Disruption of marine organisms

Although microplastic consumption by marine organisms is difficult to define in terms of the absolute number of individuals and species affected, the exposure of microplastics to marine organisms is evident – literally swimming in a microplastic soup (Kühn and van Franeker, Reference Kühn and van Franeker2020; Amjad et al., Reference Amjad, Mohyuddin, Ulfat, Goh, Othman and Kurniawan2024). Studies have over decades shown that marine organisms ingest microplastics, a phenomenon occurring at every trophic level (Cole et al., Reference Cole, Lindeque, Halsband and Galloway2011; Chatterjee and Sharma, Reference Chatterjee and Sharma2019). The discovery of microplastic particles in the Mariana Trench, the deepest part of the world’s ocean, reveals the limitless exposure of microplastic particles to organisms (Peng et al., Reference Peng, Chen, Chen, Dasgupta, Xu, Ta, Du, Li, Guo and Bai2018). Microplastics have been found in deep-sea benthic organisms, and evidence shows that a wide range of marine invertebrates consume microplastics (Wright et al., Reference Wright, Thompson and Galloway2013; Courtene-Jones et al., Reference Courtene-Jones, Quinn, Gary, Mogg and Narayanaswamy2017). Indeed, over 1,565 species have been proven to ingest microplastics, with some scientists estimating that 10% of marine species are directly at risk of extinction due to microplastics (Amjad et al., Reference Amjad, Mohyuddin, Ulfat, Goh, Othman and Kurniawan2024; Villarrubia-Gómez et al., Reference Villarrubia-Gómez, Almroth, Eriksen, Ryberg and Cornell2024). Yet there is also significant concern that the smallest microplastic particles could be systemically undercounted in studies. Most of the research on microplastic ingestion by marine organisms focuses on larger microplastics, meaning smaller microplastics, including nanoplastics, may escape detection (Ribeiro et al., Reference Ribeiro, Okoffo, O’Brien, O’Brien, Harris, Samanipour, Kaserzon, Mueller, Galloway and Thomas2021; Kokilathasan and Dittrich, Reference Kokilathasan and Dittrich2022; Pitt et al., Reference Pitt, Aluru, Hahn, Shumway and Ward2023). In addition, detection of fragments is usually focused on the digestive organs and gastrointestinal tract, meaning concentrations of microplastics in other tissues may be unobserved (Gouin, Reference Gouin2020; Pitt et al., Reference Pitt, Aluru, Hahn, Shumway and Ward2023). A similar pattern may occur in samples gathered from the deep ocean with serious under-reporting of smaller microplastics in deep sea water, sediments and benthic organisms (Courtene-Jones et al., Reference Courtene-Jones, Quinn, Gary, Mogg and Narayanaswamy2017).

In terms of ingestion rates and impacts once ingested, there appears to be a consensus that the rate of uptake and impacts is highly variable depending on the size of the particles. Ingestion has been shown to increase as particles degrade and become smaller (Wright et al., Reference Wright, Thompson and Galloway2013; Xu et al., Reference Xu, Ma, Ji, Pan and Miao2020). However, uncertainties extend to the movement of different-sized microplastics once inside an organism, with smaller particles likely staying inside organisms for a longer time (Xu et al., Reference Xu, Ma, Ji, Pan and Miao2020). Once inside the digestive track, there is also the threat of translocation, whereby microplastics move from digestive organs into other organs or body tissues (Hale et al., Reference Hale, Seeley, La Guardia, Mai and Zeng2020; Covernton et al., Reference Covernton, Cox, Fleming, Buirs, Davies, Juanes, Dudas and Dower2022). It is not known, however, what sizes of particles are most likely to translocate (Lusher et al., Reference Lusher, Hollman and Mendoza-Hill2017). Research into the bioaccumulation and biomagnification potential of microplastic particles has reached disparate conclusions (Provencher et al., Reference Provencher, Ammendolia, Rochman and Mallory2019; Walkinshaw et al., Reference Walkinshaw, Lindeque, Thompson, Tolhurst and Cole2020; Covernton et al., Reference Covernton, Davies, Cox, El-Sabaawi, Juanes, Dudas and Dower2021; McIlwraith et al., Reference McIlwraith, Kim, Helm, Bhavsar, Metzger and Rochman2021; Covernton et al., Reference Covernton, Cox, Fleming, Buirs, Davies, Juanes, Dudas and Dower2022; Pitt et al., Reference Pitt, Aluru, Hahn, Shumway and Ward2023). With respect to nanoplastics, a recent analysis of 100+ studies found evidence of both bioaccumulation and biomagnification (Kokilathasan and Dittrich, Reference Kokilathasan and Dittrich2022). In addition, many hydrophobic chemicals and heavy metals transmitted on the surface of microplastic particles are known to biomagnify (Landrigan et al., Reference Landrigan, Raps, Cropper, Bald, Brunner, Canonizado, Charles, Chiles, Donohue, Enck, Fenichel, Fleming, Ferrier-Pages, Fordham, Gozt, Griffin, Hahn, Haryanto, Hixson, Ianelli, James, Kumar, Laborde, Law, Martin, Mu, Mulders, Mustapha, Niu, Pahl, Park, Pedrotti, Pitt, Ruchirawat, Seewoo, Spring, Stegeman, Suk, Symeonides, Takada, Thompson, Vicini, Wang, Whitman, Wirth, Wolff, Yousuf and Dunlop2023). An extensive review further found that exposure to the constituent chemicals of plastic particles can cause severe damage to marine organisms, as can the persistent organic pollutants and heavy metals which adhere to particles (Muniz and Rahman, Reference Muniz and Rahman2025).

