Flooding as a driver of emerging contaminants, pathogens, and microplastics in environmental systems: A systematic review of mechanisms, transport pathways, and exposure risks

Abstract

Climate change and urbanization are increasing the frequency and impact of flood events and intensifying contaminant transport across environmental systems. Despite growing evidence, the available literature remains fragmented across contaminant groups and environmental pathways, and data from arid and semi-arid regions where episodic flooding follows prolonged dry periods are largely absent. This systematic review examined how flooding drives the mobilization of pathogens, emerging contaminants, and microplastics across environmental pathways. Following PRISMA guidelines, searches were conducted in Scopus, Web of Science, and Ovid up to February 2026. Studies addressing flooding and extreme rainfall in relation to emerging contaminants, microplastics, pathogens, climate change, and public health were included. After screening 892 records, 82 studies met the inclusion criteria. The protocol was registered in PROSPERO (CRD420261298977). The evidence identified hydrological transport, including surface runoff, overland flow, and infrastructure exceedance, as the main mobilization pathway. Pathogens were the most frequently investigated contaminant group (41%), followed by studies assessing multiple contaminant classes within the same event (28%). Microplastics, pesticides, pharmaceuticals, and antibiotic resistance genes were less frequently studied. Reported risks were dominated by microbial contamination and infectious disease exposure, whereas chemical toxicity and microplastic-related ecological effects were mostly examined within single-contaminant studies. The evidence base was concentrated in high-income regions, with limited data from arid and semi-arid settings. Findings indicate that flooding enhances contaminant transport by increasing hydrological connectivity across environmental systems. Future research should prioritise longer-term monitoring, integrated assessment of contaminant mixtures, and broader geographic coverage.