Elucidating how much plastic debris by mass is contained in major reservoirs in the marine environment has long been a knowledge gap in the field. Knowledge of major reservoirs and solving the mass balance can inform mitigation and remediation efforts. Our objective was to review the field’s progress in quantifying major reservoirs of plastic pollution in the marine environment, and to assess whether achieving a mass balance is currently feasible with the information available. We compiled estimates of global marine reservoirs to date, and compared the approaches used to generate these estimates. We identified a total of 22 global marine reservoir estimates across 14 studies: four estimates of the coastline reservoir spanning two orders of magnitude, 12 estimates of the ocean surface reservoir spanning three orders of magnitude, one estimate of the ocean water column reservoir (40–90 MMT), one estimate of the ocean floor reservoir (3–11 MMT), and four estimates of the ocean sediment reservoir spanning three orders of magnitude. Studies obtain estimates of global reservoirs in one of two ways: by taking environmental samples and scaling them up in some way to reservoir size or by prescribing inputs and propagating them through the reservoir using computational modelling. The quantity of observational data used to inform reservoir estimates ranged from <100 samples to 10 000+ samples, which were extrapolated globally. While some studies scale based solely on the reservoir size, most attempt to account for heterogeneity using the output of a computational model that takes into account numerous transport processes. No two numerical modelling studies considered the same hydrodynamic processes, particle properties, or compartment-level processes, showing the diversity of model parameterizations used. In addition, the complexity of these models has increased over time. While studies have previously conducted mass balances of plastic across spatial scales, given the current state of knowledge, we conclude that these efforts will be associated with substantial levels of uncertainty and discuss next steps.

Microplastics are found floating on natural waters. Sunlight-driven photochemistry can dissolve buoyant microplastics, producing dissolved organic carbon (DOC). We hypothesized that plastic dissolution would increase linearly with increasing surface area (SA)-to-volume (V) ratio as plastics decrease in size. To test this, samples of expanded polystyrene (EPS) and polypropylene (PP) spanning a range of sizes were irradiated while floating on water in a solar simulator. A linear relationship between SA:V and DOC accumulation rate was significant for EPS (p < 0.0001) and PP (p = 0.0086), suggesting SA-controlled reactions. However, a power relationship with an exponent of approximately 0.5 between PP dissolution and SA:V provided a significantly better fit, suggesting that non-SA-controlled processes may limit PP photodissolution. Using these relationships, it was estimated that macroplastics ∼10 cm should take ∼250 to ∼8000 years to photochemically dissolve. However, estimated lifetimes are shorter for smaller plastics, with 1 mm EPS beads and 100 nm PP nanoplastics estimated to have lifetimes of 5.3 years and 3 to 196 days, respectively, with the range in lifetimes for PP dependent upon whether linear or power fits are applied.

A diversity of chemicals are intentionally added to plastics to enhance their properties and aid in manufacture. Yet, the accumulated chemical composition of these materials is essentially unknown even to those within the supply chain, let alone to consumers or recyclers. Recent legislated and voluntary commitments to increase recycled content in plastic products highlight the practical challenges wrought by these chemical mixtures, amid growing public concern about the impacts of plastic-associated chemicals on environmental and human health. In this Perspective, we offer guidance for plastics manufacturers to collaborate across sectors and critically assess their use of added chemicals. The ultimate goal is to use fewer and better additives to promote a circular plastics economy with minimal risk to humans and the environment.

This paper aims to guide the stakeholder engagement process related to plastic pollution research in marine environments. We draw on advice identified during an online workshop (Ocean Plastic Workshop 2022) organized by Early Career Ocean Professionals (ECOPs) from 11 countries, held in April 2022. International experts and workshop participants discussed their experiences in the collaborative development and implementation of ocean plastic pollution projects held worldwide, guided by three main questions: (i) What is the role of scientists in a multi-stakeholder project? (ii) How should scientists communicate with other stakeholders? (iii) Which stakeholders are missing in collaborative projects, and why are they missing? This multidisciplinary, co-learning approach highlights the value of stakeholder engagement for ocean plastic projects with an end goal to identify and implement ocean plastic solutions via innovative technologies, informing policy, community engagement, or a combination of all three approaches. The target outcomes of the workshop described in this paper include the identification of transdisciplinary (academic-stakeholder) engagement frameworks and specific suggestions that can serve as guidelines for the development of future plastic pollution projects.

