3. Results and discussion
3.1. Existing indicators
3.1.1. General remarks
This section will provide an overview of currently applied indicators in different international frameworks and indicators under development. Section 3.2 will describe in detail the indicators for leakages along the plastic value chain, from production and use to plastic waste. For an indicator to be applicable in a scientific and regulatory context it must be quantifiable. Therefore, this document also includes a summary of existing databases that are available and in use as data repositories for indicator data.
3.1.2. The indicator landscape
A number of stakeholders address plastic pollution and associated indicators in various frameworks and directives, approaching the issue from different angles. Combining these activities shows that some, but not all, components of the DPSIR are well represented. Most of them indicate the state and impact indicators for the marine environment. This uneven distribution of indicators does not necessarily mean that indicators are missing and should be developed, as the relevance and need of developing and using indicators may not be equal for the different part of the DPSIR scheme. A summary of the existing indicators is given in Table 1. It summarizes the detailed catalogue of indicators that is given in Annex 5.2 and Annex 5.3. Considering the typical plastic value chain consisting of production, use and waste disposal, production and use would be Drivers in the DPSIR concept, while waste would be a Pressure.
Table 1: Approximate number of indicators in brackets, for each framework. Numbers for Regional Sea Conventions and Action Plans (RSCAP) state the number of frameworks that use the environmental indicators. OECD: Organization of Economic Cooperation and Development. EU: European Union. SDG: Sustainability Development Goal. Directive 2008/98/EC states the use of necessary indicators (not specified) to fulfill the requirements in the directive.
Drivers | Pressures | State | Impacts | Responses |
Socio-economic context and characteristics of growth (OECD, Green Growth indicators: 14) Environmental and resource productivity of the economy (OECD, Green Growth indicators: 12) Socio-Economic indicators (OECD: 8) Circular Economy indicators (OECD: 8, EU: 15) | Environmental indicators (OECD: 13) Emissions to environment (SDG: 1) Waste management (SDG: 1) Raw material extraction) (SDG: 1) | Environmental indicators (RSCAP: biota (6), beach litter (10), seafloor litter (5), micro-plastic (5), water column/or floating litter (3)) Natural asset base (OECD, Green Growth indicators: 10) Marine and coastal environment (SDG: 1) Waste generation and management (SDG: 2) | Impacts on biota (RSCAP: 6) Environmental dimension of quality of life (OECD, Green Growth indicators: 4) Ecosystem health (SDG: 2) | Proof of action implementation (RSCAP: 10) Economic opportunities and policy responses (OECD, Green Growth indicators: 19) Tracking progress (New Plastic Economy Global Commitment: 5) Policy and law (SDG: 1) Waste prevention measures and management (Directive 2008/98/EC, use of indicators: 3) |
UNEP (2022b) provides an approach to the development of headline-, core- and sub-indicators, based on existing frameworks. The suggested indicators listed in detail in section III in UNEP (2022b) incorporate goals, targets and indicators developed under the Sustainable Development Goals (SDG), the Framework for the Development of Environment Statistics (FDES), the System of Environmental Economic Accounting (SEEA), Green Growth Indicators and other OECD initiatives, the Strategic Approach to International Chemicals Management (SAICM), and the Basel Convention. The approach to developing the recommended indicators is based on three phases of 1) consolidation, 2) geographic expansion, and 3) improved monitoring of effectiveness of broader holistic and integrated policy measures (UNEP, 2022b).
The OECD has developed several frameworks and initiatives that include indicators related to a sustainable use of plastics. These include the framework of Green Growth and Sustainable Development and the Global Plastics Outlook (OECD, 2022a; 2022b). Indicators are grouped according to: 1) Environmental and resource productivity of the economy, 2) Natural asset base, 3) Environmental dimension of quality of life, 4) Economic opportunities and policy responses. A fifth group of indicators is recommended to describe the socio-economic context and characteristics of growth. Main and proxy indicators which can be considered for plastic data are shown in detail in Annex 5.3.
The Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and their Disposal (Basel, 2019) controls the transboundary movement of plastic waste. In 2019, the Conference of the Parties to the Basel Convention adopted the amendments BC 14/12 with additional provisions to improve transparency and regulations in the global trade in plastic waste and BC 14/13 on actions to prevent and minimize the generation of plastic waste and to improve its environmentally sound management. The framework supports the SDG indicator on waste generation and management: 12.4.2 a) Hazardous waste generated per capita; and b) Proportion of hazardous waste treated, by type of treatment. Annex 5.2 includes related obligations.
Following decision BC 14/13 of the Conference of the Parties to the Basel Convention, a Small Intersessional Working Group (SIWG) was established to update the technical guidelines for the identification and environmentally sound management of plastic wastes and for their disposal, which had originally been established in 2002. Updated draft versions are currently available (Basel, 2022).
UNEP’s Regional Seas Programme consists of 21 Regional Seas Conventions Action Plans (RSCAPs) (UNEP, 2022b). Of these, 14 have developed indicators, including indicators for biota, beaches, seafloors, microplastics, water and proof of action implementation. These are predominantly impact indicators and further discussed under environmental indicators in section 3.1.3 (see also Annex 5.4 and Annex 5.5).
The European Union (EU) Marine Strategy Framework Directive (MSFD) addresses plastic litter in the marine environment. The Zero Pollution Action Plan (EC, 2021) defines specific reduction targets for waste generation, plastic litter at sea and input of microplastics, and EEA (2022) considers marine litter in Europe in an integrated assessment from source to sea. EEA (2022) describes socio-economic drivers, such as trends in plastic production, pressures such as generation of waste (from plastic packaging and small non-packaging plastic items) and particularly the mismanaged fraction, and the state of pollution in coastal and marine environments. Policy objectives and targets set out by key European policies, e.g., the 7th and 8th Environmental Action Programme and Waste Framework Directive, are assessed by considering selected indicators. These are included in the DPSIR scheme shown in Annex 5.2. Furthermore, EEA (2022) makes use of existing indicators and data sources, which are defined by frameworks such as OSPAR and HELCOM, see Annex 5.4 and Annex 5.5.
The EU has developed a set of circular economy indicators under the headlines: Production and consumption, Waste Management, Secondary raw materials and Competitiveness and innovation, all of which could relate to the lifecycle of plastics.
The Waste Framework Directive 2008/98/EC and its amendment Directive (EU) 2018/851 lay down measures to protect the environment and human health by preventing or reducing the generation of waste, the adverse impacts of the generation and management of waste and by reducing overall impacts of resource use and improving the efficiency of use. Directive 2008/98/EC on waste and repealing certain directives mentions the development of effective and meaningful indicators of the environmental pressures associated with the generation of waste aimed at contributing to the prevention of waste generation at all levels, from product comparisons at community level through action by local authorities to national measures (Annex 5.3).
