This report illustrates the limited, or absent, data from which to inform and implement effective plastic intervention actions. To inform source reduction strategies and policies, a national-scale tracking and monitoring program (or system of systems) is needed that spans the plastic life cycle—that is, from plastic production to leakage into the ocean (Figure 6.1). Tracking and monitoring plastic waste in the environment are essential to understanding and subsequently addressing the problem, but no comprehensive life-cycle tracking and monitoring of ocean plastic waste presently exists. Tracking and monitoring systems currently in place focus on solid waste management inputs and plastic waste items detected in the environment and ocean (Figure 6.1). This chapter explores tracking and monitoring systems currently in use and their limitations, and offers recommendations to inform the design, implementation, and benefits of a system or a system of systems to comprehensively track and monitor ocean plastic waste. Optimal systems will contribute to identifying and understanding the sources, transport pathways, distribution, and fate of ocean plastic waste, including legacy waste, to inform source reduction strategies or policies at multiple, if not all, intervention stages.
As noted in previous chapters, there are still immense gaps in understanding these processes, and there is an opportunity to utilize and expand tracking and monitoring programs to fill these gaps. Observational data are particularly valuable to inform scholarly modeling of plastic waste, such as mass-balance models that integrate and assess plastic material entering and leaving a system, as well as the fate of discarded plastics
(Borrelle et al. 2020, Geyer, Jambeck, and Law 2017, Jambeck et al. 2015, Lau et al. 2020). Tracking and monitoring are two tightly related methods; in this report, tracking means following the transport of marine debris over time, whereas monitoring typically involves detection and measurement of plastic waste in the environment at various temporal and spatial scales. Most existing activities qualify as monitoring efforts. However, throughout the chapter, the committee refers to the value of both approaches.
Documentation of the extent and character of plastic waste and potential sources or hotspots (reservoirs and sinks) informs prevention, management, removal, and cleanup strategies (UNEP 2020). Moreover, it plays a critical role in evaluating the effectiveness of any interventions or mitigation actions, such as source reduction strategies or policies (described further in Chapter 7). Thus, information obtained through tracking and monitoring efforts is critical to share with the public and decision makers involved in motivating and designing intervention strategies.
There is no national-scale monitoring system, or “system of systems,” to provide a baseline to track important sources, pathways, and sinks at the current scale of public or governmental concern. Under U.S. environmental management and protection law, monitoring systems are designed to achieve specific authorized purposes: legal compliance (e.g., waste generation or discharge monitoring), source detection (e.g., drinking water monitoring), and assessment of status and trends (e.g., ambient or in situ monitoring). The U.S. Environmental Protection Agency (U.S. EPA), the states, and other agencies operate a range of monitoring systems to meet such requirements, including those that monitor point and nonpoint sources and waste streams for pollutants or hazardous substances. These systems do not track or monitor plastic waste because it is not classified as a pollutant or constituent of concern. Much of the data on plastic waste is derived from data on municipal solid waste and, in a few cases, from nonpoint source trash monitoring, or from the efforts of research and community-based initiatives.
Part of the charge to the committee is to assess the value of a national marine debris tracking and monitoring system and how it could be designed and implemented. As specified in the task, this chapter considers
how such a system may help in identifying priorities for source reduction and cleanup and assessing progress in reducing U.S. contributions to global plastic waste, and specifies existing systems and technologies that would be effective. The chapter gives particular attention to the National Oceanic and Atmospheric Administration’s (NOAA’s) Marine Debris Monitoring and Assessment Project (MDMAP), part of the NOAA Marine Debris Program (MDP), and potential improvements.
The chapter first explains existing tracking and monitoring strategies and programs. The following section describes considerations, enhancements, and opportunities for tracking and monitoring in the United States. The third section delves into the potential value of a national tracking and monitoring system. The final two sections outline priority knowledge gaps and present the committee’s findings and recommendations.
Due to the lack of federal regulation of plastics as a pollutant in the United States and with the attendant lack of tracking and monitoring requirements, approaches to ocean plastic waste tracking and monitoring, including by the federal government, have been grounded in either research-based efforts or community science-based approaches.
Research-based monitoring for ocean plastic waste is often driven by government initiatives at various levels and geographic scales: local, regional, state, national, and tribal. One example is NOAA’s MDP, which is directed by Congress to maintain an inventory of marine debris and its impacts. To help achieve this directive, NOAA’s MDP offers several nationwide, competitive, short-term (<3 years) funding opportunities. Funds support “original, hypothesis-driven research projects focused on ecological risk assessment, exposure studies, and the fate and transport of marine debris” (NOAA Marine Debris Program 2021a). These projects may be conducted by government agencies, industry, or academic institutions.
Many local and regional research-based programs design their programs around concerns specific to that region. For example, plastic pollution is a central concern for the state of California. Among western U.S. regions, Southern California holds the greatest assemblage of plastic processors (Moore 2008), and California is the nation’s most populous state with approximately 40 million citizens (U.S. Census Bureau 2019). As a microcosm of the national (and global) plastic pollution problem, California is leading research, removal, and prevention efforts.
While other U.S. states may not have the same focus and funding profile, lessons learned in California and other states can inform state and national efforts through research, removal, and prevention experiences.
Discrete, competitive ad hoc funding is appropriately employed to identify and fund hypothesis-driven research on aquatic plastic pollution but does not operate as a plastic waste tracking and monitoring system. While the information gained from this research can inform such a system, ad hoc research funding results in a disjointed monitoring record when individual projects end. This can contribute to a mosaic of plastic waste tracking and monitoring data collected using a diversity of methods, making it difficult to synthesize and interpret at meaningful spatial and temporal scales.
