Marine Plastic Pollution Treaty and the Law of the Sea

1. Introduction

The marine plastic pollution treaty represents the most ambitious attempt to date to regulate plastic pollution at the global level through a legally binding instrument grounded in public international law. Negotiated under the mandate of United Nations Environment Assembly Resolution 5/14 (UNEA 2022), the treaty seeks to address plastic pollution across its full life cycle, including its impacts on the marine environment. Although the negotiations are framed within international environmental law, the treaty’s legal significance cannot be understood without careful analysis through the law of the sea. Marine plastic debris constitutes “pollution of the marine environment” within the meaning of Article 1(1)(4) of the United Nations Convention on the Law of the Sea (UNCLOS), and therefore engages the binding obligations contained in Part XII of that Convention (UNCLOS 1982).

The scale of the problem is now beyond dispute. An estimated 11 million tonnes of plastic enter the oceans annually, with projections suggesting that this figure could double by 2040 without systemic intervention (UNEP 2021). Scientific assessments demonstrate that plastics are present in every marine ecosystem, including deep-sea sediments and Arctic ice, and have entered food chains through microplastics and nanoplastics (GESAMP 2015; Jambeck et al. 2015). The environmental harm is not limited to physical entanglement or ingestion by marine species; plastics act as vectors for toxic additives and persistent organic pollutants, raising concerns for human health and marine biodiversity (Rochman et al. 2013; SAPEA 2019). The accumulation of plastic debris has therefore moved from a conservation issue to a systemic governance challenge implicating international trade, production systems, chemical regulation, fisheries, shipping, and waste management.

Despite this severity, the current international legal framework remains fragmented. UNCLOS establishes a general obligation for States to “protect and preserve the marine environment” (Article 192) and to prevent, reduce, and control pollution from land-based sources, vessels, and other activities (Articles 194, 207–212). However, UNCLOS does not prescribe concrete standards for plastic production or consumption. Instead, it requires States to adopt national laws and cooperate at the regional and global level. Sectoral treaties supplement this framework. The International Convention for the Prevention of Pollution from Ships (MARPOL) Annex V prohibits the discharge of plastics at sea (IMO 1973/1978), while the Basel Convention regulates transboundary movements of certain plastic wastes (Basel Convention 1989; COP14 2019 amendments). Yet these instruments do not regulate the upstream drivers of plastic production, product design, or chemical additives. They address disposal rather than generation.

The legal gap is particularly evident with respect to land-based sources, which account for the majority of marine plastic pollution (Jambeck et al. 2015). UNCLOS Article 207 obliges States to adopt laws to prevent pollution from land-based sources, but it leaves the content of those measures largely to domestic discretion and regional cooperation. There are no binding global caps on plastic production, no harmonized design standards, and no enforceable reduction pathways. The consequence is regulatory asymmetry: strict rules govern dumping and ship-based discharge, while the production of virgin polymers continues to expand without comparable international constraint (OECD 2022). The marine plastic pollution treaty aims to address precisely this imbalance by adopting a life-cycle approach that targets plastics at the stage of production, design, and waste management.

The decision to negotiate a legally binding instrument is itself significant in doctrinal terms. UNEA Resolution 5/14 mandates the development of an international legally binding instrument on plastic pollution, including in the marine environment, with a comprehensive life-cycle perspective (UNEA 2022). This formulation reflects the evolution of environmental governance since the 1992 Rio Conference, combining precaution, sustainable development, and differentiated responsibilities. It also raises structural questions: will the treaty function as a framework convention relying on nationally determined plans, or will it impose uniform global obligations with measurable targets? The answer will determine its capacity to operationalize the due diligence obligations already embedded in UNCLOS.

The marine plastic pollution treaty also intersects with broader principles of international environmental law. The precautionary principle has gained wide acceptance in marine environmental protection and supports early regulatory action in the face of scientific uncertainty regarding microplastics and chemical additives (Birnie, Boyle and Redgwell 2021). The principle of common but differentiated responsibilities may influence the distribution of obligations between major plastic-producing States and developing coastal States that bear disproportionate impacts (Rajamani 2006). At the same time, the treaty must remain compatible with existing obligations under international economic law, including trade and investment regimes.

A further dimension concerns the relationship between general and specialized regimes. UNCLOS Article 237 permits the conclusion of further agreements that reinforce marine environmental protection, provided they are consistent with the Convention’s objectives. The marine plastic pollution treaty, therefore, has the potential to transform the broad framework obligations of Part XII into detailed regulatory standards. This dynamic mirrors developments in other areas of ocean governance, such as the 2023 Agreement on Biodiversity Beyond National Jurisdiction (BBNJ), which elaborates conservation obligations within the UNCLOS system (UN 2023). The plastics negotiations may similarly mark a transition from framework duties to precision-based regulation in the context of marine pollution.

The urgency of the negotiations is underscored by scientific and economic assessments. The OECD estimates that global plastic production doubled between 2000 and 2019, reaching 460 million tonnes annually, with recycling rates remaining below 10 percent (OECD 2022). Without structural intervention, marine plastic stocks are projected to increase significantly, imposing ecological damage and economic losses on fisheries, tourism, and coastal communities (UNEP 2021). These findings demonstrate that voluntary initiatives and regional action plans have not achieved sufficient scale. A binding global regime is increasingly regarded as necessary to harmonize standards, reduce leakage, and align national measures.

This article examines the marine plastic pollution treaty through the lens of the law of the sea and public international law more broadly. It argues that the treaty’s effectiveness will depend on its ability to translate existing due diligence obligations under UNCLOS into concrete, enforceable, and measurable commitments that address both upstream production and downstream marine impacts. The analysis proceeds by identifying the baseline obligations under the law of the sea, assessing the fragmented regulatory landscape, and evaluating the doctrinal design choices facing negotiators. By situating the treaty within the established architecture of ocean governance, the article clarifies both its transformative potential and its structural limits.

The marine plastic pollution treaty is, therefore, not merely an environmental policy initiative; it is a structural development in the evolution of marine environmental law. Its final design will determine whether international law continues to rely on broad framework duties or advances toward precise global standards capable of addressing one of the most pervasive forms of marine pollution in the twenty-first century.

2. The Legal Mandate to Negotiate

2.1 UNEA Resolution 5/14

The negotiations for the marine plastic pollution treaty were formally launched by the United Nations Environment Assembly Resolution 5/14, adopted in March 2022. The Resolution mandates the development of “an international legally binding instrument on plastic pollution, including in the marine environment,” and specifies that the instrument should address the full life cycle of plastics (UNEA 2022). This wording is legally and politically significant. It confirms that States have opted for a binding treaty rather than a voluntary framework and that the regulatory scope extends beyond marine litter to upstream production, product design, and waste management.

Although UNEA resolutions are not themselves legally binding, they may constitute authoritative political mandates that initiate treaty negotiations under the auspices of the United Nations system (Sands et al. 2018). UNEA derives its competence from the General Assembly’s establishment of the United Nations Environment Programme (UNEP) and its mandate to promote international environmental cooperation (UNGA 1972). Resolution 5/14 does not create obligations for States directly; rather, it provides the procedural and institutional basis for negotiating a treaty that, once adopted and ratified, will generate binding commitments under international law.

The mandate’s reference to “including in the marine environment” situates the instrument within the existing law of the sea framework. Plastic pollution qualifies as pollution of the marine environment under Article 1(1)(4) of the United Nations Convention on the Law of the Sea (UNCLOS 1982). The Resolution therefore operates against a backdrop of pre-existing treaty obligations under UNCLOS Part XII, particularly Articles 192 and 194, which require States to protect and preserve the marine environment and to prevent, reduce, and control pollution from any source. The marine plastic pollution treaty is designed to elaborate on these general duties with specific standards tailored to plastics.

The life-cycle approach mandated by Resolution 5/14 also reflects developments in environmental governance. Rather than focusing exclusively on waste management or marine disposal, the mandate encompasses production, consumption, product design, and end-of-life management. This approach recognizes that most marine plastic pollution originates from land-based activities and that prevention requires intervention at earlier stages of the value chain (OECD 2022; UNEP 2021). Legally, this broad scope raises complex questions regarding sovereignty over natural resources, industrial policy, and trade regulation.

The limits of UNEA authority must also be acknowledged. UNEA cannot impose binding rules on States without their consent. The eventual legal force of the marine plastic pollution treaty will depend on adoption and ratification according to the constitutional processes of participating States, consistent with the Vienna Convention on the Law of Treaties (VCLT 1969). The Resolution establishes a negotiation process, not a pre-determined substantive outcome. States retain discretion over the final content of the treaty, and the mandate’s breadth leaves room for divergent interpretations of what constitutes a “comprehensive” life-cycle instrument.

2.2 The Institutional Framework

Resolution 5/14 established an Intergovernmental Negotiating Committee (INC) tasked with developing the marine plastic pollution treaty. The INC is composed of representatives of all Member States and operates under the rules of procedure adopted at its first session. These rules govern participation, decision-making, and the submission of draft texts. Observers, including intergovernmental organizations and accredited non-governmental organizations, may participate but do not possess voting rights.

The INC process reflects established practice in multilateral environmental treaty negotiations. Negotiations proceed through successive sessions, draft texts are consolidated by the Chair, and informal consultations address areas of disagreement. While the rules allow for decision-making by voting where consensus cannot be achieved, practice in environmental treaty negotiations strongly favors consensus adoption (Bodansky 2010). Consensus enhances perceived legitimacy and encourages broader ratification, but it may dilute ambition by requiring accommodation of divergent economic interests.

