Factors and Zones of Accumulation

Accumulation of microplastics is dependent on many factors including the supply of amount released and concentration loads, topography, and flow conditions. While the gravitational forces act to deposit the particles at their nearest point of source/delivery, the density dependent buoyancy controls the transport-accumulation characteristic of the plastics in aquatic media. Microplastics accumulate within freshwater bodies from surface runoff, discharges from municipal and industrial effluents, and atmospheric fallout. Beaching acts as a major sink for plastics delivered into the sea. Of the total plastics that enter into the marine environment, only 1% is found to be floating, and the fate of the remaining 99% can be in the water column or in the bottom sediment and/or ingested and likely to undergo bioaccumulation by the organisms. Marine sediments cover about 70% of the Earth’s surface and are the most important sinks for microplastics. In seawater, most of the plastic is buoyant, but the biofouling processes contribute to sinking plastic particles below the surface in concert with the gradual progression of the sinking particles toward the bottom which is controlled by ocean dynamics and turbulence, leading to accumulation in the ocean basin.