Community Science-Based Approaches
Community science-based approaches often include citizen-science activities or other experiential activities that also build public awareness and engagement. Experiential activities engage individuals through active participation, such as beach cleanups conducted through a variety of entities (often nonprofit organizations). Here, the term “community science-based” rather than “citizen science-based” is used to more accurately reflect the diversity of individuals engaging in the broader plastic waste tracking and monitoring enterprise. Community science-based efforts therefore may encompass citizen-science while recognizing diversity, seeking equity, and promoting inclusion.
A wide variety of community-based approaches are used to gather data on plastic pollution in the environment. Most approaches are focused on coastal areas, but a multitude of electronic mobile applications (apps) do not limit data gathering to coastal regions. This enhanced accessibility by a broader demographic has increased the transparency and availability of litter and other debris data along inland waterways and urban areas. The majority of these apps gather data and are not designed to answer specific research questions. The interpretation of those data to answer specific questions occurs a posteriori; therefore, the available data may not always be suitable to the questions. Furthermore, community science-based approaches do not routinely select locations in a scientifically rigorous manner, and thus the data collected may not be representative of plastic pollution at regional or national scales. Despite these limitations, several of these systems have been consistently gathering data on plastic waste for many years at various temporal and spatial scales.
A recent river basin-scale community science-based project illustrates the integration of community-based data collection with targeted research data collection in three pilot communities along the Mississippi
River (Youngblood, Finder, and Jambeck 2021). Researchers engaged the public in data collection using consistent transect-based methods so that the data could be compared with data from other research-based work in urban and riverine systems. The distinction between research- and community-based approaches is often blurred, and there is increasing interest in integrating research- and community-based science approaches (e.g., Earp and Liconti 2020, Liboiron et al. 2016). As with the Mississippi River project (Youngblood, Finder, and Jambeck 2021, NOAA Marine Debris Program 2021b), tracking and monitoring efforts may provide volunteers with specific research question-derived protocols that are distinct from cleanup-type protocols or opportunistic debris sightings used in other cases.
Selected Examples of Tracking and Monitoring Efforts
The following examples of plastic waste tracking and monitoring efforts are not intended to be comprehensive. Rather, they illustrate various approaches at assorted spatial and temporal resolutions. They may also potentially be integrated into a national-scale marine debris tracking and monitoring network or system of systems.
NOAA’s Marine Debris Monitoring and Assessment Project
NOAA’s MDP operates the MDMAP, a federal marine debris (plastics and other waste) inventory called for under the Marine Debris Act. MDMAP is the flagship community-science initiative of the MDP, engaging partner organizations and volunteers in a national shoreline monitoring program. The program has met many important national goals, including raising the issue to the public and decision makers, informing understanding of the risk and extent of marine debris in coastal and ocean areas, and identifying cleanup and mitigation priorities. Data collected and shared through the MDMAP are also intended to foster capacity at the local level in developing marine debris mitigation strategies to reduce impacts (NOAA Marine Debris Program. 2020b).
The foundation of MDMAP surveys is the NOAA-developed set of shoreline monitoring protocols (Lippiatt, Opfer, and Arthur 2013, Opfer, Arthur, and Lippiatt 2012) that standardize marine debris monitoring for consistent assessment of marine debris status and trends. The MDMAP surveys occur every 28 days (±3 days), as close to low tide as possible for shoreline sites that meet NOAA’s criteria (i.e., sandy beach or pebble substrate, year-round access, no breakwaters or other structures that may affect coastal circulation, and no known regular cleanup activities). In 100-m-long sections, shoreline sites are surveyed for debris larger than
2.5 cm. Monitoring protocols include two shoreline survey types: standing stock and accumulation. Standing stock surveys are rapid visual assessments of debris concentration at a shoreline site. Accumulation surveys are tactile assessments that provide estimates of the flux, or accumulation rate, of debris at a shoreline site. For standing stock surveys, the 100-m-long sections are divided into twenty 5-m-long transects that extend from the back shoreline barrier to the water’s edge. Surveyors identify and record debris items within four replicate, randomly selected transects. For accumulation surveys, debris is identified and removed from the entire 100-m site. To date, there are 9,055 surveys at 443 sites that span 21 U.S. states and territories and nine countries.
Studies, such as Uhrin et al. (2020), have demonstrated the utility of MDMAP data to estimate marine debris abundance and temporal trends, while also identifying associated limitations. The most extensive study on the benefits and challenges of existing marine debris monitoring programs, including MDMAP, is provided by Hardesty et al. (2017). The study was a collaborative project among Australia’s Commonwealth and Industrial Research Organization, the Ocean Conservancy, and NOAA’s MDP to better understand marine debris within the United States. Example survey issues identified include the following:
- Spatial sampling. Most of the United States is not covered by existing data. Accumulation data are adequate for the West Coast, but standing stock is limited to concentrated efforts (Hardesty et al. 2017).
- Temporal sampling. Accumulation rates are driven by regional/local biogeophysical forcing as well as debris type, such that the 28-day (±3 days) sampling window might be insufficient (Hardesty et al. 2017, Smith and Markic 2013, Uhrin et al. 2020).
- Site selection. Environmental and anthropogenic factors impact debris counts (e.g., distance to the nearest town, freshwater outfall, nearest river) but were not strategized/prioritized when designing a long-term monitoring program (Uhrin et al. 2020).
- Substrate type selection criteria. Shoreline debris monitoring methods are not analogous for rocky shores, and thus limited data exist for these environments (McWilliams, Liboiron, and Wiersma 2018, Thiel et al. 2013).
