By Pat Pepper, NCWQ Environmental Adviser
In this report, marine plastic debris is revisited, and removal and remedial measures investigated. Removal of floating plastic from ocean garbage patches and from rivers which researchers calculated had a high probability of entering the oceans were considered together with the ocean currents which could distribute the debris to the gyres. In addition, methods to remove microplastics were also considered. While advances using plastic-eating microorganisms look promising to break polymers into monomers from which more plastics can be created, there are serious concerns about releasing genetically engineered microorganisms into the environment. Hence, it is imperative that plastic waste be captured at its source and, in particular, plastic waste from rivers and other outlets does not make it to the open sea.
It is heartening that 175 countries endorsed a resolution at the United Nations Environment Assembly (UNEA) on 2 March 2022 to negotiate an international legally binding agreement to end plastic pollution by the end of 2024. There are many challenges to confront not least microplastics and nanoplastics already in the ocean. The UN Resolution on an Enhancing Circular Economy was also endorsed at UNEA and should help achieve stainable consumption and production in the future. Adoption of a circular economy for plastics with advanced recycling technologies and utilising existing manufacturing infrastructure could help Australia reach it targets.
Global treaty to end plastic pollution
More than 8.3 billion tons of plastic has been produced since the early 1950s with about 60% ending up in either a landfill or the natural environment. 80% of land-based plastic ends up in the ocean1. On 2 March 2022 at the United Nations (UN) Environment Assembly in Nairobi, UNEA-5, a resolution was endorsed by 175 countries, to negotiate an international legally binding agreement to end plastic pollution by the end of 2024. The treaty will require countries to meet set pollution reduction targets or action plans in other environments as well as the marine environment, and address the full lifecycle of plastic, including its production, design and disposal2. The resolution was adopted after negotiations at the Open Ended Committee of Permanent Representatives which saw the merge of three separate draft resolutions on the topic, by Rwanda and Peru , by Japan and by India3. Australia supported the resolution drawing attention to National Waste Policy Action Plan and National Plastics Plan addressing the impacts of plastics along its life cycle and the Pacific Ocean Litter Project, in which Australia is working with Pacific Island countries to tackle single use plastics that harm marine and coastal ecosystems4.
Previous reports and submissions to Federal and Queensland Governments have drawn attention to the problems of Plastic Waste, Marine Debris and the Impact of microplastics and nanoplastics on the marine environment, including the potential of toxins incorporated during manufacture or absorbed from the environment onto microplastics, and then being transferred to marine organisms and potentially up the food chain. (NCWQ Submissions to Government:- Microplastics, April 2015; Microplastics and Nanoplastics, November 2017; Marine Debris, February 2018; Plastic Waste, October 2018).
Ocean garbage patches
Of the five known gyres (Great (North) Pacific, South Pacific, North and South Atlantic, Indian Ocean) where rotating ocean currents have pulled marine debris which range in size from large abandoned fishing nets to microparticles into huge garage patches, the Great Pacific Garbage Patch is the most well known and covers an estimated 1.6 million square kilometres (Oct 2021- cf size of Qld 1.7 million square kilometres) and rapidly expanding5,6.
Figure 2 Ocean Currents and Sea Ice from Atlas of World Maps8
Original by US army, successively modified by Jack · talk · (removed borders and rivers ,
Public domain, via Wikimedia Common. Attribution not legally required.
Lebreton et al predicted that at least 79 (45–129) thousand tonnes of ocean plastic was floating in the Great Pacific Garbage Patch from a model, calibrated with data from multi-vessel and aircraft surveys9. The South Pacific Garbage Patch, estimated to be 2.6 square kilometres in a largely unstudied area of the South Pacific Ocean. The plastic in South Pacific Patch is primarily microplastics10.
