Marine Litter and Plastics Accounting

1. Outcome

This Circular provides guidance on establishing stock-flow accounts for marine litter and plastics within the Ocean Accounts framework. Upon completing this Circular, readers will understand how to categorise marine litter by material type and source, compile flow accounts tracking litter from land-based and maritime sources to the marine environment, develop stock accounts for accumulated litter in coastal zones, surface waters, the water column, and the seafloor, address the measurement challenges associated with microplastics, attribute litter flows to economic sectors and geographic sources, align marine litter accounts with SDG Target 14.1 indicators on marine pollution, derive circular economy indicators linking litter accounts to plastics reduction targets under emerging international frameworks, and compile material flow accounts for synthetic materials from production through disposal to marine leakage.

The accounts compiled using this guidance support derivation of indicators for environmental pressure assessment in TG-2.7 Pollution Flows, contribute to comprehensive assessment of residual flows from economy to environment in TG-3.4 Flows from Economy to Environment, inform circular economy indicators in TG-2.11 Resource Efficiency, and support reporting to the multilateral environmental agreements described in TG-2.10 MEA Indicators. Marine litter accounting also informs climate-related assessments through its intersection with plastics lifecycle emissions, as addressed in TG-2.8 Climate Indicators, and complements maritime transport activity accounts in TG-6.10 Maritime Transport where vessel-sourced litter is concerned. This Circular builds on the conceptual framework established in TG-0.1 General Introduction and the physical flow accounting principles in TG-3.4 Flows from Economy to Environment.

2. Requirements

This Circular requires familiarity with:

• TG-0.1 General Introduction -- provides foundational understanding of Ocean Accounts components, the relationship between environmental and economic accounting frameworks, and SIDS-specific considerations that are particularly relevant for marine litter accounting in small island contexts.

• TG-3.4 Flows from Economy to Environment -- for the general framework of residual flow accounting, solid waste accounts, and attribution of emissions and waste to economic sectors, which underpins the marine litter flow accounting approach presented in Section 3.3 of this Circular.

3. Guidance Material

Marine litter, defined as any persistent, manufactured or processed solid material discarded, disposed of, or abandoned in the marine and coastal environment, constitutes one of the most visible and pervasive forms of marine pollution^[1]. Plastics represent the dominant material category in marine litter globally, accounting for approximately 80 percent of all marine debris by count^[2]. The persistence of plastic materials, their fragmentation into microplastics, and their distribution across all ocean compartments from surface waters to deep-sea sediments make marine plastic pollution a significant environmental and policy concern.

The United Nations Sustainable Development Goal 14 Target 14.1 calls upon states to "prevent and significantly reduce marine pollution of all kinds, in particular from land-based activities, including marine debris and nutrient pollution" by 2025^[3]. SDG indicator 14.1.1 specifically includes "floating plastic debris density" as a component of the index of coastal eutrophication and plastic debris density^[4]. Comprehensive accounting for marine litter and plastics supports countries in monitoring progress toward this target and in developing effective policy responses.

The international policy landscape for plastics is evolving rapidly. The United Nations Environment Assembly Resolution 5/14 (March 2022) established an Intergovernmental Negotiating Committee (INC) to develop a legally binding instrument on plastic pollution, including in the marine environment^[5]. The INC process has advanced discussion of national action plans, extended producer responsibility provisions, and harmonised reporting requirements. Compilers should monitor treaty developments for emerging reporting obligations that may shape accounting requirements. As of February 2026, the treaty text remains under negotiation, with the fifth session of the INC having convened but not yet finalised binding provisions. Anticipated elements include mandatory national reporting on plastic production, trade, and waste management, which will align closely with the accounting framework described in this Circular^[6]. The institutional context for such international frameworks is addressed in TG-0.1 General Introduction.

The System of Environmental-Economic Accounting Central Framework (SEEA CF) provides the foundation for solid waste accounting, defining waste as substances or objects that the holder discards or intends to discard^[7]. The SEEA CF presents a physical supply and use table structure for solid waste that records waste generation by economic sector and tracks flows to collection, treatment, and disposal destinations^[8]. For marine litter accounting, this framework must be extended to capture waste that escapes management systems and enters the marine environment, as well as litter generated directly by maritime activities.

3.1 Decision Use Cases and Upward Connections

Marine litter accounts support a diverse range of policy decisions and performance assessments across environmental protection, circular economy, and sustainable development domains. Understanding the decision contexts enables compilers to prioritise data collection and account design to maximise policy relevance.