- Number of survey participants. A linear relationship exists between debris counts and the number of participants, such that some surveys could be severely underestimated if the volunteer threshold is not met (Hardesty et al. 2017, Uhrin et al. 2020).
- Characteristics of survey participants. The quality of the data collected by community scientists can be equivalent to that collected
- by professional researchers, though variability may exist, for one example, younger primary school students detecting more debris than secondary students (van der Velde et al. 2017).
A key shortcoming of MDMAP identified by Hardesty et al. (2017) was the lack of a comprehensive national baseline for debris densities along the coast. This hinders the ability to monitor change in general, as well as change in association with the implementation of new policies and other interventions. In addition to a nationwide baseline survey, Hardesty et al. (2017) suggested regular surveys be conducted every 5 to 10 years at strategically selected sites in addition to continued citizen science efforts at self-selected sites. Aspects of these recommendations (i.e., one protocol, two approaches—community science and a national survey) appear in the NOAA MDP 2021–2025 Strategic Plan.
The International Coastal Cleanup
Developed and launched in 1986 by the nonprofit Center for Marine Conservation (now known as Ocean Conservancy), the International Coastal Cleanup (ICC) volunteer effort grew from a small local cleanup in Texas to an annual international effort, engaging with people in more than 100 countries. The Ocean Conservancy leveraged its partnerships with volunteer organizations and individuals worldwide to expand toward the Ocean Conservancy’s Trash Free Seas initiative.1 A pioneer in citizen science, the ICC was notable from inception insofar as it asked participants not only to collect coastal litter but also to document it using a standardized data card.
The ICC is the longest-running and most consistent community science data set, proving itself useful in both research and discussions around decision making. The ICC has been collecting largely the same data set since 1988, with comparable data available on local, regional, state, and nationwide perspectives. This data set has been used to track the effectiveness of regulations on plastic pollution. For example, the data set was used to evaluate the impacts of beverage deposit return schemes in the United States and Australia, finding that states that have a beverage container deposit result in 40% fewer containers littered (Schuyler et al. 2018). Data for the ICC are typically collected on a paper data card; however, an app (Clean Swell) is now available that mimics the paper data card, albeit with limited items. The full ICC data card is also integrated into the mobile app Marine Debris Tracker (described below), and the Ocean Conservancy
and University of Georgia are now coordinating on data collection and management. Both apps allow for more widespread collection of plastic pollution data through the engagement of a broader public demographic.
Marine Debris Tracker
Launched in 2011, the mobile app Marine Debris Tracker was the first litter or debris tracking app developed and has the longest history of electronic data collection (Jambeck and Johnsen 2015). In addition, it is one of few applications and programs to allow complete open access to all data ever collected. The Marine Debris Tracker was originally sponsored by a grant award from NOAA to the University of Georgia. NOAA subsequently sponsored research work with the app, with other partners contributing over time. The app has been used for various community science-based projects, as well as education and research initiatives (Ammendolia et al. 2021, Martin et al. 2019, National Geographic 2021, Thiel et al. 2017, Youngblood, Finder, and Jambeck 2021, Youngblood et al. In Review). In 2019, the app became sponsored by the global financial services company Morgan Stanley to professionalize it in partnership with the National Geographic Society, but the University of Georgia independently maintains science and data management for the app.
The Marine Debris Tracker database provides insights on managing, compiling, harmonizing, and visualizing plastic pollution data because it is a harmonized background database that allows for the creation of customized litter lists for individual organizations that vary in individual items cataloged. The app’s harmonization allows for combined data compilation and statistics to be completed on the entire data set. To date, approximately 4 million items have been cataloged with the Marine Debris Tracker, with 2.33 million items originating in the United States. For example, the Mississippi River Plastic Pollution Initiative collected data on more than 75,000 debris items by both researchers and community members over 3 weeks in April 2021. Marine Debris Tracker was an early example of the successful application and acceptance of app use in community science, and remains the foremost and most comprehensive extant plastic pollution app.
Supporting Plastic Waste Mitigation with Monitoring Data
Data integration between electronically collected databases can provide a more complete picture of plastic waste and marine debris in the United States. While integrating these databases is not trivial, it is possible. The current three largest electronic research and community science-based data sets in the United States—the ICC, Marine Debris Tracker, and NOAA’s MDMAP—are not well integrated.
Growing online and wireless connectivity nationwide and worldwide is making community science-based tracking and monitoring of plastic waste in the environment increasingly accessible. Many existing data collection efforts already allow the data to be visualized in map form.2 Increased accessibility of plastic waste data through visualization tools has the potential to engage a larger, more diverse sector of society in community science-based activities—such as data crowdsourcing—toward awareness of and solutions to the ocean plastic waste problem.
California established its Water Quality Monitoring Council’s Trash Monitoring Workgroup “to support current practices and advances in trash monitoring” (California Trash Monitoring Methods Projects 2021). This Trash Monitoring Workgroup is “developing data analysis and visualization tools aimed at assessing the effectiveness of policies and practices for limiting the amounts of trash in the environment” (California Trash Monitoring Methods Projects 2021). One outcome was the 2021 publication of the California Trash Monitoring Methods and Assessment Playbook, which provides an overview of the methods in use to monitor trash in the environment (M. L. Moore et al. 2021).