Eriksen et al estimated that 5.25 trillion plastic particles weighing 268,940 tons were floating in the world’s oceans, using an oceanographic model of floating debris dispersal calibrated by data from 24 expeditions (2007–2013) across all five sub-tropical gyres, costal Australia, Bay of Bengal and the Mediterranean Sea, and correcting for wind-driven vertical mixing 11
Removal of floating plastic
After years of development and trials, Ocean Cleanup, a not-for-profit organisation, now believes its latest development, System 002 will be able to clean up 90% of floating ocean plastic by 204012. Two thousand feet-long floating rods will corral floating plastic to be periodically collected by ships. While this will not collect the microplastic, the large pieces of plastic will be removed before sunlight and waves breaks them into thousands of microplastic bits. From surveys, Ocean Cleanup estimate an 80,000 metric tons in the Great Pacific garbage patch, with 1.8 trillion plastic pieces, out of which 92% of the mass is to be found in objects larger than 0.5 centimeters13.
Figure 314 https://theoceancleanup.com/media-gallery/
Eighty percent of the world’s ocean plastics enter the ocean via rivers and coastlines.
The other 20% come from marine sources such as fishing nets, ropes, and fleets.
Meijers et al calculated the probability for plastic waste to reach a river and subsequently the ocean using geographically distributed data on plastic waste, land use, wind, precipitation, and rivers. They estimate that 1656 rivers account for 80% of global annual riverine plastic emissions, which range between 0.8 million and 2.7 million metric tons per year, with small urban rivers among the most polluting and illustrated this on global basis15.
the probability for plastic entering the ocean [P(E)] metric tons (MT) Figure 4. Global emissions of plastic into the ocean. (A)
J. J. Meijer, T. van Emmerik, R. van der Ent, C. Schmidt, L. Lebreton, More than 1000 rivers account for 80% of global riverine plastic emissions into the ocean.
Sci. Adv. 7, eaaz5803 (2021).
Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).
As these rivers can present very different characteristics, including river width, flow dynamics, marine traffic, and urbanization, a wide range of mitigation measures must be applied to these rivers across the globe to substantially decrease the amount of waste entering the oceans from rivers. The Ocean Cleanup has developed river cleanup technology, interceptors, which can extract substantial amounts of waste from rivers and be deployed in several waterway types. Stopping plastics at the river mouth with log booms and barriers could complement riverbank cleanups that include active plastic skimming and other measures such as trash racks and nets. Therefore, The Ocean Cleanup is adopting other technologies to add to the Interceptor range of solutions to extract plastic waste from rivers based on their specific characteristics16.
Adelaide operates a number of trash racks or “gross pollutant traps” on the Torrens River17.
Small, innovative businesses e.g. Plastic Fischer and RiverRecycle are deploying low-cost, low-tech solutions to capture plastic from rivers.
Plastic Fischer have made a floating barrage (TrashBoom) consisting of floats made from standard plastic piping, attached to wire mesh barriers which extends down into the water to capture pieces of plastic floating below the surface. Plastic Fischer joined forces with the Indonesian army in Bandung to develop and test the TrashBoom on heavily polluted Citarum River in Bandung. In another project, Plastic Fischer have deployed 26 meter wide walkable TrashBoom in one of the most polluted tributaries to the Ganges, the Varuna River. The company will make the technology open source, to increase opportunities to capture plastic in rivers around the world.
RiverRecycle’s projects include a facility on the Mithi River in Mumbai, India. Plastic collected from the river is fed into a chemical recycling facility18 Details and photographs of projects are available on their websites Plastic Fischer, RiverRecycle
Because commonly applied plastic sampling techniques i.e. plankton nets with mesh sizes of several μm, are not suitable for nanoplastic (<1 μm) sampling, their abundance/concentration and distribution is unknown. The distribution of microplastics (1 μm to 5 mm) could be underestimated. Given the potential toxicity of nano and microplastics and especially nanoplastics, their presence in the food chain is serious. Since these microplastics and nanoplastics are so small in size, continuously mixed by wind and wave action and spread from the surface to the ocean floor it is very difficult to find cost effective technological means of removing them19,20.
Removal of microplastics
Badola et al have reviewed physical, chemical and biological methods for microplastics removal.
