Physical transport properties of marine microplastic pollution

Abstract

Given the complexity of quantitative collection, knowledge of the distribution of microplastic pollution in many regions of the world ocean is patchy, both spatially and temporally, especially for the subsurface environment. However, with knowledge of typical hydrodynamic behavior of waste plastic material, models predicting the dispersal of pelagic and benthic plastics from land sources into the ocean are possible. Here we investigate three aspects of plastic distribution and transport in European waters. Firstly, we assess patterns in the distribution of plastics found in fluvial strandlines of the North Sea and how distribution may be related to flow velocities and distance from source. Second, we model transport of non-buoyant preproduction pellets in the Nazaré Canyon of Portugal using the MOHID system after assessing the density, settling velocity, critical and depositional shear stress characteristics of such waste plastics. Thirdly, we investigate the effect of surface turbulences and high pressures on a range of marine plastic debris categories (various densities, degradation states and shapes tested) in an experimental water column simulator tank and pressure laboratory. Plastics deposited on North Sea strandlines varied greatly spatially, as a function of material composition and distance from source. Model outputs indicated that such dense production pellets are likely transported up and down canyon as a function of tidal forces, with only very minor net down canyon movement. Behaviour of plastic fragments under turbulence varied greatly, with the dimensions of the material, as well as density, playing major determining roles. Pressure was shown to affect hydrodynamic behaviours of only low density foam plastics at pressures ≥ 60 bar

The vertical distribution of buoyant plastics at sea: an observational study in the North Atlantic Gyre

“…As shown here, and in two modelling studies (Ballent et al, 2012;Isobe et al, 2014), vertical mixing affects the size distribution of plastics floating at the surface. We observed that the proportion of plastics mixed into deeper waters increases towards smaller sizes even under low wind speed (1 kn) conditions (see Fig.…”

“…These sea surface samples have shown that the world's sea surface contains many millimetre-sized plastic pieces known as "microplastics" when smaller than 5 mm in length (Arthur et al, 2009;Hidalgo-Ruz et al, 2012). This type of plastic pollution is widespread across oceans, with Figure 1.…”

“…A model developed by Kukulka et al (2012) predicted that the largest decrease in plastic concentration occurs over the first metres of the water column, where only a few low-resolution measurements exist (Lattin et al, 2004;Doyle et al, 2011;Kukulka et al, 2012;Isobe et al, 2014). As studying ocean turbulent transport is heavily dependent on observations (Ballent et al, 2012;D'Asaro, 2014), high-resolution multi-level plastic sampling is urgently needed to test this prediction. A better understanding of the vertical transport of buoyant plastics is fundamental for improving estimates of concentration, size distribution, and dispersal of plastics in the world's ocean (Kukulka et al, 2012;Reisser et al, 2013;Law et al, 2014;Isobe et al, 2014).…”

A review of possible pathways of marine microplastics transport in the ocean

“…Simulating the transport of microplastics is challenging because the transportation includes physical, chemical, and biological processes (Andrady 2011). Moreover, the physical properties (e.g., size, shape, density, buoyancy) of microplastics, which vary considerably, influence their transport (Ballent et al 2012(Ballent et al , 2013Kowalski et al 2016). The density values for microplastics range from <0.05 g cm −3 for polystyrene foam to 2.1-2.3 g cm −3 for polytetrafluoroethylene (Chubarenko et al 2016).…”

“…To better understand the extent and fate of marine microplastics, several studies have been conducted to simulate the microplastic transport considering different processes (e.g., Ballent et al 2012;Critchell et al 2015;Critchell and Lambrechts 2016). This paper systematically reviews recent research results about the transport of microplastics in the ocean and links transport pathways and the fate of microplastics in marine environments.…”