Floating microplastics are susceptible to sunlight-driven photodegradation, which can convert plastic carbon to dissolved organic carbon (DOC) and can facilitate microplastic fragmentation by mechanical forces. To understand the photochemical fate of sub-millimeter buoyant plastics, ∼0.6 mm polypropylene microplastics were photodegraded while tracking plastic mass, carbon, and particle size distributions. Plastic mass loss and carbon loss followed linear kinetics. At most time points DOC accumulation accounted for under 50% of the total plastic carbon lost. DOC accumulation followed sigmoidal kinetics, not the exponential kinetics previously reported for shorter irradiations. Thus, we suggest that estimates of plastic lifespan based on exponential DOC accumulation are inaccurate. Instead, linear plastic-C mass and plastic mass loss kinetics should be used, and these methods result in longer estimates of photochemical lifetimes for plastics in surface waters. Scanning electron microscopy revealed that photoirradiation produced two distinct patterns of cracking on the particles. However, size distribution analyses indicated that fragmentation was minimal. Instead, the initial population of microplastics shrank in size during irradiations, indicating photoirradiation in tranquil waters (i.e., without mechanical forcing) dissolved sub-millimeter plastics without fragmentation.

Plastic entering the environment is a growing threat for ecosystems. We estimate the annual mass of known Dutch plastic waste generated and littered and where it ends up. We use two methods: (1) a material flow analysis of plastic waste separately collected from 13 economic sectors (including households, industry and imports) and estimate the amount sent to processing plants or exported and (2) a mismanagement model from observations of litter (on Dutch beaches and riverbanks) plus estimates of inadequately managed exported plastic scraps entering the environment abroad. In 2017 (the most recent complete data set available), an estimate of 1990 (±111) kilotonnes [kt] of plastic waste was separately collected. The top three plastic waste generating sectors (74% of the total) were households, clothing and textiles, and importation. Our mismanagement model estimates that 4.3-21.2 kt enters the environment annually; almost all of which occurs in foreign countries after inadequate management of imported Dutch waste. We highlight unknowns, including the source and/or destination of imported (623 kt) and exported (514 kt) plastics, plastics in non-household mixed waste streams and the plastic fraction of some separately collected waste, for example, e-waste. Our results stress the need for improved monitoring and reporting of plastic waste. Beyond the Netherlands, our recommendations could also help other high-income countries' decision-makers reach their circular economy goals.

mbitious campaigns to sample plastic pollution in coral-reef and freshwater ecosystems demonstrate the value of international cooperation in assessing contamination to identify drivers and inform management.

[This corrects the article DOI: 10.5334/aogh.4056.].

Predicting the vertical distribution of microplastics in the ocean surface mixed layer is necessary for extrapolating surface measurements and comparing observations across conditions. The competing mechanisms that control the vertical distribution are particle buoyancy, which is primarily a function of particle properties and drives microplastics to accumulate at the ocean surface, and turbulent mixing, which disperses microplastics throughout the mixed layer and depends on local hydrodynamics. In this study, we focused on the physical properties of microplastics collected within one vertical profile in the North Pacific. We measured the size, shape, and rise velocity of all microplastics collected, finding that average size and rise velocity decay with depth. In addition, we demonstrate how the vertical distribution of the microplastics depends on the rise velocity of the microplastics by segregating the data into three regimes based on a ratio of microplastic rise velocity and a characteristic turbulence velocity scale. Using an individual model for each regime, we can extrapolate the vertical distribution of microplastics to the bottom of the mixed layer and find the total concentration of microplastics. The total extrapolated concentration using the combined model results in 10× the concentration of the surface net alone and 47% more than a model which does not consider the different microplastic regimes. Finally, we discuss how the vertical distribution also depends on microplastic form, finding that lines are approximately well-mixed whereas the concentration of fragments decays with depth. These observations indicate the importance of considering the appropriate rise velocity regime when predicting the vertical distribution of microplastics.