The choice of consensus has direct implications for the strength of the marine plastic pollution treaty. Major plastic-producing States and petrochemical exporters may resist production caps or binding reduction targets, while vulnerable coastal and small island developing States advocate ambitious upstream controls. The institutional framework must balance inclusivity with effectiveness. Experience from other environmental agreements demonstrates that excessive reliance on consensus can result in lowest-common-denominator outcomes, whereas carefully structured voting mechanisms can preserve legal certainty while preventing paralysis (Rajamani 2016).

Participation in the INC is universal in principle, but negotiation dynamics are shaped by geopolitical considerations and economic asymmetries. High-income States often possess greater technical expertise and negotiating capacity, while developing States may require capacity-building support to engage effectively. These disparities affect both the content of obligations and the design of financial mechanisms.

2.3 Legal Nature of the Future Instrument

The legal architecture of the marine plastic pollution treaty remains under negotiation. Several structural models are possible. The treaty could adopt the form of a framework convention, establishing general principles and requiring States to submit nationally determined action plans. Alternatively, it could incorporate binding global standards, quantitative targets, or annex-based technical regulations subject to amendment procedures. A hybrid structure combining framework obligations with protocols or technical annexes is also conceivable.

Each model carries distinct legal consequences. A framework convention approach, similar to the United Nations Framework Convention on Climate Change, emphasizes flexibility and national discretion. It may facilitate broad participation but risks uneven implementation and limited enforceability (Bodansky, Brunnée and Rajamani 2017). A more prescriptive regulatory instrument, by contrast, would impose harmonized obligations and could reduce competitive distortions in plastic production and trade. However, such precision may deter ratification by States concerned about economic impacts.

The treaty’s design will also affect compliance and interpretation. If obligations are framed in general terms, compliance assessment may rely primarily on reporting and peer review mechanisms. Detailed annexes with technical standards could enable clearer evaluation of performance but require dynamic amendment procedures to accommodate scientific and technological developments. The Vienna Convention on the Law of Treaties provides interpretive guidance, requiring that treaty terms be interpreted in good faith in accordance with their ordinary meaning and in light of the treaty’s object and purpose (VCLT 1969, Article 31). The more precise the treaty text, the more predictable its interpretation will be.

Another unresolved question concerns dispute settlement. The marine plastic pollution treaty may establish its own compliance committee or dispute resolution mechanism, or it may rely on general international law and, where applicable, UNCLOS Part XV procedures. If the treaty is explicitly linked to UNCLOS obligations, questions may arise regarding the jurisdiction of the International Tribunal for the Law of the Sea or arbitral tribunals in cases involving marine pollution.

Ultimately, the legal nature of the future instrument will determine whether the marine plastic pollution treaty functions primarily as a coordination framework or as a transformative regulatory regime. Its structural design will shape the extent to which it operationalizes existing law of the sea duties and establishes enforceable global standards capable of addressing the systemic drivers of plastic pollution.

3. The Law of the Sea Baseline

3.1 The Duty to Protect the Marine Environment

Any assessment of the marine plastic pollution treaty must begin with the binding framework already established by the United Nations Convention on the Law of the Sea (UNCLOS). Articles 192–194 form the normative core of marine environmental protection under international law. Article 192 imposes a general obligation on States to “protect and preserve the marine environment.” This provision is not programmatic language; it is a binding obligation of conduct applicable to all States Parties (UNCLOS 1982).

Article 194 elaborates this duty by requiring States to take “all measures consistent with this Convention that are necessary to prevent, reduce and control pollution of the marine environment from any source.” The phrase “from any source” is expansive and includes land-based pollution, vessel-source pollution, dumping, seabed activities, and atmospheric inputs. Plastic debris entering the oceans through rivers, coastal mismanagement, or maritime activities clearly falls within this formulation.

The International Tribunal for the Law of the Sea (ITLOS) has clarified that obligations under Part XII are obligations of due diligence rather than strict liability standards. In its Advisory Opinion on Responsibilities and Obligations of States Sponsoring Persons and Entities with Respect to Activities in the Area, the Tribunal held that due diligence requires States to adopt and enforce appropriate laws and administrative measures and to exercise a level of vigilance commensurate with the risk involved (ITLOS 2011). Due diligence is not static; it evolves in light of scientific knowledge and technological capacity.

Applied to plastic pollution, this interpretation implies that States must adopt regulatory measures capable of addressing foreseeable marine harm, including harm caused by microplastics and chemical additives once such risks are scientifically established. The duty is complemented by the principle of prevention of transboundary harm, reflected in customary international law and affirmed by the International Court of Justice in cases such as Pulp Mills on the River Uruguay (ICJ 2010). States must ensure that activities within their jurisdiction or control do not cause significant damage to the marine environment of other States or to areas beyond national jurisdiction.

Articles 207–212 further require States to adopt laws and regulations addressing specific pollution sources and to cooperate at regional and global levels. These provisions confirm that the marine plastic pollution treaty does not create the duty to regulate plastics; rather, it may define the content of that pre-existing obligation with greater precision.

3.2 Land-Based Sources under UNCLOS

Land-based sources account for the majority of marine plastic pollution. UNCLOS Article 207 addresses this category directly, requiring States to adopt laws and regulations to prevent, reduce, and control pollution of the marine environment from land-based sources, including rivers, pipelines, and outfalls. States are further required to take into account internationally agreed rules, standards, and recommended practices and procedures.

However, Article 207 does not establish specific global standards. It leaves the substance of regulation largely to domestic legal systems and regional arrangements. Unlike vessel-source pollution, where MARPOL provides detailed global rules, there is no equivalent global convention prescribing quantitative limits on plastic production or leakage into waterways.

This structural weakness reflects the historical context of UNCLOS negotiations, which prioritized navigational freedoms and seabed governance over comprehensive land-based pollution control. As a result, the regime relies heavily on national implementation and regional seas conventions (Tanaka 2019). Regional agreements, such as those under the Regional Seas Programme, have adopted action plans on marine litter, but their effectiveness varies significantly depending on political will and institutional capacity.

The reliance on domestic legislation has produced uneven regulatory outcomes. Some States have adopted bans on certain single-use plastics, extended producer responsibility schemes, and recycling targets, while others lack basic waste management infrastructure (OECD 2022). The absence of harmonized standards creates regulatory gaps and competitive distortions in global plastic production and trade.

The marine plastic pollution treaty seeks to address this deficit by establishing common obligations that give operational content to Article 207. By setting binding global requirements or harmonized standards, the treaty could transform a broadly framed obligation of conduct into measurable commitments capable of reducing land-based leakage into the marine environment.

3.3 Vessel-Source Pollution

Plastic pollution also arises from maritime activities, including accidental loss of containers, illegal discharge of waste, and abandonment of fishing gear. UNCLOS Articles 211 and 217 regulate vessel-source pollution and allocate jurisdiction among flag, coastal, and port States. These provisions operate in conjunction with the International Convention for the Prevention of Pollution from Ships (MARPOL).

MARPOL Annex V prohibits the discharge of plastics into the sea from ships, without exception (IMO 1973/1978). This prohibition covers synthetic ropes, fishing nets, plastic garbage bags, and incinerator ashes from plastic products. The regime represents one of the clearest global bans on marine plastic disposal.

Enforcement, however, depends primarily on flag State jurisdiction. Under UNCLOS Article 217, flag States must ensure that vessels flying their flag comply with applicable international rules and standards. Coastal States may exercise limited enforcement powers within their territorial sea and exclusive economic zone under Articles 220 and 218, while port States may inspect vessels voluntarily entering their ports.

In practice, enforcement gaps persist. Flag States with limited capacity or weak oversight may fail to ensure compliance. Coastal State jurisdiction in the exclusive economic zone is constrained by evidentiary thresholds and navigational freedoms. Port State control has emerged as an important compliance tool, but inspections are resource-intensive and cannot eliminate all violations.

Moreover, MARPOL addresses discharge at sea but does not regulate the upstream production of plastics used in maritime industries. Lost or abandoned fishing gear, often referred to as “ghost gear,” remains a significant source of marine debris (FAO 2018). A comprehensive marine plastic pollution treaty could strengthen obligations regarding gear marking, retrieval schemes, and reporting requirements, thereby reinforcing existing vessel-source pollution controls.

3.4 Relationship with Other Agreements

UNCLOS Article 237 explicitly recognizes that the Convention’s provisions on marine environmental protection are without prejudice to specific obligations undertaken under special conventions and agreements that further the protection of the marine environment. This clause allows for the development of additional treaties that elaborate or strengthen Part XII obligations, provided they remain compatible with the Convention’s objectives.

The marine plastic pollution treaty must therefore operate within this systemic framework. It cannot diminish rights and obligations established under UNCLOS, such as navigational freedoms or jurisdictional allocations. At the same time, it may specify substantive standards that give practical effect to the general duties of prevention and due diligence.

Compatibility also extends to other environmental instruments. The Basel Convention regulates transboundary movements of plastic waste, and its 2019 amendments expanded control procedures for certain plastic categories (Basel Convention 1989; COP14 2019). A marine plastic pollution treaty must coordinate with Basel to avoid duplication or normative conflict. Similarly, it must complement MARPOL rather than create parallel maritime discharge standards.