Monitoring waste transport through watersheds (i.e., waste transported from the source via freshwater rivers and other waterways to the ocean) offers a more comprehensive understanding of plastic waste sources to guide targeted interventions. A recent research-based effort in Japan has quantified plastic emissions into the ocean using microplastic and macroplastic observations, correlations between microplastic concentrations in rivers and basins, and a water balance analysis (Nihei et al. 2020). This analysis estimated plastic input from Japanese land to the ocean as 210–4,776 tons per year. This work has also produced a plastic emissions map (Figure 6.2), which allows more efficient and effective deployment of plastic interventions throughout the country with a scale of 1-km grid cells. However, Nihei et al. (2020) did not include higher flow conditions or wastewater treatment plant outputs in the analysis.
The United Nations’ Economic and Social Commission for Asia and the Pacific’s Closing the Loop program3 seeks to reduce plastic waste entering the ocean. This program has four main components: a plastic pollution calculator, a digital mapping tool informed by monitoring efforts, local action plans, and resource sharing. The International Solid Waste Association and the University of Leeds have worked with the
Closing the Loop program to use the Plastic Pollution Calculator to look at four cities to determine how plastics move from land to rivers and eventually to the ocean. The calculator provides information on sources, pathways, hotspots, and sinks of plastic waste to inform interventions to reduce ocean plastics. A digital mapping tool can examine images to determine the presence of plastic waste that could enter the ocean. This method can utilize images from a variety of sources, therefore reducing costs. The third component is creating a local action plan from the data gained from the plastic pollution calculator and the digital mapping tool. These plans are in process in Da Nang, Vietnam; Kuala Lumpur, Malaysia; Surabaya, Indonesia; and Nakhon Si Thammarat, Thailand. Last, a resource platform is being created along with an eLearning course to share information with stakeholders.
An additional program focused on Asia and the Pacific is CounterMEASURE,4 conducted by the United Nations’ Environment Programme’s Regional Office for Asia and the Pacific, which works alongside a variety of local and international partners. This work is funded by the Government of Japan. CounterMEASURE focuses on rivers as a source and transport mechanism of plastic pollution. CounterMEASURE has completed
Phase I, which included the development of a conceptual framework for monitoring plastic pollution in rivers and a geographic information system data visualization platform, and is now expanding to Phase II to reduce plastic pollution in rivers regionally and globally. A description of CounterMEASURE Phase II, the “theory of change” to reduce plastic waste in rivers, is provided in Figure 6.3 and shows the interconnected nature of understanding the distribution of plastics and developing tools, policies, technologies, and innovative financial mechanisms to reduce marine plastic pollution.
Spatial and Temporal Scales
The spatial and temporal scales of plastic waste data collection are very important because they will define the nature of the information gleaned from tracking and monitoring, as well as its potential usefulness in answering key questions. Data collected on marine debris items during coastal cleanups may illustrate waste management issues at local,
regional, or national scales (Ribic, Johnson, and Cole 1997, Ribic, Sheavly, and Klavitter 2012, Ryan and Moloney 1993, Schuyler et al. 2018, Sheavly 2007, and see Ryan et al. 2009) but have been less effectively synthesized and interpreted at a global scale (Browne et al. 2015). Spatial monitoring of plastic waste is also commonly informed by elements of human geography such as the built environment, population density, and land use (Jambeck et al. 2015). Emerging technologies, described below, can expand our ability to collect data on plastic waste at a larger scale.
The timing of tracking and monitoring efforts will also shape the resulting findings. Widespread geographic monitoring at a “single” point in time can provide a static “snapshot” of aquatic plastic waste at various spatial or temporal scales; this type of monitoring is also known as standing stock sampling or standing stock surveys (Opfer, Arthur, and Lippiatt 2012, Ryan et al. 2009). Longitudinal sampling of locations at defined time intervals—ideally after initial cleanup—can provide dynamic information on plastic waste accumulation or reduction (Boland and Donohue 2003, Dameron et al. 2007, Morishige et al. 2007, Opfer, Arthur, and Lippiatt 2012, Ribic, Johnson, and Cole 1997, Ribic, Sheavly, and Klavitter 2012, Ryan et al. 2009), though sampling frequency may bias results from such factors as beach litter turnover or litter burial (Ryan et al. 2014).
A multitude of temporal factors may inform repeated sampling designs such as seasonality and the frequency and patterns of resource use such as beach attendance and fishing effort, among others (Jambeck et al. 2015). Opportunistic tracking and monitoring of ocean plastic waste associated with episodic or pulsed events such as tsunamis (e.g., Murray, Maximenko, and Lippiatt 2018), hurricanes/tropical cyclones (e.g., Lo et al. 2020), floods and precipitation events (e.g., Pasternak et al. 2021, Yu et al. 2002), or the capture of these events within established monitoring programs is also informative. When tracking and monitoring programs use standardized protocols, regional and site-specific comparisons are possible, greatly improving the ability of monitoring data to set priorities for source reduction and evaluate the success of intervention measures. To support site-specific and regional comparisons, NOAA developed standardized protocols and data collection for shoreline sampling (Opfer, Arthur, and Lippiatt 2012). Last, the scale of ocean plastic waste tracking and monitoring both in space and time is determined by the capital, including human capital, available and invested in such efforts.
Historically, data collection methods have been inconsistent among plastic waste tracking and monitoring efforts, resulting in detailed place-based studies but failing to form a body of research that can be compared
geographically or temporally (Browne et al. 2015). Consistent methods used across geographic scales do allow for geographic comparisons, trend analyses, and data compilations. This has been possible through U.S. federal programs such as the National Marine Debris Monitoring Program, which ran from 1996 through 2007 (Ribic et al. 2010), and currently via the NOAA MDMAP (Hardesty et al. 2017).
