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Article

Occurrence and Distribution of Microplastics on the Beaches of Limón on the Southern Caribbean Coast of Costa Rica

by
Emanuelle Assunção Loureiro Madureira
1,
André Luiz Carvalho da Silva
1,*,
Gustavo Barrantes-Castillo
2 and
Fábio Vieira de Araújo
3
1
Department of Geography, Universidade do Estado do Rio de Janeiro, Francisco Portela, 1470, Patronato, São Gonçalo 24435-005, RJ, Brazil
2
Escuela de Ciencias Geográficas, Universidad Nacional, Avenida 1, Calle 9, Heredia 86-3000, Costa Rica
3
Department of Sciences, Universidade do Estado do Rio de Janeiro, Francisco Portela, 1470, Patronato, São Gonçalo 24435-005, RJ, Brazil
*
Author to whom correspondence should be addressed.
Micro 2025, 5(1), 1; https://doi.org/10.3390/micro5010001
Submission received: 14 August 2024 / Revised: 4 September 2024 / Accepted: 25 December 2024 / Published: 30 December 2024
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Abstract

:
This study aimed to characterize the temporal and spatial occurrence of microplastics on the beaches of the Caribbean coast of Limón, Costa Rica. The selected beaches comprise a stretch of 70 km, characterized by large environmental protection areas, agricultural and residential areas with low occupation density, urban areas, and port areas. Despite the great importance of the beaches for the country, studies related to solid waste pollution remain scarce on the Caribbean coast. The methodology consisted of conducting fieldwork in 2017 and 2019 to collect materials on five beaches and laboratory analyses for extraction using hypersaline solution and the quantification and characterization of microplastics based on type, size, and color. The results show that the beaches studied in the northwestern sector had the highest concentrations of microplastics, with emphasis on Cieneguita Beach and Airport Beach, with a predominance of pellets (56.7%) followed by fragments (21.8%). These beaches are inserted in a coastal stretch with a strong concentration of industrial, port, and airport activities. The lower occurrence of microplastics in the southeastern sector (Manzanillo and Gandoca) may be related to the greater number of preservation areas. With varying sizes, shapes, and colors, most microplastics had a worn appearance, which suggests reworking by coastal processes and subsequent deposition on the studied beaches. The impact of this type of pollution on the coast of Limón is notorious and shows the need for further research into the occurrence and distribution of microplastics on Caribbean beaches so that possible sources and damage to coastal ecosystems can be identified.

1. Introduction

The increasing occupation of coastal areas has caused problems arising from the irregular disposal of solid waste on beaches and in other coastal and marine environments. This scenario is of great concern, especially when considering the dynamics and rich biodiversity present on coasts and adjacent marine areas, in addition to the impact on leisure, transport, tourism, and fishing activities [1,2,3,4]. Beaches represent one of the environments most directly affected by the irregular disposal of solid waste due to their widespread use for recreation and housing activities. Beaches have dynamic environments and are almost always formed by sands of different sizes subject to the influence of waves, currents, and daily tidal fluctuations [5,6,7].
Materials composed of various plastics are among the most common solid waste found on coasts and in the ocean [2,3,4,8,9]. The widespread use of plastic is due, in most cases, to its durability, strength, lightness, low production cost, and impermeability [10,11]. The inefficient management of plastic waste results in the deposition of up to 12.7 million t/m2 per year of these materials in the ocean [12].
When plastic waste is less than 5 mm in size, it is called microplastics, a classification widely accepted by the scientific community [13]. Marine animals are the most impacted by microplastics and die largely from starvation, as they ingest microplastics mistaking them for food, among other causes [14,15]. When the animal ingests the microplastic, it acts as a vector for transferring toxic materials to organisms [16,17].
In addition to ingestion ability and mechanical obstruction in organisms, microplastics are potentially toxic due to the various substances and elements used as additives that can be leached into the environment [18]. They also have a high capacity to adsorb hydrophobic substances, such as persistent organic pollutants (POPs), which concentrate on their surface, causing different effects in organisms [18,19,20,21,22,23]. The microplastic surface can also serve as a site for the colonization of microorganisms, including pathogens, and can act to spread such species [23,24,25,26,27].
In recent years, there has also been concern about microplastics in the human body, which can enter through ingestion and inhalation [28,29]. The occurrence of these particles in marine species consumed by humans, such as fish and bivalves, can accumulate and cause serious damage to human health [30,31,32].
Several studies on solid waste pollution on the Caribbean coast have been carried out recently in Panama [33,34], Guatemala [35], Colombia [36,37,38,39,40,41,42,43,44], Mexico [45], Puerto Rico [46], Venezuela [34], and on beaches in the Antilles [47], among others. The Caribbean Sea region has been identified as one of the areas with the highest concentration of solid waste in the Atlantic Ocean [48]. On the southern Caribbean coast of Costa Rica, studies on contamination by microplastics are incipient or even non-existent.
One of the most important sectors of the Costa Rica economy is tourism, which has numerous natural attractions for a large number of people from different parts of the world [49,50]. As such, it is necessary to develop studies aimed at monitoring solid waste pollution on the Caribbean coast of Costa Rica to know the level of contamination and the variables involved in the process of the accumulation and transport of these materials. Studies of this nature are equally important in guiding actions aimed at the urban and environmental planning of this coastal stretch. Thus, this study aims to analyze the spatiotemporal occurrence of microplastics on the Caribbean coast of Limón, Costa Rica, in 2017 and 2019, as support for solid waste management in the coastal zone.

