Persistence of Plastic Litter in the Oceans

Abstract

The increasing global production and use of plastics has led to an accumulation of enormous amounts of plastic litter in the world's oceans. Characteristics such as low density, good mechanical properties and low cost allow for successful use of plastics in industries and everyday life but the high durability leads to persistence of the synthetic polymers in the marine environment where they cause harm to a great variety of organisms. In the diverse marine habitats, including beaches, the sea surface, the water column, and the seafloor, plastics are exposed to different environmental conditions that either accelerate or decelerate the physical, chemical and biological degradation of plastics. Degradation of plastics occurs primarily through solar UV-radiation induced photo oxidation reactions and is, thus, most intensive in photic environments such as the sea surface and on beaches. The rate of degradation is temperature-dependent resulting in considerable deceleration of the processes in seawater, which is a good heat sink. Below the photic zone in the water column, plastics degrade very slowly resulting in high persistence of plastic litter especially at the seafloor. Biological decomposition of plastics by microorganisms is negligible in the marine environment because the kinetics of biodegradation at sea is particularly slow and oxygen supply for these processes limited. Degradation of larger plastic items leads to the formation of abundant small microplastics. The transport of small particles to the seafloor and their deposition in the benthic environment is facilitated by the colonization of the material by fouling organisms, which increase the density of the particles and force them to sink.

Global Distribution, Composition and Abundance of Marine Litter

“…Floating litter items can be transported by the currents until they sink to the seafloor, be deposited on the shore or degrade over time (Andrady 2015). While the occurrence of anthropogenic litter items floating in the world oceans was reported already decades ago (Venrick et al 1972;Morris 1980), the existence of accumulation zones of Floating Marine Debris (FMD) in oceanic gyres has only recently gained worldwide attention (Moore et al 2001b).…”

Microplastics Baseline Surveys at the Water Surface and in Sediments of the North-East Atlantic

“…The transport of small particles to the seafloor and their deposition in the benthic sediments is facilitated by the colonization of the material by fouling organisms, which increase the density of the particles and force them to sink (Andrady, 2015). Plastics degrade very slowly resulting in high persistence of plastic litter especially at the seafloor (Andrady, 2015). Several microplastics of a few micron were found in marine sediments with a rapid-screening approach based on fluorescent tagging with Nile Red, highlighting the role of marine sediments as a sink .…”

Sources and Pathways of Microplastics to Habitats

“…Fragmentation is the pathway, by which plastic debris breaks into smaller pieces, which is distinct from the more subtle processes of degradation that reduces the molecular mass of plastic debris (Andrady 2011(Andrady , 2015. These processes occur through the action of light (photolysis), heat and oxygen (thermal-oxidation), water (hydrolysis), organisms (see review by Andrady (2011) for more details about weathering experiments with pieces of plastic >1 mm) and physical abrasion by particles of sediment.…”