Impact statement

This perspective is co-authored by an international and interdisciplinary group of scientists from 10 different countries. Many of us have spent years, and in some cases decades, studying plastic pellets and their impacts. The X-Press Pearl disaster of 2021, as well as a series of other large-scale spills, has highlighted the urgent need for science-based regulatory action on plastic pellets (nurdles). Our commentary synthesizes decades of research on the physical and chemical hazards of plastic pellets, contextualized within recent international policy developments. We argue that classifying plastic pellets as environmentally hazardous substances (aquatic environment) and/or harmful substances under the International Maritime Organization’s regulatory framework is both scientifically justified and essential to reducing risks to ecosystems and coastal communities.

Physical hazards

The potential for ingested plastics to cause physical harm to seabirds was highlighted 40 years ago when a study of 60 seabird species indicated that plastics were present in at least 60% (n = 36) (Ryan, Reference Ryan1986). Following that discovery, another early study, based on a feeding trial with chickens, suggested the ingestion of plastic pellets could reduce food consumption and result in slower growth of birds (Ryan, Reference Ryan1988). Moreover, in New Zealand, pellets were detected in five species of prion (7–20% of individual birds, depending on the species) despite many of the carcasses having been collected in the 1950s and 1960s (Harper and Fowler, Reference Harper and Fowler1987), prior to pellets being documented in the oceans (Carpenter and Smith, Reference Carpenter and Smith1972). The prions’ cause of death was attributed to starvation, with the ingested pellets potentially playing a role in this (Harper and Fowler, Reference Harper and Fowler1987).

Since then, studies have shown that plastic pellets are frequently ingested by dozens of seabird species (e.g., Lavers and Bond, Reference Lavers and Bond2016; Lavers et al., Reference Lavers, Hutton and Bond2021) and other marine organisms (e.g., Van Franeker and Law, Reference Van Franeker and Law2015; Day et al., Reference Day, Swadling, Huggett and Gaston2024), potentially because they resemble fish eggs (Galgani and Rangel-Buitrago, Reference Galgani and Rangel-Buitrago2024). For instance, Miranda and de Carvalho-Souza (Reference Miranda and de Carvalho-Souza2016) reported that 62.5% of king mackerel (Scomberomorus cavalla) and 33% of sharpnose sharks (Rhizoprionodon lalandii) in Brazil had ingested plastic pellets. Besides being present in the gut, pellets can enter the gills of fish, as demonstrated for two pelagic fish species in Ghana (Nuamah et al., Reference Nuamah, Tulashie, Debrah and Pèlèbè2023). Ingestion of pellets has also been documented in sea turtles (Santos et al., Reference Santos, Andrades, Boldrini and Martins2015; Di Renzo et al., Reference Di Renzo, Mascilongo, Berti, Bogdanovic, Listes, Brkljaca, Notarstefano, Gioacchini, Giorgini, Olivieri, Silvestri, Matiddi, D’Alterio, Ferri and Di Giacinto2021). Globally, an estimated 445,970 tons of pellets are thought to enter the environment each year (Galgani and Rangel-Buitrago, Reference Galgani and Rangel-Buitrago2024) – enough to “feed” millions of young seabirds. Thus, there is an urgent need to address this issue as the ingestion of plastic, including pellets, has been linked with a raft of serious health conditions, including plasticosis (Charlton-Howard et al., Reference Charlton-Howard, Bond, Rivers-Auty and Lavers2023), organ failure (Rivers-Auty et al., Reference Rivers-Auty, Bond, Grant and Lavers2023) and neurodegeneration (de Jersey et al., Reference de Jersey, Lavers, Bond, Wilson, Zosky and Rivers-Auty2025).