A wide range of consequences exist for different marine organisms. This includes negative impacts on reproduction, growth, energy levels, the ability to feed normally and direct mortality. Impacts also include biochemical and behavioural changes (Sazlı et al., Reference Sazlı, Nassouhi, Ergönül and Atasağun2023; Khanjani and Mohammadi, Reference Khanjani and Mohammadi2026). These consequences stem from the direct impact of the microplastics themselves but also include the indirect effects of the multiple chemicals, heavy metals, pathogens and other pollutants which cling to the surface of microplastic particles, serving as a vector for toxic cocktails of organic and inorganic pollutants (Chatterjee and Sharma, Reference Chatterjee and Sharma2019; Sharma et al., Reference Sharma, Bhardwaj, Thakur and Saini2024). Moreover, particles carrying these pollutants, especially pathogens living in the plastisphere, can be picked up in the ocean and transported thousands of kilometres by wind before being deposited in remote areas, resulting in the spread of pathogens and other pollutants throughout the marine environment (Trainic et al., Reference Trainic, Flores, Pinkas, Pedrotti, Lombard, Bourdin, Gorsky, Boss, Rudich, Vardi and Koren2020). This can compound the risks posed by marine epidemics, which are already a threat to many species.

Available information on marine microplastic impacts on specific marine organisms is unsettling, with various risks to species and populations with knock-on implications for food webs and ecosystem functions.

• ▪ Phytoplankton and microalgae. Phytoplankton are single-celled primary producer microorganisms at the base of the ocean’s most important systems and the foundation of marine food webs. Phytoplankton can be classified into two primary groups: photosynthetic cyanobacteria and microalgae (Falkowski, Reference Falkowski2012). Most of the most serious threats posed by microplastic pollution in the ocean begin with their interactions with and effects on phytoplankton, which can aggregate with plastic particles and impact growth (Lagarde et al., Reference Lagarde, Olivier, Zanella, Daniel, Hiard and Caruso2016; Long et al., Reference Long, Paul-Pont, Hégaret, Moriceau, Lambert, Huvet and Soudant2017). Although some research suggests that some algae may be able to recover from microplastic exposure in time, others studies suggest a wide range of extremely serious effects, such as toxicity decreasing phytoplankton populations, resulting in a loss of ecosystem productivity and causing a cascade of consequences for biodiversity and ecosystem services (Mao et al., Reference Mao, Ai, Chen, Zhang, Zeng, Kang, Li, Gu, He and Li2018; Muniz and Rahman, Reference Muniz and Rahman2025). Aggregation can have substantial effects on microalgae growth, a consequence which may become more pronounced as particle size decreases (Sjollema et al., Reference Sjollema, Redondo-Hasselerharm, Leslie, Kraak and Vethaak2016). Aggregation can also alter the buoyancy of microalgae and microplastic fragments (Lagarde et al., Reference Lagarde, Olivier, Zanella, Daniel, Hiard and Caruso2016). Moreover, nanoplastics can directly penetrate the cell membranes of phytoplankton (Kokilathasan and Dittrich, Reference Kokilathasan and Dittrich2022). When aggregated or penetrated by microplastic particles, the effects on phytoplankton could be incredibly harmful, including reducing photosynthesis, inhibiting growth, inducing oxidative stress and decreasing density (Zhang et al., Reference Zhang, Chen, Wang and Tan2017; Mao et al., Reference Mao, Ai, Chen, Zhang, Zeng, Kang, Li, Gu, He and Li2018; Prata et al., Reference Prata, Lavorante, Montenegro and Guilhermino2018; Chatterjee and Sharma, Reference Chatterjee and Sharma2019; Fu et al., Reference Fu, Zhang, Fan, Qi, Wang and Peng2019; Shen et al., Reference Shen, Ye, Zeng, Zhang, Xing, Tang, Wen and Liu2020; Sheela et al., Reference Sheela, Manimekalai and Dhinagaran2022; Salomone et al., Reference Salomone, Passucci and Areco2023; Li et al., Reference Li, Du, Qin, Bolan, Wang and Wang2024). Phytoplankton provide nourishment, either directly or through the food web, to practically the entire marine ecosystem (Falkowski, Reference Falkowski2012). Indeed, it is highly likely that changes to the global phytoplankton – and by extension zooplankton – populations will have deleterious effects on the ocean carbon sink, while also contributing to other tipping points, discussed below. In addition, marine phytoplankton produces approximately 55–80% of atmospheric oxygen (Richardson, Reference Richardson2008; Boyce et al., Reference Boyce, Lewis and Worm2010; McPherson et al., Reference McPherson, Sirmacek, Massa, Kallfelz and Vinuesa2023).