International environmental law increasingly operates through regime complexes composed of overlapping agreements (Keohane and Victor 2011). The effectiveness of the marine plastic pollution treaty will depend on its capacity to integrate with existing instruments while addressing regulatory gaps. Its legal design should reinforce, clarify, and operationalize pre-existing obligations under UNCLOS rather than create fragmentation.

By situating the marine plastic pollution treaty within the law of the sea baseline, it becomes clear that the negotiations are not occurring in a legal vacuum. The treaty represents an effort to convert established but broadly framed obligations into a structured and enforceable global regime capable of addressing one of the most pervasive sources of marine environmental degradation.

4. Fragmentation in Marine Plastic Governance

4.1 Shipping Regulation

International shipping regulation provides the clearest set of binding rules that directly address plastics in the marine environment, but its scope is structurally limited. The core instrument is MARPOL, adopted under the International Maritime Organization (IMO). MARPOL Annex V prohibits the discharge of plastics from ships into the sea, covering synthetic ropes, fishing nets, plastic garbage bags, and residues from plastic products (IMO 1973/1978). This is a major strength: it establishes a uniform global standard for ship-generated plastic garbage and frames discharge as unlawful conduct rather than a discretionary practice.

MARPOL’s second strength is operationalization through shipboard garbage management systems and port reception facility requirements, which create compliance pathways beyond abstract prohibitions. In legal terms, Annex V functions as a “generally accepted international rule or standard,” relevant to coastal and port state enforcement powers under UNCLOS Articles 211 and 220 (UNCLOS 1982; Tanaka 2019). This gives the regime practical bite, especially when port state control is used effectively.

The limits are equally clear. First, MARPOL is a ship-source instrument. It cannot regulate land-based leakage, the upstream production of plastics, product design, or waste systems, which dominate marine plastic inputs (UNEP 2021; OECD 2022). Second, enforcement relies heavily on flag state control, which is uneven in practice due to capacity constraints and divergent incentives among flag registries (Tanaka 2019). Third, MARPOL does not fully capture major sea-based plastic pathways that are not well characterized as “discharge,” such as accidental container losses during storms, losses during cargo handling, and abandoned, lost, or otherwise discarded fishing gear, which often falls within fisheries governance rather than classic ship-garbage paradigms (GESAMP 2015; FAO 2018). Fourth, MARPOL’s compliance architecture is not designed to handle life-cycle accountability. It addresses disposal behaviour at sea, not the material flows that generate persistent plastic stocks in the ocean.

Dumping conventions partially fill gaps for intentional disposal, but do not solve the problem. The London Convention (1972) and the London Protocol (1996) regulate the deliberate disposal of wastes at sea. Their strength is a clear jurisdictional focus: dumping is treated as a controlled activity requiring permitting and prohibition for certain categories (IMO 1972; IMO 1996). Their limits in the plastics context are fundamental. Dumping is not the dominant source of marine plastics. Most plastic debris reaches the ocean through land-based pathways, fragmented coastal management, and diffuse leakage. Even for sea-based inputs, the most significant plastic pathways often occur as operational losses, poor waste handling, and gear loss rather than licensed dumping. The dumping regime, therefore, addresses a legally important but empirically narrower slice of the plastics problem (UNEP 2021; GESAMP 2015).

This creates a fragmentation problem: the strictest binding rules target ship discharge and dumping, while the largest sources remain weakly regulated or regulated through dispersed national measures. A marine plastic pollution treaty must be drafted to reinforce existing maritime rules without duplicating them and to connect sea-based measures (ports, fisheries, shipping) with upstream controls that reduce plastic generation.

4.2 Waste Trade Regulation

Waste trade regulation is central to marine plastic governance because the transboundary movement of plastic waste can externalize environmental risks and amplify leakage when recipient states lack adequate waste management capacity. The Basel Convention provides the global framework for controlling transboundary movements of hazardous wastes and other wastes through prior informed consent and environmentally sound management obligations (Basel Convention 1989). The 2019 plastic waste amendments expanded controls on certain plastic wastes, introducing stricter consent requirements and clearer classification of plastic waste streams (Basel COP 2019). This is a major legal development: it shifts plastic waste trade away from an assumption of permissibility and toward a permission-based system grounded in transparency and consent.

The strengths of the Basel amendments include: (i) a clearer legal basis for regulating mixed, contaminated, and difficult-to-recycle plastic wastes; (ii) enhanced information duties for exporters and importing states; and (iii) stronger alignment with environmentally sound management standards as a compliance expectation (Basel Convention 1989; Basel COP 2019). These elements can reduce shipments that function as disguised disposal and can constrain the export of high-leakage waste streams, which can indirectly reduce marine pollution.

The limits are jurisdictional and practical. Basel regulates transboundary movements, not domestic plastic generation or national waste systems. It cannot solve leakage within a state’s territory or address the upstream production and design decisions that create hard-to-manage waste. It is also reactive: it governs waste once created and classified as such. For plastics, the most effective legal leverage often lies earlier in the chain—design standards, chemical restrictions, producer responsibility, and reduction measures—areas outside Basel’s traditional mandate (OECD 2022; UNEP 2021).

Enforcement challenges are persistent. Compliance depends on customs capacity, accurate classification, and reliable documentation. Illegal trafficking and misdeclaration can bypass prior informed consent procedures, and enforcement varies widely among states (UNEP 2021). Jurisdictionally, Basel’s controls attach to “movements,” but major leakage can occur before waste is formally designated, during internal transport, or after import through mismanaged processing. A marine plastic pollution treaty that aims to address the full life cycle could complement Basel by (i) harmonizing traceability standards, (ii) requiring producer-financed end-of-life systems, and (iii) setting minimum waste-management performance benchmarks, reducing incentives for waste export as a substitute for domestic system building.

A further fragmentation issue is normative overlap: trade-related measures in a plastics treaty must be coordinated with Basel classifications to avoid conflicting definitions and compliance burdens. If the plastics treaty introduces product bans, polymer restrictions, or extended producer responsibility requirements, it should specify how these interact with Basel’s waste categories and consent procedures to avoid loopholes and duplicative reporting.

4.3 Regional Seas Instruments

Regional seas instruments are often the most operationally grounded layer of marine environmental governance, but they are uneven and cannot substitute for global harmonization. Through UNEP’s Regional Seas Programme and associated regional conventions and protocols, states have adopted action plans addressing marine litter, plastic waste management, port reception facilities, fishing gear management, and monitoring initiatives (UNEP 2021). Their key strength is contextual specificity: regions can target major pathways such as riverine inputs, tourism-driven waste, or fishing gear losses and can coordinate neighbouring states around shared ecosystems and shared enforcement problems.

Regional instruments can also reduce collective-action problems by creating shared monitoring frameworks, joint targets, and cooperative enforcement programmes, making them especially relevant for semi-enclosed seas and areas with intense coastal use. They also provide platforms for technical assistance and capacity building, which is decisive for implementation in states facing infrastructure constraints (UNEP 2021).

The limits are structural. Regional seas regimes vary in legal form, institutional strength, and funding. Some operate with robust secretariats and compliance-oriented practices; others rely on soft-law action plans with limited reporting and weak follow-up. This unevenness produces patchwork protection, where high-ambition regions can reduce leakage while neighbouring regions with weaker capacity remain major sources of marine plastic inflows. Plastic pollution is transboundary by nature; currents, shipping routes, and waste trade connect regions. A purely regional approach cannot adequately address upstream production, global markets, or cross-regional waste flows (GESAMP 2015; OECD 2022).

A second limit is the absence of harmonized standards. Without global minimum rules on product design, polymer additives, producer responsibility, and measurement methodologies, regional regimes risk incompatible metrics and non-comparable reporting. This undermines accountability and weakens incentives for industry transformation across global supply chains. A marine plastic pollution treaty can function as a floor-setting instrument—establishing baseline definitions, monitoring standards, and minimum obligations—while allowing regions to adopt stricter measures tailored to local conditions.

The necessity of global harmonization follows from three practical realities. First, plastics are produced and traded through global value chains, so regulatory impact requires common standards that influence manufacturing and product design at scale. Second, marine ecosystems are interconnected, so regional success can be offset by external inflows. Third, capacity gaps are uneven, so a global instrument is needed to operationalize finance, technology transfer, and assistance mechanisms in a coordinated way rather than leaving them to ad hoc regional initiatives (UNEP 2021; OECD 2022). This is the core fragmentation diagnosis that the marine plastic pollution treaty is expected to address.

5. Core Regulatory Choices

5.1 Scope and Definitions

For the marine plastic pollution treaty, definitional choices will decide the treaty’s real regulatory reach. In treaty practice, definitions are not neutral drafting details; they determine what activities are covered, what obligations are triggered, and how compliance can be measured. Ambiguous definitions allow evasion, complicate domestic implementation, and weaken dispute settlement and compliance review (VCLT 1969; Bodansky 2010).

A first question is what counts as “plastic.” A narrow, polymer-centric definition may fail to capture blends, composites, and plastics with bio-based content that behave similarly in the marine environment. A broad definition can capture polymers regardless of feedstock but must avoid sweeping in materials that do not create comparable persistence or harm, which could undermine political feasibility. The treaty’s scope must also decide whether to cover all plastic polymers or only certain categories, and whether “plastic products” includes packaging, textiles, tyres, agricultural plastics, and industrial pellets, each of which is associated with distinct leakage pathways (OECD 2022; UNEP 2021).