2. Materials and Methods

2.1. Study Area

The Limón coast is located on the southern Caribbean coast of Costa Rica and is approximately 220 km long, with a predominant northwest–southeast orientation (Figure 1). The beaches selected for the present study include Cieneguita, Airport, and Bananito in the northwest sector of Limón (09°58′25.3″ N and 083°01′47.4″ W), and Manzanillo and Gandoca in the southeast sector, close to the border with Panama (09°34′38.79″ N and 082°34′31.0″ W) (Figure 1).
Costa Rica’s population, currently around 5 million people, is concentrated in the central region of the country, where about 60% of the inhabitants live [51]. Despite the low population density on the Caribbean coast, it is experiencing an accelerated process of expansion of agricultural activities, with emphasis on the cultivation of bananas for export [49], industrial activities, and tourism [50].
The Limón coast is influenced by the moisture-laden Caribbean trade winds [52], which blow in a northeast–southwest direction [51]. The average annual rainfall varies between 2500 and 4800 mm [51]. The average annual temperature varies between 20° and 31 °C, with little change along the coast [53]. The geomorphology of the region is marked by the presence of the Guanacaste and Talamanca mountain ranges, hills of tectonic origin, and river valleys, such as the Sixaola and Estrella. The coastal plains have varying widths, where the presence of beaches, marshy areas, and cliffs can be observed [54]. The coast is very active, with frequent records of seismic activities, including those of great magnitude.
The diurnal mixed tidal regime has an average amplitude of only 21 cm [55], and the waves are the most responsible for the sedimentary dynamics of the beaches and the fragmentation of the corals. The predominant coastal current is from northwest to southeast, influenced by the cyclonic circulation of the Panama–Colombia Gyre (PCG) [56], forming eddies in the opposite direction along the coast [57]. The Caribbean coast has extensive high-energy beaches, cut by rivers in several stretches along the coast. In the southern sector, towards Panama, the beaches are limited by fossil reefs and sandstones in some areas [58,59]. The composition of beach sediments varies greatly, with an expressive presence of volcanic material from local rivers [60]. Most beaches on the southern Caribbean coast of Costa Rica are of great importance for tourism. However, some beaches, such as those chosen for this study, have been showing serious erosion problems, with shoreline retrogradation on different stretches of the Limón coastline and the concomitant destruction of urban structures [61,62].