- Physical methods based on adsorption/filtration
- Chemical methods based on coagulation and flocculation mechanism.
- Biological methods using degradation by microbial activities.
Most research has been conducted in-vitro under controlled conditions. However some experiments in wastewater treatment plants have shown good efficiency21.
A series of other breakthroughs have been reported in recent years e.g. bacteria, Ideonella sakaiensis, which can decompose a particular kind of plastic called polyethylene terephthalate (PET), from which bottles are commonly made. The bacterium could grow PET and use it as its main source of nutrients, degrading the PET in the process. Enzymes produced by the bacterium reduce PET to its constituent chemicals. However, to make any of these naturally occurring bacteria useful, they must be bioengineered to degrade plastic hundreds or thousands of times faster22,23.
Zrimec et al claim synergistic degradation of plastics by microorganisms holds great potential to revolutionize the management of global plastic waste. Their study uncovered the earth microbiome’s potential to degrade 10 different plastics. While differences between the ocean and soil microbiomes could reflect the base compositions of these environments, the researchers found that ocean enzyme abundance increases with depth as a response to plastic pollution and not merely taxonomic composition24.
Experts caution that large-scale commercial use of plastic-eating microorganisms could be years away and if released into the environment could create more issues than would be solved. Bacteria typically don’t break up the polymers out of which plastics are composed, into their core elemental building blocks, including carbon and hydrogen, Rather the polymers are broken up to monomers, which are often useful only to create more plastics. While this recycling is useful, biodegrading the polymers could risk releasing chemical additives that are normally stored up safely inside the un-degraded plastic. Others warn that genetically engineered microorganisms could be needed and releasing these into the environment could have unknown side-effects22.
Hence, it is imperative that plastic waste be captured at its source and, in particular, plastic waste from rivers and other outlets does not make it to the open sea.
Future sustainable consumption and production
UN Environment Programme Executive Director, Inger Andersen stressed that a systemic transformation is needed to transition to a circular economy25. The Resolution on an Enhancing Circular Economy as a contribution to achieving sustainable consumption and production was endorsed at the UNEA on 2 March 202226. Australia has set a national target of 80% average recovery rate from all waste streams by 2030, and 70% of plastic packaging recycled or composted by 2025.
A circular economy for plastics
Although advanced recycling conversion technologies can convert plastic waste to oil to be further processed and used as a fuel, King et al describe how the oil can be also used to produce other plastic by cracking the oil (the process of breaking the chemical bonds of long chain hydrocarbons to smaller units) to produce a monomer (the building block of polymers) and then further processed into recycled polymers that are able to be manufactured into new plastic products with recycled content (a desirable circular economy proposition). Advanced recycling can process mixed, multi-layer, flexible and contaminated plastics which cannot be processed by other means (e.g. mechanical recycling). Adoption of a circular economy for plastics with advanced recycling technologies and utilising existing manufacturing infrastructure could help Australia reach its targets27.
CSIRO scientists are researching biodegradable bioplastics sourced from petro-chemical-based materials or renewable natural materials which will fully degrade into carbon dioxide and water leaving no residual microplastics or toxic residues. Products that currently benefit from biodegradability include food and soil-contaminated plastics that are unable to be recycled. However, since moisture is a trigger for the degradation of biodegradable bioplastics, they are currently limited to short-term storage of foods28.
As an alternative to petroleum-based plastic, seaweed is being converted into sugars and then fermented in vats to produce natural polyesters. Seaweed-derived polymers can be re-used, recycled or composted29.