Plastics treaty reporting and compliance monitoring

The anticipated international legally binding instrument on plastic pollution under development through the INC process will require countries to track plastic production, consumption, trade, waste generation, and environmental leakage^[9]. Marine litter accounts provide the integrated data infrastructure for such reporting by linking plastics material flow accounts (tracking production and use) to waste management accounts (tracking collection and disposal) to residual flow accounts (tracking marine leakage). This eliminates redundant data collection across multiple reporting obligations and ensures consistency between national waste statistics and international environmental monitoring.

Circular economy metrics for plastics

Countries adopting circular economy policies for plastics require indicators tracking material circularity, including recycling rates, reuse rates, product lifetime extension, and leakage reduction^[10]. The SEEA CF solid waste account structure (paragraphs 3.268-3.278) provides the methodological foundation for these indicators by recording waste generation by source industry, waste collection by material type, and allocation to treatment and disposal pathways^[11]. Marine litter accounts extend this structure by quantifying the proportion of plastic waste that escapes collection and treatment systems, providing the "leakage rate" indicator fundamental to circular economy assessment. These indicators feed directly into TG-2.11 Resource Efficiency, which provides comprehensive guidance on deriving circular economy indicators from Ocean Accounts.

Beach and ocean cleanup investment justification

Governments and organisations allocating resources to beach cleanup programmes and marine debris removal operations require evidence of accumulated litter stocks and annual deposition rates to justify investment and evaluate effectiveness^[12]. Stock accounts by environmental compartment (beach, floating, benthic) provide baseline estimates of litter volumes requiring removal. Flow accounts by source category enable prioritisation of interventions targeting high-contribution pathways. Time-series accounts tracking stock changes before and after cleanup programmes provide the quantitative basis for return-on-investment assessment and adaptive management. This use case links marine litter accounts to environmental protection expenditure accounts addressed in TG-3.7 Governance Accounts, Section 3.4 on environmental expenditure.

Microplastic monitoring and health risk assessment

The proliferation of microplastics in marine food webs and their potential accumulation in seafood consumed by humans has elevated microplastic monitoring to a public health priority^[13]. Flow accounts distinguishing primary microplastics (manufactured at small size) from secondary microplastics (formed through fragmentation) support targeted interventions such as restrictions on microbeads in cosmetics. Stock accounts for microplastic concentrations in marine waters and sediments provide exposure baselines for ecological and human health risk assessments. The methodological challenges of microplastic measurement are addressed in Section 3.5 of this Circular.

Upward connections to indicator frameworks

Marine litter accounts provide the data foundation for multiple indicator frameworks:

• SDG 14.1.1 (Marine pollution) -- directly supplies floating plastic debris density component and informs coastal eutrophication index through nutrient pollution attribution^[14]
• Pollution pressure indicators (TG-2.7) -- provides the physical flow data for deriving litter generation intensity, mismanaged waste rates, and marine leakage indicators that assess environmental pressure
• Circular economy indicators (TG-2.11) -- enables calculation of recycling rates, waste utilisation rates, and decoupling factors comparing economic growth to waste generation
• MEA reporting (TG-2.10) -- supports Kunming-Montreal Global Biodiversity Framework Target 2 on ecosystem restoration by tracking litter removal from marine protected areas, and UNFCCC reporting by linking plastic lifecycle emissions to waste management pathways

The combined presentations approach described in TG-3.8 Combined Presentations provides practical methods for integrating marine litter account data with economic accounts and ecosystem condition accounts to derive these indicators efficiently.

3.2 Marine Litter Framework: Categories, Sources, and Pathways

Marine litter encompasses a diverse range of materials that reach and persist in the marine environment. A systematic accounting framework requires classification of litter by material type, identification of sources, and characterisation of pathways from source to marine environment.

Material categories

The Classification of Environmental Protection Activities and Expenditure (CEPA) addresses waste management activities under CEPA 3, distinguishing between hazardous and non-hazardous waste and addressing collection, treatment, and disposal^[15]. For marine litter accounting, material classification should distinguish:

Plastics -- the dominant component of marine litter, requiring further disaggregation by:

• Polymer type (polyethylene, polypropylene, polystyrene, PET, PVC, other polymers)
• Product category (packaging, single-use items, fishing gear, consumer goods, industrial materials)
• Size class (macroplastics >25mm, mesoplastics 5-25mm, microplastics <5mm)

Bioplastics and materials marketed as biodegradable warrant careful treatment in classification. Many bioplastics do not degrade under marine conditions and should be accounted equivalently to conventional plastics in marine litter stock and flow accounts. The EU Single-Use Plastics Directive (2019/904) provides definitions that may inform national classification decisions. Compilers should classify materials based on their actual persistence in the marine environment rather than their marketed characteristics.