Chemical hazards

The ability of plastic pellets to transport hazardous chemicals across ocean basins and through marine food webs has been recognized since at least the 1970s (Carpenter et al., Reference Carpenter, Anderson, Harvey, Miklas and Peck1972). More recently, this was highlighted during evaluations of the plastic additive UV-328 under the Stockholm Convention, which concluded that leaching of UV-328 from ingested plastics is a significant exposure pathway for the chemical (Yamashita et al., Reference Yamashita, Tanaka, Yeo, Takada, van Franeker, Dalton, Dale, Takada and Karapanagioti2019; Tanaka et al., Reference Tanaka, Watanuki, Takada, Ishizuka, Yamashita, Kazama, Hiki, Kashiwada, Mizukawa, Mizukawa, Hyrenbach, Hester, Ikenaka and Nakayama2020). The toxicity of plastic pellets depends on several factors, including their original chemical composition, the extent of weathering and degradation and chemicals sorbed from the surrounding environment (Lavers et al., Reference Lavers, Howell, Bond, Howard, de Jonge, Puskar and Banati2025).

Globally, more than 350,000 synthetic chemicals are registered for production and use (Wang et al., Reference Wang, Walker, Muir and Nagatani-Yoshida2020). Of these, the formulation and safety of >50,000 chemicals are claimed as confidential or ambiguously described (Wang et al., Reference Wang, Walker, Muir and Nagatani-Yoshida2020; Wiesinger et al., Reference Wiesinger, Wang and Hellweg2021). Despite this uncertainty, more than 16,000 synthetic chemicals are known to be regularly used or present in plastics, including 4,200 chemicals of concern (Monclús et al., Reference Monclús, Arp, Groh, Faltynkova, Loseth, Muncke, Wang, Wolf, Zimmermann and Wagner2025). Yet, the composition of plastics is rarely disclosed, making it nearly impossible to know the full chemical composition of specific pellets. A range of hazardous chemicals has, however, been identified in pellets, including persistent organic pollutants and heavy metals (e.g., Holmes et al., Reference Holmes, Turner and Thompson2012, Mato et al., Reference Mato, Isobe, Takada, Kanehiro, Ohtake and Kaminuma2001, Yamashita et al., Reference Yamashita, Tanaka, Yeo, Takada, van Franeker, Dalton, Dale, Takada and Karapanagioti2019, Yeo et al.2017, Alidoust et al. Reference Alidoust, Yeo, Mizukawa and Takada2021, Arias et al., Reference Arias, Alvarez, Pozo, Pribylova, Klanova, Pirani, Picone, Alvarez and Tombesi2023, Matsunaga et al., Reference Matsunaga, Takada, Sakane, Hirai, Alidoust, Yeo, Mizukawa, Tanaka, Akita, Karapanagioti, Eriksson and Burton2025), and pellets disperse the chemicals across the globe (Karlsson et al., Reference Karlsson, Brosché, Alidoust and Takada2021; Matsunaga et al., Reference Matsunaga, Takada, Sakane, Hirai, Alidoust, Yeo, Mizukawa, Tanaka, Akita, Karapanagioti, Eriksson and Burton2025).

The situation is even more complex for recycled plastic pellets as those have been shown to contain a broader array of contaminants than virgin materials, including pesticides, pharmaceuticals, flame retardants and heavy metals (Huang et al., Reference Huang, Xie, Li and Zhang2021; Carmona et al., Reference Carmona, Rojo-Nieto, Rummel, Krauss, Syberg, Ramos, Brosché, Backhaus and Almroth2023; Lavers et al., Reference Lavers, Howell, Bond, Howard, de Jonge, Puskar and Banati2025). These are non-intentionally added substances that come from the materials that are being recycled. Additional substances, such as dioxins, can unintentionally form during the processing (Zennegg et al., Reference Zennegg, Schluep, Streicher-Porte, Lienemann, Haag and Gerecke2014).

