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.