Other materials -- including:

• Glass and ceramics
• Metal (ferrous and non-ferrous)
• Rubber
• Textiles
• Paper and cardboard (limited persistence but present in coastal and nearshore surveys)
• Wood (processed, including pallets, crates, construction materials)
• Other manufactured materials

The GESAMP Guidelines for the monitoring and assessment of plastic litter in the ocean provide a harmonised categorisation framework that countries may adopt for national marine litter accounting^[16]. The European Waste Catalogue (EWC-Stat) classification offers additional detail for waste source identification^[17].

Source categories

Marine litter originates from two primary source categories:

Land-based sources -- estimated to contribute approximately 80 percent of marine litter globally^[18]:

• Municipal solid waste (uncollected waste, littering, illegal dumping)
• Industrial waste and manufacturing residues
• Construction and demolition waste
• Agricultural plastics (mulch films, irrigation equipment, greenhouse materials)
• Sewage-related debris (sanitary items, microplastics from wastewater)
• Coastal tourism and recreation waste
• Riverine transport of waste from inland areas

Sea-based sources -- including:

• Fishing activities (abandoned, lost, or discarded fishing gear -- ALDFG, also termed "ghost gear")
• Shipping (cargo loss, operational waste, accidental discharge)
• Offshore energy operations (operational waste, equipment loss)
• Aquaculture (equipment, floats, cages, feed bags)
• Recreational boating
• Maritime structures and port operations

The relative contribution of different sources varies significantly by location and requires national or regional assessment. Small Island Developing States (SIDS) may have higher proportionate contributions from sea-based sources, while coastal nations with large populations may have predominantly land-based inputs^[19]. The SIDS-specific considerations addressed in TG-0.1 General Introduction are particularly relevant for marine litter accounting in these contexts.

Pathways to the marine environment

Understanding the pathways by which waste enters the marine environment is essential for effective accounting and policy intervention. Key pathways include:

1. Direct coastal input -- waste deposited, blown, or washed directly from coastal zones into the sea
2. Riverine transport -- waste carried by rivers from upstream sources; rivers are major conduits for land-based marine litter^[20]
3. Stormwater and urban runoff -- waste transported through drainage systems during precipitation events
4. Wastewater discharge -- microplastics and other debris not removed during wastewater treatment
5. Atmospheric transport -- lightweight items and microplastics transported by wind
6. Direct disposal at sea -- deliberate dumping (regulated under the London Convention and Protocol)^[21]
7. Accidental loss at sea -- cargo loss, equipment failure, vessel incidents

The SEEA CF notes that controlled landfills are considered within the economy, while uncontrolled disposal to the environment represents a residual flow^[22]. For marine litter accounting, this boundary is critical: waste reaching marine waters represents a flow to the environment that should be recorded in residual flow accounts.

Figure 6.12.1: Marine litter stock-flow relationships (see also TG-3.4 Section 3.2)

3.3 Flow Accounting: Litter Inputs to the Marine Environment

Flow accounts record the quantity of litter entering the marine environment during an accounting period, measured in mass units (tonnes) or, for monitoring purposes, item counts. Flow accounting distinguishes between:

Land-based source flows

Land-based litter flows require estimation of:

• Mismanaged waste -- waste not formally collected or improperly disposed after collection that has potential to reach the marine environment
• Leakage rates -- the proportion of mismanaged waste that actually reaches marine waters (dependent on proximity to coast, hydrological connectivity, and waste characteristics)

The methodology developed by Jambeck et al. (2015) provides an established framework for estimating plastic waste input from land to ocean, based on coastal population, waste generation rates, waste management infrastructure, and modelled leakage^[23]. This approach uses:

Plastic marine debris = Coastal population ×
                        Waste generation rate ×
                        Plastic content of waste ×
                        Inadequately managed waste share ×
                        Leakage factor to ocean

Subsequent refinements to this methodology have extended the analytical framework. Lau et al. (2020) developed scenario analysis capability for evaluating pathways toward reduced plastic pollution, incorporating waste management interventions, material substitution, and consumption reduction^[24]. Borrelle et al. (2020) projected plastic waste growth trajectories and assessed the scale of intervention required to mitigate pollution^[25]. These more recent approaches are particularly valuable for compilers seeking to link accounts to policy evaluation and scenario analysis, an area where guidance on model selection and uncertainty treatment continues to develop.