Consistent, scientifically robust methods such as the use of randomized transects in cities, villages, and communities, often considered geographic sources of litter and leakage, are being used for projects to obtain data comparable across locations, over time, and in regional settings such as river basins (National Geographic 2021, Youngblood, Finder, and Jambeck 2021). In some cases, these methods are only applied by researchers. In other instances, community scientists with some level of training in the use of guiding tools such as mobile apps can meaningfully contribute to robust tracking and monitoring data collection. Participatory sensing of litter data can be opportunistic or led by research protocols. The latter improve data quality and facilitate the answering of specific research questions (Ammendolia et al. 2021, Jambeck and Johnsen 2015, Martin et al. 2019, Youngblood, Finder, and Jambeck 2021, Youngblood et al. In Review).
Development of standardized or harmonized (i.e., comparable) sampling and analysis protocols is a commonly asserted need, with known challenges (GESAMP 2019, Hartmann et al. 2019, Hung et al. 2021) that is gaining attention both in the United States and internationally. For example, an International Standards Organization (ISO) subcommittee on environmental aspects of plastics is currently working on standards to be used in a regulatory structure.5 In the United States, U.S. EPA Region 9 is focusing on water quality monitoring methods and ASTM standards for sampling microplastics, which would enable microplastics to be included in the National Coastal Condition Reports and monitored in support of Clean Water Act § 303d impairment monitoring in states such as Hawaii and California; it could also be used in remediation and cleanup (Allen 2021). The state of California has already adopted a formal definition of microplastics for use in developing standards for drinking water and has developed a standardized methodology, sampling and analysis plan, health effects, and accreditation for drinking water by fall 2021 (California Water Boards 2021). Such standardization will allow for multiple tracking and monitoring efforts by researchers, communities, and industrial entities to be interpreted in aggregate.
5 See ISO/CD 24187.2: Principles for the Analysis of Plastic and Microplastic Present in the Environment.
The a priori definition of the purpose of a tracking or monitoring program is essential to effective program design. For example, monitoring for the quantity of plastics entering the environment differs from monitoring for the quantity of plastics entering the ocean. A first step in designing a monitoring system is often to articulate the questions to be answered through the establishment of the monitoring program. These questions guide the appropriate development and implementation of the monitoring program. In considering a design to address the entire life cycle of plastics (Figure 6.1), tracking and monitoring could occur from the production of resin polymers (the ultimate source of the material) through manufacturing, distribution, use, and disposal.
However, most often plastic monitoring is done at the waste management intervention stage and environment stages (Figure 6.1). This is often considered the de facto source of pollution because a majority of macroplastic pollution stems from mismanaged municipal waste. However, other pathways into the ocean exist, such as derelict fishing gear and direct input of microplastics from sources such as direct discharge, stormwater runoff, and tire wear, among others. Monitoring for leakage of waste can be used to pinpoint where the materials management system is disjointed or broken. Monitoring leakage of plastic waste could include measuring litter in cities, or along riverbanks or coastlines; capturing floating debris in rivers and waterways; or documenting plastics in the ocean. While leakage of plastic waste into the environment can be an indicator of a system that is not working properly, data further upstream in the plastic life cycle (e.g., production) can inform interventions that might have the most impact and be most cost-effective (Figure 6.1). In this role, tracking and monitoring can provide a more holistic understanding of the plastic materials management system toward enhanced and more informed policy-making and decision-making.
Some challenges related to designing a tracking and monitoring system include the following:
- inaccessible data, including proprietary data, which is why open, accessible data are so important;
- difficulty in collecting data over time for a large area such as the entire United States and its territories;
- limited data collection and analysis speed (which is improving with near-real-time data available from sites such as the Marine Debris Tracker);
- rapid and episodic changes in plastic use for which it is difficult to predict and plan monitoring (e.g., increased single-use plastic consumption and waste during the COVID-19 pandemic); and
- the ongoing degradation of larger plastic items or fragments into ever smaller pieces in the environment.
Given the degradation of plastics in the environment (see Chapters 4 and 5), there is a clear need for the identification, adaptation, or development of technologies to detect ever-smaller plastics. Current analytical practices are insufficient to detect environmental plastics at nanoscale sizes.
Available and Emerging Technologies
Intergovernmental agencies, environmental groups, and the research community have begun to assess all existing and emerging technologies for tracking and monitoring marine plastic debris, including in situ sensing, remote sensing, and numerical modeling, toward the goal of an integrated marine debris observing system (Maximenko et al. 2019 and depicted in Figure 6.4). These in situ sensing, remote sensing, and modeling initiatives could be integrated into already existing surface, inland, and coastal observing systems (e.g., NOAA’s Integrated Ocean Observing System and state or federal water monitoring systems) and could form the basis for nationwide coordination around monitoring among different groups and using multiple technologies (similar to NOAA’s National Mesonet Program for weather prediction). To do this effectively would require coordination between emerging technology programs and existing monitoring programs. Such coordination would focus on expanding collection measurements and protocols to allow remote sensing to measure plastic information already collected, GPS coordinates, photos, and, optimally, plastic spectra.
Remote sensing has been emphasized as an underutilized and viable option for near-surface tracking and monitoring of plastic debris on land and at sea, and from land to sea (Figure 6.4) given the following: (1) the variety of available platforms (unmanned aerial vehicles or UAVs, aircraft, and satellites) and sensors; (2) its ability to provide spatially coherent coverage and consistent surveillance in time across scales—local to global (see also Martínez-Vicente et al. 2019); (3) its ability to access difficult-to-reach areas (Candela et al. 2021, Lavers and Bond 2017); and (4) its possibility to design a national monitoring program and illustrate where marine plastic debris is found (Candela et al. 2021).