2.2. Fieldwork and Laboratory Analyses

In the study area, two fieldwork sessions were carried out (December 2017 and May 2019) to collect 14 sediment samples distributed across 5 beaches along a 70 km stretch of the Limón coast (Figure 1). To this end, 7 sampling sites were selected and distributed on the beaches of Cieneguita (1), Airport (1), Bananito (1), Manzanillo (2), and Gandoca (2).
Monitoring sites were defined based on beach arc extension and accessibility. Surface sediment sampling was performed at the syzygy high tide line, in an area of 1 m2 by 1 cm depth (upper sediments), adapted from [63,64,65].
Beach sediment collection was performed using metal materials to avoid sample contamination. Work surfaces in the laboratory were cleaned with alcohol and paper. White 100% cotton lab coats were used. The samples were covered whenever possible at each stage of the procedure with aluminum foil. All solutions used were pre-filtered before use. Contamination-free filters and Petri dishes with ultra-pure water were exposed during sample processing time in the laboratory to assess contamination mainly from airborne fibers. The extraction of microplastics was performed based on the following steps: initial weighing of the samples; drying in an oven at 60 °C for 24 h; dry sample weighing; removal by sieving of materials with a diameter greater than 5 mm; preparation of the hypersaline solution, with 358.9 g of NaCl per liter of water; sample agitation for 5 min; sediment decantation for 5 h; removal of floating material; filtration with vacuum pump; and drying qualitative paper filters (5.5 cm and 205 µm thick) in the oven for 72 h [66,67].
Each microplastic waste found in the samples was counted, identified, and analyzed according to the classification proposed by [68], which classifies microplastics into the following categories: plastic foam, fibers, films, fragments, pellets, and styrofoam. The morphology, color, and state of preservation of the microplastics were also analyzed based on the same manual. These steps were carried out using a trinocular magnifying glass (45× Zoom—DI-152T Stereo Microscope with 5 MEGAPIXEL USB Camera, DIGILAB, Piracicaba-SP, Brasil) and with ToupView 4.1 software for the digital analysis of the materials.

3. Results

3.1. Microplastics on the Limón Coast in 2017

A total of 81 microplastic items/m2 (42.6 items/kg−1) were found on the beaches studied on the Limón coast in December 2017, mainly on the Cieneguita beach with 48 items/m2, which represents 35% of the total found in this monitoring session (Table 1 and Table 2; Figure 2). Styrofoam (with 29 items) was the main microplastic found in the beach sands on the northwestern coast of Limón in 2017, followed by fragments (11), pellets (7), and fiber (1) (Table 2; Figure 3 and Figure 4). Most of the materials observed were between 2 and 5 mm in size (Figure 5A), with a predominance of irregular shape (Figure 5B) and white color (styrofoam) (Figure 5C).
A total of 28 items/m2 were identified on Airport Beach (which corresponds to 21% of the total), of which fragments (18), fibers (5), pellets (4), and styrofoam (1) predominated (Table 2; Figure 2, Figure 3 and Figure 4). Most of the fragments found were between 2 and 5 mm in size (Figure 5A), with an angular shape (Figure 5B) and colors predominantly between transparent and blue (Figure 5C).
Only 5 items/m2 (4%) were found on Bananito Beach, among which 3 fibers and 2 plastic fragments were identified (Table 2; Figure 2, Figure 3 and Figure 4). Bananito Beach was the only one in the northwestern sector that showed a low concentration of microplastics in 2017 (Figure 2). The microplastics exhibited a size between 2 and 5 mm (Figure 5A), with angular (in the case of the fragments) and elongated (fibers) morphology (Figure 5B), and most-observed colors of transparent and green (Figure 5C).
The lowest concentrations of microplastic were found on the southeastern coast of Limón (Figure 1) in 2017, with a total of 55 items (23 items/kg−1) (Table 1 and Table 2; Figure 2). The highest amount of microplastics in the southeastern section was observed on Manzanillo beach, specifically in sector 1, with a total of 41 items/m2 (30% of the general total of this monitoring session) distributed among fragments (20), pellets (6), fibers (6), films (6), and foams (3). Sector 2 of Manzanillo had only 8 items/m2 (6% of the total in 2017), identified as fragments (5), fibers (2), and pellets (1) (Table 2; Figure 2, Figure 3 and Figure 4). Most of the materials found in both sectors were between 2 and 5 mm in diameter (Figure 5A), with quite varied morphology, with a predominance of sub-angular microplastic fragments (Figure 5B) in transparent, black, and opaque colors (Figure 5C).
Gandoca was the beach that had the lowest concentrations of microplastic in 2017. In sector 1 of Gandoca Beach, only 3 items/m2 of microplastic fragments were counted; in Gandoca 2, 3 film-type items/m2 were observed (Table 2; Figure 2, Figure 3 and Figure 4). The materials presented sizes between 2 and 5 mm (Figure 5A). The fragments exhibited a subangular morphology (Figure 5B) and the film-like microplastics were highly degraded. Crystalline (film) and opaque (fragments) colors predominated among the analyzed materials (Figure 5C).