• ▪ Cetaceans. Marine microplastics pose multifaceted threats to marine megafauna, including cetaceans, threatening long-term survival with broader ecological and conservation implications. In the case of cetaceans, marine microplastics enter their systems through three main pathways, namely direct ingestion during feeding, incidental intake while surfacing and trophic transfer from contaminated prey (Hernandez-Gonzalez et al., Reference Hernandez-Gonzalez, Saavedra, Gago, Covelo, Santos and Pierce2018; Paul et al., Reference Paul, Nath, Bhattacharjee and Mukherjee2024). Marine microplastics block filtering apparatuses in baleen whales (Mysticetes), which feed at depths of 50–250 m, a stratum which tends to hold the highest level of microplastic concentrations, making these species particularly vulnerable. A study found that a single blue whale (Balaenoptera musculus) may ingest up to 10 million microplastic particles per day while filter-feeding, contributing to gastrointestinal blockages, chronic inflammation, internal injuries and reduced feeding efficiency (Kahane-Rapport et al., Reference Kahane-Rapport, Czapanskiy, Fahlbusch, Friedlaender, Calambokidis, Hazen, Goldbogen and Savoca2022). Toothed whales (Odontocetes), such as dolphins and killer whales (Orcinus orca), primarily accumulate microplastics through trophic transfer, reflecting contamination across the food web (Zantis et al., Reference Zantis, Carroll, Nelms and Bosker2021; He and Yin, Reference He and Yin2024). Moreover, exposure to marine microplastics and the chemicals therein, such as plasticizers, persistent organic pollutants and heavy metals, can leach into cetacean tissues (Paul et al., Reference Paul, Nath, Bhattacharjee and Mukherjee2024). These compounds have been linked to immunotoxicity, endocrine disruption and reproductive impairment, increased susceptibility to disease and reduced fecundity (He and Yin, Reference He and Yin2024). Recent studies confirm the presence of microplastics with fibres in the gastrointestinal tracts of multiple species, including franciscana dolphins (Pontoporia blainvillei) and Indo-Pacific humpback dolphins (Sousa chinensis), predominantly polyester and polypropylene, comprising the majority of detected particles (Zhu et al., Reference Zhu, Yu, Zhang, Li, Tan, Li, Yang and Wang2019; Padula et al., Reference Padula, Ronda, Rodríguez Pirani, Picone, Romano, Giardino, Seco Pon, Machado, Gerpe, Rodriguez and Denuncio2025). This evidence of absorption into intestinal wall tissues suggests systemic exposure, raising concerns about long-term physiological impacts. Moreover, climate change is altering cetacean habitats globally and is likely to intensify their risk of microplastic exposure, particularly in polar regions and coastal zones that are hotspots for microplastic pollution from melting sea ice and terrestrial runoff and fishing activities, increasing ingestion (Kelly et al., Reference Kelly, Wright, Woodward and Fussell2025).

• ▪ Keystone species. Marine microplastics also pose multifaceted threats to primary producers, bivalves and filter feeders, categories which include many keystone species such as zooplankton, oysters and some crustaceans (Kokilathasan and Dittrich, Reference Kokilathasan and Dittrich2022; Salomone et al., Reference Salomone, Passucci and Areco2023; Khanjani and Mohammadi, Reference Khanjani and Mohammadi2026). Lower trophic animals, especially zooplankton, are more at-risk from microplastics (Covernton et al., Reference Covernton, Cox, Fleming, Buirs, Davies, Juanes, Dudas and Dower2022). Planktonic feeders are much more likely than other species to have microplastics in their digestive track with higher quantities relative to body mass (Covernton et al., Reference Covernton, Davies, Cox, El-Sabaawi, Juanes, Dudas and Dower2021). When biofilms form around microplastic particles, it increases the likelihood of consumption (Hale et al., Reference Hale, Seeley, La Guardia, Mai and Zeng2020). In addition, the pattern of microalgae aggregating with microplastics may turn microplastics into a more attractive “food source” for zooplankton and filter feeders (Lagarde et al., Reference Lagarde, Olivier, Zanella, Daniel, Hiard and Caruso2016). These patterns may be most pronounced in sea shelf regions, where the high levels of biological productivity overlap most significantly with higher levels of marine microplastic pollution due to proximity to sources of terrestrial pollution. Zooplankton, which are active and abundant in these areas, are especially threatened, making them of particular concern as a keystone species (Clark et al., Reference Clark, Cole and Lindeque2016; Botterell et al., Reference Botterell, Beaumont, Dorrington, Steinke, Thompson and Lindeque2019). Zooplankton play a key role in marine ecosystem services, including in maintaining the food web (Lomartire et al., Reference Lomartire, Marques and Gonçalves2021). The ingestion of microplastics by zooplankton is linked with a wide range of detrimental effects, including abnormal feeding behaviour, lack of reproduction and slowed or inhibited growth, development and lifespan (Botterell et al., Reference Botterell, Beaumont, Dorrington, Steinke, Thompson and Lindeque2019; Chatterjee and Sharma, Reference Chatterjee and Sharma2019; Shen et al., Reference Shen, Ye, Zeng, Zhang, Xing, Tang, Wen and Liu2020; Kvale et al., Reference Kvale, Prowe, Chien, Landolfi and Oschlies2021; Pan et al., Reference Pan, Long, Hui, Xiao, Yin, Li, Liu, Tian and Chen2022). Moreover, ingestion of marine microplastics by zooplankton reduces their ingestion of phytoplankton, seriously inhibiting the regulation of phytoplankton populations (Kvale et al., Reference Kvale, Prowe, Chien, Landolfi and Oschlies2021). The pivotal role that zooplankton play in the transfer of energy and organic carbon from primary producers to higher order animals is therefore critically threatened (Lomartire et al., Reference Lomartire, Marques and Gonçalves2021). A study of microplastic exposure on copepods, an abundant and globally ubiquitous class of zooplankton, observed detrimental effects including impeded feeding, smaller eggs with reduced hatching success and reduced energy levels, culminating in starvation and death (Cole et al., Reference Cole, Lindeque, Fileman, Halsband and Galloway2015). The effects on feeding were pronounced even at relatively low microplastic concentrations. Given the impacts on zooplankton combined with their key role in marine ecosystems, the threats to ecological systems posed by microplastic pollution may be more pervasive and serious than previously thought (Pan et al., Reference Pan, Long, Hui, Xiao, Yin, Li, Liu, Tian and Chen2022).