Directive (EU) 2019/904 on the reduction of the impact of certain plastic products on the environment, also described in brief as Directive on Single-Use Plastics (SUP), has the objectives to prevent and reduce the impact of plastic products on the aquatic environment in particular, and on human health, as well as to promote the transition to a circular economy with innovative and sustainable business models, products and materials. The directive applies to SUP products, to products made from oxo-degradable plastic and to fishing gear containing plastic. Where easily available and affordable alternatives exist to SUP products, SUPs cannot be placed on the market anymore, including, for examples, plastic cutlery, plates, straws and containers for food and beverages. For other SUP products, limited use is intended, for example through reduced consumption, design and labelling requirements (e.g., plastic caps attached to bottles) and waste management and clean-up responsibilities for producers. Specific aims include a 90% separate collection target for plastic bottles by 2029. The directive also promotes circular approaches that give priority to sustainable and non-toxic re-usable products and re-use systems rather than to single-use products, aiming to reduce the quantity of waste generated. This is planned by fostering innovative and sustainable business models, products and materials, as well as limitations on SUP products, making alternatives more interesting. The directive holds no specific indicators, but focus and target areas are included in Annex 5.2.
Directive 94/62/EC on packaging and packaging waste has the objectives to harmonize national measures on the management of packaging and packaging waste in order to prevent or reduce any impact on the environment, thus providing a high level of environmental protection. These measures are directed at preventing the production of packaging waste and at enhancing reuse and recycling of packaging waste, and hence, to reduce the final disposal of packaging waste. No specific indicators are stated, but measures and aims are included in Annex 5.2. The directive is currently being revised to comply with the ambitions of the European Green Deal and the Circular Economy Action Plan, aiming at fully recyclable and reusable packaging by 2030. This action includes new targets for waste reduction, recycling and reuse.
Microplastics are intentionally added in a range of products and applications, such as artificial turf sports pitches. A wide-ranging restriction has been proposed on microplastic in products placed on the European market to avoid or reduce their release to the environment (ECHA, 2020). No specific indicators are suggested. However, the European Commission has also launched an initiative to address the unintentional release of microplastics in the environment, as part of its Plastic Strategy and the Circular Economy Action Plan (EC, 2020).
3.1.3. Environmental indicators
State and impact indicators for various parameters that are currently in use and that can be considered relevant for macro- and microplastic in the marine environment are listed in Annex 5.3. The indicators are proposed by a number of organizations and initiatives on local, regional and global scales, that specifically address plastics, but also by frameworks that allow for disaggregation of plastic data. Table 1 aggregates the indicators in Annex 5.3.
Environmental indicators should be scientifically valid, easy to understand by a variety of stakeholders, sensitive and responsive to change, cost-effective; and policy relevant (GESAMP, 2019). Core (or primary) environmental indicators are often agreed on at the regional level (e.g., within RSCAPs) where consensus has been reached regarding methods with associated harmonized guidelines, protocols and QA/QC procedures, and which can be implemented immediately. Core indicators are used to initiate national activities and activities on a regional scale.
Candidate (secondary) indicators have typically not reached the same broad consensus and lack guidelines for the suggested methods or supporting QA/QC procedures. Further efforts are usually needed for candidate indicators to develop methodologies before they are implemented at regional and global levels. Secondary monitoring indicators may also serve other specific monitoring purposes, e.g., effect monitoring in relation to chemicals associated with plastic pollution.
UNEP (2022b) includes a summary of the environmental indicators in RSCAPs. It states that 14 action plans have developed associated indicators, while two more action plans highlight that their indicators still need to be developed (UNEP, 2022b). Table 2 lists the environmental indicators that are suggested in the individual RSCAPs and thus details what is summarized under “State” in Table 1.
Table 2: Environmental indicators included in action plans of the Regional Seas Conventions.
Action Plan | Biota | Beach litter | Seafloor litter | Microplastics | Water column and/or floating litter | Implementation actions defined |
Regional Plan on Marine Litter Management in the Mediterranean | X | X | X | X | X | X |
PERSGA – Regional Action Plan for the sustainable Management of Marine Litter in the Red Sea and Gulf of Aden | X | X | X | X | ||
PAME- Regional Action Plan on Marine Litter in the Arctic* | X | X | X | X | ||
OSPAR – Regional Action Plan for Prevention and Management of Marine Litter in the North-East Atlantic | X | X | X | X | ||
Black Sea Marine Litter Regional Action Plan | X | X | X | X | X | X |
HELCOM Regional Action Plan for Marine Litter in the Baltic Sea | X | X | X | |||
Commission for the Conservation of Antarctic Marine Living Resources | X | X | ||||
NOWPAP Regional Action Plan on Marine Litter | X | X | X | |||
Western Ocean Regional Action Plan on Marine Litter (WIO-RAPMaLi) | X | X | ||||
Regional Action Plan on Marine litter Management for the Wider Caribbean Region 2014; | X | |||||
SPREP – Pacific Regional Action Plan Marine Litter | X | |||||
ASEAN Framework of Action on Marine Debris | X | |||||
Abidjan Convention | X | |||||
TEHERAN Convention – Caspian Sea | X |
* Indicators proposed by the Arctic Monitoring and Assessment Programme (AMAP), see text for details.
The Regional Action Plan of the Protection of the Marine Environment in the Arctic (PAME, 2021) is supported by indicators proposed by the Arctic Monitoring and Assessment Programme (AMAP, 2021a), both working groups under the Arctic Council. The primary environmental indicators developed by AMAP (2021a; 2021b) include biota (seabirds), beach litter and microplastics (in water and/or sediment). Secondary indicators, which are considered less mature for environmental monitoring, include air/atmospheric deposition and biota (fish, invertebrates).
3.1.4. Databases
Several databases exist hosting national and international datasets for plastics in the environment. The datasets can represent research data (e.g. the online portal LITTERBASE; Bergmann et al., 2017), citizen science data (e.g. Debris Tracker
Table 3: Examples of databases and users on different geographical scales.
