Microplastic Exposure for Pinnipeds (Pinnipedia): A Rapid Review
1
Analytical Research Laboratory Microplastics, Microplastics Research Center, A Yaroslav-the-Wise Novgorod State University, B. St. Petersburgskaya Str. 41, Veliky Novgorod 173003, Russia
2
Department of Applied Ecology, Faculty of Biology, Saint Petersburg State University, Universitetska-ya nab., 7–9, Saint Petersburg 199034, Russia
*
Author to whom correspondence should be addressed.
Ecologies 2025, 6(2), 26; https://doi.org/10.3390/ecologies6020026
Submission received: 23 January 2025
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Revised: 2 March 2025
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Accepted: 3 March 2025
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Published: 31 March 2025
Abstract
:The widespread distribution of microplastics (MPs) is causing increasing concern among the scientific community and the public. Marine mammals are considered indicators of the ecological health of marine ecosystems, and many species, suffering from numerous anthropogenic factors, have been granted protected status. Pinnipeds (Pinnipedia) are susceptible to ingestion and bioaccumulation of MPs from their environment, through direct consumption and trophic chain transfer. This literature review describes MP exposure for representatives of the three pinniped families—true seals (Phocidae), eared seals (Otariidae), and walruses (Odobenus)—and is based on 26 studies. Data on MP content was reported in scat in 17 articles, in the gastrointestinal tract (GIT) in 8 articles, and in the blubber in 1 article. Plastic material was detected in 22 studies, with its overall occurrence varying from 0 to 100% of samples. In addition to the quantitative assessment of MP content, one study provides data on the correlation between MP levels in animal organisms and pollution biomarkers such as phthalates and porphyrins. The contemporary experience of studying MP ingestion and MP exposure for pinnipeds (Pinnipedia) is discussed step-by-step, focusing on: (1) collection, (2) extraction, and (3) identification methods. This review provides current and collated information on the methods and results of studies concerning MP exposure for pinnipeds (Pinnipedia), which can serve as a guide for future researchers in this area.
1. Introduction
Global plastic production is increasing exponentially, with the current doubling period of 11 years. It is estimated that up to 10% of the plastic produced ends up in the oceans where it can persist and accumulate. Marine organisms are vulnerable to plastic pollution through various mechanisms, including ingestion, seafloor accumulation, the promotion of invasive species, and entanglement. For example, among pinnipeds, entanglement rates can reach as high as 7.9% of local populations, with fur seals, monk seals, and California sea lions being the most affected, and gray seals, common seals, and harbor seals experiencing entanglement to a lesser extent [1,2].
Plastic fragments from 1 µm to 5 mm are commonly referred to as microplastics (MPs) [3]. The sources of particles are either directly from industrial pellets, plastic balls from cosmetics, or gradually fragmenting large plastic waste [4]. MP pollution is a worldwide phenomenon, from the poles to the equator and at various depths, including in the deep and abyssal oceans in the same concentrations as tidal and shallow subtidal sediments [5].
Plastics and microplastics are ingested by a diverse array of marine biota. These include crustaceans, fish, marine turtles, seabirds, manatees, numerous cetaceans and seals [6,7,8,9,10]. Environmental microplastic exposure occurs through ingestion, inhalation, and dermal contact. Marine mammals and sea turtles, experiencing all three exposure routes like humans, are therefore particularly relevant for studying human exposure in marine environments [10]. Plastic microparticles can be ingested directly by an animal through incidental consumption, such as indiscriminate feeding strategies such as filter feeding (e.g., in right whales), or indirectly through trophic transfer when predators eat parts of prey contaminated with polymer particles (e.g., in most seals and dolphins) [11]. Little is known about the extent of trophic transfer in wildlife.
Ingestion of MPs can interfere with the permeability of the digestive tract and/or traumatize the gastric mucosa, which can contribute to emaciation of the animal. The surface area to volume ratio of MP fragments and fibers is such that it can absorb pollutants, including heavy metals; contamination of six times the concentration of ambient seawater has been reported [5]. The subsequent transfer of some substances from the MP surface to marine organisms has been confirmed under experimental conditions [12]. The absorption of polycyclic aromatic hydrocarbons, polychlorinated biphenyls, dioxin-like chemicals, polybromodiphenyl ethers, heavy metals, hydrophilic organic compounds (ciprofloxacin), and pharmaceuticals (antibiotics and antidepressants) has been confirmed [13,14]—the possible adverse effects on animal health remain poorly studied, especially for birds and mammals, although some studies have examined potential toxicological and dysbiotic effects. For example, based on the study of the microbiome of the gastrointestinal tract of grouse (Fulmarus glacialis) and Cory’s petrels (Calonectris borealis), it was shown that the amount of MPs in the intestine correlated with microbial diversity, a decrease in the number of commensal microbiota, and an increase in the number of zoonotic pathogens, as well as antibiotic-resistant strains and microorganisms that degrade microplastics [15]. By studying the microbiome, effects on energy metabolism, lipid metabolism, oxidative stress, and neurotoxic responses in vitro in mice have been reported [16,17].