• ▪ Coral reefs. Microplastics could compound the serious challenges already faced by coral reefs around the world. Reefs have been identified as one of the most at-risk systems to change induced by anthropogenic stressors (IPBES, 2019). Coral reef dieback is already recognised as a serious tipping point, which could have unprecedented consequences for marine food webs and ecosystems (Armstrong McKay and Loriani, Reference Armstrong McKay, Loriani, Lenton, Armstrong McKay, Loriani, Abrams, Lade, Donges, Milkoreit, Powell, Smith, Zimm, Buxton, Bailey, Laybourn, Ghadiali and Dyke2023). Existing challenges which could be compounded by microplastics include warming-induced bleaching, acidification and deoxygenation (Pearce-Kelly et al., Reference Pearce-Kelly, Altieri, Bruno, Cornwall, McField, Muñiz-Castillo, Rocha, Setter, Sheppard, Roman-Cuesta and Yesson2025). A microplastic-induced population crash in phytoplankton, a key food source for corals, could lead to mass starvation. Corals may also ingest microplastic particles directly, with potentially unexplored consequences. These particles could serve as a vector to transmit pathogens living in microbial film into corals (Chatterjee and Sharma, Reference Chatterjee and Sharma2019). This phenomenon has been demonstrated with E. coli bacteria whereby the accumulation of E. coli on marine microplastics infected corals which had ingested the particles, leading to rapid death of the corals (Rotjan et al., Reference Rotjan, Sharp, Gauthier, Yelton, Lopez, Carilli, Kagan and Urban-Rich2019). Bleaching itself reduces the resilience of corals to disease, potentially allowing microplastic-bound pathogens to wreak greater havoc once introduced (Pearce-Kelly et al., Reference Pearce-Kelly, Altieri, Bruno, Cornwall, McField, Muñiz-Castillo, Rocha, Setter, Sheppard, Roman-Cuesta and Yesson2025).

Marine organisms living in certain fragile ecosystems are also at increased risk. For example, the waters around the Galapagos Islands, a highly unique and sensitive ecosystem, are already inundated by a concentration of microplastics higher than that accumulated in the Great Pacific Garbage Patch (Lebreton et al., Reference Lebreton, Egger and Slat2019; McMullen et al., Reference McMullen, Calle, Alvarado-Cadena, Kowal, Espinoza, Domínguez, Tirapé, Vargas, Grant, Hunt, Pakhomov and Alava2024), which is the most widely recognised example of plastic accumulation in the ocean.

Loss of ocean carbon sink function

The ocean is the biggest natural sink for CO₂ on the planet, sequestering around 30% of anthropogenic CO₂ emissions (Shen et al., Reference Shen, Ye, Zeng, Zhang, Xing, Tang, Wen and Liu2020; Croot, Reference Croot2021). Already, as atmospheric CO₂ increases from human activities, the ocean absorbs less and less carbon, increasing the amounts of CO₂ that remain in the atmosphere (Sabine et al., Reference Sabine, Feely, Gruber, Key, Lee, Bullister, Wanninkhof, Wong, Wallace, Tilbrook, Millero, Peng, Kozyr, Ono and Rios2004). Disruptions to the ability of the ocean to sequester CO₂ could fundamentally unsettle the global carbon cycle, triggering apocalyptic consequences for humanity (Shen et al., Reference Shen, Ye, Zeng, Zhang, Xing, Tang, Wen and Liu2020; Nawab et al., Reference Nawab, Khan, Ihsanullah, Nafees and Shah2026).

Marine microplastic pollution impacts both major mechanisms of the ocean carbon sink: (i) the biological carbon pump and (ii) the sea-air gas exchange.

• ▪ Biological carbon pump. The biological carbon pump plays a critical role in moving carbon to deeper levels, where it is stored for long periods of time (Heinze et al., Reference Heinze, Meyer, Goris, Anderson, Steinfeldt, Chang, Le Quéré and Bakker2015; Vincent et al., Reference Vincent, Jennerjahn, Ramasamy, Vincent, Jennerjahn and Ramasamy2021). The efficacy and efficiency of the biological carbon pump is the primary determinant of a carbon balance between the ocean and the atmosphere and maintains a vertical equilibrium of carbon in the water column (Sabine et al., Reference Sabine, Feely, Gruber, Key, Lee, Bullister, Wanninkhof, Wong, Wallace, Tilbrook, Millero, Peng, Kozyr, Ono and Rios2004; Cavan et al., Reference Cavan, Henson, Belcher and Sanders2017). Phytoplankton is the core driver of the biological carbon pump, converting CO₂ to oxygen and particulate organic carbon via photosynthesis for the massing of carbon upon which the biological pump relies (Falkowski, Reference Falkowski2012). Zooplankton are equally crucial, consuming phytoplankton and the sequestered carbon (Basu and Mackey, Reference Basu and Mackey2018). Much of marine snow, the continuous shower of mostly organic detritus falling from the upper layers of the water column, is zooplankton faecal pellets, which carry carbon to the seafloor (Shen et al., Reference Shen, Ye, Zeng, Zhang, Xing, Tang, Wen and Liu2020). Through these processes, phytoplankton and zooplankton are key regulators of planetary carbon cycling and play a determining role in deep ocean chemistry (Falkowski, Reference Falkowski2012). Microplastic pollution threatens the biological carbon pump on multiple fronts. Microplastics can prevent the light penetration necessary for photosynthesis in phytoplankton (Zhao et al., Reference Zhao, Tan, Huang and Wang2019; Shen et al., Reference Shen, Ye, Zeng, Zhang, Xing, Tang, Wen and Liu2020; Kokilathasan and Dittrich, Reference Kokilathasan and Dittrich2022; Hou et al., Reference Hou, Mu, Hu and Guo2023; Li et al., Reference Li, Du, Qin, Bolan, Wang and Wang2024). Microplastic exposure can directly induce reductions in chlorophyll and cause cytotoxicity in phytoplankton (Zhao et al., Reference Zhao, Tan, Huang and Wang2019). Zooplankton consumption of microplastic pellets reduces their consumption of phytoplankton, therefore reducing the rates of carbon cycling to the deep ocean (Shen et al., Reference Shen, Ye, Zeng, Zhang, Xing, Tang, Wen and Liu2020). Microplastic particles aggregate with marine snow and infiltrate zooplankton faecal pellets via consumption, causing them to sink at slower rates and subjecting them to fragmentation, causing less carbon to reach the deep ocean (Cole et al., Reference Cole, Lindeque, Fileman, Clark, Lewis, Halsband and Galloway2016; Shen et al., Reference Shen, Ye, Zeng, Zhang, Xing, Tang, Wen and Liu2020; Sheela et al., Reference Sheela, Manimekalai and Dhinagaran2022; Galgani et al., Reference Galgani, Goßmann, Scholz-Böttcher, Jiang, Liu, Scheidemann, Schlundt and Engel2022).