Microplastics present a second definitional test. If the treaty defines microplastics solely by size thresholds, it must still address two distinct categories: (i) intentionally added microplastics (microbeads, abrasives) and (ii) secondary microplastics formed through fragmentation of larger items and abrasion (textiles, tyres). The treaty’s capacity to regulate microplastics depends on whether it treats intentional use as a direct prohibition issue and abrasion-based microplastics as a design-and-performance regulation issue (GESAMP 2015; SAPEA 2019). If the treaty treats microplastics purely as “waste,” it will miss major sources, because many microplastics are emitted during normal product use rather than at end-of-life.

Definitions of “polymers” and “additives” will also be central. Many plastics contain chemical additives that influence durability, colour, flexibility, and flame resistance. Some additives present toxicity risks and complicate recycling. If additives are not within scope, the treaty may fail to address chemical drivers of harm and circularity constraints. A treaty that aims for life-cycle control must align definitions with chemical governance and ensure that obligations can cover problematic additives without depending on fragmented domestic chemical controls (UNEP 2021; Rochman et al. 2013).

Finally, “waste” definitions matter because many legal obligations attach to the moment a material becomes waste. The treaty must decide whether it adopts Basel Convention concepts, creates an autonomous definition, or uses functional concepts linked to leakage risk. Misalignment with Basel categories may create compliance burdens and loopholes in trade and reporting (Basel Convention 1989; Basel COP 2019). The treaty must also define “leakage,” “environmentally sound management,” and “legacy pollution” if it aims to address existing marine stocks, not only future flows.

5.2 Production Controls

Production controls are the most contested regulatory choice in the marine plastic pollution treaty negotiations because they directly implicate industrial policy, natural resource sovereignty, and economic strategy. Yet they are also the most important for effectiveness. If global plastic production continues to rise, downstream waste measures are likely to be outpaced by volume growth, especially in jurisdictions with limited infrastructure (OECD 2022; UNEP 2021).

Legally, caps or reduction pathways for virgin polymer production can be framed as obligations of conduct rather than result, consistent with due diligence approaches in environmental treaties. States could commit to adopting domestic measures designed to achieve reduction targets, leaving policy instruments to national choice. Another model is the Montreal Protocol approach: binding reduction schedules for listed products, paired with financial support and differentiated timelines. This model is legally feasible but politically difficult due to the centrality of plastics to consumer goods and industrial supply chains (Bodansky 2010; Sands et al. 2018).

Sovereignty concerns will be raised through the principle of permanent sovereignty over natural resources and states’ control over their industrial development pathways (UNGA 1962). Producer states may argue that binding caps infringe economic sovereignty. However, international law permits states to undertake self-limiting commitments by treaty, and such commitments are common in environmental regimes when transboundary harm is at stake (VCLT 1969; ICJ 2010). The doctrinal argument for production controls is strongest when linked to the prevention of transboundary harm and the duty to protect the marine environment already established under UNCLOS Articles 192–194 (UNCLOS 1982; ITLOS 2011).

Trade implications must be addressed. Production caps could affect supply and prices and may encourage industry relocation unless obligations apply broadly. Border measures or product standards can raise compatibility issues under WTO law, particularly the General Agreement on Tariffs and Trade (GATT) rules on non-discrimination and quantitative restrictions (WTO 1994). The treaty must therefore be drafted with careful attention to designing non-discriminatory product standards and ensuring legitimate environmental objectives are clearly embedded. This is not a barrier to regulation; it is a drafting discipline. Environmental exceptions under GATT Article XX have been used to justify trade-restrictive measures when they are not arbitrary or disguised restrictions (WTO Appellate Body 1998; WTO Appellate Body 2001).

5.3 Product Design and Phase-Outs

Product design obligations translate the treaty’s life-cycle approach into concrete prevention tools. Phase-outs or bans on “problematic and avoidable” plastic products are among the most direct measures available, especially for items with low utility, high leakage risk, and available substitutes. Legally, bans are a classic regulatory method in environmental treaties, but their durability depends on clear criteria, annex-based listing mechanisms, and procedures for scientific updating (Bodansky 2010).

Design standards can address leakage at source. Requirements for reusability, refill systems, durability, and recyclability directly reduce waste generation and environmental dispersion. Design rules can also target major microplastic sources, such as synthetic textiles and tyres, by mandating abrasion standards, filtration requirements, or performance thresholds (SAPEA 2019; UNEP 2021). If the treaty only targets end-of-life measures, it will fail to reduce abrasion-based emissions that occur during normal use.

Reuse obligations and packaging reduction rules raise implementation challenges but offer measurable outcomes. Treaty design can require national action plans to meet quantified packaging reduction targets, supported by reporting and review. Extended producer responsibility (EPR) schemes can be anchored in treaty obligations requiring producers to finance collection and treatment, internalizing costs that are otherwise externalized to municipalities and coastal communities (OECD 2022). A treaty that makes EPR optional risks preserving the current misalignment between production incentives and disposal burdens.

5.4 Waste Management Obligations

Waste management obligations are necessary but insufficient on their own. In the marine plastic pollution treaty, the legal challenge is to define minimum performance standards that are ambitious yet realistic across diverse state capacities. Obligations may include universal waste collection targets, safe disposal requirements, controlled landfilling standards, and restrictions on open dumping and uncontrolled burning (UNEP 2021). These measures directly reduce leakage into rivers and coastal systems.

Recycling obligations require particular caution. Many policy narratives treat recycling as a primary solution, but recycling rates remain low globally, and material downgrading and contamination limit circularity (OECD 2022). A treaty that mandates recycling without addressing upstream design and additive restrictions may push states toward symbolic targets rather than effective leakage prevention. Legally, waste obligations should focus on leakage prevention and environmentally sound management, while recycling targets should be linked to design standards and realistic market capacity.

Developing state capacity constraints are central. Many states lack infrastructure for collection, sorting, and safe disposal. Under international environmental law, differentiated implementation timelines, capacity-building, and financial mechanisms are standard approaches to align ambition with feasibility (Sands et al. 2018; Rajamani 2006). If the treaty imposes uniform obligations without finance and technology transfer, it will replicate the implementation failures seen in other regimes. If it relies only on voluntary assistance, it will not overcome structural deficits. The treaty’s waste management chapter must therefore connect substantive duties with institutional support.

5.5 Fisheries and Maritime Obligations

Fisheries and maritime measures address a distinct set of sea-based plastic pathways that are not fully captured by ship garbage rules. Lost and abandoned fishing gear is a major contributor to macroplastic pollution and can continue to harm marine life for years through ghost fishing (FAO 2018). A marine plastic pollution treaty can reinforce this area through binding obligations on gear marking, reporting of gear loss, retrieval requirements where feasible, and financing systems that incentivize return and proper disposal.

Port reception facilities are another critical node. Even with MARPOL’s discharge ban, vessels require practical disposal options. Where port reception facilities are inadequate or costly, incentives for illegal disposal increase (IMO 1973/1978). The treaty can require states to ensure adequate reception infrastructure, transparency on fees, and monitoring of port waste flows. It can also strengthen cooperation on inspection and enforcement to support port state control.

Monitoring obligations must be realistic and harmonized. Marine plastics monitoring involves beach litter surveys, riverine inputs measurement, at-sea observations, and microplastics sampling. Without standard methods, data will not be comparable and compliance review will be weak (GESAMP 2015; UNEP 2021). The treaty can establish standardized indicators and require national monitoring plans with periodic reporting. It can also require cooperation through regional bodies to pool resources and harmonize methodologies, linking back to UNCLOS cooperation duties and to regional seas structures.

The maritime and fisheries chapter is where the treaty can most directly connect the law of the sea baseline to new operational obligations. It can strengthen compliance with existing maritime rules while extending regulatory reach into fisheries gear and port waste systems—areas where current fragmentation has left persistent gaps.

6. Compliance and Enforcement

6.1 Reporting and Monitoring

For the marine plastic pollution treaty, compliance credibility will depend less on symbolic commitments and more on the ability to measure performance consistently across jurisdictions. Reporting and monitoring are therefore not auxiliary administrative features; they are the enforcement backbone of a global regime where violations are often diffuse, incremental, and difficult to attribute to a single actor or incident (Bodansky 2010).

A treaty-level transparency system typically has four elements: (i) legally defined reporting duties; (ii) standardized indicators and methodologies; (iii) independent or peer review of reports; and (iv) public accessibility sufficient to generate reputational pressure. This architecture has become central to modern environmental regimes because it enables verification and accountability without relying exclusively on adversarial enforcement (Bodansky, Brunnée and Rajamani 2017).

Data harmonization is decisive for plastic pollution because inputs and stocks vary widely by pathway. The treaty’s monitoring framework must distinguish between at least four categories: (a) production and consumption metrics; (b) waste collection and treatment performance; (c) leakage proxies (mismanaged waste, riverine inputs, coastal hotspots); and (d) environmental presence indicators (beach litter, seabed debris, microplastics concentration). Without this differentiation, states can report high recycling initiatives while leakage remains unchanged, or report waste collection improvements while upstream production accelerates (OECD 2022; UNEP 2021).