Geographical scale | Examples of databases | Users and types of data |
Global | Global Partnership on Marine Litter (GMPL) | UN organisations, e.g. UN Environmental Programme (UNEP), International Maritime Organization (IMO), Food and Agricultural Organisation (FAO) |
Regional | EMODNET | EU |
ICES | Research and monitoring projects, data on seafloor litter | |
OSPAR | Regional Seas Convention, Research and monitoring projects, data on beach litter and seabirds | |
Marine Litter Watch | Citizen science data | |
LITTERBASE | Research data | |
National | Marine Debris Monitoring and Assessment Programme (MDMAP) | US Environmental Protection Agency; US National Oceanic and Atmospheric Administration (NOAA) |
Local | Data collected by cities and municipalities, e.g. on mismanaged waste, plastic leakage from wastewater and stormwater | |
3.2. Indicators for leakages along the value chain and for the lifespan of plastics
3.2.1. General remarks
This section provides a synthesis of the most recent studies that have sought to estimate plastics leakage to the environment across the full plastics value chain and on the global scale. We have identified three key studies by OECD (OECD, 2022a, 2022b), Lau and colleagues (Lau et al., 2020; SYSTEMIQ & The Pew Charitable Trusts, 2020) and UNEP (Ryberg et al., 2019; UNEP, 2018). We have, per default, used the most recent estimates from (OECD, 2022a, 2022b) and report these. However, important findings from the two other studies have also been included. Moreover, we have included estimates and findings from other studies where relevant.
In general, the three studies use similar approaches to estimate plastics leakages, however, they differ for certain key model assumptions. The OECD report presents a comparison of key estimates in the studies with relation to plastic use as well as waste generation and treatment and concluded that the studies gave similar results at an overall level, considering the high uncertainty that accompanies these estimates (Table 4).
Table 4: Comparison of estimates for global plastic use, plastic waste generation, and mismanagement of plastic waste across three different studies.
Model key figure | Amount for 2015/2016 [million metric tonnes] | Reference |
Global plastic use | 388 | Ryberg et al. (2019); UNEP (2018) |
413 (460 in 2019) | OECD (2022a; 2022b) | |
Global plastic waste generation | 161 | Ryberg et al. (2019); UNEP (2018) |
220 | Lau et al. (2020); SYSTEMIQ & The Pew Charitable Trusts (2020) | |
308 (353 in 2019) | OECD (2022a; 2022b) | |
Global total mismanagement of plastic waste | 41 | Ryberg et al. (2019); UNEP (2018) |
91 | Lau et al. (2020); SYSTEMIQ & The Pew Charitable Trusts (2020) | |
74 (82 in 2019) | OECD (2022a; 2022b) |
OECD (2022a) developed complete estimates of plastic production, use, and waste management as well as leakages to the environment (Figure 2). Moreover, the OECD study also provides estimates of the fate of plastics in the environment and the amounts that are transported to rivers and lakes, and to the marine environment. Estimates of the accumulated stock are also provided.
According to OECD (2022a), the societal in-use stock was 3120 Mt in 2019, of which about 139 Mt (4.5% of the societal stock) were accumulated in rivers, lakes, and oceans. Furthermore, while 460 Mt of plastics were used in 2019, 6.3 Mt and 13 Mt of macroplastics were lost to the aquatic environments (lakes, rivers and oceans) and terrestrial environments, respectively. Additional 2.7 Mt of microplastics were lost to the environment. In total, approximately 4.8% of the annual amount of plastic use is released to the environment.
The following sections will provide further details on the plastic use and waste management and on the main sources of plastic leakage across the plastics value chain. It is important to analyze if meaningful indicators for plastic pollution exist in these upstream processes, closer to the sources of plastic pollution. Indicators in the plastic value chain could show effects of potential management efforts. They could also be linked to environmental indicators for a better process understanding, in the context of the DPSIR framework, and for an evaluation of effectiveness of management actions on downstream processes.
Figure 2: Global plastics flows in 2019, focusing on plastic production and use, plastic waste, and plastics in the environment. Accumulated stocks refer to amounts accumulated from 1970 to 2019. The figure is modified from OECD (2022a).
3.2.2. Plastic use
Plastic use has increased steadily since 1950, and the annual global production of plastics was 460 Mt in 2019 (Geyer et al., 2017; OECD, 2022a). The amounts of plastics being used is projected to triple around 2060, based on a “business as usual” scenario (OECD, 2022b). The majority (approximately 46%) of plastic used in 2019 was used in OECD countries in America and Europe. Another 20% and 15% of plastic use was in China and the rest of Asia, respectively. Further information on the use of plastics by world region, polymer type, and plastic application can be found in Annex 5.6.
Figure 3: Overview of global plastics use split into world regions. World map is Image by rawpixel.com on Freepik.
According to OECD (2022a), most plastics are used for packaging followed by use in construction and in transportation (Figure 4). The main polymers used for different types of application are shown in Figure 5. Polyethylene (PE) as high-density PE (HDPE), low density PE (LDPE) and linear LDPE (LLDPE) are the main polymers in packaging, accounting for almost 50% of total packaging plastics. This is followed by polypropylene (PP; 26%) and polyethylene terephthalate (PET; 17%). The most dominant polymers in construction are polyvinylchloride (PVC) and PE with 47% and 18%, respectively. The construction industry also uses several special plastics for various specialized applications.
Figure 4: Relative plastic use in 2019 by application, based on data in OECD (2022a).
Figure 5: Plastic use in 2019 by application and polymer type, based on data in OECD (2022a).
PP: Polypropylene. HDPE: High density polyethylene. LDPE: Low density polyethylene. LLDPE: Linear low density polyethylene. PVC: Polyvinylchloride. PET: Polyethylene terephthalate. “Synthetic fibres” are fibres made of different polymers, used in textiles and other applications. “Rest” includes polystyrene, polyurethane and other polymers, such as (styrene) butadiene rubber used in car tyres.
3.2.3. Plastic waste generation and treatment
Plastic waste generation generally follows plastic use trends. It is clear to see that the per capita plastic waste generation varies greatly among regions. The largest per capita generation is seen in high income countries that also have a large per capita use of plastics (Table 5).
Table 5: Plastic waste generation in 2019. Shown as total plastic waste generation and generation per capita. Data from OECD (2022a).
Region | Plastic waste generation [Mt] | % of total | Plastic waste generation [kg/cap] |
OECD America | 91 | 26% | 161 |
OECD Europe | 67 | 19% | 114 |
China | 65 | 19% | 47 |
Other Asia | 44 | 12% | 18 |
Middle East and Africa | 33 | 9% | 21 |
Other America | 19 | 6% | 43 |
Eurasia | 19 | 5% | 55 |
OECD Pacific | 14 | 4% | 68 |
Total | 353 | 100% | 46 |
About 50% of the plastic waste generated is related to packaging (40%) and various personal, consumer and institutional products (12%) (Figure 6). Both categories have relatively short product lifetimes with an average of 0.5 to 3 years, respectively (OECD, 2022a). Hence, these products are likely to be produced, used, and disposed of within a year. The polymer composition of waste for these two categories is shown in Figure 6. This clearly shows that most of the waste results from PP, PE, and PET products. Thus, placing a focus on these polymers in these plastic applications appears relevant when targeting the largest mass amounts of plastics waste, as further discussed in section 3.3.3.
