Microplastic dynamics and land contamination in deltaic environments- A systematic review of current understanding and knowledge gaps

Coastal deltas are increasingly exposed to microplastic (MP) pollution due to complex interactions among hydrological dynamics, land use change and anthropogenic pressures. While marine MP contamination is widely studied, their fate and transport in deltaic floodplains-particularly inland soils-remain poorly understood. This review synthesizes empirical evidence from 76 peer-reviewed studies to assess MP distribution in deltaic environments and identify critical knowledge gaps. Evidence reveals consistent MP presence across diverse deltas, with highest concentrations often found in low-energy zones influenced by flooding, proximity to urban areas, and agricultural activity. MPs commonly appear as fibres and fragments, and are frequently associated with metals and other co-contaminants. Despite this growing body of research, there is a notable absence of mechanistic models that explain how MPs are transported, deposited, and remobilized across deltaic floodplains. To address this, we propose a conceptual model capturing the cyclical deposition, contaminant enrichment and remobilization of MPs in floodplains. The Bengal Delta is highlighted as a representative system illustrating how large, densely populated catchments intensify MP fluxes. This review emphasizes the need for integrated modelling and monitoring approaches that consider delta-specific drivers. Closing these knowledge gaps is essential to predict long-term impacts and to develop effective mitigation policies for vulnerable and ecologically important deltaic environments.