• ▪ Sea-air gas exchange. The sea-air gas exchange is the process by which atmospheric CO₂ dissolves into the ocean. This is facilitated by the sea-surface microlayer, a unique boundary between the atmosphere and the ocean with specific physical, chemical and biological properties, and in which organic compounds accumulate (Wurl et al., Reference Wurl, Stolle, Van Thuoc, Thu and Mari2016; Galgani et al., Reference Galgani, Goßmann, Scholz-Böttcher, Jiang, Liu, Scheidemann, Schlundt and Engel2022). Sea-slicks, organic formations with biofilm-like properties, are characterised by the presence of active microbial colonies which contribute to slicks of enriched gelatinous and particulate matter (Wurl et al., Reference Wurl, Stolle, Van Thuoc, Thu and Mari2016). Microplastic fragments accumulate at the surface of the ocean and, as particles biofoul and develop a plastisphere, the concentration of organic matter in the microlayer is increased (Garabétian, Reference Garabétian1990; Wurl et al., Reference Wurl, Stolle, Van Thuoc, Thu and Mari2016; Wan Mahari et al., Reference Wan Mahari, Anuar, Lam, Ibrahim, Bhubalan, Vijayan, Joseph, Vandana, Juraij, Priya, Hernandez Santos, Govinda, Katiyar, Ayyamperumal, Gaur and Chinglenthoiba2026). These plastispheres around individual particles have implications for the cycling of CO₂ (and N₂O) in the water column, potentially altering fundamental biogeochemical processes (Cornejo-D’Ottone et al., Reference Cornejo-D’Ottone, Molina, Pavez and Silva2020; Zhang et al., Reference Zhang, Liang, Zeng, Tang, Lu, Luo, Xing, Tang, Ye, Li and Huang2020). The plastisphere could seriously damage the sea-air gas exchange, as a result of the presence of microplastics with their corresponding biofilms increasing the production of carbohydrate-like substances and proteinaceous gel compounds on the sea surface (Cornejo-D’Ottone et al., Reference Cornejo-D’Ottone, Molina, Pavez and Silva2020; Galgani et al., Reference Galgani, Goßmann, Scholz-Böttcher, Jiang, Liu, Scheidemann, Schlundt and Engel2022). In extreme scenarios, intensified microbial respiration in the sea-air microlayer could make the ocean a net source of CO₂, completely upending the planetary carbon cycle (Garabétian, Reference Garabétian1990; Wurl et al., Reference Wurl, Stolle, Van Thuoc, Thu and Mari2016).

In summary, both the biological carbon pump and sea-air exchange, mechanisms that maintain the ocean carbon sink function, are extremely vulnerable to marine microplastic pollution, with potentially catastrophic impacts on atmospheric CO₂ concentrations (Falkowski, Reference Falkowski2012; Galgani et al., Reference Galgani, Goßmann, Scholz-Böttcher, Jiang, Liu, Scheidemann, Schlundt and Engel2022; Hou et al., Reference Hou, Mu, Hu and Guo2023).

Ocean deoxygenation

Ocean deoxygenation via harmful algae blooms could be both a cause and effect of food web collapse. Bivalves such as mussels and oysters are a keystone species in the regulation of phytoplankton activity. Damage to bivalve populations can upset the regulatory balance and result in massive harmful algae blooms followed by deoxygenation and mass mortality among other marine species (Huang et al., Reference Huang, Leung, Hu, Xu and Wang2022; Kokilathasan and Dittrich, Reference Kokilathasan and Dittrich2022; Li et al., Reference Li, Du, Qin, Bolan, Wang and Wang2024). Microplastic consumption by zooplankton could trigger similar dynamics (Kvale et al., Reference Kvale, Prowe, Chien, Landolfi and Oschlies2021). When zooplankton ingest microplastic particles, the subsequent decrease in feeding and vulnerability to predators could impact zooplankton populations and result in uncontrolled algae growth (Pan et al., Reference Pan, Long, Hui, Xiao, Yin, Li, Liu, Tian and Chen2022). In addition, the settling and accumulation of microplastic particles on the seafloor can reduce oxygen transfer and trigger hypoxic conditions for aquatic organisms while promoting anaerobic processes (Wang et al., Reference Wang, Li, Peng, Wang, Zeng and Zeng2018). Taking different mechanisms into account, one study concluded that the physical effects of marine plastic pollution could have an impact on ocean oxygenation equal to 50% of the effect of global climate warming (Kvale et al., Reference Kvale, Prowe, Chien, Landolfi and Oschlies2021).