Figure 6: Polymer composition of plastic waste for Packaging and Consumer & Institutional Products, based on data in OECD (2022a).
HDPE: High density polyethylene. ABS: Acrylonitrile butadiene styrene. ASA: Acrylonitrile styrene acrylate. LDPE: Low density polyethylene. LLDPE: Linear low-density polyethylene. PET: Polyethylene terephthalate. PP: Polypropylene. PS: Polystyrene
In terms of plastic waste treatment, we see large variations among regions. While only about 6% of the plastic waste in OECD countries is considered mismanaged or littered, 37% of the plastic waste is considered mismanaged or littered in non-OECD countries (OECD, 2022a). The largest percentage of mismanaged waste relates to plastic waste in Africa, Asia and Latin America (Figure 7). Addressing this would be particularly efficient, as further discussed in the recommendations in section 3.3.3.
Mismanagement refers to poor handling of the plastic waste, such as open dumping where the waste can be released to the environment. The amount of waste released to the environment due to mismanaged waste management is highly uncertain and relies on best estimates that can range from 10% to 70%. The uncertainty is linked to a lack of monitoring data on the leakage. Naturally, the mismanaged waste, such as waste dumped near or in water bodies, is not part of the formal waste management system and is therefore not regulated. Moreover, leakages from different dump sites are likely to vary considerably due to their different characteristics, such as proximity to water and use of crude mechanisms for containing waste, such as fences.
Figure 7: Share of plastics treated by waste management category in 2019, before recycling losses, based on data in OECD (2022a).
3.2.4. Leakage across the plastics supply chain
Based on OECD’s global plastic outlook report (OECD, 2022a), total amount of plastics lost to the environment was estimated to be 22.1 Mt in 2019. As stated in section 3.2.1, this consisted of 19.4 Mt of macroplastics from mismanaged plastics and littering and 2.7 Mt of microplastics from plastics production and use.
Given the uncertainty of the estimates, this leakage from mismanaged plastics and littering can range from 13 Mt to 25 Mt, or even more. Indeed, while an increasing number of studies confirm that plastic leakage is an environmental issue, the exact estimates differ among studies. This is mainly due to differences in the modelling approaches and to the assumptions made to generate plastic leakage estimates. A comparison of leakage numbers presented in some of the main studies in this field (Borrelle et al., 2020; Jambeck et al., 2015; Lau et al., 2020; Lebreton et al., 2017; OECD, 2022a; Ryberg et al., 2019) is shown in Figure 8. The comparison also shows that the OECD estimates are close to the middle of the individual estimates, thus not representing extreme cases, but rather a best estimate.
Figure 8: Comparison of estimates of plastic leakage from mismanaged waste and littering (OECD, 2022a), in key studies in the field. Note that the type of estimate and its coverage is not identical across studies
While a large part of the plastic usage occurs in high-income OECD countries, most of the plastics leakage is from emerging low- to middle-income countries, with 69% from Asia, the Middle East and Africa. This is in accordance with the study by Jambeck et al. (2015) who also described these areas as those with the highest plastic leakage. As shown in Figure 9, macroplastic leakage accounts for most (approximately 88%) of the total global plastics leakages. Thus, on a mass basis, focus should be on reducing macroplastics.
Figure 9: Plastic leakage from different world regions in 2019 (OECD, 2022b).
Macroplastic waste will undergo transformation in the environment and be fragmentated into microplastic particles. Consequently, the most important source of microplastics is likely the degradation of macroplastics in the environment. Given that the major source of plastics in the environment is mismanaged plastic waste, in particular in emerging low- and middle-income countries, indicators are needed that focus on proper waste management of macroplastics in these countries, as further discussed in section 3.3.3. By extension, this will also include microplastics, with the breakdown of macroplastics as the main source.
Figure 10: Sources of macroplastic leakage to the environment (terrestrial and aquatic leakage), based on data in OECD (2022a).
As described in section 3.2.3, most of the plastics leakage from mismanaged waste is comprised of Packaging and Consumer & Institutional Products with the main polymers being PP, PE, and PET. This is also the case for the mismanaged plastics waste leakage from Other Asia, China, and Middle East and Africa.
The second most important source of macroplastic leakage is the littering of end-of-life plastic products (1.1 Mt). Waste littering is a large issue and relates to plastics being thrown away by citizens and not correctly disposed by consumers (OECD, 2022a). The exact amounts of plastics that are littered globally each year are highly uncertain due to poor monitoring of littering. However, studies on e.g., ocean clean-ups show that plastics or plastic-containing consumer products are often found on beaches due to littering. Beach litter data collected in several countries could be a relevant starting point to assess trends and effects of regulations, such as the EU Directive 2019/904 on SUP plastics. Moreover, a large part of sweepings in cities contain plastic littering, such as cigarette buds and various types of plastic packaging and wrapping.
Fishing activities and other marine activities also contribute substantially to the leakage of macroplastics due to the loss or discarding of nets at sea, the abrasion of other fishing gear such as dolly ropes and other non-netting waste (0.26 Mt). The leakage estimates for marine activities are highly uncertain and will be further discussed in Section 3.2.5. This is important as there is reason to believe that leakage from marine activities is more problematic per kg plastics released due to the longer environmental lifetime of plastic materials that are specifically designed to be used in marine environments. In addition, detrimental effects on marine wildlife have been associated with the entanglement in fishing gear, and the issue of “ghost fishing” has been described as a global problem (NOAA, 2014; Lively and Good, 2019). Thus, although the contribution to the total amount of plastics is small, its ecological effects can be substantial.
Figure 11: Sources of microplastics leakage to the environment (terrestrial and aquatic leakage), based on data in OECD (2022a).
Total microplastic leakage added up to 2.7 Mt in 2019, 35% of which was generated in OECD countries. The largest source of microplastic leakage is from road transport including tyre abrasion (0.7 Mt), brake wear (0.05 Mt) and eroded road markings (0.2 Mt). Another source of microplastic release is the “dust” from the abrasion of shoe soles (Lee et al., 2022; OECD, 2022a), paint wear from interior and exterior surfaces, losses from construction and demolition activities and household textile dust (in total 0.8 Mt). The losses of plastic pellets from production processes and from artificial turfs account for 0.28 and 0.05 Mt, respectively (OECD, 2022a), i.e., a non-negligible, but not the greatest contribution to the overall loss of microplastics.