Current remote sensing approaches under investigation with potential for marine debris detection include Synthetic Aperture Radar (Arii, Koiwa, and Aoki 2014, Matthews et al. 2017), bistatic radar (Evans and Ruf 2021), LIght Detection And Ranging (LIDAR) systems (Ge et al. 2016, Pichel et al. 2012), polarimeters, thermal infrared sensors (Garaba, Acuña-Ruz, and Mattar 2020, Goddijn-Murphy and Williamson 2019), and passive optical remote sensing (e.g., Acuña-Ruz et al. 2018, Biermann et al. 2020, Ciappa 2021, Garaba and Dierssen 2018, Goncalves et al. 2020, Kikaki et al. 2020, Topouzelis, Papakonstantinou, and Garaba 2019, Topouzelis et al. 2020). Assessment of the capabilities and limitations of remote sensing techniques are the subjects of active research (see Hu 2021, Martínez-Vicente et al. 2019, Maximenko et al. 2019). However, certain technologies have shown success in detection and thus could already be utilized as part of a tracking and monitoring system. Specifically, passive optical remote sensing is the most explored option with demonstrated potential in literature for inland, coastal, and open ocean marine debris detection (see Martínez-Vicente et al. 2019, Maximenko et al. 2019 for more information on all techniques).
Passive optical remote sensing includes red-green-blue (RGB) cameras, multispectral imagers, and hyperspectral imagers on various platforms (UAVs, aircraft, and satellites) with different spatial resolutions (on the order of submeter to hundreds of meters). RGB cameras simulate human eyesight, focusing on three bands within the visible portion (400–700 nm) of the spectrum. Multispectral imagers collect measurements in a limited number of wavelength bands (typically less than 10–15). Hyperspectral imagers (otherwise referred to as imaging spectroscopy) provide narrow, contiguous sampling across the spectrum (spectral sampling typically less than 10 nm translating to hundreds of wavelength bands). The spectral range covered by multispectral imagers and imaging spectroscopy is sensor dependent but can span the visible, near-infrared (NIR), and shortwave infrared (SWIR) spectral range (700–2500 nm).
RGB cameras on UAVs have been used extensively for indirect detection of marine litter on beaches and shorelines (e.g., Bao et al. 2018, Deidun et al. 2018, Fallati et al. 2019, Goncalves et al. 2020, Martin et al. 2018, Moy et al. 2018) with some application in coastal waters (e.g., Themistocleous et al. 2020, Topouzelis et al. 2020, Topouzelis, Papakonstantinou, and Garaba 2019), providing a cost-effective solution for localized image acquisitions at very high spatial resolution (on the order of centimeters). However, the practicality of RGB detection degrades as the platform changes to those at higher elevations, such as aircraft or satellite for regional to global coverage, wherein individual plastic targets will become less distinct with respect to their environment such that more wavelength bands are necessary to ensure accuracy between plastic debris and radiometric properties.
Recent laboratory studies revealed that marine plastic debris has unique spectral features in the NIR and SWIR spectrum (e.g., Garaba and Dierssen 2018, Hu et al. 2015, Knaeps et al. 2021, Moshtaghi et al. 2021, Tasseron et al. 2021). Therefore, passive methods that include the NIR and SWIR offer the greatest potential for direct plastic debris detection (Martínez-Vicente et al. 2019). Several recent papers have used NIR and SWIR spectral information from airborne imaging spectroscopy (Garaba and Dierssen 2018) and multispectral satellite imagery (e.g., Acuña-Ruz et al. 2018, Biermann et al. 2020, Ciappa 2021, Kikaki et al. 2020, Topouzelis, Papakonstantinou, and Garaba 2019, Topouzelis et al. 2020) to detect marine plastic debris in inland, coastal, and open ocean environments. Optical passive sensors provide an opportunity to identify and monitor leakage sources and accumulation regions (or hotspots), guide removal efforts, aid with the design or refinement of a national monitoring program (areas where field collection is a priority), and enable trend assessment over time with repeat observations.
Passive optical remote sensing has the potential to detect marine macroplastics at the ocean surface but likely not microplastics (from aircraft and satellite) and especially not at depth. For detection of microplastics, in situ methods have been applied to various environments, including marine and freshwater environments (e.g., Choy et al. 2019, Enders et al. 2015, Ghosal et al. 2018, Koelmans et al. 2019, Lenz et al. 2015, Tagg et al. 2015, van Cauwenberghe et al. 2013, Wolff et al. 2019, Zhang et al. 2017). Typically, water is sampled using bulk collection for small volumes or using plankton nets to filter large volumes, and samples are analyzed for potential plastic particles that must be identified via various techniques. Methods currently recommended by GESAMP (2019) for monitoring include optical identification (naked-eye detection, visual and fluorescence microscopy, and flow cytometry) and chemical identification/quantification methods (Fourier transform infrared [FTIR], Raman spectroscopy, pyrolysis-gas chromatography-mass spectrometry [py-GC-MS], and
thermal extraction-desorption gas chromatography-mass spectrometry [TED-GC-MS]). See literature reviews from Araujo et al. (2018, Table 1), Mai et al. (2018), Primpke et al. (2020), Silva et al. (2018), and Zarfl (2019) for detailed information on all approaches and additional techniques (e.g., hyperspectral imaging, scanning electron microscopy), as well as sampling and sample extraction.
