1 Department of Building, Civil and Environmental Engineering, Concordia University, Montreal, QC H3G 1M8, Canada.
2 Department of Building, Civil and Environmental Engineering, Concordia University, Montreal, QC H3G 1M8, Canada. Electronic address: chunjiang.an@concordia.ca.
3 Center for Natural Resources, Department of Civil and Environmental Engineering, New Jersey Institute of Technology, 323 MLK Blvd., Newark, NJ 07102, USA.

Since nearly half of the world's population lives near the coast, coastal areas have become hotspots for microplastic (MP) pollution due to human activity. The ubiquity of natural colloids in coastal waters plays a critical role in the potential fate of, and risks posed by, MPs. Nevertheless, far less has been known regarding the aggregation of MPs with inorganic natural clay colloids, especially in the complicated nearshore environment. In this study, the aggregation behavior of MPs as well as the interaction between MPs and clay particles were investigated under different nearshore environmental conditions (MP-to-clay ratio, salinity gradient, humic acid concentration, and wave energy). The aggregation behavior was subjected by the repulsive energy barrier between particles and external energy transferred to the system. The low energy associated with mild wave conditions was favorable for the occurrence of aggregation, whereas sustained high energy under intense wave conditions was found to be detrimental to the aggregation behavior, and the aggregates were prone to fragmentation even if particles coalesced into large clusters. The analysis for the environmental fate of MPs demonstrated that the shoreline was likely to be the sink for most MPs ultimately.