For ocean accounting purposes, this estimation approach should be:

• Disaggregated to record flows by economic sector where possible (using waste composition data linked to industry sources)
• Geographically referenced to identify priority coastal areas
• Time-series consistent to track trends

The SEEA CF physical supply and use table for solid waste provides the structural framework^[26]:

For marine-specific accounting, the "waste to environment" category is disaggregated to distinguish:

• Waste to marine and coastal waters
• Waste to inland waters (with subsequent marine pathway)
• Waste to land (coastal littering, beach deposits)

Maritime source flows

Maritime sources require recording of waste generated by marine activities that enters the ocean:

Fishing gear losses -- Abandoned, lost, or discarded fishing gear (ALDFG) is estimated at 5.7 percent of fishing nets, 8.6 percent of traps, and 29 percent of fishing lines lost globally each year^[27]. Accounting requires:

• Data on fishing fleet composition and gear types
• Estimated loss rates by gear type and fishery
• Conversion to mass units using gear weight specifications

This component of marine litter accounting links to fisheries accounting in TG-6.7 Fisheries Stock Assessment which addresses fishing fleet characteristics and effort data.

Vessel operational waste -- The International Convention for the Prevention of Pollution from Ships (MARPOL) Annex V regulates discharge of garbage from ships^[28]. Despite regulations, operational discharges and accidental losses occur. Accounting draws on:

• Port reception facility records
• MARPOL incident reporting
• Vessel surveys and inspections

Offshore operations -- Waste from offshore energy platforms, aquaculture installations, and other maritime structures. Recording should align with industry reporting requirements and operational data. Cross-reference to TG-3.10 Offshore Energy for offshore accounting context.

Cargo losses -- Container losses and other cargo overboard incidents. Reporting under maritime incident databases provides partial coverage.

Riverine inputs

Rivers transport substantial quantities of litter from inland areas to the marine environment. Studies indicate that a relatively small number of rivers contribute a disproportionate share of global riverine plastic input^[29]. Accounting for riverine inputs requires:

• Monitoring of litter concentrations in river outflows
• Estimation of total transport based on flow volumes
• Attribution to upstream catchment sources where possible

For national ocean accounts, riverine inputs represent the cumulative effect of upstream waste management and thus should be linked to waste generation and management accounts for inland areas. Rivers function as both water resources and transport pathways for litter, and compilers developing integrated water-waste accounts should ensure methodological consistency between water flow accounts and litter transport estimates. The hydrological data used for water flow accounting may serve as a basis for estimating litter transport volumes, particularly where direct litter monitoring data are limited.

3.4 Stock Accounting: Marine Litter Accumulation

Stock accounts record the quantity of litter accumulated in the marine environment at the opening and closing of an accounting period. Marine litter accumulates in multiple environmental compartments. The following stock-flow account template provides a compilation framework for recording litter quantities across these compartments.

Table 3.4.1: Marine litter physical stock-flow account (tonnes)

The account template records litter stocks by environmental compartment and tracks changes through inflows, outflows, and inter-compartment transfers. The "primary entry" notation indicates the compartment where each source type is first recorded; subsequent redistribution across compartments is captured through transfer rows. Inter-compartment transfers must balance: total outflows as transfers (190 tonnes) should equal total inflows from transfers (215 tonnes in this example -- the discrepancy indicates further refinement needed to ensure mass balance). Compilers should populate this template using the data sources and estimation methods described in Section 4 of this Circular.

Beach and coastal stocks

Beach litter is the most accessible stock for monitoring, with established survey methodologies^[30]. Stock accounts record:

• Mass or item counts per unit area (beach length, surface area)
• Aggregated to total coastal stock based on coastline characteristics
• Disaggregated by material category

Beach stock accounts must recognise that beaches are dynamic interfaces where:

• New litter deposits during each tidal cycle and storm event
• Removal occurs through clean-up activities, burial, and resuspension
• Opening and closing stocks relate through: Closing stock = Opening stock + Deposits - Removals - Degradation

Clean-up activities should be recorded as economic flows (environmental protection expenditure under CEPA 3) and their effect on beach stocks quantified^[31]. This links marine litter accounts to environmental expenditure accounts addressed in TG-3.7 Governance Accounts.