It is important to note that while these leakages are estimated to be the dominant microplastic losses, these microplastics are not commonly found in the oceans (OECD, 2022a). This might be unexpected and could have several reasons. For instance, vulcanized rubber used in tyres was not originally considered microplastic material. It is likely to sink to the bottom of the oceans and will not be found in samples taken from the water surface. It is also possible that microplastics from abrasion are so small, that they are below the detection limit in sampling of marine microplastics. Finally, it is possible that the plastics are accumulated elsewhere, e.g. in soils before reaching the oceans (UNEP, 2018). In general, the lack of harmonized methods has been an obstacle in monitoring of tyre abrasion particles (Wik and Dave, 2009).
3.2.5. Plastic losses from marine activities
Direct leakages of plastics from marine activities are generally poorly accounted for in global plastic leakage models. Monitoring data on leakage are generally dated, scarce or completely absent. Still, it is likely that losses from marine activities are important as they are directly lost to marine environments and cause effects there. Moreover, they are designed to last in marine environments, hence they are likely to stay in the marine environment for an extended time.
Direct leakage of plastics to sea can be from:
- Fisheries and aquaculture: Maintenance and repairing damaged nets at sea, general abrasion of nets, ropes and strings, abandoned, lost or otherwise discarded fishing gear (ALDFG)), i.e. nets, pots, ropes etc., and loss of different types of equipment and user plastic products including galley waste.
- Commercial shipping and offshore activities (merchant shipping, ferries, cruise liners, military fleets, offshore constructions), galley and grey waste disposal at sea, loss of cargo/containers, equipment and user plastic on board, abrasion of equipment on board.
- Recreational activities at sea, e.g. boating: loss of user plastic incl. galley waste, abrasion of ropes and strings.
While significant progress have been made in quantifying the amounts of land‐based sources of marine litter, less information exists for sea‐based sources including ALDFG (Jambeck et al., 2015; Lebreton et al., 2018). With regards to ALDFG, this is largely due to the challenges arising from the focus on different gear types and/or geographic areas in the literature (GESAMP, 2021; Richardson et al., 2019). In addition, one major challenge in comparing ALDFG estimates on a regional or global scale is the lack of a harmonised reporting system.
The often-referred estimate that 640,000 tonnes of ALDFG enter the ocean annually has been incorrectly cited for over a decade (Richardson et al., 2021) and is unfortunately still being used (seame.net). This number was traced back to a 1975 publication by the USA’s National Academy of Sciences, which stated that roughly 6.4 million tonnes of marine litter entered the ocean every year (NAS, 1975; Richardson et al., 2021). This estimate included sources of marine litter from passenger vessels, merchant ships, recreational boats, commercial fishing vessels, military vessels, oil and drilling platforms and catastrophic events (NAS, 1975). Another publication provided a rough estimate of < 10% of marine litter being ALDFG, by volume (Macfayden et al., 2009). Later publications incorrectly turned this into an annual input mass of 640,000 tonnes of ALDFG.
A recent study has attempted to estimate the global loss of fishing gear (Richardson et al., 2019) and found that 5.7% of all fishing nets, 8.6% of all traps, and 29% of all lines were lost around the world each year, but did not provide mass estimates. Depending on the type of fishing gear, masses will vary considerably. As very little or no information exists from the Southern Hemisphere, this estimate is skewed towards the Northern Hemisphere. Thus, as of 2022, we still have no reliable information on the amount of ALDGF entering the marine environment on a global scale. The importance of acquiring this information has been recognized by several organizations, and efforts to provide solutions have been initiated by the Food and Agricultural Organization (FAO) of the United Nations, UNEP and the International Maritime Organization (IMO). A significant positive association between fishing effort and gear loss has been found in the Arafura Sea-Gulf region (Richardson et al. 2018 and references therein).
Another gap in our knowledge regarding ALDFG in the marine environment is information from recreational fishing. In spite of a high number of people fishing recreationally around the world, no estimates of ALDFG resulting from this type of fishing exists (Drinkwin, 2022). Presumably, the share will be small compared to losses from commercial fishing, but it remains to be quantified.
Despite the steady increase in the production of seafood for human consumption (FAO, 2018; GESAMP, 2021), information about the global amount of plastic pollution entering the marine environment from aquaculture is missing (FAO, 2017; GESAMP, 2021). This is mostly due to the lack of appropriate observation and monitoring systems at the national or regional level (Skirtun et al., 2022). In addition, there are currently no requirements or standardized processes for aquaculture farms to monitor gear loss (FAO, 2017; Huntington, 2019; Skirtun et al., 2022). However, regional data and assessments do exist. For example, in the European Economic Area, gear and debris loss associated with aquaculture is grossly estimated to be in the range of 3,000–41,000 tons annually (Sherrington et al., 2016).
Shipping vessels (including fishing vessels) generate waste daily (e.g., wire straps, plastic sheets, sewage). The discharge of garbage and sewage is regulated by the International Convention for the Prevention of Pollution of Pollution from Ships (MARPOL) of the IMO. However, the waste may end up in the marine environment due to mismanagement (either at sea or at reception facilities in ports) or unfavourable weather conditions (GESAMP, 2016). The type of waste generated from shipping is relatively well known, but few detailed studies exist on the amount of plastic waste (GESAMP, 2021). GESAMP (2021) made a best estimate of what is (potentially) discharged at sea by developing an alternative approach, a ‘waste gap’ calculation. A waste gap calculation is defined as the gap between the waste expected to be generated onboard the ship (and the part expected to be delivered in ports), and the waste actually delivered in ports.
A significant number of containers are lost at sea every year, adding to marine pollution. In 2020/2021 an average of 3.113 containers were lost at sea (WSC, 2022) which is an increase from previous years. Although it is unknown how many contained plastics, it has been argued that many goods transported by cargo ships contain plastics and that microplastics in the oceans could be related to lost pellets (Jo, 2020). Furthermore, given the increase in maritime transport and an associated increase in container ship accidents (Wan et al., 2022), this leakage source may deserve more attention.
3.2.6. The lifespan of plastics and the fate of plastics in the ocean
One of the primary properties of plastics is their durability. Thus, they persist in the environment long after they have been introduced. The understanding of the life cycle and end-of-life fate of plastics is very limited. Depending on the type of plastics used to manufacture a product, the breakdown process in the marine environment will vary, further influenced by variations in environmental conditions (Arp et al., 2021). Plastics made of HDPE (e.g., buoys) and PVC (e.g., pipes) are chemically resistant and therefore take longer to fragment and abrade, whereas expanded polystyrene (EPS, e.g., insulation boxes) breaks into small pieces more easily. Moreover, actual degradation of the plastics in the environment also varies greatly among plastic application and polymers. For instance, Chamas et al. (2020) estimated plastic half-lives of 58 years and 1200 years for HDPE plastic bottles and HDPE pipes, respectively. This is mainly due to different physical characteristics of the plastics, such as thickness of the plastic.