Beyond the chemicals incorporated during different production stages or blended during recycling, plastics can also sorb chemicals from the surrounding environment (Mato et al., Reference Mato, Isobe, Takada, Kanehiro, Ohtake and Kaminuma2001; Richard et al., Reference Richard, Carpenter, Komada, Palmer and Rochman2019; Yamashita et al., Reference Yamashita, Tanaka, Yeo, Takada, van Franeker, Dalton, Dale, Takada and Karapanagioti2019; Lavers et al., Reference Lavers, Howell, Bond, Howard, de Jonge, Puskar and Banati2025). These are often present at lower concentrations than the plastic chemicals themselves but may nonetheless add to their toxicity.

As plastics often contain mixtures of chemicals with differing modes of action (e.g., carcinogenicity and endocrine disruption), their combined toxicity is difficult to predict. Field studies have repeatedly documented toxic substances in pellets collected from the environment (e.g., Holmes et al., Reference Holmes, Turner and Thompson2012, Mato et al., Reference Mato, Isobe, Takada, Kanehiro, Ohtake and Kaminuma2001, Yamashita et al., Reference Yamashita, Tanaka, Yeo, Takada, van Franeker, Dalton, Dale, Takada and Karapanagioti2019) and experimental studies have demonstrated toxic effects across a range of bio- and petroleum-based plastic pellets (Schiavo et al., Reference Schiavo, Oliviero, Romano, Dumontet and Manzo2018; Zimmermann et al., Reference Zimmermann, Dombrowski, Völker and Wagner2020; Chen et al., Reference Chen, Gong, McKie, Almuhtaram, Sun, Barrett, Yang, Wu, Andrews and Peng2022; Shigeishi et al., Reference Shigeishi, Yamashita, Tanaka, Kazama, Sena, Takada, Ikenaka, Ishizuka, Koyama, Yoda and Watanuki2025). While this is unlikely to reflect environmentally relevant conditions where animals are exposed to a “cocktail” of chemicals simultaneously (Rochman Reference Rochman2015), single-pollutant studies continue to provide useful information. For example, pellet leachates have been shown to induce stress responses in algae (Krienitz et al., Reference Krienitz, Bock, Nozaki and Wolf2011; Machado and Soares, Reference Machado and Soares2024), cell damage (Khoshnamvand et al., Reference Khoshnamvand, Hanachi, Ashtiani and Walker2021) and to negatively affect development in at least 10 marine invertebrate species (Jimenez-Guri et al., Reference Jimenez-Guri, Paganos, La Vecchia, Annona, Caccavale, Molina, Ferrández-Roldán, Donnellan, Salatiello, Johnstone, Eliso, Spagnuolo, Cañestro, Albalat, Martín-Durán, Williams, D’Aniello and Arnone2024). Chemicals in plastic pellets are also known to impact vertebrate metabolism and the endocrine system (James et al., Reference James, Medvedev, Medvedeva, Martsen, Gorman, Lin, Makarov, Aluwihare, de Vos, Reddy and Hahn2024; Kardgar König et al., Reference Kardgar König, Carmona, Karlsson, Brosché and Carney Almroth2025).

In addition to the concerns associated with the toxicity of plastic chemicals, it is also important to note that the longevity (persistence) of chemicals has been highlighted as a key issue (Cousins et al., Reference Cousins, Ng, Wang and Scheringer2019). Many plastic chemicals are persistent pollutants, such as polybrominated diphenyl ethers, hexabromocyclododecane and chlorinated paraffins (Monclús et al., Reference Monclús, Arp, Groh, Faltynkova, Loseth, Muncke, Wang, Wolf, Zimmermann and Wagner2025). The plastic polymers themselves are also persistent, varying by composition and environmental conditions, but generally estimated to be in the range of decades or centuries (Chamas et al., Reference Chamas, Moon, Zheng, Qiu, Tabassum, Jang, Abu-Omar, Scott and Suh2020).