FTIR and Raman spectroscopic techniques (e.g., Araujo et al. 2018, Elert et al. 2017, Kappler et al. 2016) are the two most commonly used techniques to characterize microplastics and their polymers. The European Union expert group on marine litter recommended that all suspected microplastics in the 1–100 mm size range should have their polymer identity confirmed by spectroscopic analysis (Gago et al. 2016, MSFD Technical Subgroup on Marine Litter 2013). Within the literature, FTIR and Raman techniques have been used for analytical identification of microplastics ranging from biota, sediment, seawater, freshwater, and wastewater, to foods, beverages, and cosmetics (see Table 1 of Araujo et al. 2018 for a comprehensive list of Raman literature up to January 2018, and Primpke et al. 2020 for FTIR literature up to May 2019). The current limitation of Raman and FTIR imaging is the resource-intensive, both in time and dollars, nature of singular particle characterization.
Numerous agencies within the U.S. federal government have mandates or programs that directly or indirectly intersect with the issue of ocean plastic waste (U.S. GAO 2019). The value of interagency coordination has long been recognized, if not yet exhaustively achieved. The Marine Plastic Pollution Research and Control Act of 1987 (33 U.S.C. § 1914) (amending the Act to Prevent Pollution from Ships) provided for an “Interagency Committee,” later amended by the Marine Debris Research, Prevention, and Reduction Act of 2006 (Marine Debris Act, 33 U.S.C. § 1954, as amended), to establish the Interagency Marine Debris Coordinating Committee (IMDCC). With the reauthorization and amendment of the Marine Debris Act by the 2020 Save Our Seas 2.0 Act (Public Law 115–265), the IMDCC remains a primary vehicle for enhanced interagency connectivity. Members include NOAA (which chairs the committee), U.S. EPA, U.S. Coast Guard, U.S. Navy, U.S. Department of State, U.S. Department of the Interior, U.S. Agency for International Development, Marine Mammal Commission, and the National Science Foundation.
The IMDCC serves as a legislated foundation for interagency coordination, including with regard to tracking and monitoring, but has unrealized potential in several areas, in part stemming from a lack of clarity on IMDCC membership (U.S. GAO 2019). The IMDCC has predominantly focused on
its information-sharing role, citing the challenges of interagency collaboration such as mandate, mission, and budgetary appropriations variability among NOAA and other IMDCC members as barriers to expanded member coordination (U.S. GAO 2019). Research and technology development and coordination were among topics identified by experts in an audit report by the Government Accountability Office (GAO) of the IMDCC as areas of suggested action (U.S. GAO 2019). GAO suggested enhanced coordination among federal, local, state, and international governments and other nonfederal partners to address marine debris, as well as research on sources, pathways, and location of marine debris, inclusive of upstream elements such as rivers and stormwater. Tracking and monitoring environmental plastic waste is foundational to such efforts.
A national approach to tracking and monitoring mismanaged plastic waste that includes “upstream” source areas in the watershed has the potential to identify and inform intervention opportunities earlier, eliminating or reducing the time plastic waste is present in the environment. This necessitates enhanced collaboration and coordination with entities, including local, state, federal, and tribal agencies that have jurisdiction or other interests in the watersheds and waterways upstream of the coastal deposition of plastic waste. For example, the U.S. Geological Survey (USGS) maintains 27 regional Water Science Centers with core capabilities in hydrologic data collection, research and assessments, and information services. Their inland river and streamflow measurements, as well as flood forecasts, could inform aquatic plastic waste tracking and monitoring and potentially be co-located with plastic debris sensors as part of a monitoring network. USGS scientists have contributed to research-based monitoring and analysis efforts for microplastics (Baldwin, Corsi, and Mason 2016). A national approach may constitute a “system of systems,” where programs and data collection efforts by various agencies, as well as research and community-based initiatives, are coordinated.
Effective Approaches to Tracking and Monitoring to Reduce Plastic Waste in the Ocean
Using their own experience and expertise, open session presentations from speakers, and research illustrated in this report, committee members created a list of tracking and monitoring program attributes expected to have the greatest efficacy in informing strategies to reduce plastic waste inputs to aquatic systems. Figure 6.5 illustrates a conceptualized approach to designing, implementing, evaluating, and adapting tracking and monitoring systems for plastic waste.
The following describes tracking and monitoring systems of plastic waste items expected to have the greatest efficacy in ultimately reducing
plastic waste inputs to aquatic systems. The specific type or types of plastic waste addressed by any system, including polymer types, associated chemicals, or other characteristics or parameters of interest, will necessarily reflect the aims and drivers of those entities establishing the tracking and monitoring system.
- Tracking and monitoring systems that are scientifically robust, hypothesis-driven, and conceptualized a priori to answer critical knowledge gaps, rather than approaches applied post hoc to plastic waste tracking and monitoring questions.
- Technologically adaptive tracking and monitoring systems that can incorporate and utilize current and emerging technologies to
improve the spatial and temporal resolution of mismanaged plastic waste including the application of
- remote sensing, autonomous underwater/remotely operated vehicles, sensor advances, passive samplers, and others;
- crowdsourcing apps;
- barcode tracking for recyclability and traceability;
- biochemical markers and tracers that provide information on organismal exposure to environmental plastics, including legacy exposure and that which relates to organismal, including human, health; and
- other current or emergent technologies.
- Tracking and monitoring systems that are applied with sufficient spatial and temporal resolution to capture meaningful data concerning knowledge and policy needs. For example, monitoring from a watershed perspective or including pre- and post-intervention tracking and monitoring to assess progress.
- Tracking and monitoring systems that collect data that are comparable and, when scientifically robust, compatible with prior efforts. Examples include using standardized measurement units or experimental design.
- Tracking and monitoring systems that leverage, rather than separate, U.S. federal investment in the reduction of mismanaged plastic waste among government departments and create synergies in the federal response to such waste.