Among the studies on the interaction with microplastics in pinnipeds, more works are devoted to the former. The study of trophic transfer, accumulation, and influence on physiological processes in the organism of MPs in pinnipeds (Pinnepedia) is represented by a limited number of works, but in recent years, interest in the study of the problem has increased.
MP exposure is analyzed based on the study of gastrointestinal tract (GIT) contents and/or scats of animals. Translocation of absorbed microplastics into tani has been detected by examining blubber [18]. In addition, relationships with other pollutants found in animals, such as phthalates, are being sought [19].
However, there are currently no standardized protocols for applying specific methods for collecting and analyzing samples and for preventing contamination with MPs from the environment, so it is difficult to compare the results of studies correctly. The most relevant recommendations for the standardization of techniques were given in the first extensive systematic review by Zantis et al., 2021 [20], which focused on MP exposure for marine mammals. Of the 30 articles analyzed, 11 were from pinnipeds (Pinnepedia) and the rest were cetaceans. No such reviews have been conducted after 2020. However, the number of published papers on MP exposure for harbor seals (Phocidae), eared seals (Otariidae), and walruses (Odobenus) has almost doubled in recent years.
The aim of this study is to conduct a literature review on MP exposure for pinnipeds (Pinnepedia), summarize the existing literature, and identify gaps in the current study of the problem.
2. Methodology
2.1. Literature Search Parameters
This literature review was compiled based on the recommendations of Siddaway et al., 2021 [21]. The search and selection of relevant peer-reviewed literature was conducted by one reviewer in December 2024 using two online publication databases: PubMed and ScienceDirect.
The selection was based on published observational, empirical, or review studies that examined MP exposure for pinnipeds (Pinnepedia). The following search terms were used to find relevant articles: “Microplastic”, “Plastic particle”, “Pinniped”, “Seals”, “Walruses”, “Phocid”, and “Otariid” (Figure 1).
Potentially relevant articles were read in full, and the materials in the appendices were analyzed.
2.2. Literature Selection
The articles found were evaluated for inclusion in a two-stage screening process.
Step 1: Inclusion criteria for the study
The relevance of the title and abstract of each publication was assessed using the following inclusion criteria:
Topic: examines the relationship between environmental microplastic pollution and pinnipeds (Pinnipedia).
Results: information is presented on the impact of microplastics on pinnipeds (Pinnipedia).
Study Type: an observational, empirical study, or review published in a peer-reviewed journal.
Step 2: Data extraction and presentation
Potentially relevant articles were read in full, and the information in the appendices was also analyzed. The collected data (if available) on the species under study, the research site, the methods for identifying the polymer, and its characteristics (species, color, type), etc., are presented in Table 1.
3. Results and Discussion
Following a search of the main search queries in two databases, removing duplicates and checking the titles and abstracts, as well as studying the lists of references used by the authors of the selected articles, 26 articles were selected.
The majority of studies on MP exposure for pinnipeds (Pinnipedia) were conducted in Europe (43%; n = 9)—primarily in the United Kingdom; followed by North America (24%; n = 5), South America (14%; n = 3), Asia (9.5%; n = 2), and Antarctica (9.5%; n = 2). Most of the research (57%; n = 12) focused on true seals (Phocidae), with the grey seal (Halichoerus grypus) being the subject in half of those studies (n = 6). MPs bioaccumulation in eared seals (Otariidae) received slightly less attention (38%; n = 8), and only one study (5%; n = 1) investigated the interaction of walruses (Odobenus) with microplastic particles (Figure 2).
Plastic debris was detected in 22 studies (84.6%), with its overall occurrence varying from 0 to 100% of the samples. Data on MP content in excrement was reported in 17 (65%) articles, in the GIT in 8 (31%) articles, and in blubber in 1 (4%) article (Table 2).
In addition to the quantitative assessment of MP content, one article provided data correlating MP content in animal organisms with such pollution biomarkers as phthalates and porphyrins.
3.1. Microplastics in the Gastrointestinal Tract
Eight studies investigated MP ingestion by examining the gastrointestinal tract contents of beached or harvested marine mammals (Table 3).
MPs were found in the stomachs and intestines of marine mammals in five studies conducted in Europe [24,32,40,44] and one study conducted in China [43].
However, microplastics were not detected in the stomachs of any of the 142 individuals from three species of true seals (Phocidae) studied (ringed seal (Phoca hispida), n = 135; bearded seal (Erignathus barbatus), n = 6; and harbor seal (Phoca vitulina), n = 1) (Bourdages et al., 2020) [23], and none in ringed seals (Pusa hispida) and walruses (Odobenus rosmarus) (though researchers only examined the stomach contents and identified particles equal to or larger than 80 µm) in the Canadian Arctic Archipelago [41,42]. Comparisons among studies are difficult due to the lack of information on the amount of GI tract contents analyzed and differences in the methods used to identify MPs. For example, only one study examined the entire contents of the whole digestive tract and reported the number of microplastic particles per animal [35]. Rigorous laboratory protocols minimized sample contamination. Analysis revealed fibers as the predominant particle morphology, with blue and black coloration and polyamide composition (confirmed via Fourier transform infrared (FTIR) spectroscopy) most frequent. Microplastics (MPs) were detected in all examined marine mammals.
