1 Department of Building, Civil and Environmental Engineering, Concordia University, Montreal H3G 1M8, Canada.
2 Department of Natural Resource Sciences, McGill University, Montreal H9X 3V9, Canada.
3 Energy, Mining and Environment Research Centre, National Research Council of Canada, Montreal H4P 2R2, Canada.

Tidal zones providing habitats are particularly vulnerable to microplastic (MP) pollution. In this study, the effects of tidal cycles on the transport of MPs (4-6 µm polyethylene, PE1; 125 µm polyethylene, PE2; and 5-6 µm polytetrafluoroethylene, PFTE) in porous media combined with various environmental and MPs properties were systemically investigated. The results indicated that smaller substrate sizes exhibited higher retention percentages compared to those of larger substrate sizes under different tidal cycles. In terms of the size of MPs, a larger size (same density) was found to result in enhanced retention of MPs in the column. As the number of tidal cycles increased, although the transport of MPs from the substrate to the water phase was enhanced, PE1 was washed out more with the change in water level, compared to PTFE. Additionally, more MPs were retained in the column with the increase of salinity and the decrease of flow velocity under the same tidal cycles. Ultraviolet and seawater aged PE1 showed enhanced transport, while aged PTFE showed enhanced retention under the same tidal cycles. These results can help understand the MP behaviors in the shoreline environment and provide support for future cleanup and sampling in tidal zones.