From particle tracking modelling to species impact forecasting: a framework for microplastic exposure risk quantification in the largest freshwater lake of China

Microplastics (MPs) are among the most widely studied pollutants, yet their transport pathways and mass concentrations have been relatively unexplored using numerical modelling in aquatic environments. In this study, we investigated the transport dynamics, spatial distribution, and impact levels of MPs in Poyang Lake, China's largest freshwater lake, utilizing a hydrodynamic model coupled with the particle tracking module. An improved risk matrix approach was applied to semi-quantitatively assess the Species Impact Index ($SII$) of MPs on Finless Porpoises and Siberian White Cranes. This study showed that PA/PVC particles were largely retained outside the main basin, while PP/PE particles entered the central lake with shape- and density-dependent lag times. PE settled faster and exhibited longer retention than PP, with high-surface-area morphotypes (e.g., fibres, films) accelerating sedimentation through biofilm-mediated density increase. Spatially heterogeneous MP accumulation occurred in resuspension-prone regions driven by complex bathymetry and hydrodynamics. $SII$ results indicated significant spatial overlap between MP footprints and critical habitats of the sensitive species, with PP/PE fibres and foams posing Grade III (significant) risks in northern and southwestern subregions. Based on the evaluation results, targeted recommendations were proposed for the management and control of MPs in Poyang Lake, providing a protective framework for lake administrators.