Plastic pollution is a leading environmental issue because of its demonstrated and potential harms to wildlife, as well as to ecosystem and human health. The Gulf of Maine has already suffered ecological shifts due to recent unprecedented warming of ocean waters, with consequences to coastal economies that rely on ecosystem services. Here, we explore the prevalence of plastic pollution as a potential compounding threat to Gulf of Maine ecosystems by analyzing microplastics and plastic debris collected in surface-towed plankton nets since 1987. Although we find low concentrations of small floating plastic particles, 20 years of coastal and remote-island shoreline cleanup activities demonstrate the continued accumulation of large plastic debris. Policies to address plastic pollution in the Gulf of Maine could strive to minimize littering or at-sea disposal, while also supporting environmental cleanup.

In the global ocean, more than 380 species are known to ingest microplastics (plastic particles less than 5 mm in size), including mid-trophic forage fishes central to pelagic food webs. Trophic pathways that bioaccumulate microplastics in marine food webs remain unclear. We assess the potential for the trophic transfer of microplastics through forage fishes, which are prey for diverse predators including commercial and protected species. Here, we quantify Northern Anchovy ( Engraulis mordax ) exposure to microplastics relative to their natural zooplankton prey, across their vertical habitat. Microplastic and zooplankton samples were collected from the California Current Ecosystem in 2006 and 2007. We estimated the abundance of microplastics beyond the sampled size range but within anchovy feeding size ranges using global microplastic size distributions. Depth-integrated microplastics (0–30 m depth) were estimated using a depth decay model, accounting for the effects of wind-driven vertical mixing on buoyant microplastics. In this coastal upwelling biome, the median relative exposure for an anchovy that consumed prey 0.287–5 mm in size was 1 microplastic particle for every 3399 zooplankton individuals. Microplastic exposure varied, peaking within offshore habitats, during the winter, and during the day. Maximum exposure to microplastic particles relative to zooplankton prey was higher for juvenile (1:23) than adult (1:33) anchovy due to growth-associated differences in anchovy feeding. Overall, microplastic particles constituted fewer than 5% of prey-sized items available to anchovy. Microplastic exposure is likely to increase for forage fishes in the global ocean alongside declines in primary productivity, and with increased water column stratification and microplastic pollution.

Plastic contamination of the environment is a global problem whose magnitude justifies the consideration of plastics as emergent geomaterials with chemistries not previously seen in Earth’s history. At the elemental level, plastics are predominantly carbon. The comparison of plastic stocks and fluxes to those of carbon reveals that the quantities of plastics present in some ecosystems rival the quantity of natural organic carbon and suggests that geochemists should now consider plastics in their analyses. Acknowledging plastics as geomaterials and adopting geochemical insights and methods can expedite our understanding of plastics in the Earth system. Plastics also can be used as global-scale tracers to advance Earth system science.

Plastics are a ubiquitous class of synthetic polymer materials used in virtually all commercial and industrial sectors. The majority of global plastics consists of polymers with carbon–carbon backbones, whose environmental persistence and low cost have resulted in a massive reservoir of plastic waste that resides in landfills and the environment. Although plastic debris contaminating the ocean has been documented for decades, details about plastic debris composition, distribution, impact and ultimate fate in the environment remain elusive. In this Review, we present an overview of environmental plastic contamination and discuss the origin (feedstock) and degradation behaviour of plastics to help inform material design principles addressing end-of-life management. We argue that designing materials to be ‘marine biodegradable’ or universally biodegradable is not, in itself, a solution to plastic pollution. Instead, material and product design principles must include a feasible plan for recovery and treatment based upon existing (or, possibly, simultaneously developed) systems.