Marine litter indicators require standard definitions and survey protocols. Existing practice includes beach litter monitoring, floating macro-litter surveys, seabed trawl surveys, and microplastics sampling. Each method has biases and cost implications. The treaty can address this by adopting annexed technical standards or guidance adopted by a conference of parties, enabling updating as science evolves. The legal advantage of annex-based standards is interpretive clarity: once a methodology is agreed, reported data becomes comparable and disputes about measurement are reduced (VCLT 1969; Tanaka 2019).

Transparency rules also have a jurisdictional function. Plastic pollution is transboundary and often affects areas beyond national jurisdiction. Monitoring obligations that include reporting on riverine inputs, coastal discharges, and maritime sources can support the due diligence duty under UNCLOS Part XII by demonstrating whether states are adopting and enforcing appropriate measures commensurate with risk (UNCLOS 1982; ITLOS 2011). When reporting reveals persistent high leakage, it can trigger engagement by the compliance committee, targeted assistance, or dispute settlement pathways.

The most common weakness in environmental monitoring regimes is not the absence of obligations but the absence of capacity. For many developing coastal states, the limiting factor is infrastructure for data collection, laboratories, and trained staff. A credible treaty monitoring system must therefore be linked to capacity-building, finance, and technical assistance obligations; otherwise reporting duties will become formalities rather than enforcement tools (UNEP 2021; Rajamani 2006).

6.2 Compliance Mechanisms

The main institutional choice for the marine plastic pollution treaty is between facilitative compliance and enforcement-based compliance. Most modern multilateral environmental agreements lean toward facilitative structures because they are politically acceptable and can improve implementation across diverse capacities. However, facilitative systems can be toothless if they do not impose consequences for persistent non-compliance or if they lack independence and transparency (Bodansky 2010).

A facilitative compliance committee typically has a non-adversarial mandate: it reviews reports, identifies implementation gaps, recommends corrective actions, and links states to technical assistance and finance. The compliance logic is managerial: non-compliance is often attributed to capacity constraints, lack of information, or institutional barriers rather than deliberate breach. This model is consistent with the life-cycle scope of plastics because implementation requires domestic regulatory overhaul, infrastructure investment, and industry transformation (Bodansky, Brunnée and Rajamani 2017).

An enforcement-based approach would include stronger tools, such as legally defined consequences for non-compliance, trade-related measures, or suspension of treaty privileges. In practice, environmental treaties rarely impose punitive sanctions comparable to those in trade regimes, but they can exert strong compliance leverage indirectly. Examples include conditional access to financial mechanisms, reputational consequences through public findings of non-compliance, or restrictions on certain activities unless minimum standards are met. Such approaches can increase treaty credibility but may reduce ratification rates, especially among major plastic producers and states concerned about economic competitiveness.

The plastics context raises a specific enforcement challenge: the principal regulated actors include corporations and supply chains, yet international treaties bind states. The treaty, therefore, needs compliance mechanisms that incentivize states to regulate private actors effectively. This can be done through: (i) legally binding national implementation obligations (for example, mandatory extended producer responsibility laws); (ii) product standards enforced at borders; and (iii) reporting obligations that require disclosure of producer compliance and market surveillance results. These tools create enforceability through domestic legal systems rather than direct treaty sanctions (OECD 2022; UNEP 2021).

A balanced model is likely the most legally sustainable: a facilitative compliance committee paired with clear minimum obligations, measurable indicators, and the possibility of escalated procedures for persistent non-compliance. Escalation can include intensified review, compliance action plans, targeted capacity support, and ultimately referral to dispute settlement. The core point is that facilitation without escalation becomes voluntarism.

6.3 Dispute Settlement

Dispute settlement design will be a decisive indicator of how “legal” the marine plastic pollution treaty will be in practice. There are three main options: (i) no treaty-specific dispute settlement, relying on general international law and diplomatic channels; (ii) optional dispute settlement, such as arbitration or adjudication by consent; or (iii) compulsory procedures, similar to those under UNCLOS Part XV for law of the sea disputes.

Environmental treaties often avoid compulsory dispute settlement because states prefer cooperative implementation and fear litigation over complex scientific evidence. Nevertheless, the absence of meaningful dispute settlement can weaken compliance, particularly where state conduct causes transboundary marine harm (Sands et al. 2018). Plastic pollution disputes are difficult but not impossible: they can concern failure to adopt required domestic measures, systematic leakage affecting neighbouring states, illegal waste exports, or non-compliance with product bans and standards.

If the treaty is drafted as an instrument that elaborates and operationalizes UNCLOS Part XII obligations, an important question is whether UNCLOS dispute settlement can indirectly apply. UNCLOS Part XV provides compulsory dispute settlement for disputes concerning the interpretation or application of the Convention, subject to certain limitations. If a plastics treaty is framed as implementing obligations already required under UNCLOS Articles 192–194 and 207, a claimant state might argue that persistent failure to regulate constitutes a breach of UNCLOS itself, bringing the dispute within UNCLOS tribunals. However, this strategy depends on jurisdictional framing and the claimant’s ability to establish a sufficient legal nexus between plastic pollution harm and UNCLOS obligations (UNCLOS 1982; Tanaka 2019).

A treaty-specific compulsory dispute settlement clause would strengthen enforceability but may reduce political feasibility. A more realistic approach is a tiered system: consultation and negotiation first, followed by optional arbitration or adjudication, with compliance committee procedures operating in parallel. The treaty could also include provisions encouraging the use of existing forums, including ITLOS, where disputes overlap with law of the sea obligations, while preserving state consent boundaries.

In doctrinal terms, the core trade-off is predictable. Compulsory dispute settlement increases legal certainty and deterrence but raises ratification barriers and can shift treaty politics toward defensive drafting. Optional dispute settlement preserves flexibility but risks undermining compliance for high-impact states. Given the scale of marine plastic pollution and the likely economic stakes, a treaty without meaningful dispute settlement may struggle to generate credible incentives for upstream change.

7. Common but Differentiated Responsibilities

7.1 Historical Contribution and Equity

The principle of common but differentiated responsibilities (CBDR) occupies a central position in contemporary environmental treaty-making and is likely to shape the final architecture of the marine plastic pollution treaty. CBDR recognizes that all States share responsibility for addressing environmental harm, but that obligations may differ in light of historical contribution, capacity, and levels of development (Rio Declaration 1992; Rajamani 2006).

Plastic pollution presents a complex equity landscape. Historically, high-income States have dominated plastic production, consumption, and petrochemical development. They have also exported significant volumes of plastic waste, often to developing countries lacking adequate waste management infrastructure (OECD 2022; Basel Convention 1989). This has created asymmetries in environmental burden: coastal and riverine states with limited capacity frequently bear the ecological consequences of mismanaged plastic imports and global consumption patterns (UNEP 2021).

CBDR in the plastics context can be grounded in two distinct but related rationales. The first is a historical contribution. States that have contributed disproportionately to cumulative plastic production and global waste flows may be expected to assume stronger obligations, including earlier implementation timelines, deeper production reductions, or higher financial contributions. The second is capacity-based differentiation. Even if contemporary plastic production is geographically diversified, the ability to regulate production, redesign products, and implement waste systems varies significantly among States (Rajamani 2006; Sands et al. 2018).

Applying CBDR to the marine plastic pollution treaty does not necessarily imply legally binding quotas based strictly on historical tonnage. Rather, differentiation can be operationalized through phased implementation schedules, conditional obligations linked to capacity, or enhanced reporting and mitigation duties for major producers. This approach has precedent in climate governance and ozone protection regimes, where differentiated timetables and financial mechanisms enabled broader participation while maintaining substantive ambition (Bodansky, Brunnée and Rajamani 2017).

Waste exports are a particularly sensitive equity issue. Even with Basel Convention controls, trade in plastic waste has externalized environmental risks to states with weaker regulatory oversight (Basel Convention 1989; OECD 2022). The marine plastic pollution treaty can address this by requiring exporting states to ensure that exported plastic waste is managed in an environmentally sound manner, and by linking export permissions to demonstrated capacity in recipient states. Such measures would give operational meaning to CBDR by reducing the transfer of environmental risk across borders.

At the same time, CBDR must be balanced against the principle that marine environmental protection is a shared obligation under UNCLOS Articles 192–194. Differentiation should not become a basis for indefinite exemption from core duties. The legal challenge is to calibrate obligations in a manner that recognizes structural inequities while maintaining universal baseline standards. If differentiation is too weak, it risks perpetuating environmental injustice. If it is too rigid, it may undermine treaty cohesion and compliance incentives.

7.2 Financial Mechanisms

Financial architecture will determine whether the marine plastic pollution treaty can translate legal commitments into implementation. Waste management infrastructure, recycling systems, monitoring laboratories, and regulatory oversight require sustained investment. Without dedicated financial mechanisms, ambitious obligations risk remaining aspirational, particularly in low-income and small island developing States that face acute marine impacts (UNEP 2021).

Several funding models are available. One option is a dedicated multilateral fund financed by assessed or voluntary contributions from States, potentially weighted by production levels or economic capacity. This model mirrors the Multilateral Fund under the Montreal Protocol, which has supported compliance in developing countries through predictable financing (Sands et al. 2018). A second option is integration with existing financial institutions, such as the Global Environment Facility, which already supports marine and waste-related projects. A third approach is hybrid financing, combining public contributions with private-sector obligations, particularly through extended producer responsibility schemes.