3.2. Microplastics in Scat Samples
A total of 16 peer-reviewed publications have examined MPs in seal and walrus scat. The relatively high level of research effort likely reflects the ease of sample collection due to the use of terrestrial habitats (e.g., rookeries), the availability of long-term data on other parameters for which scat was also collected (e.g., diet), and the non-invasive nature of the approach, given that many species are protected (walrus, Atlantic subspecies (Odobenus rosmarus), harbor seal, European subspecies (Phoca vitulina vitulina), ringed seal, baltic subspecies (Phoca hispida botnica), Mediterranean monk seal (Monachus monachus) (Table 4).
Bravo et al. (2012) did not detect plastic particles in the scats of harbor seals (Phoca vitulina) in the Netherlands, although they did find plastic particles in the stomachs and intestines of these animals (11% and 1%, respectively). However, their study focused on general plastic particles rather than specifically targeting microplastics (MPs), and the extraction methods employed were likely not sensitive enough to capture the smallest particles [24]. Furthermore, the fact that the seals were beached due to a neuronal disease suggests that this study may not accurately reflect natural foraging behavior or representative plastic concentrations. In studies that have focused specifically on plastic particles <5 mm in size and used contemporary extraction and identification methods, the frequency of occurrence has ranged from 0% in Antarctic fur seal (Arctocephalus gazella) scats collected on Deception Island, Antarctica [31] (to 100% in subantarctic and Antarctic fur seal (Arctocephalus spp.) scats from the Falkland Islands [30], grey seal (Halichoerus grypus) scats from Ireland [19], and crabeater seal (Lobodon carcinophaga), leopard seal (Hydrurga leptonyx), and Weddell seal (Leptonychotes weddellii) scats from Potter Cove, King George Island) [26]. Reporting of MP abundance varied: some studies reported mean abundances or frequencies of occurrence across all samples analyzed, whereas others only provided statistics for those samples in which microplastics were detected. A key study by Nelms et al., 2018 provided the first experimental confirmation of the trophic transfer hypothesis by measuring microplastic in fish fed to captive seals and in the scat of the mammals [35].
Most studies report fibers as the predominant microplastic particle morphology, with fragments less frequent, and films and/or beads rarely observed. Most studies also identified the colors of the particles detected: blue, black, white, and transparent particles were the most common; and the polymer types: polyethylene (most common), polypropylene, polyethylene-polypropylene copolymers, polyester, polyamide, polychloroprene, polystyrene, polyurethane, polyethylene terephthalate, polyvinyl chloride, and phenolic resin. Polymer type was most commonly identified using Fourier transform infrared (FTIR) spectroscopy, with one study [26] additionally using Raman spectroscopy.
Heterogeneity in the prevalence of microplastics has been shown to be primarily influenced by anthropogenic activities, such as wastewater discharge, industrial effluents, aquaculture, and human settlements. For example, the predominance of fibers observed in many studies may be attributed to wastewater emissions, which introduce substantial quantities of microplastics in fibrous form due to the washing of synthetic clothing (accounting for approximately 33% of microplastic pollution overall). Furthermore, the prevalence of blue and black colors may indicate ropes as a potential source of these fibers, given the widespread use of these colors in rope and fishing gear [45].
3.3. Microplastics in Blubber
Merrill et al. (2024) confirmed microplastic (MP) translocation in pinnipeds, identifying MP fibers and fragments in the blubber of various species, including protected bearded seals (Erignathus barbatus) (Table 5). The high density of MPs (PVC—polyvinyl chloride, PC—polymethyl methacrylate, PMMA—polymethyl methacrylate, PS—polystyrene) found in bearded seal blubber suggests trophic transfer, as these particles sink and are consumed by benthic organisms—a primary food source for this species.
The underlying mechanisms of further translocation are still unknown but can be assumed to occur by transcellular uptake through intestinal epithelial cells into the circulating fluid or by paracellular diffusion between dense junctions of neighboring cells for particles <130 µm in size. However, not only the smallest (24.4 μm) but also the largest (1387 μm) plastic particles, averaging 383 μm, were found in subcutaneous fat tissue. Perhaps the ability to translocate could be facilitated by abrasion and perforation of intestinal tissue. A total of 70% of MPs found in subcutaneous fat were fibers, so perhaps the degree of translocation is influenced by the shape of the MPs and fibers which pass more easily into the bloodstream. However, a definite conclusion cannot be drawn, as fibers are generally found more frequently in both GI tract and scats studies—which is consistent with observations regarding the frequency of occurrence of different forms in the environment [18].
3.4. Methodological Variation
There are three main steps involved in quantifying MPs in GI tracts and scats: (1) collection, (2) extraction, and (3) identification. Additionally, preventing and accounting for contamination of samples by MPs during laboratory steps is essential. Significant variation exists among studies in all of these steps, which makes comparisons across studies challenging.
3.4.1. Sample Collection
The mass of GI tract contents analyzed varied considerably among studies. Some authors analyzed entire GI tracts, while others only analyzed stomach contents.