Food web collapse

The risk of microplastic particles being transported up marine food webs is extremely high (Sazlı et al., Reference Sazlı, Nassouhi, Ergönül and Atasağun2023). A recent review of over 200 studies published to date concluded that there is “convincing evidence” of trophic transfer of microplastics occurring (McIlwraith et al., Reference McIlwraith, Kim, Helm, Bhavsar, Metzger and Rochman2021). Models identifying thresholds for which microplastics could lead to food web collapse in aquatic environments have already been suggested on at least two occasions (Leoni et al., Reference Leoni, Nava and Patelli2018; Kong and Koelmans, Reference Kong and Koelmans2019). In addition, in-situ examples of high levels of microplastic pollution threatening food web collapse in freshwater lakes in India also exist (Sruthy and Ramasamy, Reference Sruthy and Ramasamy2017). Another study suggested a causal link between microplastic pollution and food system tipping points, finding that microplastic consumption at intermediate trophic levels could cause cascading effects on populations both above and below the intermediate level (Qian et al., Reference Qian, Lai, Chen and Xu2024). These could include abrupt and irreversible declines in marine populations, including a triggering of the “predator loop,” a positive feedback mechanism where the biomass of predator species rises uncontrollably in relation to the biomass of consumer species, leading to eventual population collapse. In the ocean, these dynamics could have devastating consequences for the population health of fish species with high degrees of economic importance, such as seabass and mackerel (Khanjani and Mohammadi, Reference Khanjani and Mohammadi2026). There is compelling evidence to suggest that microplastics do not need to directly affect every marine species to have devastating impacts on an ecosystem (Villarrubia-Gómez et al., Reference Villarrubia-Gómez, Almroth, Eriksen, Ryberg and Cornell2024). For example, by providing an abundant hard substrate for ocean-dwelling insect species such as Halobates sericeus to lay eggs, which had previously been limited in population growth due to the natural scarcity of such substrates, microplastics may enable the sudden proliferation of certain species beyond what was previously possible. Sudden changes in the populations of these insects, a predator of plankton, may have dire results for plankton populations (Goldstein et al., Reference Goldstein, Rosenberg and Cheng2012). This is just a single example.

Some scientists, however, caution for more research on how microplastics may affect food webs and how impacts on individual organisms may scale up to influence ecosystem tipping points (Kühn and van Franeker, Reference Kühn and van Franeker2020; Qian et al., Reference Qian, Lai, Chen and Xu2024). Multiple studies have warned against attaching undue credibility to laboratory studies due to the complexities of the natural marine environment being extremely difficult to replicate (Sjollema et al., Reference Sjollema, Redondo-Hasselerharm, Leslie, Kraak and Vethaak2016; Long et al., Reference Long, Paul-Pont, Hégaret, Moriceau, Lambert, Huvet and Soudant2017; Nava and Leoni, Reference Nava and Leoni2021).

Sea ice melting

Sea ice melting, most urgently of the Greenland and West Antarctic ice sheets, is considered a highly at-risk climate tipping point (Armstrong McKay and Loriani, Reference Armstrong McKay, Loriani, Lenton, Armstrong McKay, Loriani, Abrams, Lade, Donges, Milkoreit, Powell, Smith, Zimm, Buxton, Bailey, Laybourn, Ghadiali and Dyke2023). Sea ice is a key regulator of the global climate, with a high albedo that restricts solar radiation absorption by the Earth’s surface. This process is known as ice-albedo feedback, where increased warming leads to ice melting, in turn leading to greater solar radiation absorption and more warming, contributing to yet more melting (Comiso et al., Reference Comiso, Parkinson, Gersten and Stock2008). Microplastic pollution could increase this melting, hastening tipping points for sea ice. Microplastics are absorbed into sea ice in significant quantities, concentrating in the first centimetre of ice (Geilfus et al., Reference Geilfus, Munson, Sousa, Germanov, Bhugaloo, Babb and Wang2019). Once microplastics are present in ice, they increase light absorption and decrease surface albedo, which makes melting more rapid and releases previously trapped particles (Geilfus et al., Reference Geilfus, Munson, Sousa, Germanov, Bhugaloo, Babb and Wang2019; Evangeliou et al., Reference Evangeliou, Grythe, Klimont, Heyes, Eckhardt, Lopez-Aparicio and Stohl2020; Chen et al., Reference Chen, Huang, Gao and Wu2021; Ming and Wang, Reference Ming and Wang2021). These freed particles could be carried into and captured by other ice, causing more melting (Ming and Wang, Reference Ming and Wang2021). As the climate warms, thick and permanent ice may shift to thinner seasonal or annual ice. This change will create a net release of microplastics back into the ocean, flipping the Arctic from being a microplastic sink to a microplastic source (Obbard et al., Reference Obbard, Sadri, Wong, Khitun, Baker and Thompson2014). In addition to contributing to positive feedback loops in ice melting, microplastics in ice could impact ice algae and other biological processes taking place in ice or settle in Arctic melt pools with unexplored ecological consequences (Geilfus et al., Reference Geilfus, Munson, Sousa, Germanov, Bhugaloo, Babb and Wang2019; Evangeliou et al., Reference Evangeliou, Grythe, Klimont, Heyes, Eckhardt, Lopez-Aparicio and Stohl2020). Moreover, microplastics contributing to changing albedo in the Greenland Ice Sheet could hasten melting, with increased meltwater entering the North Atlantic Ocean weakening the Atlantic Meridional Overturning Circulation and potentially causing a system collapse (Klose et al., Reference Klose, Karle, Winkelmann and Donges2020). While climate change is the primary culprit of sea ice melting, the contribution of microplastics as a contributor factor could be prove decisive for a system operating on the margins.

Science–policy interfaces

Science–policy interfaces can take many forms. The overarching objective is to create a framework that enables science to contribute to policy formulation and vice versa (Zhang et al., Reference Zhang, Zhao and Chen2024).

The literature on effective science–policy interfaces identify a range of institutional and operational traits, including multi-level engagement (Wagner et al., Reference Wagner, Velander, Biber-Freudenberger and Dietz2023), high levels of transparency (Zhang et al., Reference Zhang, Zhao and Chen2024), collaborative structures (Koetz et al., Reference Koetz, Farrell and Bridgewater2012), high levels of relevance for policymakers (Koetz et al., Reference Koetz, Farrell and Bridgewater2012; Zhang et al., Reference Zhang, Zhao and Chen2024), and inclusivity and transdisciplinary work (Wagner et al., Reference Wagner, Sarkki and Dietz2024; Zhang et al., Reference Zhang, Zhao and Chen2024). Science–policy interfaces also create positive trends in funding availability, open spaces for regional dialogue and grow public awareness and interest in environmental issues. Taken together, these factors have been identified as contributing to the development of “science diplomacy” whereby diplomatic action facilitates international scientific collaboration and vice versa (Mastrángelo et al., Reference Mastrángelo, Torres, Borbor-Cordova, Hurlbert, Silva and Stewart2024).