Technology transfer and capacity-building are closely linked to financial support. Article 202 of UNCLOS already calls for scientific and technical assistance to developing States in marine environmental protection (UNCLOS 1982). The marine plastic pollution treaty can operationalize this provision by mandating cooperation in waste management technologies, recycling innovation, monitoring methodologies, and alternative material development. Capacity-building obligations may include training programs, institutional strengthening, and support for regulatory drafting.

An important question is whether financial contributions should be legally binding or voluntary. Binding contributions enhance predictability but may deter ratification by major economies. Voluntary pledges are politically easier but often insufficient and unpredictable. A compromise approach could establish binding commitments for certain categories of States combined with replenishment cycles and oversight mechanisms, similar to climate and ozone regimes (Bodansky, Brunnée and Rajamani 2017).

Private-sector financing also warrants attention. Because plastic production is concentrated among identifiable corporations and supply chains, the treaty can require national legislation establishing extended producer responsibility systems that internalize waste management costs. This shifts financial burden from public budgets to producers and consumers and aligns economic incentives with environmental objectives (OECD 2022). International coordination of EPR standards reduces the risk of regulatory arbitrage and industry relocation.

Equitable finance is not a peripheral issue; it is structurally linked to compliance. Without adequate funding, developing States may struggle to meet monitoring, reporting, and waste management obligations, undermining both environmental outcomes and treaty legitimacy. The financial mechanism must therefore be integrated into the treaty’s compliance system, ensuring that failure to implement due to lack of capacity triggers assistance rather than automatic non-compliance findings.

In doctrinal terms, financial and capacity-building provisions reflect both CBDR and the cooperative duties embedded in the law of the sea. They provide the material foundation for implementing due diligence obligations in a manner that is both effective and equitable. If designed with sufficient scale and predictability, they can convert normative commitments under the marine plastic pollution treaty into operational transformation across global production and waste systems.

8. Interaction with International Economic Law

8.1 Trade Restrictions

The effectiveness of the marine plastic pollution treaty will depend in part on its compatibility with international economic law, particularly the World Trade Organization (WTO) framework. Product bans, polymer restrictions, recycled-content mandates, and border measures designed to prevent regulatory evasion all raise questions under the General Agreement on Tariffs and Trade (GATT 1994) and related WTO agreements.

The primary disciplines implicated are GATT Articles I (most-favoured-nation treatment), III (national treatment), and XI (prohibition of quantitative restrictions). A treaty-mandated ban on certain plastic products must be implemented in a manner that does not discriminate between imported and domestic products. If a State prohibits a specific plastic item, the measure must apply equally to domestic producers and foreign exporters to comply with Article III. Similarly, a restriction that targets imports alone may constitute a prohibited quantitative restriction under Article XI (WTO 1994).

However, WTO law does not prohibit environmental regulation per se. GATT Article XX provides general exceptions, including measures “necessary to protect human, animal or plant life or health” (Article XX(b)) and measures “relating to the conservation of exhaustible natural resources” (Article XX(g)), provided they are not applied in a manner constituting arbitrary or unjustifiable discrimination or a disguised restriction on international trade. WTO jurisprudence has clarified that environmental measures can fall within these exceptions if they pursue legitimate objectives and are applied even-handedly (WTO Appellate Body 1998; WTO Appellate Body 2001).

For the marine plastic pollution treaty, this means that product bans and design standards must be grounded in credible environmental objectives and supported by scientific evidence. A prohibition on intentionally added microplastics, for example, can be justified if supported by evidence of marine harm and if applied without discrimination between domestic and imported goods. Similarly, recycled-content requirements or eco-design standards can be WTO-consistent if they are origin-neutral and proportionate.

Border adjustment measures present a more complex challenge. If production caps or reduction pathways are adopted, States may seek to impose border measures to prevent carbon- or plastic-intensive goods from undercutting domestic regulation. WTO compatibility would depend on careful design. Measures that mirror domestic standards and apply equally to imported and domestic products are more defensible than measures targeting specific countries. Transparency, due process, and flexibility for equivalent foreign measures strengthen legal defensibility.

Another trade-related dimension concerns technical regulations under the Agreement on Technical Barriers to Trade (TBT Agreement). Product standards on polymer composition, additives, labelling, or recyclability must avoid unnecessary obstacles to trade and should be based on international standards where available. A globally negotiated plastics treaty can function as such an international standard, strengthening the legitimacy of national measures adopted pursuant to it.

The key doctrinal insight is that WTO law disciplines the manner of regulation, not its existence. A carefully drafted marine plastic pollution treaty, implemented through non-discriminatory and scientifically grounded measures, can coexist with WTO obligations. Poor drafting, discriminatory enforcement, or politically motivated trade restrictions risk dispute settlement challenges.

8.2 Investment Protection

Beyond trade law, production limits, product bans, and regulatory shifts under the marine plastic pollution treaty may trigger claims under international investment agreements. Bilateral investment treaties (BITs) and investment chapters in free trade agreements commonly provide protections against expropriation, unfair and inequitable treatment, and discrimination (Dolzer and Schreuer 2012).

Plastic production facilities, petrochemical plants, and recycling infrastructure represent significant capital investments. If a State adopts binding reduction targets or prohibits certain polymer categories pursuant to the treaty, investors may argue that such measures impair the value of their investments. Claims could arise under indirect expropriation doctrines if regulatory changes substantially deprive investors of economic use, even without a formal transfer of ownership.

International investment law, however, recognizes that States retain the right to regulate in pursuit of legitimate public objectives, including environmental protection. Arbitral tribunals have increasingly acknowledged that non-discriminatory, proportionate environmental measures adopted in good faith do not constitute compensable expropriation merely because they reduce profitability (Saluka v Czech Republic 2006; Methanex v United States 2005). The proportionality and reasonableness of the measure, as well as the investor’s legitimate expectations, are central to this analysis.

To reduce investment dispute risk, treaty design should incorporate several safeguards. First, obligations should be framed in general regulatory terms rather than targeting specific enterprises. Second, implementation timelines should allow for gradual adjustment, reducing abrupt economic shocks. Third, transparency and consultation processes during regulatory development can mitigate claims of arbitrariness.

Some modern investment agreements include explicit carve-outs for environmental measures or clarify that non-discriminatory public interest regulation does not constitute indirect expropriation. States negotiating the marine plastic pollution treaty may consider parallel reforms in investment agreements to ensure coherence between environmental commitments and investor protections.

There is also a strategic dimension. Clear, predictable, and internationally harmonized standards reduce regulatory uncertainty for investors. If the marine plastic pollution treaty establishes globally coordinated production pathways and design standards, it may reduce the likelihood of fragmented and unpredictable domestic regulation, thereby lowering dispute risk over time.

The interaction between environmental protection and investment protection reflects a broader structural tension in international law. The marine plastic pollution treaty will test whether environmental governance can advance through binding production and design controls while remaining compatible with established economic protections. Legal coherence will depend on precise drafting, proportional implementation, and careful integration with existing trade and investment regimes.

9. Scientific Uncertainty and Precaution

9.1 Microplastics and Emerging Risks

A central design challenge for the marine plastic pollution treaty is that the science of microplastics and associated chemical risks is extensive but still developing, particularly regarding long-term ecosystem effects, human exposure pathways, and the combined toxicity of plastic particles and additives. International environmental law addresses this situation through the precautionary principle, which supports regulatory action when there are plausible risks of serious or irreversible harm, even if full scientific certainty is not yet available (Rio Declaration 1992; Sands et al. 2018).

Precaution is doctrinally relevant for plastics because delay has structural consequences. Once plastics enter the marine environment, they persist for decades, fragment into microplastics, and become effectively irreversible at scale. Remediation is limited and extremely costly, especially for microplastics dispersed through the water column and sediments (GESAMP 2015). This makes the legal logic of precaution more compelling than in contexts where harm can be reversed through later intervention.

The legal status of precaution varies across treaties and customary law debates, but it is firmly embedded in treaty practice and has influenced international adjudication in environmental cases. In Southern Bluefin Tuna, the arbitral tribunal supported cautious measures in the face of scientific uncertainty and serious environmental risk (Southern Bluefin Tuna 2000). In Pulp Mills, the International Court of Justice emphasized the need for environmental impact assessment and ongoing monitoring where there is risk of significant transboundary harm (ICJ 2010). These cases illustrate an international law trend: where uncertainty exists but risk is credible, States must adopt precaution-oriented decision-making and monitoring procedures.

Within the marine plastic pollution treaty, precaution can be operationalized through two categories of obligations.

First, controls on intentionally added microplastics. These are legally straightforward because the emission pathway is direct, and alternatives often exist. The case for prohibition or severe restriction is strengthened by the fact that microplastics used in cosmetics, detergents, and industrial abrasives are purposefully released into wastewater systems, where capture is incomplete (SAPEA 2019). A treaty that avoids binding controls on intentionally added microplastics would be hard to justify doctrinally because the harm pathway is foreseeable and preventable.

Second, controls on secondary microplastics generated through abrasion and fragmentation. Major sources include tyre wear particles, synthetic textiles, paints, and industrial pellets. Regulatory measures in this category require performance standards, design requirements, and infrastructure obligations rather than simple bans (SAPEA 2019; OECD 2022). Precaution supports adopting such standards even when the precise contribution of each source varies by geography, because the combined environmental burden is significant and cumulative.

