How can we quantify & monitor the amount of plastics via ocean observation systems?
February 7, 2020
by René Garello, IEEE Fellow, Hans-Peter Plag, IEEE senior member, and Jay Pearlman, IEEE Fellow
How much plastic is out there?
Have you ever thought about how much plastic we use in our daily lives? Walk around your local market and start to count. Plastics are ubiquitous and integrated in almost everything we produce, trade and use from the cloths we wear to the way our food is protected to the many tools we utilize. This massive use of plastics, along with an estimated average use time of 5 year  compared to a plastic materials life-time of between 500 and 5000 years has led to a steadily increasing and potentially catastrophic burden of plastics in all aspects of the Earth’s ecosystems. About five years ago, Marcus Eriksen, et al  reported an estimate of the total number of plastic particles and their weight floating in the world’s oceans from 24 expeditions (2007–2013) across all five sub-tropical gyres, costal Australia, Bay of Bengal and the Mediterranean Sea. Using an oceanographic model of floating debris dispersal, he estimated a minimum of 5.25 trillion particles weighing 268,940 tons.
In a paper on the New Plastics Economy  the Ellen McArthur Foundation, working with the McKinsey Center for Business and Environment, noted that the best research currently available estimates that there are over 150 million tons of plastics in the ocean today. In a business-as-usual scenario, the ocean is expected to contain 1 ton of plastic for every 3 tons of fish by 2025, and by 2050, more plastics than fish (by weight). This is dramatic, but estimates vary and the need for quantitative measurements cannot be understated. For example, the distribution of microplastics on the surface was less than expected by Eriksen. and there are still questions on the dynamics of plastic transformations and depth profiles that need further study.
Why are we concerned ?
Why are we concerned about plastics if they are small pieces of inert matter? Plastics have been found in the guts of marine mega fauna and humans and in the tissues of fish. The smallest components that are still plastic (nanoplastics) have become integrated at the cellular level in some organisms. Plastics are not inert and can be a breeding platform for bacteria. Plastics can transport harmful organisms that will have deleterious effects when they are ingested by fish and marine mammals. The extents of this and other issues is not well quantified.
- How much plastic is out there ?
- Why are we concerned ?
- How to monitor plastics?
- Indicators of plastics presence
- IEEE OES program to tackle the Plastics pollution issue
What can be done to quantify the amount of plastics in the ocean? There are many challenges here also. There are several scales to the size of plastics pieces in the ocean form whole fishing nets and contents of lost cargo container content to nanoparticles. The impact of plastics varies according to their size and chemical characteristics. Larger pieces (macroplastics) are 5 mm or more in dimension. Microplastics are plastic fragments or particles that are less than 5.0 mm in size. In , nanoplastics have been defined as particles unintentionally produced (i.e. from degradation and the manufacturing of the plastic objects) and presenting a colloidal behavior, within the size range from 1 to 1000 nm.
In the monitoring of plastics, very different techniques are required to understand the dynamics of different sizes of plastics in the rivers and oceans. However, it has been noted that most of the plastic pollution in the ocean can be originating from river flows, with the ten top-ranked rivers accounting for roughly 90% of the global load being located in Asia and Africa . For further debris, the river assessments are essential, but there are analyses such as those referenced above, which implore us to address both the current ocean inputs and the existing pool of plastic debris across the oceans. This may require different techniques depending on the size and type of the plastic fragments.
How do we monitor it ?
How can we routinely monitor ocean plastics? There are alternative approaches that include remote sensing (from space, airborne and ground based systems) and in situ observations. There are generally many challenges for the space-based remote sensing of plastic pollution in the coastal and marine environment. First, the size of plastic, generally sub-meter size is difficult to image from existing space platforms, which typically have resolutions from 5 meters up to 1 km depending on the system. In addition, fragmentation and decomposition reduces the plastic size over time, and thus reduces the possibility of detection. Airborne systems offer higher spatial resolution, but have limited temporal and spatial coverage. Ground-based systems such as HF radar can monitor coastal surface currents that transport plastics, but will not see small plastic debris. Thus, we need to be able to synthesize results from many data acquisitions from multi sources to improve the spatial and temporal resolutions and then use larger scale, coupled models of surface current circulation (with a 10m depth extent). A critical part of modeling is to have validated data whose collection methods and uncertainties are well understood. This includes adequate description of the data through metadata. It also needs methods documentation that is readily accessible through a global repository such as the Ocean Best Practices System .