Depending on their density, and possibly degree of biofouling, some plastic types will float on the surface, whereas other types will sink. The distribution in the ocean will have implications for physical and chemical weathering. It is therefore important to differentiate between different types of plastics in research and monitoring campaigns to improve the understanding of their fate in the environment.
3.3. Gap analysis, recommendations and outlook
3.3.1. General remarks
The indicators in the DPSIR framework cover significant parts of the plastics value chain. Indicators representing Drivers, Pressures and Responses are largely covered by global initiatives, including those by UNEP, OECD and the SDGs. Indicators representing State and Impact are generally addressed at the regional or national level, however, also in combination with global settings. The local geographical level is hardly represented in the current indicator landscape and might require adaptations in monitoring and impact considerations, depending on local conditions.
In the following, recommendations are given for possible indicators, including new and further developments. A summary of potential new, not fully developed indicators with their advantages and disadvantages is given in Table 6. These consider different stages of the lifespan of plastics, including both plastic leakages and the state in the marine environment. We have based the recommendations on the following criteria (EC-JRC, 2010; Persson et al., 2022):
- Relevance: Is the indicator relevant for expressing the overall problem of marine plastic pollution?
- Measurability: Can the indicator be measured relatively easily and at reasonable costs? Is it possible to monitor developments over time? Can policy targets be set for the indicator?
- Comprehensiveness: Does the indicator present a broad and comprehensive reflection of the problem of marine plastic pollution?
A summary of the indicators we consider most recommendable, based on these discussions, is given in Table 7.
3.3.2. Gaps and challenges
As summarized in section 3.2, estimates have been established for the loss of plastic from the value chain, resulting in an overall leakage of plastic to the environment of 22.1 Mt in 2019. This number includes a number of assumptions with associated uncertainties as well as extrapolations and aggregations of different sources of information. This process is not always fully transparent, and data aggregation might lack standardization. While production numbers are relatively well-known, uncertainties related to the plastic loss from mismanaged waste are considerable. Therefore, it is important to note that the numbers currently available for this type of leakage are estimates that present an order of magnitude, but not a precise measurement. This has implications for the usefulness of indicators for e.g., time series. If uncertainties are large, it will be difficult to detect statistically significant changes.
Since this report combines leakages from the plastic value chain and plastic occurrence in the environment, it becomes apparent that these approaches have been disconnected and lack a common denominator. In many cases, indicator data for leakages from production, use and waste cannot directly be compared with or linked to indicator data for occurrence, composition and fate in the environment. Two main reasons are different geographical scales and different reporting units.
While data are available for estimates of the total leakage of plastics to the environment, it is not meaningful to upscale the plastic measurements in the environment in the same way, for example beach litter surveys or water manta trawls. Although there is general consensus that the oceans are a sink of plastics, no aggregated amounts exist, due to the heterogeneity of indicators. For example, beach litter is commonly recorded per item and could be recorded in hundreds of kilograms. Plastics in water manta trawls are usually reported as number of items per volume of water. Converting them to a mass unit would result in a low mass. The same case can be made for sediment measurements. Furthermore, while environmental analyses often include polymer identifications, leakages from the plastic values chains are rarely estimated on a polymer-basis, but rather related to sources or size classes (Figure 11). An example of a compilation of polymer-based identification in different indicators is given in Figure 12.
Figure 12: Composition of plastics at different stages in the plastic value chain and in the marine environment. Based on Geyer et al. (2017), Erni-Cassola et al. (2019) and Ask et al. (2020)
The reporting of plastic-related data holds a number of inconsistencies that hamper comparability and combination of indicator data. Specifically, no consensus exists on how to report the production of plastics, which can be given as, for instance, mass and type of primary plastics (i.e. pellets) or number of plastic items produced from these pellets. Typical examples of the characterisation of plastic losses are shown in Figure 10 and Figure 11. For environmental indicators, units have generally been specified to make monitoring programmes operational and allow comparisons across space and time (e.g. AMAP, 2021a; 2021b). However, in the determination of microplastics, discussions continue on e.g. lower size limits of detection, also based on the recognition that smaller particles may be particularly relevant from a toxicological point of view.
Two examples of plastic issues that lack connection between losses from the value chain and impacts on the environment are those of tyre abrasion and ALDFG. Tyre abrasion has been identified as a significant source of microlitter to the environment (Figure 11). Besides the abrasion during use, tyre granulates are also used on artificial grass fields and other surfaces, for example playgrounds. Originally, tyre particles were not frequently included in plastic studies, as they were not considered microplastic particles, also resulting in a pronounced lack of harmonised methods. Furthermore, despite representing a major loss of microplastics to the environment, these particles are not commonly found in marine environmental monitoring (OECD, 2022a). This may be related to strong retainment in the terrestrial or freshwater environment or to an efficient sedimentation in the oceans, probably close to the coast, in estuaries or near wastewater outlets. These processes are not fully understood, but present another mismatch between important potential indicators in the plastic value chain and in the environment.
On the other hand, fisheries are a major contributor to plastics in the marine environmental, including the occurrence of ALDFG in sea surface, beach litter and seafloor measurements. However, ALDFG is estimated as a rather small contributor in the global leakage chain (Figure 10). Given that fishing takes place worldwide, this points at poor estimates of leakages of ALDFG in the global assessment of plastic losses to the environment. Further monitoring needs are related to cuts from net repair on fishing vessels, which are difficult to quantify. In addition, plastic waste related to fishing gear has an extremely long lifetime as these products are designed for harsh environmental conditions, potentially including time scales from emission to detection that are different from other plastic products.
Although indicators from leakage and environmental indicators have different purposes, it is desirable with some level of consistency and complementarity. In fact, data on upstream leakage and environmental occurrence have the potential of supporting each-other. They can be important in identifying and verifying sources, for example, of the plastic particles detected in the environment. Section 3.3.3 includes examples of environmental state indicators that have the potential to provide information of relevance for assessing trends in leakages from different steps of the plastic value chain.