Accelerated weathering of LDPE laminates, with samples exposed to ultraviolet radiation (UVR) in air and while floating in seawater at the same temperature, was investigated in this study. The depth profiles of the concentrations of oxidation products in the two sets of samples was assessed by FTIR (Fourier Transform Infrared Spectroscopy) and suggest the oxidation on weathering to be diffusion-controlled in both air and in seawater, localizing the reaction to a thin surface layer. While the thickness of this layer is several hundred microns in air-weathered samples it is too small to be discernible by FTIR spectroscopy in sea water-weathered samples. A naturally weathered polyethylene microplastic pellet from floating ocean debris was also similarly studied by FTIR and the depth profile compared with that from accelerated weathering of LDPE laminates. Tensile properties of the LDPE weathered in air and in sea water were also compared to better understand the impact of diffusion-controlled oxidation on their mechanical integrity. How the origin of apparent retardation of the rate of weathering degradation of LDPE in seawater relative to that in air, is related diffusion-controlled oxidation due to the low concentrations of dissolved oxygen in seawater, is also discussed.

Microplastics (MP) are defined as “any synthetic solid particle or polymeric matrix, with regular or irregular shape and with size ranging from 1 μm to 5 mm, of either primary or secondary manufacturing origin, which are insoluble in water”.

Plastic waste affects environmental quality and ecosystem health. In 2010, an estimated 5 to 13 million metric tons (Mt) of plastic waste entered the ocean from both developing countries with insufficient solid waste infrastructure and high-income countries with very high waste generation. We demonstrate that, in 2016, the United States generated the largest amount of plastic waste of any country in the world (42.0 Mt). Between 0.14 and 0.41 Mt of this waste was illegally dumped in the United States, and 0.15 to 0.99 Mt was inadequately managed in countries that imported materials collected in the United States for recycling. Accounting for these contributions, the amount of plastic waste generated in the United States estimated to enter the coastal environment in 2016 was up to five times larger than that estimated for 2010, rendering the United States' contribution among the highest in the world.

Marine litter (ML) consists of any item of anthropogenic origin that has been lost, discarded or intentionally disposed of into the environment, being acknowledged as a worldwide environmental and ecological threat. In the last decade, there has been an attempt across different sectors to tackle, reduce and mitigate sources of litter. In this study, meso and macrodebris between 2 and 30 cm was recorded and classified in two established study areas (Porto Pim and Conceição beaches), throughout five monitoring years (2012-2018). The litter abundance, density and weighted average by abundance were evaluated in eight main categories: plastics, cloths/fabrics, glass, metals, rubber, processed lumber, other and large. Field surveys provided evidence that plastic represented 95% of all litter. ML abundance was treated as an "environmental variable" and used to determine its anomalies, temporal trends and forecasts. Results from this time-series addressed possible periodic oscillations and density peaks of litter. Reference values of ML presence were obtained and could potentially be used for developing a diagnostic tool for anthropogenic pollution in the Azores.

Plastic pollution is a planetary threat, affecting nearly every marine and freshwater ecosystem globally. In response, multilevel mitigation strategies are being adopted but with a lack of quantitative assessment of how such strategies reduce plastic emissions. We assessed the impact of three broad management strategies, plastic waste reduction, waste management, and environmental recovery, at different levels of effort to estimate plastic emissions to 2030 for 173 countries. We estimate that 19 to 23 million metric tons, or 11%, of plastic waste generated globally in 2016 entered aquatic ecosystems. Considering the ambitious commitments currently set by governments, annual emissions may reach up to 53 million metric tons per year by 2030. To reduce emissions to a level well below this prediction, extraordinary efforts to transform the global plastics economy are needed.

Marine plastic debris floating on the ocean surface is a major environmental problem. However, its distribution in the ocean is poorly mapped, and most of the plastic waste estimated to have entered the ocean from land is unaccounted for. Better understanding of how plastic debris is transported from coastal and marine sources is crucial to quantify and close the global inventory of marine plastics, which in turn represents critical information for mitigation or policy strategies. At the same time, plastic is a unique tracer that provides an opportunity to learn more about the physics and dynamics of our ocean across multiple scales, from the Ekman convergence in basin-scale gyres to individual waves in the surfzone. In this review, we comprehensively discuss what is known about the different processes that govern the transport of floating marine plastic debris in both the open ocean and the coastal zones, based on the published literature and referring to insights from neighbouring fields such as oil spill dispersion, marine safety recovery, plankton connectivity, and others. We discuss how measurements of marine plastics (both in situ and in the laboratory), remote sensing, and numerical simulations can elucidate these processes and their interactions across spatio-temporal scales.