The precautionary approach also applies to chemical additives. Plastics can contain additives that are persistent, toxic, and capable of bioaccumulation. The scientific concern is not only particle presence but the interaction between microplastics and chemical exposure, including sorbed pollutants (Rochman et al. 2013). If the treaty focuses only on waste volumes without addressing additives, it may undermine its own circularity goals because hazardous additives limit safe recycling and encourage disposal.

Precaution does not mean unbounded regulation. It requires a rational link between plausible risk and proportionate measures, supported by scientific assessment and subject to periodic review. The treaty can embed this discipline through scientific advisory bodies, annex updating procedures, and review clauses that adjust obligations as evidence strengthens.

9.2 Standard-Setting Authority

The success of the marine plastic pollution treaty will depend on its capacity to adapt to evolving science and technology. Plastic materials, additives, and product designs change rapidly. Microplastics research is expanding, and measurement standards continue to evolve. A static treaty text risks becoming obsolete or being interpreted narrowly by states seeking to avoid regulatory costs. For this reason, modern environmental treaties often rely on subsidiary bodies and technical annexes that can be updated through simplified amendment procedures (Bodansky 2010; Sands et al. 2018).

Standard-setting authority can be designed in several ways.

One model is annex-based regulation. The treaty text sets core obligations and principles, while annexes list regulated polymers, restricted additives, phase-out products, standardized monitoring methods, and reporting templates. Annexes can be updated by the conference of parties through majority voting or consensus, often with opt-out mechanisms. This model balances legal stability with scientific responsiveness. It is particularly suitable for plastics because technical detail is extensive and likely to change (Bodansky 2010).

A second model is protocol-based regulation. The treaty would function as a framework convention, while protocols would later establish more detailed obligations. This can increase initial ratification, but risks delay and fragmentation if protocols take years to negotiate or attract uneven participation.

Subsidiary bodies perform two roles: scientific assessment and regulatory drafting support. A scientific and technical body can evaluate evidence on microplastics, additives, and best available technologies. It can recommend updates to annexes and propose new indicator methodologies. A compliance-oriented body can translate technical recommendations into implementable legal standards, ensuring that obligations remain measurable and enforceable.

The main legal risks are legitimacy and delegation limits. States may resist granting broad regulatory authority to subsidiary bodies if they fear loss of sovereignty or “rule-making without consent.” This can be addressed through procedural safeguards: transparent decision-making, defined mandates, conflict-of-interest rules, and review mechanisms. The treaty can also specify that annex updates must be grounded in scientific findings and must consider feasibility and equity implications, linking standard-setting authority to CBDR and capacity-building provisions (Rajamani 2006).

Standard-setting authority is also essential for monitoring. Without agreed methodologies, compliance reporting will be incomparable. The treaty’s subsidiary bodies can standardize microplastics sampling protocols, beach litter survey methods, and reporting categories for plastic waste flows (GESAMP 2015; UNEP 2021). This is not a technical luxury; it is necessary for the compliance regime to function.

In doctrinal terms, subsidiary bodies and annex updating procedures allow the marine plastic pollution treaty to operate as a living instrument, maintaining regulatory relevance as science develops. Without such mechanisms, the treaty risks repeating a familiar pattern in environmental governance: ambitious political declarations followed by weak implementation due to outdated standards and unmeasurable obligations.

10. Non-State Actors and Corporate Responsibility

10.1 Extended Producer Responsibility

Although international treaties formally bind States, the effectiveness of the marine plastic pollution treaty will depend heavily on its capacity to influence corporate behaviour. Plastic production, polymer innovation, packaging design, and global supply chains are controlled primarily by private actors. The doctrinal question is whether and how international law can support binding producer obligations.

International law traditionally operates through the doctrine of State responsibility: States are responsible for ensuring that activities within their jurisdiction or control do not cause transboundary harm (ICJ 2010; ITLOS 2011). This creates a legal basis for States to regulate private corporations operating within their territory. A treaty can therefore require States to enact domestic legislation imposing obligations on producers, including extended producer responsibility (EPR), design standards, reporting requirements, and take-back schemes.

Extended producer responsibility shifts the financial and operational burden of post-consumer waste management from municipalities to producers. Legally, EPR can be framed as a treaty obligation requiring States to establish national systems ensuring that producers finance collection, recycling, and environmentally sound disposal (OECD 2022). This approach is consistent with the “polluter pays” principle recognized in international environmental law (Rio Declaration 1992; Sands et al. 2018). Under this principle, those who generate pollution should bear the costs of preventing and remedying it.

The treaty cannot directly impose obligations on corporations under classical treaty doctrine, unless it is designed as a regime conferring direct rights and obligations on non-State actors, which is uncommon outside specific fields such as international criminal law. However, it can require States to regulate corporate actors in a manner that is binding and enforceable domestically. This is the standard architecture used in environmental, human rights, and anti-corruption treaties.

A robust EPR framework within the marine plastic pollution treaty could include:

• Mandatory producer registration and reporting.

• Financial responsibility for collection and treatment of plastic products placed on the market.

• Eco-modulation of fees based on recyclability or toxicity.

• Obligations for take-back and recycling infrastructure.

The legal challenge is harmonization. Without minimum global standards, producers may shift production to jurisdictions with weaker EPR obligations. A treaty-level requirement for comparable EPR systems reduces regulatory arbitrage and aligns incentives across supply chains. It also strengthens the link between upstream production and downstream marine impacts, reinforcing due diligence obligations under UNCLOS Articles 192–194 (UNCLOS 1982).

10.2 Transparency and Due Diligence

Transparency is increasingly central to corporate regulation in international law. The marine plastic pollution treaty can incorporate due diligence obligations requiring States to ensure that corporations assess, prevent, and mitigate environmental harm associated with plastic production and distribution. These obligations would not create direct international liability for corporations but would require States to legislate and supervise corporate conduct.

Reporting and disclosure requirements are a first step. Producers could be required to disclose polymer volumes, additive compositions, recycled content percentages, and waste management performance. Such information is necessary for monitoring national compliance and for evaluating global production trajectories (OECD 2022). Transparency obligations also facilitate consumer awareness and market-based incentives for sustainable design.

Supply-chain traceability is another key component. Plastic supply chains are global and complex. Resin production, product manufacturing, packaging, distribution, and waste trade often occur in different jurisdictions. Without traceability, enforcement is difficult, and waste exports can obscure responsibility. The treaty could require States to implement traceability systems for polymer pellets and plastic products, reducing accidental loss and illegal disposal. Traceability obligations are consistent with emerging due diligence models in environmental and human rights law, where States must ensure that corporate actors identify and address environmental risks throughout their operations (Sands et al. 2018).

Due diligence in this context has two dimensions. First, corporate due diligence: producers must evaluate environmental risks linked to product design and supply chains. Second, State due diligence: governments must ensure effective regulation and enforcement. The marine plastic pollution treaty can integrate both by requiring States to adopt mandatory environmental due diligence legislation covering plastic production and waste management sectors.

A transparency regime also strengthens compliance review. Reliable corporate data improves the accuracy of national reporting and reduces the risk of underestimation of plastic production and leakage. Without disclosure obligations, national inventories may rely on incomplete or voluntary industry data, undermining accountability.

Also read

• Customary International Law: How It Forms and Works

• The Principle of Good Faith in International Law

• The Sources Of International Law

• Principles Of Jurisdiction In International Law

• Fisheries Case (United Kingdom v Norway)

• Territorial Disputes and International Law: Principles, Cases and Resolutions

• Strait of Hormuz Tensions: Law, Security & Global Trade

• Climate Refugees and International Law

11. Implementation Challenges

11.1 Capacity Gaps

The implementation of the marine plastic pollution treaty will confront significant structural capacity gaps, particularly in developing coastal and small island States. These gaps are not limited to financial constraints; they include institutional weaknesses, technical expertise shortages, infrastructure deficits, and competing development priorities (UNEP 2021; OECD 2022).

Waste collection infrastructure remains incomplete in many regions. Inadequate collection systems lead to mismanaged waste that enters rivers and coastal areas. Even where collection exists, sorting and treatment capacity may be insufficient, resulting in open dumping or uncontrolled burning. Regulatory agencies may lack laboratory facilities for microplastics monitoring or trained personnel for compliance inspections.

Legal capacity is another barrier. Drafting and enforcing complex producer responsibility laws, product standards, and monitoring frameworks requires technical expertise. Many coastal States face overlapping environmental challenges, including fisheries management, climate adaptation, and biodiversity protection. Plastic governance competes with other urgent priorities.

Financial mechanisms and technology transfer provisions in the treaty are therefore not optional additions but prerequisites for effective implementation. Differentiated timelines, phased obligations, and targeted assistance can align ambition with feasibility. However, prolonged exemption from core duties risks perpetuating marine pollution patterns and undermining treaty credibility.

Institutional coordination is also a challenge. Plastic governance spans multiple ministries: environment, trade, industry, fisheries, customs, and finance. Fragmented domestic governance can impede implementation even where political commitment exists. The treaty may encourage States to designate national focal points or coordination bodies to ensure coherence.

11.2 Monitoring Marine Debris

Monitoring marine debris presents evidentiary and methodological challenges that directly affect enforcement and dispute resolution. Marine plastics are mobile, persistent, and often fragmented into microplastics. Establishing causal links between national conduct and specific marine impacts can be complex.