3.2. Microplastics on the Limón Coast in 2019

In 2019, Cieneguita was also the beach that presented the highest amount of microplastics, with 290 items/m2, which corresponds to 57% of the total materials accounted for in this monitoring session (Table 2; Figure 2). Among the analyzed materials, pellets are the predominant type (162), followed by fragments (61), styrofoam (35), films (17), fibers (11), and foam (4) (Table 2; Figure 3 and Figure 4). Most of the microplastics found showed a predominant size between 2 and 5 mm (Figure 5A), with a predominance of spheroid (in the case of pellets) and angular (concerning fragments) particles (Figure 5B). The colors of the microplastics varied greatly, with emphasis on transparent pellets, blue fragments, and white styrofoam (Figure 5C).
Airport Beach, again, presented the second-highest concentration of microplastics among all the monitored locations in the study area, with a total of 180 items/m2, equivalent to 35% of the total materials found in 2019 (Table 2; Figure 2). Among the analyzed microplastics, almost all were represented by pellets (173), followed by fragments (3), fibers (3), and film (1) (Table 2; Figure 3 and Figure 4). Most of the microplastics measured between 2 and 5 mm (Figure 5A), with a predominance of disc-shaped materials, in the case of pellets (Figure 5B), which were mostly transparent in color (Figure 5C).
As in 2017, Bananito Beach had the lowest concentration of microplastics in the northwestern portion of the studied coast (Table 2; Figure 2), with only 1 fiber-type item/m2 (Figure 3 and Figure 4), between 2 and 5 mm, which was elongated and blue (Figure 5).
Lower concentrations of microplastic were found in the southeastern portion of the Limón coast (Figure 1) compared to the northwestern sector (Table 1). Manzanillo Beach had a relatively low amount of microplastics at both sampling sites (Table 2; Figure 2). Manzanillo 1 presented only 1 item/m2, a plastic fragment smaller than 2 mm, which was subangular and pink (Figure 5). In sector 2 of Manzanillo Beach, 10 microplastic items/m2 were identified (Table 2; Figure 2). The microplastics found were classified as pellets (7), fragments (2), and fiber (1) (Table 2; Figure 3 and Figure 4). Among these materials, there was a predominance of particles with a size between 2 and 5 mm (Figure 5A), in the shape of a disk (Figure 5B), and transparent in color concerning the pellets (predominant microplastic) (Figure 5C).
In the southeastern portion of the coast studied, the highest concentration of microplastics was observed on Gandoca Beach in 2019, totaling 29 items/m2. Gandoca 2 was the sector with the highest amount of microplastics, with 25 items/m2 (the third-largest concentration observed in 2019; 5% of the total) (Table 2; Figure 2). Among the analyzed microplastics, fragments (15), pellets (7), and fibers (3) were identified. In sector 1 of Gandoca, only 4 items/m2 were found, which were fibers (3) and film (1) (Table 2; Figure 3 and Figure 4). The microplastics found on Gandoca Beach ranged in size from 2 to 5 mm (Figure 5A), mostly with an angular shape (fragments) (Figure 5B) and transparent in color (Figure 5C).

4. Discussion

The results presented here represent a pioneering effort aimed at investigating the occurrence of microplastics on the southern Caribbean beaches of Costa Rica. This study made it possible to identify and classify microplastics on all the studied beaches, with a wide and varied distribution (Figure 2 and Figure 3). According to [42], microplastics are found throughout the Caribbean, with concentrations ranging between 90 and 10,000 items per m2, similar to that found on certain beaches in this study, such as Cieneguita (338 items/m2) and Airport (208 items/m2) (Table 2; Figure 2). The total number of microplastics on the beaches studied on the southern Caribbean coast of Costa Rica corresponds to 647 items/m2, which represents an average of 92.4 items/m−2 (70.3 items/kg−1) per site, with significant differences between the seven monitored sites (Table 1 and Table 2; Figure 2).

