Transport and deposition of plastic particles in porous media during seawater intrusion and groundwater-seawater displacement processes

Visible flow chamber systems packed with porous media (at both macroscale and pore scale) and packed column systems for the first time were used to systematically investigated the impacts of seawater intrusion and groundwater-seawater displacement on the transport behaviors of marine plastic particles with different sizes in porous media. We found that seawater intrusion could transfer all three sized plastics into coastal porous media and their transport would be affected by seawater flow velocity. For example, 8.5%, 24.8%, 39.8% of 1 mm plastic particles could pass through the columns during the 10, 50 and 250 m/d seawater intrusion processes, respectively. The groundwater-seawater displacement process could re-mobilize plastic particles pre-attached onto sand. The percentages of released plastic particles were negatively correlated with the sizes of plastic particles and the ionic strength of displacement groundwater. Groundwater velocity did not obviously affect the release of plastic particles from sand. The percentage of released plastic particles were affected by seawater intrusion cycles. XDLVO was employed to theoretically explain the transport behaviors of plastic particles under different conditions. Our study showed that seawater intrusion would transfer marine plastic particles into coastal aquifer and groundwater-seawater displacement could affect the release of plastic particles from porous media.