Variation in scat collection methods was less pronounced. Scats for all studies were collected from rookeries, except for Nelms et al. (2018) [35], in which scats were collected from captive animals. The mass and percentage of the total collected sample that was analyzed varied and were often not reported. The effect of time since defecation was investigated in one study, but no significant difference in MP abundance was found between fresh and aged scat [38].
3.4.2. Extraction Methods
MPs were extracted from organic material using three principal methods:
- Physical (filtration)
- Chemical or enzymatic digestion
- A combination of methods
Potassium hydroxide (KOH) digestion (10% or 20% concentration for 1–3 weeks) was the most commonly used chemical digestion method (Table 3, Table 4 and Table 5)—likely due to their relative simplicity and economic accessibility, but Nelms et al., 2018, 2019, 2019a [35,36,44] and Desclos-Duces et al. (2022) [35] used enzymatic digestion with proteinase K [28,35,36,44]
The range of mesh sizes used for filtration also varied considerably, from 1.2 to 3000 μm, which could influence the size and number of particles detected in different studies (Table 6).
3.4.3. Microplastic Identification Methods
The authors used a variety of approaches to identify MP particles (Table 6). Visual identification is the simplest but least reliable approach. Some form of further analysis is highly desirable, as only spectroscopic methods can provide strong evidence that isolated particles are polymeric plastics. Two studies did not use any methods beyond visual microscopy to confirm that isolated particles were polymers and the results of these studies should therefore be interpreted with caution [27,38]. Most studies used additional methods to characterize the polymer type, with an increasing tendency in the past 5 years to do so—most commonly using Fourier transform infrared (FTIR) spectroscopy, supplemented by Raman spectroscopy in Cebunar et al. (2024) [45].
When using FTIR, it is important to follow rigorous quality control protocols, such as matching thresholds, to minimize false positives. Zantis et al. (2021) [20] recommend using the term “putative” unless the polymer type has been confirmed. They also note that assigning a color to an MP particle can be highly subjective and may vary between observers as well as depending on the color of the background or the light source used during microscopy.
3.4.4. Contamination Prevention
MPs from the environment can contaminate samples and confound study results. To obtain accurate estimates, it is therefore essential to implement contamination prevention measures. The extent to which authors addressed contamination in their studies varied considerably, from no apparent contamination controls to rigorous and detailed contamination prevention protocols.
Virtually all researchers indicate working at the laboratory stage in non-synthetic clothing (mostly cotton lab coats). Common practices during sample preparation included storing samples in sealed containers when not in use and cleaning equipment with 70% ethanol and/or Milli-Q water. Some researchers work in a laminar flow hood with positive pressure [28,35,38]. Given the potential for airborne contamination, many authors implemented additional contamination control measures, such as exposing a petri dish containing a filter to the same conditions as the samples to test for the presence of polymer particles, including negative controls or blanks to assess background contamination, and sampling plastic equipment for comparison with the results obtained from their samples. There are also original ideas at different stages of sample processing, e.g., wrapping Petri dishes in which filters were placed with aluminum foil both from the bottom and from the lid [19]. Microscopic observations were carried out in a unique glass cabinet [37].
Two studies described the most comprehensive contamination control protocols [35,36]. They addressed potential contamination at all stages. During sample collection, they collected clothing blanks, conducted laboratory work in a positive-pressure laminar flow hood, cleaned all equipment beforehand, wore cotton lab coats and gloves, and tried to avoid using plastic equipment whenever possible.
In contrast, several other studies used less robust methods, did not implement controls at all stages, or used methods that were potentially contaminated, such as rinsing with tap water [23]. It is not specified whether laboratory glassware was pre-rinsed with purified water, or this step was not performed [22]. Several contamination control measures were implemented during the laboratory analysis, and plastic bags were used for scat collection in the field [27].
3.5. Phthalates and Other Contaminants as Biomarkers
Only one study has investigated MP exposure for pinnipeds in combination with other contaminants, namely phthalates and porphyrins. Phthalates are added to plastics to increase their flexibility and make them able to leach into the environment when polymers degrade [30]. They can also bioaccumulate in organisms and have been linked to developmental and reproductive toxicity and endocrine disruption. Hernandez-Milian et al. (2023) analyzed 12 Mediterranean monk seal (Monachus monachus) scat samples and identified 166 microplastic particles. Based on the analysis of scat samples for 11 phthalates, including Dimethyl phthalate (DMP), Diethyl phthalate (DEP), Diallyl phthalate (DAP), Dipropyl phthalate (DPrP), Diisobutyl phthalate (DIBP), Dibutyl phthalate (DBP), Benzyl butylphthalate (BBzP), Dicyclohexyl phthalate (DChP), Bis(2-ethylhexyl) phthalate (DEHP), Diisononyl phthalate (DINP), and Di-n-octyl phthalate (DNOP), the authors identified 9 phthalates: DMP, DEP, DAP, DPrP, DIBP, DBP, BBzP, DChP, and DEHP. Coproporphyrins, uroporphyrins, and protoporphyrins were also detected, but protoporphyrins were the only porphyrins identified in all samples [19]. They also found a positive correlation between the abundance of MPs and the concentration of phthalates.