The most well-known science–policy interfaces are the independent panels dedicated to the planetary crises, namely the: Intergovernmental Panel on Climate Change (IPCC), Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) and Intergovernmental Science-Policy Panel on Chemicals, Waste and Pollution (ISP-CWP). The IPCC, IPBES and ISP-CWP co-exist with dedicated scientific bodies established under the treaties on climate change, biodiversity and chemicals. The IPCC, established in 1988 by the United Nations Environmental Programme (UNEP) and the World Meteorological Organisation (WMO), conducts international scientific assessments of climate change and has become the preeminent body understanding the science of global climate change (Wagner and Hornidge, Reference Wagner and Hornidge2025). Its reports, such as the Special Report on Global Warming of 1.5 Degrees Celsius, are highly influential (Zhang et al., Reference Zhang, Zhao and Chen2024). Although the IPCC does not necessarily conduct its own research, rather acting as collators and synthesisers of the best existing information, it provides the scientific foundation for climate-related policymaking and international negotiations (Wagner and Hornidge, Reference Wagner and Hornidge2025). Policymakers tend to hold a deep trust in the IPCC to deliver scientifically sound findings (Wagner and Hornidge, Reference Wagner and Hornidge2025). The IPBES, established in 2012, fulfils a similar function for biodiversity. More recently, in 2025, the ISP-CWP was established as an independent panel to strengthen the global science–policy interface on chemicals, waste and pollution and advance scientific understanding – modelled on the IPCC and IPBES (UNEP, 2022). A main advantage of an independent panel is its ability to decide on its own programme of work, producing thematic or timely analyses of cross-cutting relevance and addressing issues that fall outside the remit of the subsidiary body or remain overlooked (Busch et al., Reference Busch, Schulte and Simon2021).

Other science–policy interfaces aim for a closer relationship among scientists and policymakers. Perhaps the most impactful is the Scientific Assessment Panel (SAP) and Environmental Effects Assessment Panel (EEAP) of the Montreal Protocol on Substances That Deplete the Ozone Layer, which bring together top scientists from around the world to assess ozone layer depletion, its effects and related issues (UNEP Ozone Secretariat, n.d.-a). Every 4 years, the Parties to the Montreal Protocol determine the composition and terms of reference of the panels, which produce reports periodically for policymakers, referred to as quadrennial assessments (UNEP Ozone Secretariat, n.d.-b). In support, the Parties also convene a panel of technical and economic experts via the Technical and Economic Assessment Panel (TEAP) to assess technical and economic aspects, such as feasibility of alternatives, mitigation potential and cost implications of proposed measures. In addition, policymakers frequently request ad hoc reports on specific topics, in an iterative process that can span several years, to resolve concerns and create a shared understanding of the science and its implications – upon which to then base decisions. In this way, the Montreal Protocol ensures a steady drumbeat of actionable and policy-relevant scientific evidence and technical and economic information, tethered to the priorities of policymakers and decision-making (Mastrángelo et al., Reference Mastrángelo, Torres, Borbor-Cordova, Hurlbert, Silva and Stewart2024).

Designing a science–policy interface

As a starting point, to avoid marine microplastic tipping points, scientists should develop reliable quantitative analyses and models for marine microplastic pollution, identifying scenarios and reductions to stay within a safe operating zone, regularly informed and updated by research.

Three fundamental aspects require particular attention from a scientific and policy perspective.

• ▪ Baselines and trends. Assessing the spatial presence and temporal trends of microplastics in the marine environment – across the ocean surface, seabed, shoreline, water column and key biota – requires a standardised monitoring framework (Fossi et al., Reference Fossi, Pedà, Compa, Tsangaris, Alomar, Claro, Ioakeimidis, Galgani, Hema, Deudero, Romeo, Battaglia, Andaloro, Caliani, Casini, Panti and Baini2018; Sheela et al., Reference Sheela, Manimekalai and Dhinagaran2022). Several aspects have been identified as in need of standardisation, including methodologies for sampling marine microplastics as well as approaches for determining baseline, composition, distribution, retention and transport (GESAMP, 2015; Elawady et al., Reference Elawady, Mohammed and Abid2026).

• ▪ Sources and inputs. Assessing the sources and inputs of marine microplastics into the ocean – from both sea and land – requires a standardised reporting framework. Regular reporting of statistical data on plastic production, use, management and leakage should be required by policymakers, supported by the development of emission factors for different microplastic sources as well as methodologies for calculating degradation of macroplastics through processes like photo-oxidation, fragmentation and mechanical abrasion (GESAMP, 2015). In the absence of robust reporting, only best estimates based on a combination of public and proprietary data are available, providing a less accurate picture of the situation on the ground and the impacts of measures to reduce the sources and inputs.

• ▪ Hazards, risks and thresholds. Although hazards, risks and thresholds for marine microplastic tipping points remain uncertain, their existence should be undeniable. Scientists should urgently work to identify the hazards, risks and thresholds (concentration levels or ranges) for various marine microplastic tipping points, taking into account regional differences, regularly updating and revising as more scientific evidence becomes available, and outline scenarios for remaining within a safe operating zone.

Taken together, these aspects would enable a science–policy interface on marine microplastic pollution to achieve a clear objective: produce policy-relevant science to facilitate policymaker consideration and adoption of measures to reduce microplastics at the pace and scale required to stay within a safe operating zone, as illustrated in Figure 1:

Figure 1.

Visualisation of the conceptual framework for marine plastic pollution.

Figure 1. Long description

Visualisation of the conceptual framework for marine plastic pollution, premised on keeping microplastic concentrations within a safe operating zone and avoiding marine microplastic tipping points.

