Experimental study of non-buoyant microplastic transport beneath breaking irregular waves on a live sediment bed

This paper presents experimental results on the cross-shore distribution of non-buoyant microplastic particles under irregular waves propagating, shoaling and breaking on live sediment sloping beds. Eighteen microplastic particle groups having various shapes, densities, and sizes are tested. The experiments consider two initial bottom configurations corresponding to a (i) plane bed and (ii) pre-developed singly-barred profile (more representative of field conditions). Four different microplastic accumulation hotspots are identified: offshore of the breaker bar, at the breaker bar, the plateau region between the breaker bar and beach, and the beach. It is found that the accumulation patterns primarily fall within three different particle Dean number regimes. The importance of plunger-type breaking waves for both on and offshore transport of microplastic particles is highlighted. [Display omitted] •The cross-shore transport of non-buoyant microplastic particles with various shapes, densities and sizes is investigated.•Irregular waves and two distinct initial bottom configurations are considered.•Transport and accumulation processes of microplastics are studied for O(100 hr) in model scale.•Four accumulation hotspots for microplastic particles are identified, falling primarily within three Dean number regimes.