3.6. Knowledge Gaps and Recommendations for Future Research
Despite the growing number of studies on the impact of MPs on pinnipeds (Pinnipedia), three issues remain poorly understood:
- clarification of trophic transfer pathways;
- translocation and bioaccumulation of MPs within animal bodies;
- the effects of MP ingestion and accumulation on animal health.
1. A key study is Nelms et al., 2018 [17], which for the first time confirmed the hypothesis of trophic transfer. MP content was determined both in the fish that were fed to captive seals and in the mammals’ excrement. The type and color of the polymers detected were consistent. For further work, Nelms et al., 2019a [36] used DNA analysis of the diet of the grey seal (Halichoerus grypus) to clarify the pathways of MP trophic transfer. However, authors working in the field often did not formulate specific hypotheses about the routes of MP entry into the bodies of the studied organisms, or they assumed trophic transfer without experimental confirmation. The latter is a promising direction for future research and involves a comprehensive study of the habitat of selected pinniped species (Pinnipedia) to determine the presence of similar types, forms, and shapes of MPs at the ecosystem level (comparing the amount of MPs in soil, water, food, and tissues of marine mammals).
2. By detecting MPs in the blubber of bearded seals (Erignathus barbatus), Merrill et al., 2024 confirmed the translocation of MPs within the pinniped body [18]. Studying other organs and tissues is also a relevant direction, although such work may be hampered by the invasiveness of the material collection method and the need to use deceased animals. However, specialists can obtain biomaterial from live seals—for example, blood, placenta, or amniotic membranes—including those from animals kept in captivity. A greater research focus is needed on MP interactions in eared seals seals (Otariidae) [22,25,30,31,34,37,38,39] and especially walruses (Odobenus) [42,46], as these species have been the subject of considerably fewer studies than true seals (Phocidae) [18,19,23,24,26,28,29,32,33,35,36,40,41,43,44].
3. The potential pathological consequences of microplastic (MP) ingestion, as well as their possible dependence on the quantity/characteristics of plastic particles, remain largely unknown in pinnipeds (Pinnipedia). In 2023, the sole study examining the link between MP exposure and biochemical changes in animals, Hernandez-Milian et al., found a correlation between microplastic (MP) quantity and phthalate concentrations; however, specific signs of endocrine or reproductive disruption that can be influenced by phthalates were not confirmed [19]. Conversely, studies investigating the effects of MP ingestion in other mammals have demonstrated a range of specific pathological effects, including damage to the gastrointestinal tract, pathogenic (bacterial) infection, and organ failure following polyethylene (PE) and polypropylene (PP) consumption in camels [47], rumen impaction and elevated concentrations of heavy metals in the rumen, blood, liver, muscles, and kidneys of buffaloes [48], intestinal inflammation, and alterations to the intestinal mucosa in hares [49]. This lack of comprehensive research regarding the health impacts of MPs on pinnipeds (Pinnipedia) represents a key knowledge gap in this field. Further investigation is needed to identify biological or chemical markers. Another potential avenue for research involves comparing the quantity/characteristics of MPs ingested by living and deceased animals within the same ecosystem, alongside determining the cause of death and antemortem health status through necropsy and veterinary examination, followed by analysis of various organ and tissue conditions. Invasive sampling methods are vital for research addressing the aforementioned issues, enabling a more accurate determination of individual microplastic concentrations, improved insight into microplastic transfer along the trophic chain, and the evaluation of potential pathological effects within mammalian tissues.
In addition, further standardization of methodologies would be advantageous. Zantis et al. (2021) presented the most comprehensive set of recommendations to date in their systematic review [20], and Lusher, A. L.; Hernandez-Milian, G. (2018) established a detailed, sequential, and adaptable bioprotocol for the extraction of MPs from animal GIT and scats [50].
4. Conclusions
MPs have been detected in the majority of GI tract contents and scat samples analyzed to date, although there is considerable variation in abundance, even within studies.
A positive trend is a much greater consistency among authors in the methods used for extracting and identifying material—almost all studies in the last 3 years are conducted using Fourier transform infrared spectroscopy (FTIR) and identify not only the type but also the color and form of the polymer. There is also a tendency towards more frequent use of not only chemical but also enzymatic extraction (Proteinase K). Furthermore, increasing attention is being paid to protection against contamination at all stages of the work. The first group of studies on the impact of MPs on walruses (Odobenus) have also emerged. However, a unified standard for controlling MP contamination from external sources at all stages of research and methods of MP extraction/determination is still lacking, and the issues of trophic transfer, MP translocation within the animal body, and the effects on health remain poorly understood.
As charismatic megafauna, pinnipeds can help to raise public awareness about anthropogenic pollution, and research on these animals is likely to continue to increase. To fully assess the extent of exposure and elucidate potential adverse effects, it is important to continue to study MP exposure for pinnipeds from different species and in different ecosystems, using standardized protocols for sample collection and analysis.
Author Contributions
A.V., conceptualization, methodology, investigation, writing—original draft preparation, visualization; E.A., data curation, writing—review and editing, supervision, project administration, funding acquisition. All authors have read and agreed to the published version of the manuscript.
Funding
This research was funded by the Ministry of Science and Higher Education of the Russian Federation (state contract no. 075-15-2024-629, MegaGrant).