Floating litter stocks

Surface and near-surface floating litter is measured through visual surveys, net tows, or remote sensing. SDG indicator 14.1.1 specifies floating plastic debris density as a monitoring parameter^[32]. Stock accounts for floating litter face challenges:

• Highly dynamic distribution influenced by currents, winds, and convergence zones
• Variable vertical distribution (surface to depth)
• Difficulty in scaling point observations to total stock estimates

Global accumulation zones (ocean gyres) represent areas of elevated floating debris concentration. Stock accounts may record:

• Density estimates (items or mass per km2) for defined ocean areas
• Total estimated stock based on density and area
• Uncertainty ranges reflecting measurement limitations

Marine litter stock density may also serve as an ecosystem condition indicator within the SEEA Ecosystem Accounting framework. Elevated litter concentrations degrade habitat quality for marine ecosystem types including shoreline systems (IUCN Global Ecosystem Typology realm MFT1) and open ocean and deep-sea systems (realms M1-M3). The relationship between litter accumulation and ecosystem condition is addressed in TG-2.3 Ecosystem Condition, which provides guidance on recording abiotic pressures as condition variables. Compilers may report litter density as a supplementary condition indicator alongside the stock account.

Water column stocks

Litter suspended in the water column, including neutrally buoyant items and microplastics, is less well characterised than surface or benthic stocks. Accounting approaches are necessarily more experimental and may rely on:

• Depth-stratified sampling data
• Modelled vertical distribution based on particle characteristics
• Extrapolation from limited survey data

Seafloor stocks

Benthic litter accumulates on the seabed, particularly in areas of high sedimentation, submarine canyons, and deep-sea plains. Monitoring uses:

• Trawl surveys with litter quantification
• Remotely operated vehicle (ROV) transects
• Baited camera systems

Seafloor stocks represent a long-term sink for marine litter, with limited natural removal processes. Stock accounts should record:

• Density by seabed type and depth zone
• Estimated total stock within national waters
• Composition by material category

The SEEA Ecosystem Accounting framework addresses ecosystem condition, including the presence of pollutants as a condition variable^[33]. Marine litter stock density may serve as an indicator of ecosystem condition degradation for marine ecosystem types.

3.5 Microplastics: Secondary Formation and Measurement Challenges

Microplastics are plastic particles less than 5mm in diameter, present in the marine environment as:

• Primary microplastics -- manufactured at small size (microbeads in personal care products, industrial abrasives, resin pellets)
• Secondary microplastics -- resulting from fragmentation of larger plastic items through weathering, UV degradation, and mechanical breakdown

Accounting for microplastics

Microplastics present distinct accounting challenges:

Flow accounting -- Primary microplastics can be recorded as flows from specific sources (cosmetics, textiles, tyre wear, pellet loss), but secondary microplastics form continuously from accumulated stocks, making flow-stock relationships complex. Key flow sources include:

• Wastewater effluent (fibres from textiles, fragments from degradation)
• Stormwater runoff (tyre wear particles, road marking fragments)
• Direct spillage (pellet losses from plastics industry)
• Atmospheric deposition (fibres, particles from urban environments)

The SEEA CF treatment of solid waste does not specifically address microplastics, representing an area for methodological development^[34]. Compilers may record microplastic flows as a supplementary account or as a disaggregation of the plastics category within solid waste accounts.

Stock accounting -- Microplastic stocks in marine waters and sediments accumulate from both direct inputs and in situ fragmentation. Stock estimation requires:

• Concentration measurements (particles per unit volume of water or mass of sediment)
• Extrapolation to total stock based on environmental compartment volumes
• Recognition of measurement uncertainties (sampling methods, size detection limits)

Transformation recording -- The fragmentation of macroplastics into microplastics represents a transformation within the environmental stock rather than a new input flow. This transformation has parallels with the treatment of natural growth and depletion in biological resource accounts (SEEA CF Chapter V), where natural processes generate changes in stock that are distinct from economic transactions. Fragmentation may be understood as analogous to "natural loss" of macroplastic stock that generates "additions" to microplastic stock. The mass balance should be maintained, with the total mass of plastic conserved minus any material that mineralises or exits the system. This framing assists compilers familiar with natural resource accounting to approach marine litter stock accounts using established conceptual tools. The general treatment of asset stock-flow relationships is addressed in TG-3.1 Asset Accounts.