Indicators of plastic presence
There may also be “indicators” linked to the plastic presence which may be useful similar to the way oil pollution in the ocean is observed by radar due to its calming effect on ocean surface waves. Indeed, large-scale remote sensing instruments are not able to directly detect the plastic(s) per se and so the indicators need to be defined and tested. This comes not only from the scale size of the plastics vs. the resolution of satellite systems, but the limited ability of high spectral resolution systems (optical, radar or hyperspectral sensors) to differentiate water covered plastic from the surrounding water. Thus, additional inputs are necessary. For example, in situ observation sensors could be developed with an emphasis on having them on-board ships, and then comparing this real-time monitoring of measurements with a global satellite system. When using ships and considering surface macroplastic debris, optical monitoring may be a complementary step to space and airborne observations. This is still limited in that the ships travel defined routes between major commercial ports and thus global coverage is not complete.
In order to fully explore the existing observation means for the detection, monitoring and quantifying of ocean plastics, a comprehensive strategy is need. This strategy should be aligned to the Sustainable Development Goal (SDG) 14 “Life Below Water,” which has the Target 14.1 “By 2025, prevent and significantly reduce marine pollution of all kinds, in particular from land-based activities, including marine debris and nutrient pollution” and the associated Indicator 14.1.1 “Index of coastal eutrophication (ICEP) and floating plastic debris density.”
IEEE OES program to assess observation and indicators
IEEE OES has initiated a program in which we propose to develop a set of objectives for assessing the means of observation and the methods of detection, according to indicators to define. This will need the organization of seminars and workshops for a working group led by OES in collaboration with the UN Environment and the GEO (Group on Earth Observation) initiative “Blue Planet”. At the OES level, this activity will be developed by the associated Technology Committees, mainly “Ocean Observation Systems and Environmental Sustainability” and “Ocean Remote Sensing”. It is already proposed as a topic for our OCEANS flagship conference and it will be the basis for a potential growth in our members.
The major outcome of this initiative will consist of aggregating all the potential partners and stakeholders in order to propose projects at the international level. Considering the amount of plastic already present, the immediate need is to explore downstream solutions for assessing the sources and presence of plastics, as well as to detect plastics in the ocean through a range of observation means (underwater, satellite-borne, in situ, … sensors). Another objective is to perform quantitative as well as qualitative measurements, and to track the circulation of plastics in the ocean and at the coastal level. But for achieving these objectives, we need to understand how the decisions are taken that refer to scientific findings and take on the concerns of civil society.
In order to achieve these objectives, we have started to develop, as a preliminary step, a roadmap with milestones at 6 months (paper at OCEANS 2019 Marseille) and 2 years for a set of goals after 5 years. We will also be part of a town hall session on this topic at the fall conference OCEANS 2019 Seattle.
 Eriksen M, Lebreton LCM, Carson HS, Thiel M, Moore CJ, Borerro JC, 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. https://doi.org/10.1371/journal.pone.0111913
 Gigault, J., et al. (2018). “Current opinion: What is a nanoplastic?” Environmental Pollution (published January 19, 2018).
 Jay Pearlman*, Mark Bushnell, Laurent Coppola, Johannes Karstensen, Pier Luigi Buttigieg, Francoise Pearlman, et al, (2019), Evolving and Sustaining Ocean Best Practices and Standards for the Next Decade, Frontiers in Marine Science, accepted for publication.
Cover image "Plastic-Trash-Floating_River_Water-Pollution__IMG_8879"by Public Domain Photos is licensed under CC BY 2.0
1"Single-Day-PlasticLitter" by realworldvisuals is licensed under CC0 1.0
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3"Plastic Oceans Social Awareness Campaign" by Vickie de Laplante is licensed under CC BY-ND 4.0