Once this conceptual framework is mainstreamed across scientists and policymakers, questions will arise on the practical matters related to governance, decisions, responsibilities and outputs of the science–policy interface.

Policymakers and scientists must engage regularly to advance our understanding of the impacts of marine microplastic pollution and how to address it. To this end, the governing body of any new international legally binding instrument, commonly the Conference of the Parties (COP), would benefit from a scientific subsidiary body to conduct periodic assessments and ad hoc reports on specific topics related to marine microplastic tipping points, set out in the terms of reference adopted by it. This would enable scientists to shape policy, and for policies to be informed by science, through an iterative process based on the priorities and needs of policymakers to keep humanity within a safe operating zone, as illustrated in Figure 2:

Figure 2.

Approach to decision-making under the science–policy Interface.

Figure 2. Long description

Approach to decision-making under the science-policy interface, characterised by an iterative process in which scientific input is requested and refined to inform future decisions.

The iterative process above, which is drawn from successful experiences in multilateral spaces, has many benefits. First, it allows policymakers to solicit scientific information needed to inform its decision-making, ensuring high levels of relevance and transparency. Second, it fosters engagement among policymakers and scientists, in open forums, constructing a shared sense of scientific fact and uncertainty upon which to act or explore, particularly important for policymakers from different backgrounds and political persuasions. Third, it provides insights into areas for further research, creating a forum in which to present and enhancing its future impact. In terms of the composition of a scientific subsidiary body, these aspects are addressed upon its establishment and would be regularly reviewed. Similarly, complementary aspects related to baselines, trends, sources, inputs, risks, thresholds, methodologies and approaches for reporting and monitoring form part of the considerations involved.

How policymakers respond to science is the domain of balancing environmental, social and economic interests, priorities and ambitions. But for microplastics overall, and for any given source of microplastics, a series of interventions are available to reduce their contribution to marine microplastic pollution. This includes measures for pellets, personal-care products, marine coatings, cleaning agents, synthetic textile fibres, tires and plastic items that tend to end up in the marine environment where they degrade into microplastics (OECD, 2024; Pew Charitable Trust, 2025). For these reasons, the conceptual framework would further benefit from technical and economic assessment to support policymakers’ consideration of potential measures to take in response to the science, similar to the action-oriented model of the Montreal Protocol.

Finally, the science–policy interface does not operate in a vacuum. It forms a part of the larger fabric of an international legally binding instrument on plastic pollution, and should be coupled with finance, capacity-building and technology transfer to countries in need to promote implementation and scale up solutions, as well as funding for further scientific and technological research and development, as appropriate. All these activities and more would be logical outgrowths of a well-designed science–policy interface for marine microplastic pollution as policymakers seek to keep us within a safe operating zone and avoid marine microplastic tipping points.

Recommendations

Marine microplastic tipping points can only be avoided through international collaboration and coordination.

In March 2022, the United Nations Environment Assembly (UNEA) adopted resolution 5/14, titled End Plastic Pollution: Towards an International Legally Binding Instrument, convening an intergovernmental negotiating committee (INC) to develop the new global agreement on plastic pollution. The INC mandate calls for developing an international legally binding instrument on plastic pollution, including in the marine environment, based on a comprehensive approach that addresses the full lifecycle of plastic, and sets out a series of provisions to be developed. Among them are provisions “[t]o promote national and international cooperative measures to reduce plastic pollution in the marine environment, including existing plastic pollution,” and “[t]o provide scientific and socio-economic assessments related to plastic pollution,” including “the possibility of a mechanism to provide policy relevant scientific and socio-economic information and assessment related to plastic pollution” (UNEP, 2022). Shortly thereafter, the Scientists’ Coalition for an Effective Plastics Treaty was formed, creating a network of independent scientific and technical experts seeking to contribute to the treaty process with summaries and interpretations of scientific knowledge to stakeholders involved in the negotiations (Scientists’ Coalition for an Effective Plastics Treaty, n.d.). At the time of publication, negotiations on the international legally binding instrument on plastic pollution are ongoing.

Against this background, the following recommendations are made:

• ▪ Scientists: Scientists should elaborate upon the conceptual framework for marine microplastic pollution presented herein, fine-tuning and supplementing as needed, setting out an overall vision, its constituent components and an initial programme of work, among other aspects. The immediate aim should be to articulate the substrate of an effective science–policy interface within the new instrument, outlining the key elements for monitoring, reporting, subsidiary bodies, effectiveness evaluations and scientific, technical and economic assessment in order to inform policy over time. Following its entry into force, other opportunities to provide input will arise, for example the terms of reference and mandates of the subsidiary bodies and development of guidelines and methodologies for monitoring and reporting.

• ▪ International legally binding instrument on plastic pollution: Governments should include provisions in the new instrument that: set out standardised monitoring and reporting frameworks covering marine microplastic pollution; empower the governing body to establish subsidiary bodies to provide periodic and ad hoc scientific, technical and economic assessment, designed for relevance and responsiveness to the needs and priorities of policymakers, focused on avoiding marine microplastic tipping points; empower the governing body to adopt policies and measures to address microplastics, taking a comprehensive approach across their lifecycle; and provide financial and technical assistance to countries in need.

• ▪ Intergovernmental science-policy panel on chemicals, waste and pollution: The ISP-CWP should contribute to horizon-scanning and gap-identification, both of which fall within its mandate, for marine microplastic pollution and chemicals related thereto, playing a complementary and interstitial role (UNEP, 2022).

Although the focus here has been on developing a conceptual framework for marine microplastic pollution, underpinned by avoidance of tipping points, that is but one aspect of overall plastic pollution. Conceptual frameworks for enhancing the science-policy frameworks on other issues of concern will be needed, including chemicals and health as those relate to plastics.