In the stock-flow account template (Table 3.4.1), this transformation can be recorded as:

• Reduction in macroplastic stock (outflow row: degradation)
• Increase in microplastic stock (inflow row: transfer from other compartment)

Measurement challenges

Microplastic measurement faces significant methodological challenges affecting accounting reliability^[35]:

1. Size detection limits -- Sampling and analysis methods have lower size limits (typically 1 micrometer to 300 micrometers), missing smaller particles
2. Sampling standardisation -- Variability in sampling methods, units of measurement, and reporting protocols limits comparability
3. Environmental heterogeneity -- High spatial and temporal variability requires intensive sampling for representative estimates
4. Laboratory contamination -- Airborne microplastics can contaminate samples, requiring rigorous quality control
5. Polymer identification -- Spectroscopic methods for polymer identification are resource-intensive

For ocean accounting, compilers should:

• Document methods and detection limits used in microplastic data
• Apply appropriate uncertainty estimates to stock and flow values
• Use harmonised sampling protocols where available (e.g., GESAMP guidelines)
• Consider microplastic accounts as experimental pending further methodological development

Quality assurance for emerging and experimental indicators is addressed in TG-0.7 Quality Assurance.

3.6 Source Attribution and Material Flow Accounts

Effective marine litter policy requires attribution of litter to the economic units and locations responsible for its generation. The SEEA CF principle of recording residual flows by source industry applies to marine litter accounting^[36]. This section extends the general source attribution framework to present a complete material flow account for plastics from production through use to disposal and marine leakage.

Industry source attribution

Industry sources of marine litter include:

Primary material production

• ISIC 20: Manufacture of chemicals and chemical products (resin pellets, plasticisers)
• ISIC 22: Manufacture of rubber and plastics products (production waste, pellet losses)

Manufacturing with plastic content

• ISIC 10-12: Food, beverages, and tobacco (packaging waste)
• ISIC 13-14: Textiles and apparel (microfibre release)
• ISIC 17: Manufacture of paper and paper products (packaging, laminates)

Fishing and aquaculture

• ISIC 0311: Marine fishing (fishing gear losses, operational waste)
• ISIC 0312: Freshwater fishing (gear losses affecting riverine systems)
• ISIC 0321: Marine aquaculture (equipment losses, feed bags)

Transport

• ISIC 50: Water transport (vessel waste, cargo losses)
• ISIC 49: Land transport (tyre wear contributing to microplastics)

Tourism and recreation

• ISIC 55-56: Accommodation and food service (disposable items, packaging)
• ISIC 79: Travel agencies and related activities
• ISIC 93: Sports, amusement, and recreation (marine recreation debris)

Waste management

• ISIC 38: Waste collection, treatment, and disposal (leakage from collection and disposal systems)

Attribution requires data on:

• Waste generation by industry sector (physical supply table)
• Waste composition linking material types to source sectors
• Industry-specific leakage rates or mismanagement proportions

Where direct industry-level data on marine litter contributions are unavailable, compilers may use waste composition data from beach litter surveys or waste characterisation studies to attribute litter to source industries through product-to-industry concordances. For example, packaging items identified in beach surveys can be mapped to the manufacturing industry that produced them (ISIC 10-12 for food packaging) and to the retail or hospitality industry that distributed them (ISIC 47, 55-56). This back-casting approach provides a practical path for countries with limited industrial waste tracking but established litter monitoring programmes.

Detailed guidance on industry classification for ocean-related activities is provided in TG-3.3 Economic Activity.

Household source attribution

Households are major sources of marine litter through:

• Consumer product disposal (packaging, single-use items)
• Littering behaviour
• Inadequate waste storage and management
• Microplastic releases (laundry, personal care products)

Household marine litter is recorded in the household sector column of the physical supply table. Attribution of household waste to product types enables upstream analysis of producer responsibility.

Geographic allocation

Marine litter accounting benefits from geographic disaggregation:

Coastal zone delineation -- Distinguishing coastal from inland areas enables focus on highest-risk locations. Coastal zone definitions should align with administrative boundaries for data availability while recognising functional connectivity to marine waters^[37]. The coastal zone delineation approaches in TG-1.2 Accounting Boundaries provide relevant guidance.

Catchment-based accounting -- River catchments as accounting units enable tracking of riverine litter pathways and attribution of marine inputs to upstream sources.

Maritime zone accounting -- Recording of sea-based source litter by location (territorial sea, EEZ, high seas) supports jurisdictional analysis and international reporting.

The SEEA CF supports sub-national disaggregation of accounts where data permit^[38]. For marine litter, priority geographic units include:

• Coastal municipalities
• River catchments with marine outlets
• Port areas and shipping lanes
• Marine protected areas and other priority conservation zones

3.7 Material Flow Account for Synthetic Marine Litter: Worked Example

This section presents a worked example of a material flow account for synthetic materials (plastics) tracking flows from production through consumption, waste generation, collection and treatment, to marine leakage. The example demonstrates how marine litter accounts integrate with broader solid waste accounting frameworks and illustrates the compilation procedure for deriving marine litter flow estimates from economic and waste statistics.