One major knowledge gap is the plastic leakage to the environment from the agricultural sector. Plastics are used extensively in agriculture, for example as protective wraps around mulch and fodder, as cover for greenhouses, to shield the crops and for irrigations tubes, sacks and bottles. Covering products in plastics has increased crop yields, but increasing evidence suggests soil contamination from degraded plastics that can affect biodiversity and soil characteristics. Plastics also enter agricultural soil with fertilizers produced from organic matter such as manure, apparently the major source (UN, 2022). Losses from the agricultural sector could be included in an indicator focusing on riverine inputs.
Other potentially relevant losses to the environment include container losses at sea that contain plastics as well as discharges of (micro)plastics with wastewater (Sun et al., 2019). Both sources might need more attention for our understanding of plastic sources and pathways. Ghost nets could be a potential indicator of ALDGF, perhaps on a mass basis to account for size differences.
While several environmental indicators exist and are incorporated in plastic monitoring programmes, it is important to realize that their representativeness is generally limited. Measurements represent the specific time and location of sampling, and the indicators are specific as well. Beach litter surveys do not provide information on microplastic particles in the water column, for example. For this reason, most organizations have suggested a set of complementary indicators (Table 2) including indicators such as seabirds that integrate a certain geographical area. However, it is important to understand what the indicator represents, for a correct interpretation of the data. Furthermore, existing databases could be extended to include data on macro- and microplastics. However, given the complexity of plastics as well as the need for metadata, the expansion of databases is not straightforward, but needs careful consideration (Provencher et al., 2023).
Table 6: Summary of relevant new indicators to be considered for further development
Indicator | Relevance | Challenge | Potential solution |
Tyre abrasion | Significant source of microlitter in the environment | Methodological challenges | Inclusion in an integrating indicator such as wastewater or riverine inputs |
ALDFG* | Important source of plastic in the marine environment, risk of ecological impacts | Heterogenous parameter, no harmonized reporting system | Already included in beach litter |
Container losses | Increasing maritime shipping | No direct link to plastic pollution | Recorded as a general marine pollution issue, not limited to plastics |
Wastewater effluents | Source of (micro-)plastics connecting land and sea | Data on sludge needed for mass balance of plastic emissions, costly | Connection to other wastewater measurements |
Riverine inputs | Significant input pathway into the marine environment, connecting land and sea, potential for alignment with beach litter measurements | No standardization, costly | Standards from beach litter monitoring could be applied |
*Abandoned, lost or otherwise discarded fishing gear
3.3.3. Recommended indicators
Indicators on plastic production would mainly be directed at a reduced production of plastics. While a reduction of plastics can be considered the most efficient step towards a decrease of plastic pollution, it might also have counterproductive elements in terms of e.g., mitigating climate change because plastics are often used as a substitute for other carbon-intensive materials, such as glass or metals. A more efficient use of plastics, e.g., by reducing packaging could be most beneficial. Indicators related to plastic production should therefore ideally be defined to increase plastic use efficiency rather than substitution of plastics with materials that might have other disadvantages. However, while possible of lower relevance, plastic production has a better measurability than plastic use efficiency.
The largest mass leakage of plastics is that of macroplastics from mismanagement waste treatment of short-lived packaging and consumer and institutional products made from PP, PE, and PET. We recommend placing more focus on these and developing suitable indicators for covering the leakage from mismanaged plastic waste. However, there are some challenges in the data collection:
Ideally, the amount of plastic waste would be monitored that is lost to the environment. However, as discussed in section 3.2.3, mismanaged waste is usually part of the informal waste sector with no regular data collection. Hence, data for this type of indicator will be difficult to obtain. The percentage of mismanaged waste is highest in low-income countries where fewest systematic data collections exist. Alternatively, the losses of plastic waste could be determined from a mass balance, such as
Waste production in the region + Waste imports into the region – Waste exports to other regions = Generated plastic waste
These values could then be compared to data on managed treatment of the plastic waste, with the difference accounting for mismanaged plastic waste. This could be an indicator that could be monitored for increasing or decreasing values over time. However, a challenge with this approach is the determination of the percentages of plastics in the total waste. If the waste is not source-separated, but has a mixed composition, it is difficult to determine the part that consists of plastics. The residual waste fraction is often the part of the waste that is subject to mismanagement as it has little economic value, compared to pure recyclable plastic waste, even though it might contain recyclable or reusable materials. A more straightforward way of determining the extent of mismanaged waste could be a connection to e.g., beach litter monitoring, which essentially represents mismanaged and unmanaged waste, as further discussed below.
A possible indicator could also be the export of plastic products or waste from high-income countries to low- and middle-income countries to assess the risk of mismanagement of the plastic waste. However, this process is not likely to be of great relevance to indicate leakages from mismanaged plastic waste as the majority of leaked plastics is likely to originate from mixed waste and not from sorted plastics that have an economic value and that are likely to represent the main part of the exported plastic products. Furthermore, rates of export and mismanagement might be decoupled in future developments aiming at improving waste management.
An indirect indicator could be the annual recycling rate of plastics. It is indirect because it does not directly reflect plastic pollution. For example, low recycling rates combined with high rates of plastic incineration can still result in low plastic pollution. However, increasing the recycling rate will likely reduce the percentages of plastics that are subject to mismanagement and potential pollution of the environment. Focus should be on the three dominating polymers PP, PE and PET, and data would be needed on their production, import and recycling.
For microplastics, the main leakages relate to the plastics use stage and abrasion and degradation of plastic containing products. The microplastic losses from abrasion are difficult to monitor and regular updates of estimates are not feasible. Potential indicators of microplastics abrasion could be air concentrations of plastic dust in urban areas. Indeed, styrene-butadiene rubber (SBR), as used in tyres, has been measured near roads (Wik and Dave, 2009). Increasing air concentrations of plastic dust is likely to be a good proxy of potential further leakages of microplastics to the environment, but might be technically challenging. Microplastics are currently monitored in the marine environment, as further discussed below, integrating over microplastics formed in the oceans from breakdown of larger particles and inputs from land-based sources. An option of connecting microplastics from land, including tyre abrasions, with the marine environment, could be measurements in wastewater (as discussed in section 3.3.2), and in rivers. The latter could combine macro- and microplastic measurements, but is currently not well-developed or standardized.
As seen in Table 2, one of the most widely applied environmental indicators is that of beach litter, also commonly described as litter on shorelines. This indicator is relatively easy to implement, but needs a standardized reference framework for unambiguous item identification, quantification and reporting, such as those of OSPAR and HELCOM (Table 2) or of the EU (JRC, 2013). The recent AMAP monitoring plan recommends beach litter, plastics in stomachs of northern fulmars and microplastics in water and sediment as priority environmental indicators (AMAP, 2012b). The basis for this recommendation is the technical maturity and feasibility of their measurements, besides a certain complementarity regarding size classes of plastic particles. The EU guidance document for monitoring of marine litter also includes microplastics in water, sediment and biota (JRC, 2013).
