Environment Counts | 5 trillion pieces of plastic floating on World’s oceans
Author: Rick Higgins – Published At: 2015-04-26 00:20 – (2617 Reads)
A recent evidence-based study has been released which estimates the amounts of plastics floating on the oceans. The study is based on extensive surveys from 24 expeditions across the five major rotating ocean current regions (known as ocean gyres) of the sub tropics as well as coastal Australia, the Bay of Bengal and the Mediterranean Sea. The study estimates (“our estimates are highly conservative”) there are in the order of 5.25 trillion pieces of plastic weighing around 270,000 tonnes currently floating on the surface of the oceans. As around 8 million tonnes of plastic waste is added to the World’s oceans annually the majority of it sinks to the ocean floor. Plastics take in the order of 5 to 40+ years to break up and degrade/decompose in the oceans, depending on their chemical and physical composition. Some are ingested by marine life and some eventually find their way into the food chain for human consumption. Every year around 100,000 marine mammals and turtles are killed by plastic litter. A second recent study takes available data on plastics entering the oceans from major sources and models the dynamics of how the plastics are flushed from these land sources into the major ocean regions and demonstrates the subsequent transport of plastics by wind and current around the World. Together these 2 studies provide new, more robust estimates of the global situation.
Plastics are increasing
as an environmental issue in the Worldâ€™s oceans.
300 million tonnes of plastics were produced globally in 2013, which is up from only 1.5 million tonnes a year in the 1950s – Association of Plastics Manufacturers. China produces 25% and Europe 20% of the World’s plastic. Approximately 0.1% of this, or 270,000 tonnes makes its way into the ocean each year – Plastic Pollution in the Worldâ€™s Oceans.
Plastic solids, which originate as waste from human and industrial activities on land and from sea based sources, are floating in vast quantities around the oceans from the tropics to the Polar Regions. They are heavily concentrated in a number of circulating large ocean areas or gyres. It takes up to 6 years for plastic to float from the West coast of the USA to the center of the North Pacific ocean gyre (ocean region). Some plastics sink to the ocean floor while others remain floating and are transported by wind and ocean currents. Most common plastics do not degrade completely in the ocean, but break down into smaller pieces.
New study documents extent of plastic pollution in World’sÂ oceans
Until recently reliable evidence-based data on the dimensions of the issue at the global level had been considered “difficult to quantify”. The United Nations Environment Program (UNEP) published a report on Marine Litter in 2005 which provided new focus on plastics in the oceans as a significant global environmental issue. Since then UNEP has published a report on Plastic Debris in the Worldâ€™s Oceans and starting in 2011 the UNEP Year Books have provided annual updates of plastics in the oceans as an one of the key global environmental issues.
In December 2014 a major new study by a multinational team published the results of a seven year global survey of plastic debris in the Worldâ€™s oceans. Plastic Pollution in the Worldâ€™s Oceans The report provides estimates based on evidence collected from 24 expeditions from 2007-2013 surveying all five sub-tropical ocean gyres and the Bay of Bengal, coastal Australia and the Mediterranean Sea. A total of 1,571 locations in all ocean areas were surveyed including 680 surface net tows and 891 visual surveys for large debris.
This is the first study that compares all sizes of floating plastic in the worldâ€™s oceans from the largest items to small microplastics. Pollution levels were compared between ocean areas across four sizes of plastics:
- 0.33â€“1.00 mm (small microplastics)
- 1.01â€“4.75 mm (large microplastics)
- 4.76â€“200 mm (mesoplastic)
- Larger than 200 mm (macroplastics). An average size plastic water bottle is around 200 mm.
Regional distribution of plastics inÂ oceans
The following table summarizes the estimates of floating plastics across five major ocean gyres, and the Mediterranean Sea.
The results indicate the heaviest concentration is in the North Pacific. The Indian Ocean and the North Atlantic follow, and the South Pacific and South Atlantic are smaller. These results reflect proximity to population and industrial concentrations and to the major shipping lanes.
|Estimate of total particle count and weight of plastic floating in world’s oceans|
|Ocean region||Particles of plastic – trillions of items||Weight of plastic – thousands of tonnes|
|Source: Table 1 – Plastic Pollution in the Worldâ€™s Oceans|
The authors of this study include the following note: “we stress that our estimates are highly conservative, and may be considered minimum estimates.”
What happens to plastics in the oceans? According to the US EPA Marine Debris in the North Pacific approximately half of all plastics are neutrally to positively buoyant and thus remain close to the ocean surface. Over time as the plastic breaks down into smaller pieces, organism and sediment fouling add weight to the particles which can cause the plastics to sink and eventually reach the seabed. Most plastics will eventually break up and/or degrade/dissolve over between 5 and 30 years. The study of these processes is an ongoing source of enquiry.
The following table provides a summary of plastics in the oceans from this study and from UNEP.
|Plastics in the World’s Oceans||Source – see list at end of article|
|5.25 trillion pieces of plastic weighing around 270,000 tonnes are currently floating on the World’s oceans||A – Survey|
|Plastics make up 60 to 80% of all marine debris/litter||B – US EPA|
|8 million items of litter a day enter the oceans.This amounts to around 6.4 million tonnes a year||I -UNEP|
|15% of plastics are floating, 70% sink to the ocean floor and 15% return to land/shore/beaches||J – UNEP|
|80% of marine litter originates on land, and 20% originates from sea based activity||J- UNEP|
|Plastic bags take 10 to 40+ years to decompose on the sea floor||J- UNEP|
|100,000 marine mammals and turtles are killed by marine plastics every year||K – US EPA|
Sources of plastics in theÂ ocean
300 million tonnes of plastics were produced in 2013. Approximately 100 million tonnes of plastic waste is created annually by the approximately 2 billion people living within 50 km of the oceans and around 8 million tonnes goes into the oceans annually. Of this 8 million tonnes, approximately 70% sinks, 15% goes back to shore land and 15% floats where it is distributed by wind and ocean currents to until it breaks down into smaller particles or sinks.
Dynamics of plastic movements into and around theÂ oceans
Knowledge of the distribution of plastics floating in the oceans and the dynamics of their movements around the World is important. The study noted above is the first major evidence based study to address the amounts and spatial distribution of floating plastics by size. It does not however provide detailed answers to questions of how floating plastics are transported around the World.
Another study, published in 2012 Numerical modelling of floating debris in the worldâ€™s oceans simulated the 30 year input, transport and accumulation of floating plastics in the oceans. This study is not entirely evidence based, but uses a large-scale hydrodynamic model to simulate the global ocean circulations and indicate where floating plastics are transported across the oceans .
The results of the model can be seen through the following interactive graphic which provides interesting insight on the movement of plastics and the patterns of distribution across the major ocean gyres based on the country of origin of plastic debris. The graphic can be used in several ways, including selecting a country or region or origin (of plastics being introduced into the oceans) and viewing the flow and destination of the plastics to ocean regions. Alternately, an ocean gyre or region can be selected and the sources of the plastics in that region can be viewed.
|Click on image and select either map View or Source View. The graphic interactively displays the source by country of origin and the destination by ocean gyre of the land to sea contribution of plastics to ocean from coastal regions.|
|Source: Numerical modelling of floating debris in the worldâ€™s oceans. Marine Pollution Bulletin, Volume 64, Issue 3, March 2012, Pages 653-661. Lebreton et al|