Compilation procedure overview

The compilation follows six sequential steps:

1. Identify synthetic material production and imports -- from industrial production statistics and trade data
2. Estimate synthetic material consumption -- using supply-use balancing (domestic production + imports - exports)
3. Record waste generation by sector -- from waste surveys and composition studies
4. Estimate waste collection and treatment -- from municipal and industrial waste management records
5. Model mismanaged waste -- as the difference between waste generated and waste formally collected
6. Estimate marine leakage -- applying leakage factors to mismanaged waste based on proximity to marine environment

Step 1: Synthetic material production and imports

From industrial production statistics (ISIC 20, 22) and customs trade data (HS chapters 39, 54, 55):

Step 2: Synthetic material consumption by sector

Allocation of synthetic material consumption to economic sectors using input-output relationships and consumption surveys:

Step 3: Waste generation

Plastic waste generation estimated from waste composition studies showing plastic content of municipal and industrial waste streams:

The balance between consumption (151,000 tonnes) and waste generation (104,800 tonnes) reflects:

• Multi-year product lifetimes (durable goods not immediately discarded)
• Stock accumulation in the economy (plastic products remaining in use)
• Some degradation and losses during use phase

Step 4: Waste collection and treatment

From municipal waste management records and industrial waste reporting:

Step 5: Mismanaged waste estimation

Mismanaged waste (25,800 tonnes) represents plastic waste not formally collected or improperly disposed after collection. Geographic disaggregation by coastal proximity:

Step 6: Marine leakage estimation

Application of leakage factors reflecting probability that mismanaged waste reaches marine environment:

Interpretation

This material flow account reveals:

• Collection gap: 24.6% of plastic waste is mismanaged, representing the primary intervention target for reducing marine litter
• Coastal concentration: 57% of mismanaged waste is in coastal zones where leakage probability is highest (25% vs 8% for inland)
• Sector priorities: Fishing, retail/hospitality, and households are the largest sources of plastic waste, together accounting for 62% of total plastic waste generation
• Marine leakage rate: 6,050 tonnes / 104,800 tonnes = 5.8% of plastic waste generated ultimately enters marine environment

Policy implications from this account include:

• Expanding waste collection coverage in coastal zones could reduce marine leakage by ~925 tonnes annually (assuming collection increase from 75% to 85% in coastal zone)
• Extended producer responsibility for packaging (targeting ISIC 10-11, 47) could reduce 48,000 tonnes of waste at source
• Fishing gear deposit-return schemes could recover a portion of the 1,200 tonnes of gear losses
• Improved wastewater treatment to capture microplastics could address the diffuse inland pathway

This worked example illustrates the compilation procedure for marine litter material flow accounts. Real applications would require country-specific data sources, validation of assumptions, and uncertainty assessment as described in TG-0.7 Quality Assurance.

3.8 SDG 14.1 Alignment and Multi-Target Linkages

SDG Target 14.1 states: "By 2025, prevent and significantly reduce marine pollution of all kinds, in particular from land-based activities, including marine debris and nutrient pollution"^[39]. SDG indicator 14.1.1 comprises an index of coastal eutrophication (measuring nutrient pollution) and floating plastic debris density^[40].

Indicator components

Floating plastic debris density is measured as:

• Items per square kilometre of sea surface
• Mass (grams or kilograms) per square kilometre

The indicator methodology provides for monitoring at multiple scales:

• Beach litter surveys as proxies for floating debris
• Visual surveys from vessels or aircraft
• Net-based sampling (manta trawls, neuston nets)
• Remote sensing approaches (emerging)

Index of coastal eutrophication (ICEP) addresses nutrient pollution separately from plastic debris and is not the focus of this Circular (see TG-3.4 Flows from Economy to Environment for nutrient accounting, particularly Section 3.1 on emissions to water).

Multi-target linkages

Marine litter accounts contribute to monitoring and reporting across multiple SDG targets beyond 14.1:

• SDG 12.4 (Environmentally sound management of chemicals and all wastes) -- Marine litter flow accounts quantify waste escaping management systems, directly measuring gaps in environmentally sound waste management.
• SDG 12.5 (Substantially reduce waste generation through prevention, reduction, recycling, and reuse) -- Time-series accounts track progress in reducing waste generation and improving material circularity as reflected in declining leakage rates.
• SDG 6.3 (Improve water quality by reducing pollution, eliminating dumping, and minimising release of hazardous chemicals and materials) -- Riverine litter transport estimates link land-based pollution of waterways to downstream marine impacts.

