Abstract
Microplastics are accumulated in coastal regions due to human activity. Although limited data from beach surveys show an increase in microplastics in marine habitats, continuous monitoring is required on microplastics loading and distribution in the marine environment. In this study, CFD numerical simulations using VOF and Airy wave models coupled with DPM were carried out to investigate the effects of various variables on microplastics motion and distribution in a simulated coastal marine environment. PET, PU, and PP microplastic particles were released from the oceanside to investigate the effects of microplastic type, size, and shape with two different ocean–water flow velocities and temperature conditions. Particle position data from their tracking were used to determine the effect of each variable on the spatial distribution of particles. The quantitative analysis of vertical and horizontal distribution of microplastics particles revealed that, with low water velocity, most of the large denser spherical PET and PU microplastics would sink towards the bottom and settle at the ocean floor, while most of the small non-spherical particles would float near the surface and travel towards the shoreline. For lighter PP microplastics, larger spherical particles would float more readily than denser spherical ones. Large spherical and smaller non-spherical PP particles travel farthest reporting to the shoreline. Increasing the oceanwater velocity altered the distribution patterns in which lighter PP particles, almost independent of shape and size, travel swiftly to the shoreline together with smaller non-spherical denser microplastics. Lastly, the simulation results revealed that the oceanwater temperature did not play any significant role in the spatial distribution of microplastic particles.
Highlights
Over the past decades, there has been a recognition that microplastics severely pollute marine habitats
At thewater waterfree freesurface surface is its in initial its initial conditions, butentering with entering the Atzero zero time, time, the is in conditions, but with the waterfrom fromthe the related related velocity boundary, an increase in theinoceanwater free surface water velocityinlet inlet boundary, an increase the oceanwater free surface level is seen, and the surface gravity random waves are created at the water–air interface, which move towards the beach because of the prevailing wind direction from the ocean
volume of fluid (VOF) model, Open Channel Flow, discrete phase model (DPM) and Energy models to investigate the effects of various variables on microplastics motion and distribution in simulated near coastal conditions
Summary
There has been a recognition that microplastics severely pollute marine habitats. The sea surface, the water column, and the seafloor plastics are exposed to different environmental conditions, resulting in physical and chemical degradation producing microplastics. The degradation of plastics occurs primarily due to photooxidation reactions through solar UV radiation in environments such as the sea surface and on beaches, and the transport of small particles to the seafloor and their deposition is possibly facilitated by the colonization of fouling organisms [4]. A recent article by Coyle et al [5] argued that there is a lack of consensus on the influence of polymer density on the vertical distribution of microplastics in water columns, since the observations show that low-density microplastics are present in deep waters as well They suggested that the interactions of microplastics with marine organisms might better explains this occurrence. They pointed to the need for quantifying proportions of microplastics in virgin, bio-fouled, and as marine aggregate states in different depths of the ocean for better understanding the interactions between microplastics and marine organisms
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