Potential classifications under IMO

The International Convention for the Prevention of Pollution from Ships (MARPOL) already recognizes plastics as harmful to marine ecosystems and, as a result, has banned the release of plastics and other waste materials into the sea. This instrument, however, does not currently address the unintended loss of plastics when transported as cargo in packaged form, which has been described as “the logical next step” (Groot et al., Reference Groot, Groenveld and Oppentocht2024).

The IMO Correspondence Group, formed to evaluate how to address this gap, identified four measures as necessary to prevent and mitigate plastic pellet spills: improved packaging, stowage and notification, along with specialized disaster response protocols when containers with plastic pellets are lost (Norway and Spain, 2023). In a first step, the IMO adopted a circular containing voluntary recommendations (IMO Circular, 2024) and cleanup guidelines (MEPC 82).

In a second step, the IMO will develop mandatory measures (IMO Secretariat, 2023). The initial Correspondence Group identified three principal regulatory pathways (Norway and Spain, 2023) and over the past 2 years, additional paths have been proposed by IMO Members and observers (IMO Secretariat, 2025). The proposals relating to hazardous classification reflect two distinct but related regulatory approaches. The first approach is recognition of plastic pellets as harmful substances under MARPOL Annex III. Annex III applies a broad, effects-based pollution prevention approach and is not limited to substances meeting defined toxicity thresholds. As set out in previous sections, plastic pellets are persistent, widely dispersed, readily ingested by marine organisms and capable of transporting hazardous chemicals. These characteristics support treating plastic pellets as harmful substances under MARPOL. This is also increasingly reflected in policy, for example, in Canada, where microbeads have been listed as harmful under the Canadian Environmental Protection Act (Canada Gazette, 2016). The second approach is to classify plastic pellets as marine pollutants under the International Maritime Dangerous Goods (IMDG) Code, in which case MARPOL Annex III would apply automatically by reference.

Faber et al. (Reference Faber, Sander and van den Berg2023) analyzed the effectiveness and feasibility of the initial options and found all options feasible to implement. The option to amend the IMDG code by assigning the hazard class “Miscellaneous dangerous substances and articles” (Class 9) to pellets transported by sea would trigger mandatory requirements for packaging, marking, documentation, stowage and emergency response.

For inclusion of pellets under Class 9 there have been discussions on whether they can be included under the UN number 3077 (Environmentally hazardous substance, solid). However, the criteria used under the IMDG code to identify environmentally hazardous substances (UN 3077) are primarily designed to address chemical hazards. While some pellets may qualify for UN 3077 depending on composition, this would require composition and hazard data that are rarely available. Moreover, given that plastics are complex chemical mixtures and also cause physical harm, an assessment based solely on UN 3077 criteria may not capture their full hazard profile.

This potential classification was recently discussed by the UN Committee of Experts on the Transport of Dangerous Goods, which considered but did not adopt the proposal (Germany and the Kingdom of the Netherlands, 2025), noting that regulation lies within the competence of the IMO (UN Secretariat, 2025). Since then, the International Union of Marine Transporters has stated that they believe that pellets should be subject to the dangerous goods code (Hand, Reference Hand2025). Moreover, in an evaluation of the options, Groot et al. (Reference Groot, Groenveld and Oppentocht2024) noted that even without meeting the Globally Harmonized System (GHS) criteria, pellets can be classified under class 9, which covers substances posing transport dangers outside other categories. The inclusion of items, such as fish meal, first aid kits and battery-powered vehicles, (Groot et al., Reference Groot, Groenveld and Oppentocht2024) illustrates the built-in flexibility of this class.

Other proposed pathways involve amending MARPOL in different ways. These include approaches that would prescribe transport requirements for plastic pellets by revising the definition of harmful substances to explicitly include pellets under Annex III, as well as options that would regulate pellets without explicitly recognizing plastic pellets as harmful, for example, by adding a new chapter to MARPOL Annex III-However, Faber et al. (Reference Faber, Sander and van den Berg2023) note that this latter. pathway may not include requirements for packaging and may weaken notification requirements in practice.