastics and the primary pathways of human exposure. We then discuss the physicochemical factors governing contaminant adsorption onto microplastics and the mechanisms underlying microplastic-contaminant interactions. The environmental transport and trophic transfer of contaminant-bound microplastics are subsequently examined, followed by a review of toxicological evidence describing the biological effects associated with combined particle-chemical exposure. Finally, emerging evidence of microplastics detected in human tissues is discussed together with the potential role of toxicokinetic modeling approaches, including physiologically based pharmacokinetic models, in evaluating internal exposure. Overall, this review highlights the complex interactions between microplastics and environmental contaminants and emphasizes the need for integrated research approaches to better understand their implications for human health risk assessment.