4.1. Spatiotemporal Assessment of Microplastics

The results showed a great temporal and spatial variability in the concentration of microplastics between the studied beaches (Figure 2). In 2017, between 3 and 48 microplastics were identified per m2 on the five beaches analyzed, totalizing 136 items (32.3 items/kg−1). In 2019, the amount of microplastics ranged from between 1 and 290 particles per m2, with a significant increase in total compared to 2017, to 511 items (106.4 items/kg−1), which represents 79% of the entire material found in the two study periods. This higher concentration of microplastics in May 2019 is the result of heavy rains that occurred a few days before sampling, which raised the level of the Cieneguita River and the other rivers in the region, increasing the input of materials to the sea, which were later deposited on the beaches. In periods of intense rainfall, rivers tend to contribute to a higher concentration of microplastics on beaches [69].
The spatial difference in the amount of microplastics on the studied beaches is probably due to the different uses existing on the Limón coast. The northwestern sector of Limón is more urbanized, with the presence of a port and an airport, while in the southeastern sector, there are several preserved areas, including national parks, and areas dedicated to tourism, especially Manzanillo (Figure 6). Different spatial patterns of microplastic accumulation are also observed on other beaches worldwide, such as in Taiwan [70], and on the Shandong coast in China [71]. On the Niterói coast (Brazil), for example, microplastic concentrations ranged from a minimum of 11 to a maximum of 201 items/m2 [1], and between 3 and 1387 items per m2 on the Caribbean coast of Colombia [41], among others (Table 3).
The concentration of microplastics is 5.8 times higher (552 items) on the beaches located in the northwestern sector of the Limón coast compared to the southeast coast (with only 95 items). This is determined by the urban growth of the region, with the intensification of activities at the port of Limón, at the container terminal in Moín, and at the International Airport of Limón (Figure 6). According to [76,79], port regions are more likely to concentrate microplastics, mainly pellets and fibers, as observed by these authors on the Portugal and Belgium coasts, respectively. The same was verified by [37] on beaches in Cartagena, where the most important port in the Colombian Caribbean is located, and by [65] in Guanabara Bay (Rio de Janeiro, Brazil) (Table 3), which are both located in densely urbanized areas with intense port activity and airports.
Micro 05 00001 g006
Figure 6. Map of different uses and main environmental variables in Limón. Sources: Grain size of the beaches studied [80]; major shipping lanes [81]; and other information based on [51,61].
Figure 6. Map of different uses and main environmental variables in Limón. Sources: Grain size of the beaches studied [80]; major shipping lanes [81]; and other information based on [51,61].
Micro 05 00001 g006
The Cieneguita and Airport beaches presented the highest concentrations of microplastics (338 and 208 items/m2, respectively). Both are located in one of the most urbanized areas of Limón; in the case of Cieneguita, the beach is just 2 km from the port, while Airport Beach is 1.7 km south of Cieneguita and 3.4 km from the port, in addition to being located in the area of Limón International Airport (Figure 6). Ref. [41] identified between 3 and 1387 items/m2 in beach sediments in the Colombian Caribbean, while [47] found 261 ± 6 microplastics/kg in the sands of 21 beaches on the Antilles Islands (Caribbean), both located near areas of high population density. The highest concentrations of microplastic (249 to 1387 items/m−2) were on the beaches of Cartagena (Colombia) near the port and in the intense navigation zone, with a predominance of pellets [40] (Table 3). Regions with the presence of important ports and a concentration of commercial activities contribute to marine microplastic pollution [82], as seen on the northwest coast of Limón.
In this same region, there is also the presence of an important submarine outfall for wastewater, located between the port of Limón and the container terminal of Moín (Figure 6), built in 2002 by the Costa Rican Institute of Aqueducts and Sewers. Ref. [83] recently carried out a study on the effects of submarine outfall discharge and concluded that there is no direct evidence of a negative impact on the studied area. However, Refs. [1,84] draw attention to the role of emissaries in the supply of microplastics to coastal areas, as seen in their studies carried out in Guanabara Bay (Rio de Janeiro, Brazil). Wastewater, even when treated, tends to release microplastics into the environment [85]. As a result, microplastics released into the Caribbean Sea through the outfall may eventually be returning to the beach of Cieneguita and its surroundings through coastal dynamics and/or transportation to different stretches of the Limón coast.
The beaches on the coast of Limón are dynamic and present a morphological variability strongly marked by the exchange of materials between the emerged and submerged areas, which favors the deposition of anthropogenic residues on the sand. The high mobility of sediment on the beaches, with predominantly fine-to-medium sand [80], added to the proximity to the source area, may also explain the higher concentration of microplastics on the beaches of Cieneguita and Airport.
According to [56], there is a strong prevailing current from northwest to southeast, which tends to transport sediments and other materials along the coast. Thus, the microplastics released by the outfall and other sources could reach the southern end of the Limón coast through this current and/or through the winds. Refs. [86,87] point out that these two mechanisms (currents and winds) are potential agents in the transport of solid waste to areas far from its source. It should be noted that microplastics such as pellets and fibers were also found in high amounts on the more distant beaches in the southeastern sector of the study area (Figure 2 and Figure 3), which reinforces the hypothesis of transport in this direction by coastal currents. This is similar to that identified by [37] in Cartagena, where the authors found a high concentration of microplastics, especially pellets (27.2 ± 2.77 items.mg), which reached the southwestern Colombian Caribbean by marine currents.
