Terrestrial microplastics as emerging aquatic pollutants: A systematic review

Microplastics (MPs), predominantly derived from terrestrial activities such as household effluents, tire wear, landfills, agricultural runoff, and e-waste, are now pervasive in freshwater and coastal environments. This review combines a systematic bibliometric search of Scopus records (2016–2025; initial search, n = 2,243) with a focused narrative synthesis of the 137 studies that met the inclusion criteria after eligibility screening. Quantitative evidence from these studies shows wide variation in environmental loads (e.g., 6,600–8,800 items·kg⁻¹ in landfill soils; 27–609 MPs·L⁻¹ in agricultural runoff) and strong sorption of co-contaminants (lead adsorption reported up to 2,810 mg·kg⁻¹, median values substantially lower depending on polymer and ageing). MPs have been detected in human tissues (blood, lung, placenta) and are associated in the literature with oxidative stress, inflammatory responses, and endocrine-disrupting pathways. Advances in FTIR/Raman spectroscopy and AI-assisted image analysis have improved detection, but heterogeneous sampling and analytical protocols limit cross-study comparability. Priority research needs identified from the 2016–2025 evidence base include: quantitative apportionment of under-reported sources (notably e-waste and informal recycling), mechanistic phytotoxicity and trophic-transfer studies under field conditions, and freshwater fate & transport modeling that incorporates dynamic land-use and sediment–water exchange. Standardized analytical frameworks, inter-laboratory calibration, and open data repositories are recommended to translate science into policy and targeted mitigation within the polymer environment health nexus.