Data reliability varies widely. Beach litter surveys provide accessible indicators but are influenced by tourism, cleanup frequency, and local currents. Riverine monitoring requires sustained measurement at multiple points. Seabed and water column sampling for microplastics requires specialized equipment and standardized protocols (GESAMP 2015). Without harmonized methodologies, reported data may not be comparable across States.

Attribution is particularly difficult. Plastic items often lack an identifiable origin, especially once fragmented. Pellet loss and branded packaging may provide clues, but most debris cannot be traced to a specific producer or State. This complicates the application of traditional state responsibility doctrines, which require proof of attribution and breach (ICJ 2010).

The treaty can mitigate these challenges by adopting standardized indicators, reporting templates, and peer review procedures. Independent scientific advisory bodies can support methodological consistency. Data transparency enhances credibility and enables civil society and academic scrutiny.

Monitoring also intersects with precaution. Even where precise quantification is difficult, consistent evidence of accumulation and ecological harm justifies regulatory action. Waiting for perfect data risks irreversible environmental damage. The treaty must therefore balance evidentiary rigor with precautionary responsiveness.

In sum, implementation and monitoring challenges do not undermine the case for a marine plastic pollution treaty; they define its design constraints. A treaty that integrates corporate responsibility, capacity-building, standardized monitoring, and adaptive governance mechanisms stands a greater chance of transforming broad law of the sea obligations into effective global practice.

12. The Treaty’s Systemic Impact

12.1 Evolution of Ocean Environmental Law

The long-term significance of the marine plastic pollution treaty lies not only in its substantive rules but in its systemic impact on the evolution of ocean environmental law. Since its adoption in 1982, the United Nations Convention on the Law of the Sea (UNCLOS) has functioned as a constitutional framework for ocean governance. Part XII establishes a general obligation for States to protect and preserve the marine environment and to prevent, reduce, and control pollution from any source (UNCLOS 1982, Articles 192–194). Yet these provisions are framed at a high level of generality. They articulate duties but leave their detailed content largely to subsequent agreements and national legislation.

The marine plastic pollution treaty has the potential to give operational content to these framework duties. Under UNCLOS Article 207, States must adopt laws and regulations to address pollution from land-based sources, taking into account internationally agreed rules and standards. In practice, internationally agreed standards for plastic production and waste management have been limited. If the plastics treaty establishes binding global rules—such as production controls, design requirements, monitoring standards, and extended producer responsibility systems—it would effectively define what constitutes adequate implementation of Article 207.

Similarly, Article 194 requires States to take all necessary measures to prevent pollution and to ensure that activities within their jurisdiction do not cause damage to other States or areas beyond national jurisdiction. The treaty can clarify what “necessary measures” mean in the context of plastic pollution. For example, if the treaty requires national action plans with measurable reduction targets and standardized monitoring, failure to adopt such measures could strengthen arguments that a State has not fulfilled its due diligence obligations under UNCLOS (ITLOS 2011; ICJ 2010).

This dynamic resembles developments in other areas of ocean governance. The Agreement on Biodiversity Beyond National Jurisdiction elaborates conservation and environmental impact assessment obligations in areas beyond national jurisdiction, building upon UNCLOS provisions without amending the Convention itself. The marine plastic pollution treaty may function in a similar manner, reinforcing Part XII while remaining formally distinct.

Systemically, the treaty may also shift the center of gravity in marine pollution regulation. Historically, law of the sea instruments focused on vessel-source pollution and dumping, where jurisdictional control at sea was clearer. Plastic pollution, dominated by land-based sources and global supply chains, requires regulatory attention to production systems, consumer markets, and waste infrastructure. By integrating upstream controls with marine protection obligations, the treaty could reorient ocean environmental law toward a life-cycle model that bridges terrestrial and marine governance.

12.2 From Framework Duty to Regulatory Precision

A defining question is whether the marine plastic pollution treaty will merely reaffirm existing duties or transform them into concrete global standards. UNCLOS establishes binding obligations of conduct, but it does not specify numerical targets, production caps, design standards, or standardized reporting metrics. This flexibility has facilitated broad participation but has limited enforceability and comparability (Tanaka 2019).

If the treaty adopts detailed annexes listing regulated polymers, prohibited products, microplastic controls, and harmonized monitoring methodologies, it would move ocean environmental law toward regulatory precision. Precision enhances legal certainty, facilitates compliance assessment, and reduces interpretive ambiguity under the Vienna Convention on the Law of Treaties (VCLT 1969). States would know what conduct is required, and compliance bodies would have measurable benchmarks.

However, regulatory precision carries trade-offs. Highly specific obligations may constrain domestic policy flexibility and complicate ratification. States with divergent economic structures may resist uniform standards. The treaty must therefore balance clarity with adaptability, possibly through phased commitments, differentiated timelines, and dynamic annex procedures.

The transformation from framework duty to regulatory precision also affects dispute settlement and state responsibility. General obligations, such as “protect and preserve,” require interpretation and contextual analysis. Detailed obligations, such as mandatory producer responsibility legislation or quantified reduction targets, are easier to evaluate in adversarial proceedings. The treaty’s precision level will thus influence the likelihood and outcome of compliance review and dispute resolution.

Another systemic implication concerns normative diffusion. Once global standards are established, they can influence domestic legislation even in non-party States through market effects, supply-chain requirements, and soft-law convergence. Global product standards often shape corporate practice beyond formal treaty membership. In this way, regulatory precision can amplify systemic impact.

Ultimately, the marine plastic pollution treaty will be judged by whether it converts widely acknowledged environmental harm into enforceable legal commitments that alter production, consumption, and waste patterns. If it succeeds in translating broad UNCLOS duties into measurable global standards, it will mark a significant evolution in the law of the sea. If it remains confined to reaffirming existing principles without operational detail, its systemic impact will be limited.

The treaty’s systemic legacy will therefore depend on its capacity to align legal precision with equity, feasibility, and scientific adaptability. Done effectively, it can redefine how international law addresses diffuse, land-based sources of marine pollution and establish a model for integrating environmental regulation across terrestrial and ocean domains.

13. Conclusion

The marine plastic pollution treaty must be understood as more than a sectoral environmental instrument. It represents a structural development within the law of the sea and within public international law more broadly. Plastic pollution is already covered by the definition of marine pollution under UNCLOS, and States are bound by the obligation to protect and preserve the marine environment and to prevent, reduce, and control pollution from any source (UNCLOS 1982, Articles 192–194). The doctrinal question has never been whether regulation is required, but what concrete measures due diligence demands in light of contemporary scientific knowledge and global production patterns.

This article has argued that the treaty’s systemic importance lies in its capacity to operationalize existing obligations under Part XII of UNCLOS. Articles 192, 194, and 207 establish binding duties of conduct grounded in prevention and cooperation. Yet they remain framed at a level of generality that leaves wide discretion to States. The marine plastic pollution treaty offers an opportunity to define the content of those duties with precision. Production caps, product design standards, extended producer responsibility schemes, harmonized monitoring methodologies, and measurable reduction pathways would transform abstract obligations into concrete regulatory benchmarks.

The treaty’s effectiveness will depend on its integration of upstream and downstream measures. Plastic pollution is not primarily a disposal problem; it is a systemic production and design problem that manifests in marine ecosystems. Downstream waste management obligations are necessary but insufficient if global polymer production continues to expand unchecked (OECD 2022; UNEP 2021). Conversely, upstream controls without enforcement and monitoring will fail to translate into reduced marine debris. The treaty must therefore address both ends of the life cycle simultaneously, linking industrial policy with marine protection.

Compliance and enforcement architecture will be decisive. Transparent reporting, harmonized indicators, and robust compliance review mechanisms can strengthen accountability. Financial mechanisms and differentiated implementation timelines must accompany substantive obligations to ensure equity and feasibility. Without adequate capacity support, developing coastal States may struggle to meet reporting and infrastructure requirements, weakening both environmental outcomes and treaty legitimacy.

Interaction with international economic law also shapes the treaty’s systemic role. If carefully designed, product bans, design standards, and border measures can be reconciled with WTO disciplines through non-discrimination and legitimate environmental objectives. Investment protection concerns can be managed through proportionate regulation and clear treaty language affirming the right to regulate in the public interest. Legal coherence across regimes is not automatic; it requires deliberate drafting and institutional coordination.

At a doctrinal level, the treaty tests whether international law can respond effectively to diffuse, transboundary environmental harm driven by globalized supply chains. The law of the sea was crafted in an era when marine pollution was primarily conceptualized as ship-based or dumping-related. Plastic pollution exposes the limits of that model. By integrating life-cycle regulation into marine environmental protection, the treaty may redefine how ocean law addresses land-based and production-driven threats.

If the marine plastic pollution treaty succeeds in converting due diligence obligations into measurable, enforceable standards that alter production patterns and reduce marine leakage, it will mark a significant evolution in ocean environmental law. It will demonstrate that framework duties under UNCLOS can be given concrete operational content through subsequent agreements. If it fails to move beyond general principles and voluntary measures, it will leave intact the gap between acknowledged environmental harm and effective legal response.

The treaty’s structural significance, therefore, lies in its potential to bridge this gap. It is not simply an environmental agreement addressing waste; it is an attempt to recalibrate the normative architecture of the law of the sea in response to a pervasive and persistent form of pollution. Its legacy will depend on whether it transforms legal obligation into regulatory precision, and regulatory precision into measurable protection of the marine environment.

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