A global mass budget for positively buoyant macroplastic debris in the ocean

Abstract

Predicted global figures for plastic debris accumulation in the ocean surface layer range on the order of hundreds of thousands of metric tons, representing only a few percent of estimated annual emissions into the marine environment. The current accepted explanation for this difference is that positively buoyant macroplastic objects do not persist on the ocean surface. Subject to degradation into microplastics, the major part of the mass is predicted to have settled below the surface. However, we argue that such a simple emission-degradation model cannot explain the occurrence of decades-old objects collected by oceanic expeditions. We show that debris circulation dynamics in coastal environments may be a better explanation for this difference. The results presented here suggest that there is a significant time interval, on the order of several years to decades, between terrestrial emissions and representative accumulation in offshore waters. Importantly, our results also indicate that the current generation of secondary microplastics in the global ocean is mostly a result of the degradation of objects produced in the 1990s and earlier. Finally, we propose a series of future emission scenarios until 2050, discussing the necessity to rapidly reduce emissions and actively remove waste accumulated in the environment to mitigate further microplastic contamination in the global ocean.

Finding Plastic Patches in Coastal Waters using Optical Satellite Data

“…Larger plastics entering ocean waters have two fates -floating on the surface, or sinking due to bio-fouling and/or ballasting 8,9 . If not removed by clean-up operations, macroplastics (>5 mm) may harm marine life through entanglement or ingestion, but will inevitably fragment and degrade into microplastics [10][11][12][13] .…”

High concentrations of plastic hidden beneath the surface of the Atlantic Ocean

“…Microplastics of crystal-grade PS (used in houseware and rigid packaging) are denser than seawater (ρ = 1.04-1.05 g cm −3 ), and thus might be more prone to transport down the water column and surpass the depths sampled in our study. Alternatively, but not exclusive, microplastics derived from the foam expanded PS material, which is 98% gas by composition with density of~0.05 g cm −3 , might be preferentially retained above the shallowest depth sampled in our study and/or dispersed horizontally by prevailing surface currents 44 and winds.…”

Atmospheric Transport, a Major Pathway of Microplastics to Remote Regions

“…TWP concentrations in the Arctic snow ranged between 1 and 10 ng kg -1 of snow for PM2. 5 and between 4 and 80 ng kg -1 for PM10 ( Fig. 3).…”

“…Global annual plastic production reached 348 million tonnes in 2017 1 and, consequently, plastic pollution in freshwater 2 , marine 3 and terrestrial 4 ecosystems has received a lot of attention recently. Plastics are released into the environment as macroplastic (>5 mm) 5 , microplastic (1 µm to 5 mm) 6 and nanoplastic (<1 µm) 7 particles which can fragment into smaller sizes via photodegradation, physical abrasion, hydrolysis and biodegradation 8 . Plastics can affect coral reefs 9 , marine 10 and terrestrial animals 11 as well as human health 12,13 .…”