The multi-indicator framework for deriving ocean policy indicators from accounts is addressed in TG-2.7 Pollution Flows.

Alignment of accounts with SDG monitoring

Ocean Accounts for marine litter support SDG 14.1.1 reporting by:

1. Providing source attribution -- SDG monitoring tracks environmental state; accounts add information on pressures and drivers
2. Enabling trend analysis -- Time-series accounts track changes in litter generation and marine inputs
3. Supporting policy evaluation -- Accounts link litter flows to economic sectors, enabling assessment of policy interventions
4. Improving data integration -- Accounts provide a framework for combining monitoring data with waste management statistics

The relationship between accounting and monitoring is complementary:

• Monitoring provides direct observations of environmental state (debris density)
• Accounts provide modelled estimates of flows and attribution
• Together they support assessment of progress toward SDG 14.1

Indicator derivation from accounts

Marine litter accounts enable derivation of supplementary indicators:

Guidance on indicator derivation and interpretation is provided in TG-2.7 Pollution Flows.

4. Data Sources and Compilation

Compilation of marine litter and plastics accounts draws on multiple data sources. TG-4.3 Administrative Data provides detailed guidance on administrative data sources for ocean accounting.

Key data sources include:

Waste management statistics

• National waste statistics and waste composition surveys
• Municipal solid waste data from statistical offices
• Recycling and recovery rates by material type
• Industrial waste reporting

Environmental monitoring programmes

• Beach litter surveys (national programmes, OSPAR, HELCOM, regional seas conventions)
• Marine litter monitoring (at-sea surveys, research programmes)
• Microplastics monitoring (emerging programmes)
• Citizen science and clean-up organisation data

Maritime and fisheries data

• Port reception facility records (MARPOL Annex V)
• Fishing gear inventories and loss reporting
• Maritime incident databases (container losses, spills)
• Vessel tracking data (AIS) for activity intensity

Economic statistics

• Industry production data for plastic-intensive sectors
• Trade data for plastic products and materials
• Tourism statistics for visitor numbers and coastal activity

Modelling and estimation

• Waste leakage models (Jambeck methodology and derivatives)
• River transport models
• Ocean circulation and debris transport models
• Fragmentation and degradation models

International reporting

• UN Environment Programme marine litter databases
• Regional seas convention assessments
• Global Partnership on Marine Litter data

Compilation pathways and phased implementation

Data availability for marine litter accounting varies substantially across countries. Compilers may adopt a phased approach to account development:

Phase 1: Foundation -- Beach litter survey data are the most widely available starting point. Countries with established beach monitoring programmes (e.g., under OSPAR, HELCOM, or national programmes) can compile initial stock accounts for coastal compartments and use survey composition data to estimate source attribution.

Phase 2: Flow estimation -- Building on waste management statistics, compilers estimate land-based litter flows using the Jambeck methodology or national adaptations. Maritime source flows are estimated from fisheries and port data. The physical supply and use table framework (Section 3.3) provides the compilation structure.

Phase 3: Comprehensive accounts -- Integration of floating and benthic stock data, microplastics monitoring, and refined geographic disaggregation produces comprehensive stock-flow accounts. This phase requires investment in monitoring infrastructure and modelling capacity.

Guidance on data gap assessment and prioritisation is provided in TG-4.1 Data Strategy. Quality assurance considerations for marine litter accounts are addressed in TG-0.7 Quality Assurance.

5. Acknowledgements

This Circular has been approved for public circulation and comment by the GOAP Technical Experts Group in accordance with the Circular Publication Procedure.

Authors: Randika Jayasinghe, Bella Charlsworth

Reviewers: Maria Alarcon

6. References and Further Reading

This Circular should be read in conjunction with:

• SEEA Central Framework, Chapter III: Physical flow accounts, particularly section 3.6.5 on solid waste accounts^[41]
• GESAMP (2019). Guidelines for the monitoring and assessment of plastic litter in the ocean
• UNEP (2021). From Pollution to Solution: A Global Assessment of Marine Litter and Plastic Pollution
• SDG Framework, Target 14.1 and Indicator 14.1.1 methodology
• Regional seas convention marine litter monitoring protocols (OSPAR, HELCOM, Barcelona Convention, NOWPAP)
• TNFD disclosure recommendations for waste and pollution metrics^[42]
• Lau, W.W.Y. et al. (2020). Evaluating scenarios toward zero plastic pollution. Science
• Borrelle, S.B. et al. (2020). Predicted growth in plastic waste exceeds efforts to mitigate plastic pollution. Science