Conflicts of Interest
The authors declare no conflicts of interest.
Abbreviations
The following abbreviations are used in this manuscript:
| MPs | Microplastics |
| GIT | Gastrointestinal tract |
| FTIR | Fourier transform infrared |
| PVC | Polyvinyl chloride |
| PC | Polycarbonates |
| PMMA | Polymethyl methacrylate |
| PS | Polystyrene |
| PP | Polypropylene |
| PE | Polyethylene |
| CP | Polyetheretherketone reinforced with carbon fiber |
| PES | Polysulfones |
| PET | Polyethylene terephthalate |
| PAN/ PAA | Polyacrylonitrile/polyacrylamide |
| PA | Polyamide |
| PMMA | Polymethyl methacrylate |
| ABS | Acrylonitrile butadiene styrene |
| EPDM | Ethylene propylene diene monomer |
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Figure 1.
Flowchart of the literature screening. The terms within each category (“subject” and “target”) were combined using the Boolean operator “OR”. The two categories were then combined using the Boolean operator “AND”. An Asterix (∗) is a wildcard that represents any group of characters, including no characters.
Figure 1.
Flowchart of the literature screening. The terms within each category (“subject” and “target”) were combined using the Boolean operator “OR”. The two categories were then combined using the Boolean operator “AND”. An Asterix (∗) is a wildcard that represents any group of characters, including no characters.
Figure 2.
Literature analysis results summary.
Table 1.
General study characteristics extracted from the articles.
| Characteristic | Categories |
|---|---|
| Target species | Species name and taxonomy |
| Target location | Country, Region |
| Material | Scat, gut content, blubber |
| Method of polymer identification | None, microscopy, Raman spectroscopy; Fourier-transform infrared spectroscopy (FTIR) |
| Polymer characteristics | Color, shape, type |
| Contamination identification protocol | Field controls, lab controls |
Table 2.
Material investigated. «+» means was used in the study.
| GIT | Scats | Blubber | Study Location | Families | Source |
|---|---|---|---|---|---|
| + | Peru | Otariidae | Ayala et al., 2021 [22] | ||
| + | Canadian Arctic | Phocidae | Bourdages et al., 2020 [23] | ||
| + | Netherlands | Phocidae | Bravo et al., 2013 [24] | ||
| + | Spitsbergen | Odobenus | Carlsson et al., 2021 [25] | ||
| + | Antarctica | Phocidae | Cebuhar et al., 2024 [26] | ||
| + | United Kingdom | Phocidae | Desclos-Dukes et al., 2021 [27] | ||
| + | United Kingdom | Phocidae | Desclos-Duces et al., 2022 [28] | ||
| + | Pacific Coast, USA | Otariidae | Donohue et al., 2019 [29] | ||
| + | Australian Subantarctic | Otariidae | Eriksson and Burton, 2003 [30] | ||
| + | Antarctica | Otariidae | Garcia-Garin et al., 2020 [31] | ||
| + | Ireland | Phocidae | Hernandes-Milian et al., 2019 [32] | ||
| + | Greece, Zakynthos Island | Phocidae | Hernandez-Milian et al., 2023 [19] | ||
| + | Atlantic Coast, USA | Phocidae | Hudak and Sette, 2019 [33] | ||
| + | Madeira | Phocidae | McIvor et al., 2023 [34] | ||
| + | United Kingdom | Phocidae | Nelms et al., 2018 [35] | ||
| + | United Kingdom | Phocidae | Nelms et al., 2019 [32] | ||
| + | United Kingdom | Phocidae | Nelms et al., 2019a [36] | ||
| + | USA, Alaska | Phocidae | Merrill et al., 2023 [18] | ||
| + | Galapagos Marine Reserve | Otariidae | Moreira-Mendieta et al., 2023 [34] | ||
| + | Gulf of California | Otariidae | Ortega-Borchard et al., 2023 [37] | ||
| + | Peru, Chile | Otariidae | Perez-Venegas et al., 2018 [38] | ||
| + | Peru, Chile | Otariidae | Perez-Venegas et al., 2020 [39] | ||
| + | German | Phocidae | Philipp et al., 2022 [40] | ||
| + | Canada | Phocidae | Jardine et al., 2023 [41] | ||
| + | Canada | Odobenus | Jardine et al., 2023a [42] | ||
| + | Bohai Sea, China | Phocidae | Wang et al., 2021 [43] |
Table 3.
Summary of MPs characteristics detected in gastrointestinal tracts. «-» means not recorded within the study. «>10%» means more than 10% of the total content.
Table 3.