Another important source capable of contributing microplastics to the Caribbean coast is the rivers. The Cieneguita River (Figure 6), for example, cuts through part of the city of Limón, which has many residences and commercial establishments, including in areas bordering the main channel and some of its tributaries. The river flows alongside the port of Limón (Figure 6) and is located in the coastal sector that has the highest annual rainfall [54]. According to [88,89], this feature may be an important factor in the increased concentration of microplastics reaching the ocean through rivers. As a result, the large concentration of microplastics on the Cieneguita and Airport beaches could also come from local rivers, being later redistributed by coastal processes and winds. Lighter materials such as styrofoam, which was identified in a greater quantity on Cieneguita beach (Figure 7A–C), are more susceptible to wind transport. This type of microplastic (styrofoam) is generally associated with activities related to fishing, as observed by [65] on the beaches of Guanabara Bay (Brazil), and tends to be predominantly white, as seen on Cieneguita (Figure 5C).
Fiber-type microplastics found on the urbanized coast of Limón (Cieneguita and Airport) may also come from atmospheric precipitation and urban runoff. In a study carried out in Paris, ref. [90] identified a high concentration of microplastics (29–280 items/m−2day−1), with emphasis on fibers, coming from atmospheric precipitation in that region. The authors point out that, in periods of lower rainfall, there was a reduction in the amount of microplastics. Ref. [9] also emphasize the importance of urban surface runoff as a source of solid waste for beaches and bays, which is an important source to be considered, especially in more densely urbanized areas.
Bananito Beach is located in an agricultural area used for banana plantations, with few residences; it is only 13 km from the airport and 16.5 km from the port of Limón (Figure 6). This beach had the lowest microplastic concentrations on the northwestern coast in both monitoring sessions, with between 1 and 5 units per m2 (Table 2; Figure 2). In 2019, many tree trunks were observed on the beach (Figure 7D) as a result of a strong storm that occurred 3 days before monitoring. This heavy rain caused a rise in the level of the Bananito River and the flooding of the coastal plain. The river cut the sand strip and possibly removed the solid waste (macro and micro) that may have been deposited on the beach. This would explain the low concentration of microplastics on this beach, even in an area close to Cieneguita. During storm events, rainfall can increase the flow of rivers, which consequently displace solid waste into the ocean, depositing it directly into the marine environment [91].
Manzanillo (Figure 1) comprises a 3.7 km long beach arc in a sparsely urbanized area with infrastructure for tourism, with inns, restaurants, bars, etc. This part of the coast has been presenting problems related to coastal erosion [61,92], in addition to the significant accumulation of garbage on the beach. Sectors 1 and 2 of Manzanillo Beach (Figure 1) had a total of 60 microplastics, ranging from 1 to 41 items per m2 (Table 2; Figure 2), with emphasis on Manzanillo 1, which had the highest concentration on the southeastern coast (41 items/m2 in 2017) (Table 2; Figure 2). However, a significant reduction in the amount of microplastics was observed in this area in 2019 (Table 2; Figure 2). It is believed that this decrease is due to the intense erosion process this sector of Manzanillo is experiencing, with a sudden reduction in the beach sand strip. Erosion may be one of the agents responsible for the removal of sediments and microplastics from this beach, remobilizing and making these materials available at other locations.
Tourist activities, mainly on Manzanillo Beach (Figure 6), may also be contributing to the concentration of microplastics in beach sediments, as already observed by several authors on Caribbean beaches. Ref. [48] observed microplastic contamination on Caribbean island beaches receiving millions of tourists each year. In Aruba, for example, there was an increase in the amount of plastic waste on beaches produced by recreational tourist activities, reaching 7.41 units/m−2 [48]. The same was observed on the tourist beaches of Santa Maria, in the Colombian Caribbean, which have a high concentration of microplastics, especially secondary plastics, with 2 to 92 items/m−2 [40]. This is similar to the result found on the Limón coast beaches (Table 2; Figure 2), which also point to tourism and recreational activities as possible sources.
Gandoca Beach, located 7 km southeast of Manzanillo and limited to the south by the Sixaola River (on the border with Panama), is a dynamic coastline subject to the direct incidence of storm waves. Gandoca has a small village (with few buildings) and is part of the Gandoca–Manzanillo National Wildlife Refuge (Figure 6). Gandoca Beach had the lowest concentration of microplastics on the southeastern coast, especially sector 2, with 28 units (Table 2; Figure 2). The area of sector 1 of Gandoca is undergoing a very intense erosion process, with the concomitant retreat of the coastline [61]. This may explain the smaller amount of microplastics observed in this sector when compared to sector 2 (Table 2; Figure 2), where the beach is wider due to its greater proximity to the mouth of the Gandoca River. The presence of microplastics in protected areas, as in the case of Gandoca, has been reported on several other coasts in the Caribbean, as observed by [33] on the beach of Punta Galeta (294 ± 316 items/m2). In these areas, the local contribution of microplastics is generally small, due to the restrictive use of these beaches, which points to the marine environment as a potential source.