- Tracking and monitoring systems that encompass the full life cycle of plastics, thereby achieving an understanding of the “upstream” plastic waste compartments and associated leakages.
A single, national marine debris (or plastic waste) tracking and monitoring system does not exist in the United States, nor does such a system appear to be feasible given the complexity of plastic production, use, and disposal and the diversity of environments through which plastics are transported and distributed. A summary of marine debris/aquatic plastic waste tracking and monitoring systems and the intersection of such systems in addressing key aquatic plastic waste mitigation aims is provided in Table 6.1. This table illustrates that no single system or component serves as a comprehensive, stand-alone, national marine debris tracking and monitoring system. Furthermore, the specific aims of local, regional, national, and international efforts require the application of tracking and monitoring tools and technologies effective at particular spatial and temporal scales.
TABLE 6.1 A Summary of Marine Debris/Aquatic Plastic Waste Tracking and Monitoring Systems, Components, or Technologies and Their Intersection in Addressing Key Aquatic Plastic Waste Mitigation Aims
|System, Component, or Technology||Size Class Sampled or Tracked||Mitigation Aims|
|Identify Source Reduction Priorities||Identify Cleanup Priorities||Assess Progress in Reducing U.S. Inputs||Reduce Inputs to Ocean||Inform Policy|
|Community/citizen science/traditional and indigenous community cleanups||Micro
|Community/citizen science/traditional and indigenous community data collection and surveys||Meso
|Municipal solid waste organizations and entities||Micro
|Derelict fishing gear surveys||Macro|
|Passive or static capture systemsb||Macro|
|Remote sensing applications||Macro|
|Opportunistic systems or surveys of opportunityd||Macro|
|Opportunistic and episodic eventse||Micro
|Research-based systems f||Micro
a For example, reporting of plastic production data and use by sector.
b For example, Mr. Trashwheel, retention booms, capture devices, stormwater structures, outflow pipe of wastewater treatment plant.
c For example, National Oceanic and Atmospheric Administration’s Marine Debris Monitoring and Assessment Project, National Aeronautics and Space Administration, U.S. Environmental Protection Agency, the U.S. Geological Survey, government point and nonpoint source monitoring.
d For example, submersible missions, vessels of opportunities.
e For example, hurricanes/tropical cyclones, animal strandings, first-flush precipitation events.
f For example, institutes, colleges, think tanks.
NOTE: The degree of shading indicates the existing or potential value of the system, component, or technology in achieving a mitigation aim, with darker shading representing greater value. The size classes of plastic waste customarily addressed by each system, component, or technology are categorized as microplastics, mesoplastics, or macroplastics. Tracking and monitoring systems, components, or technologies are not presently available for environmental detection of nanoplastics (<100 nm in size) and are thus not included in this table. SOURCES: Koelmans, Besseling, and Shim (2015) and Mattsson et al. (2018).
However, the use of multiple, complementary tracking and monitoring systems (depicted in Figure 6.6) in a synergistic approach implemented at sufficient spatial and temporal scales would contribute to (1) understanding the scale of the plastic waste problem and (2) the identification of priorities for source reduction, management, and cleanup and the assessment of progress in reducing U.S. contribution to global ocean plastic waste. For example, an optimal monitoring system design for first flush events would be useful to inform cleanup sites, track their progress, and reduce inputs to the ocean. The design could encompass community science cleanups, capture devices, trash booms, and remote sensing approaches.
Currently, data collected by various monitoring efforts are not well integrated. There would be significant value in developing a data and information portal by which existing and emerging marine debris/aquatic plastic waste data sets could be integrated to provide a more complete
picture of the efforts currently tracking plastic pollution across the nation. Such a portal would need to be supported by (1) standardized methods of data collection and (2) support for long-term data infrastructure. The ability to visualize the data contained in the portal would greatly enhance its utility for the public and decision makers to inform and assess the progress of plastic waste reduction efforts.
Finding 13: No national-scale monitoring system, or “system of systems” exists to track important sources, pathways, and sinks of plastic waste to the ocean at the current scale of public or governmental concern. Presently, no baseline exists nor does a monitoring system to track changes from such a baseline.
Finding 14: The complexity of plastic production, use, and disposal, and the diversity of environments (inland to ocean) through which plastics are transported and distributed, requires the use of an expanded suite or network of tracking and monitoring systems to set priorities to reduce global ocean plastic waste.
Recommendation 2: The National Oceanic and Atmospheric Administration (NOAA) Marine Debris Monitoring and Assessment Project, led by the NOAA Marine Debris Program, should conduct a scientifically designed national marine debris shoreline survey every 5 years using standardized protocols adapted for relevant substrates. The survey should be designed by an ad hoc committee of experts convened by NOAA in consultation with the Interagency Marine Debris Coordinating Committee, including the identification of strategic shoreline monitoring sites.
Recommendation 3: Federal agencies with mandates over coastal and inland waters should establish new or enhance existing plastic pollution monitoring programs for environments within their programs and coordinate across agencies, using standard protocols. Features of a coordinated monitoring system include the following:
- Enhanced interagency coordination at the federal level (e.g., the Interagency Marine Debris Coordinating Committee and beyond) to include broader engagement of agencies with mandates that allow them to address environmental plastic waste from a watershed perspective—from inland to coastal and marine environments.
- Increased investment in emerging technologies, including remote sensing, for environmental plastic waste to improve spatial and temporal coverage at local to national scales. This will aid in identifying and monitoring leakage points and accumulation regions, which will guide removal and prevention efforts and enable assessments of trends.