Summary of MPs characteristics detected in gastrointestinal tracts. «-» means not recorded within the study. «>10%» means more than 10% of the total content.
| Characteristics | |||||
|---|---|---|---|---|---|
| Species | Source | Study Location | Most Common Shape (>10%) | Most Common Colors (>10%) | Common Polymers (>10%) |
| Phocidae | |||||
| Phoca hispida, | Jardine et al., 2023 [41] | Canada | 0 | 0 | 0 |
| Erignathus barbatus, Phoca vitulina | |||||
| Phoca vitulina | Bourdages et al., 2020 [23] | Netherlands | Stomach: fibers (54%), Intestimal: fragments (54%); | 0 | 0 |
| Halichoerus grypus | Hernandez-Milian et al., 2019 [32] | Ireland | Fibers (85%), fragments (14%) | - | - |
| Halichoerus grypus | Nelms et al., 2018 [35] | United Kingdom | Fibers (69%), fragments (31%) | Black (27.0%), clear (23.0%), red (23.0%), orange (12.0%) | EPDM (27.0%), PP (27.0%) PE (12.0%) |
| Halichoerus grypus Phoca vitualina | Nelms et al., 2019 [32] | United Kingdom | Fibers (84%), fragments (16%) | Blue (42.5%), black (26.4%), clear (12.8%), red (11,0%), | PA (61.2%) PET (10.2%) |
| Halichoerus grypus | Nelms et al., 2019a [36] | United Kingdom | Fibers (76.5%), fragments (23.5%) | Blue (52.9%), red (17.6%), black (11.8%) | Nylon (47.1%) PE, PET (all 17.6%) |
| Phoca largha | Wang et al., 2021 [43] | Bohai Sea, China | Fibers (60.0%), fragments (33.33%) | - | PET (40.0%), PP (20%), PAN/PAA (13.33%) |
| Odobenus | |||||
| Odobenus rosmarus | Jardine et al., 2023a [42] | Canada | 0 | 0 | 0 |
Table 4.
Summary of MPs characteristics detected in gastrointestinal tracts. «-» means not recorded within the study. «>10%» means more than 10% of the total content.
Table 4.
Summary of MPs characteristics detected in gastrointestinal tracts. «-» means not recorded within the study. «>10%» means more than 10% of the total content.
| Characteristics | |||||
|---|---|---|---|---|---|
| Species | Source | Study Location | Most Common Shape (>10%) | Most Common Colors (>10%) | Common Polymers (>10%) |
| Phocidae | |||||
| Phoca vitulina | Bravo et al., 2013 [24] | Netherlands | 0 | 0 | 0 |
| Nelms et al., 2018 [35] | United Kingdom | Fragments (69%), fibers (31%) | Black (27%), clear (23%), red (23%), blue (15%), orange (12%) | PP (54%), PE (12%) | |
| Hudak and Sette, 2019 [33] | USA, Massachusetts | Fragments (100%) | Brown and white | CP (50%), OTHER (50%) | |
| Lobodon carcinophaga, Hydrurga leptonyx, Leptonychotes weddellii | Cebuhar et al., 2024 [26] | Antarctica, Cierva Bay | Fibers (59.6%), fragments (33.8%) | Black (93.10%), blue (89.66%), white (86.20%), green (31.03%), red/purple (27.59%), yellow/orange/brown (27.59%), clear (13.79%) | PS, PES PET prevailed |
| Monachus monachus | McIvor et al., 2023 [34] | Madeira | Fragments (69%), fibers (13%) | Blue (39%), clear (19%), red (17%) | PE (28%) PES (21%) |
| Hernandez-Milian et al., 2023 [19] | Greece, Zakynthos island | Fibers (84.9%) fragments (24, 14.6%) | Blue (39.16%), clear (34.5%) | PA (72.58%), PC (15.52%) | |
| Halichoerus grypus | Hudak and Sette, 2019 [33] | USA, Massachusetts | Fragments (100%) | Purple and red | CP (50%), дp. (50%) |
| Desclos-Duces et al., 2021 [27] | United Kingdom | Fibers (61%), fragments (39%) | Light blue (36%), clear (29%), blue (14%), white (11%) | PET, PP, PAN/PAA prevailed | |
| Desclos-Duces et al., 2022 [28] | United Kingdom | Fibers (61%), fragments (39%) | Light blue (36%), clear (29%), blue (14%), white (11%) | PET, PP, PAN/PAA prevailed | |
| Otariidae | |||||
| Zalophus wollebaeki | Moreira-Mendieta et al., 2023 [34] | Southeastern part of the Galapagos Marine Reserve | Fibers—69%, fragments—26% | Blue (45%), black (32%) | PP-PE (22%), PP (17%), PE (11%), PVC (11%) |
| Zalophus californianus | Ortega-Borchard et al., 2023 [37] | Mexico, Gulf of California | Fibers (92%), fragments (8%) | Blue, black, grey prevailed | PET (37), PP (23%), PE (17%), ABS (10%) |
| Callorhinus ursinus | Donohue et al., 2019 [29] | Pacific Coast, USA | Fragments (55%), fibers (41%) | Fragments: white (99%); fibers: black, white, purple, blue, red, yellow, clear | PE |
| Arctocephalus gasella | Garcia Garin et al., 2020 [31] | Deception, Antarctica | - | - | - |
| Arctocephalus tropicalis | Eriksson and Burton, 2003 [30] | Mariana Islands, Australian Subantarctic | Fragments и fibers | White (33%), brown (19%), blue (15%), green (15%), yellow (15%) | PE (93%) |
| Arctocephalus australis | Perez-Venegas et al., 2018 [38] | Peru, Chile | Fibers (100%) | Blue (45%), white (24%), black (16%), red (15%) | - |
| Otaria flavescens, Arctocephalus phillippii | Perez-Venegas et al., 2020 [39] | Peru, Chile | Fibers prevailed | Blue (42–69%), white (21–50%), red (12–31%) for A. australis and O. flavescens, respectively | PE + PA (total 30%) |
| Otaria byronia | Ayala et al., 2021 [22] | Peru | Fragments (91%), fibers (9%) | - | - |
| Odobenus | |||||
| Odobenus rosmarus | Carlsson et al., 2021 [25] | Spitsbergen | Fibers—70%, in all samples except 1 | - | PA (31%), PE (23%) |
Table 5.