4.2. Characteristics of Microplastics

Knowledge of the different characteristics (size, morphology, and color) of microplastics available in marine and coastal environments can help identify their source areas, their impacts, and their degradation time, among other aspects [13]. Most of the identified microplastics are between 2 and 5 mm in size (Figure 5A). The smaller the microplastic, the greater its impact on marine food webs. The smallest sizes of microplastics were found in fibers, generally present in textile products and which are not retained in sewage treatment plants, and in fragments, showing the degradation they suffer in the marine environment due to the action of waves and UV radiation [93].
There was a predominance of pellets in disk, spheroid, and ovoid form and angular-shaped microplastic fragments (Figure 5B). Pellets are primary microplastics, used as raw materials for the manufacture of various plastic products, and are generally found close to ports or industries that use them [94], while fragments are secondary microplastics, usually resulting from packaging breakage [93]. The highest amounts of microplastic pellets and fragments (169 and 72 items/m2, respectively) were identified on Cieneguita, together with Airport Beach, with an emphasis on pellets (177 items/m2) (Table 2; Figure 2, Figure 3 and Figure 7A,B). The size and morphology of these pellets are the most common and have also been observed in New Zealand, Taiwan, and China by [70,71,95], respectively, while fragments similar to those found in this study (Figure 5B) were observed on beaches on the Balearic Islands of Spain [87]. Styrofoam appears mainly worn and irregularly shaped (Figure 5B), similar to that identified by [35] on Caribbean beaches in Guatemala.
The colors of the microplastics varied greatly (Figure 5C), with a predominance of transparent (pellets), white (styrofoam), and blue (fragments), a pattern similar to that found in other areas, such as the beaches of Guanabara Bay in Brazil [1], and in coastal shelf sediments in Portugal [96]. Studies [78,97] show that some marine organisms are strongly influenced by color, in addition to smell, for capturing food. Furthermore, the identification of the color of these materials is important, as this factor may be related to the presence of chemical additives and the greater adsorption of pollutants [98,99].