Seafloor litter is another widely used indicator (Table 2). Seafloor and beach litter could be most suitable for connection with leakages from the plastic value chain, as mentioned above. However, considering complex accumulation processes on the seafloor, standardized monitoring over time might be challenging. Seafloor litter might thus be most relevant to indicate ongoing accumulations on the ocean floor, including identification of hotspots and impacts on ecosystems.
Microplastic measurements might be able to provide linkages with losses from the plastic value chain as well. Using biota as environmental indicators includes measurements in seabirds and turtles that swallow small plastic particles, but also measurements in fish and invertebrates. Using biota as an indicator could create links to exposure and potential impacts. On the other hand, ecological information is needed, for example on feeding habits and migratory ranges, to interpret the data correctly.
As discussed in section 3.3.2, some environmental indicators have the potential to be connected to upstream leakages from different steps of the plastic values chain, for example:
- Trends in occurrence of industrial pellets in e.g., seabirds or on beaches can be linked to leakage from production, transport or use of these plastic materials.
- Source allocations based on compositional analyses of e.g., beach litter or seafloor litter can be used for assessing the likelihood for leakages from different important land- or sea-based sources including waste handling, e.g., by using the so-called matrix scoring techniques on a (sub)regional scale for assessment of the likelihood of leakages from specific types of sources. The matrix scoring technique is a systematic and transparent system that combines litter types, container information and indicator items with multivariate analysis, probability scores and percentage allocations (Tudor and Williams, 2004).
- Direct measurement of leakages based on environmental flux and transport data on plastic amounts and composition in e.g., effluents, stormwater, rivers, air etc.
- Laboratory-based determinations and assessments of polymer composition of micro- and macroplastic particles in the environment can be relevant for comparing data for production and uses of bulk polymers (Figure 12).
Although substantial progress has been made in monitoring efforts, there are still challenges with regard to data availability, uncertainties and consequently, the interpretation of the data. It is advisable to work with the same set of indicators in a consistent manner and over a time period. These can be developed into time series, including information on variability that will be important to assess the statistical power of the time series.
Table 7: Summary of recommended indicators for a global agreement.
DPSIR | Indicator | Relevance | Measurability | Comprehensiveness |
Drivers | Plastic production | Medium, “Plastic use efficiency” might be more relevant than plastic production, but more difficult to measure. | High, would need to be recorded globally | High |
Plastic use | Medium, needs to combine records on plastic production with export and import data | High | ||
Pressures | Plastic recycling rate | Proxy indicator for mismanaged waste, but with caveats | High, would need to be recorded globally. Needs additional information on other types of management, e.g., incineration, for correct interpretation | Medium, proxy indicator for losses to the environment, uncertainty about other types of waste management |
Plastics in wastewater | High, would connect land-based sources with the aquatic environment | High, could be combined with other parameters measured within wastewater epidemiology. Needs information on domestic sources (wastewater) vs. road run-off (stormwater) for correct interpretation | Medium, no direct connection with the marine environment. | |
Riverine inputs | High, could include macro- and microplastics and would connect land-based sources with the marine environment | Medium, may be costly | Medium, processes in the freshwater environment can influence levels in the marine environment | |
State | Beach litter | High, integrates mismanaged waste and plastic emissions without management measures | High, relatively well-standardized, no need for advanced equipment | High, but difficult to extrapolate from individual measurements |
Floating microplastics | Medium, high fluctuation | Medium, relatively well-standardized, requires equipment for sampling and analysis | Medium, misses particles that do not float (e.g., tyre abrasion) | |
Impacts | Seabirds/Turtles | High, can provide links to food webs | Medium, relatively well-standardized, requires access to samples and equipment for analysis | Medium, related to animal ecology, represents micro- and mesoplastics |
3.3.4. Outlook
The current indicator landscape is fragmented in its attempt to cover all aspects related to plastics as an environmental problem as well as all relevant geographical scales. Useful indicators exist, and recommendations have been put forward in section 3.3.3, together with discussions of their possibilities and limitations. However, future efforts should be directed at a more holistic picture that combines different types of indicators. In addition, the lack of harmonization and standardization is still an issue, both at the data collection and reporting stage. While this has generally been recognized, and multiple initiatives are trying to overcome these lacks, they usually focus on one area of plastic pollution, for example the environmental indicators. Here, more connections should be ensured as well.
It is also important to recognize that the current attempts towards more harmonized and standardized measurements should include questions of data reporting. Efforts to incorporate plastic data into existing databases are ongoing, but hampered by the complexity of plastics as an environmental parameter and the unclear indicator situation. It will be an important element of the development of globally applied indicators to provide adequate database structures. An important detail is an agreement on units for measurement. Plastics can be measured as items or on a mass basis, in fluxes or concentrations. Different indicators can be complementary in this regard, but consistency within one indicator type should be ensured.
The legally binding global agreement to end plastic pollution is a milestone. However, it is strongly dependent on reliable, robust and meaningful data on the global scale. Experience exists from other UN frameworks, such as the Stockholm Convention on Persistent Organic Pollutants (POPs) that has defined POPs in air, human blood and human milk as global indicators (besides perfluoroalkyl substances in water). This experience also shows that the agreement on indicators has to be followed by practical aspects of implementation, including, but not limited to, capacity building of laboratories on the global scale. Similar steps will need to follow the identification of plastic indicators as well.
Unlike the Stockholm Convention, the UNEA 5 resolution will not ban plastic production, but addresses the objective to end the plastic pollution problems. This will involve priorities and solutions that might differ between regions and countries/economies. Regionally identified problems, such as ALDFG in the Arctic, should still be addressed as a priority there. Ideally, actions and monitoring initiatives on national or regional scales should be used nationally and regionally, but also feed into an overall global framework. Creating these structures will be another future step to take.
The large regional and national variety in the field of plastic pollution needs to be considered, including issues of mismanagement of waste and attempts to reduce plastic use or introduce source separation. This will likely also involve long-term behavioural changes in society, related to greater awareness of the plastic pollution problem and the individual’s responsibility to reduce this problem. Furthermore, possibilities of data collection have to be assessed realistically, and capacities need to be built to obtain data in a quality assured way and report it into widely accessible systems.
Finally, research into plastic pollution needs to continue, including, for example, sources and transport patterns, degradation from macro- to microplastics, transfers between environmental compartments and impacts on ecosystems and humans. The fact that many plastic materials contain potentially harmful chemicals as additives, adds to the complexity of plastic pollution and is a further field with clear research needs.