Summary of MPs characteristics detected in gastrointestinal tracts. «-» means not recorded within the study. «>10%» means more than 10% of the total content.
Table 5.
Summary of MPs characteristics detected in gastrointestinal tracts. «-» means not recorded within the study. «>10%» means more than 10% of the total content.
| Characteristics | |||||
|---|---|---|---|---|---|
| Species | Source | Study Location | Most Common Shape (>10%) | Most Common Colors (>10%) | Common Polymers (>10%) |
| Phocidae | |||||
| Erignathus barbatus | Merrill et al., 2023 [18] | USA, Alaska | Fibers 70%, in all samples except 1 | Blue | PP, PE, PS, PMMA, PVC, PC |
Table 6.
Summary of microplastic extraction and identification variation. «-» means not recorded within the study.
Table 6.
Summary of microplastic extraction and identification variation. «-» means not recorded within the study.
| Mesh Size (μm) | Digestion | Identification | Source |
|---|---|---|---|
| - | - | Microscope | Ayala et al., 2021 [22] |
| 850, 425 | - | FTIR (no MP detected) | Bourdages et al., 2020 [23] |
| 500, 300 | - | FTIR | Carlsson, P et al., 2021 [25] |
| 500, 330 | 10% KOH (1 week) | FTIR + FT Raman | Cebuhar J.D. et al., 2024 [26] |
| 20 | K proteinase (enzyme) | FTIR | Desclos-Dukes et al., 2021 [27] |
| 20 | K proteinase (enzyme) | FTIR | Desclos-Duces et al., 2022 [28] |
| 500, 250 | NaCl (5.4 M) | FTIR | Donohue et al., 2019 [29] |
| 100, 500 | - | FTIR | Eriksson and Burton, 2003 [30] |
| 3000, 1000, 500 | 20% KOH (1 week) | FTIR | Garcia-Garin et al., 2020 [31] |
| 250, 1000 | 10% KOH (3 weeks) | Microscope | Hernandes-Milian et al., 2019 [32] |
| 1000, 500, 250 | 10% KOH (3 weeks) | FTIR | Hernandez-Milian et al., 2023 [19] |
| 2000, 1000, 500 | 10% KOH | FTIR | Hudak and Sette, 2019 [33] |
| 20 | 10% KOH | FTIR | McIvor et al., 2023 [34] |
| 1 | 20% KOH | FTIR + GC-MS | Merrill et al., 2023 [18] |
| 2000, 1000, 5000, 2000 | K proteinase (enzyme) | FTIR | Nelms et al., 2018 [35] |
| 35 | K proteinase (enzyme) | FTIR | Nelms et al., 2019 [32] |
| 35 | K proteinase (enzyme) | FTIR | Nelms et al., 2019a [36] |
| - | H2O2 | FTIR | Moreira-Mendieta et al., 2023 [34] |
| 1000, 500, 212 | 30% KOH (3–5 days) | FTIR | Ortega-Borchard et al., 2023 [37] |
| - | 20% KOH (1 week) | Microscope | Perez-Venegas et al., 2018 [38] |
| - | 20% KOH (1 week) | FTIR | Perez-Venegas et al., 2020 [39] |
| 300, 100 | Washing machine, adding enzyme detergents | Microscope | Philipp et al., 2022 [40] |
| 80, 10 | 10% KOH (2 weeks) | FTIR | Jardine et al., 2023 [41] |
| 80, 10 | 10% KOH (2 weeks) | FTIR | Jardine et al., 2023a [42] |
| - | - | FTIR | Wang et al., 2021 [43] |
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Vainberg, A.; Abakumov, E. Microplastic Exposure for Pinnipeds (Pinnipedia): A Rapid Review. Ecologies 2025, 6, 26. https://doi.org/10.3390/ecologies6020026
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Vainberg A, Abakumov E. Microplastic Exposure for Pinnipeds (Pinnipedia): A Rapid Review. Ecologies. 2025; 6(2):26. https://doi.org/10.3390/ecologies6020026
Chicago/Turabian StyleVainberg, Anastasia, and Evgeny Abakumov. 2025. "Microplastic Exposure for Pinnipeds (Pinnipedia): A Rapid Review" Ecologies 6, no. 2: 26. https://doi.org/10.3390/ecologies6020026
APA StyleVainberg, A., & Abakumov, E. (2025). Microplastic Exposure for Pinnipeds (Pinnipedia): A Rapid Review. Ecologies, 6(2), 26. https://doi.org/10.3390/ecologies6020026