- 2 Global Agreement Explanatory note and Resolution 27 October.pdf
- https://www.marineconservation.org.au/un-agreement-is-vital-step-towards-tackling-plastic-pollution-in-australias-wildest-places/ accessed 10May2022
- https://www.genevaenvironmentnetwork.org/resources/updates/towards-unea-5-2/ accessed 29April2022
- https://www.awe.gov.au/environment/international/unep accessed 29April2022
- https://en.wikipedia.org/wiki/Great_Pacific_garbage_patch; accessed 19April2022
- https://en.wikipedia.org/wiki/Marine_plastic_pollution#Microplastics accessed 19April2022
- https://sitn.hms.harvard.edu/flash/2018/plastic-oceans-cleanup/ Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. accessed 16April2022
- https://upload.wikimedia.org/wikipedia/commons/7/7b/Ocean_currents_1943.jpg Original by US army, successively modified by Jack · talk · (removed borders and rivers , Public domain, via Wikimedia Common Attribution not legally required
- Lebreton, L., Slat, B., Ferrari, F. et al. Evidence that the Great Pacific Garbage Patch is rapidly accumulating plastic. Sci Rep 8, 4666 (2018). https://doi.org/10.1038/s41598-018-22939-w. CC by 4.0 Commons Attribution 4.0 International license. accessed 24April2022
- https://en.wikipedia.org/wiki/South_Pacific_garbage_patch accessed 16April2022
- Eriksen M, Lebreton LCM, Carson HS, Thiel M, Moore CJ, et al. (2014) Plastic Pollution in the World’s Oceans: More than 5 Trillion Plastic Pieces Weighing over 250,000 Tons Afloat at Sea. PLoS ONE 9(12): e111913. doi:10.1371/ journal.pone.0111913 accessed 23May2022
- https://theoceancleanup.com/oceans/ / accessed 27May2022
- https://theoceancleanup.com/great-pacific-garbage-patch/ accessed 24April2022
- https://theoceancleanup.com/media-gallery/ accessed 27May2022
- J. Meijer, T. van Emmerik, R. van der Ent, C. Schmidt, L. Lebreton, More than 1000 rivers account for 80% of global riverine plastic emissions into the ocean. Sci. Adv. 7, eaaz5803 (2021).. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC). Accessed 20April2022
- https://theoceancleanup.com/updates/in-search-of-the-rivers-that-carry-plastic-into-the-ocean/ accessed 16April2022
- https://en.wikipedia.org/wiki/Marine_debris accessed 20April2022
- https://www.weforum.org/agenda/2022/02/plastic-pollution-rivers-innovative-solutions/ accessed 23April2022
- https://pubs.rsc.org/en/content/articlehtml/2021/em/d0em00446d. accessed 21April2022
- https://marinedebris.noaa.gov/movement/great-pacific-garbage-patch accessed 21April2022
- Badola N., Bahuguna A., Sasson Y. and S. Chauhan 2022; Microplastics removal strategies: A step toward finding the solution Front. Environ. Sci. Eng. 2022, 16(1): 7; https://doi.org/10.1007/s11783-021-1441-3 accessed 30 April2022
- https://www.forbes.com/sites/scottcarpenter/2021/03/10/the-race-to-develop-plastic-eating-bacteria/?sh=614e166c7406; accessed 21 April2022
- https://www.theguardian.com/environment/2022/feb/05/how-super-enzymes-that-eat-plastics-could-curb-our-waste-problem accessed 25April2022
- Zrimec, Kokina, Jonasson, Zorrilla and Zelezniak. (2021). Plastic-degrading potential across the global microbiome correlates with recent pollution trends. https://doi.org/10.1128/mBio .02155-21 Creative Commons Attribution 4.0 International license. accessed 30 April2022
- https://www.unep.org/plastic-pollution accessed 30 April2022
- https://www.unep.org/news-and-stories/press-release/un-environment-assembly-concludes-14-resolutions-curb-pollution accessed 29April2022
- King, S, Hutchinson, SA and Boxall, NJ (2021) Advanced recycling technologies to address Australia’s plastic waste. CSIRO, Australia
- https://ecos.csiro.au/bio-derived-plastics/ accessed 1May2022
- https://ecos.csiro.au/could-seaweed-replace-plastic/ accessed 9May2022
NCWQ Environment Adviser
background photo credit: https://theoceancleanup.com/media-gallery/
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