5. Conclusions

On the southern Caribbean coast of Costa Rica, microplastics were identified on the sands of the five beaches analyzed, distributed irregularly along the coast, with 647 items/m2 (70.3 items/kg−1). The highest concentrations of microplastics were found on the beaches studied in the northwestern sector, with emphasis on Cieneguita and Airport. These beaches are located in a region with a strong concentration of productive, port, and air activities. The lower occurrence of microplastics in the southeastern sector (Manzanillo and Gandoca) may be related to the greater number of conservation areas and the lower population density of this stretch of coast.
The comparison between the results obtained in 2017 and 2019 shows significant differences in the concentration of microplastics between the studied beaches. In 2019, the number of microplastics was 5.8 times higher, with 511 items (106.4 items/kg−1), and variations between 1 and 290 particles per m2, contrasting with 2017, when 136 items (32.3 items/kg−1) were identified, between a minimum of 3 and a maximum of 48 particles/m2. It is believed that this is due to the heavy rains that occurred in the region three days before the sampling of sediments on the studied beaches. This high-magnitude event raised the level of the Cieneguita River, causing it to make a greater amount of waste available to the sea and to the beaches of Cieneguita and Airport. In Bananito, on the other hand, this same event may have been responsible for the removal of microplastics from the beach to the sea, leaving a large quantity of logs on the sand.
Pellets, fragments, styrofoam, fibers, films, and plastic foam represent the microplastics identified in the analyzed sediments, with emphasis on pellets (367 items) and fragments (141 units), mostly between 2 and 5 mm in size, with varied shapes between different types of materials. The predominant colors were transparent (pellets and fibers), blue (fragments and films), white (styrofoam), and brown (plastic foams).
On the coast of Limón, there was a greater potential for the accumulation of microplastics in urbanized and port areas, mainly through the numerous activities existing in the region related to the most varied services, including housing, tourism, leisure, and fishing. The main rivers that cut through the most densely populated areas such as the Cieneguita River, the submarine outfall, urban surface runoff, atmospheric precipitation, and wave and current dynamics, along with winds, as well as the different local uses directly associated with the beach and marine environment, constitute the main variables capable of contributing microplastics to the studied area. The role of each of the possible sources indicated here needs to be investigated in depth in future studies based on further monitoring and analysis.
Microplastic pollution is an emerging environmental problem, and its impact on the coast of Limón is notorious, as seen in this pioneering study. This scenario exposes the need for further studies aimed at the qualitative–quantitative analysis, behavior, dispersion, and identification of the possible impacts of microplastics on the Caribbean coast of Costa Rica in the medium and long term.

Author Contributions

Conceptualization, E.A.L.M. and A.L.C.d.S.; methodology, E.A.L.M., A.L.C.d.S., G.B.-C. and F.V.d.A.; software, E.A.L.M.; validation, E.A.L.M., A.L.C.d.S., G.B.-C. and F.V.d.A.; formal analysis, E.A.L.M., A.L.C.d.S., G.B.-C. and F.V.d.A.; investigation, E.A.L.M. and A.L.C.d.S.; data curation, E.A.L.M., A.L.C.d.S., G.B.-C. and F.V.d.A.; writing—original draft preparation, E.A.L.M., A.L.C.d.S., G.B.-C. and F.V.d.A.; writing—review and editing, E.A.L.M., A.L.C.d.S., G.B.-C. and F.V.d.A.; visualization, E.A.L.M.; supervision: A.L.C.d.S.; project administration, A.L.C.d.S.; funding acquisition, A.L.C.d.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

We would like to thank the Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro—FAPERJ (Research Support Foundation of the State of Rio de Janeiro) for the master’s scholarship granted to student Emanuelle Assunção Loureiro Madureira (E-26/202.612/2018), as well as the Postgraduate Program in Geography at UERJ-FFP and the Escuela de Ciencias Geográficas de la Universidad Nacional de Costa Rica (UNA) (School of Geographic Sciences of the National University of Costa Rica), for all the support given in the realization of this research. Special thanks to professors Iliana Ramírez, Lilliam Arias, and Meylin Alvarado (UNA) for their help and encouragement.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Southern Caribbean coast of Costa Rica with the location of the beaches selected for this study.
Figure 1. Southern Caribbean coast of Costa Rica with the location of the beaches selected for this study.
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Figure 2. Number of microplastic particles on the beaches studied on the southern Caribbean coast of Costa Rica in 2017 and 2019.
Figure 2. Number of microplastic particles on the beaches studied on the southern Caribbean coast of Costa Rica in 2017 and 2019.
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Figure 3. Quantity of microplastics found on the studied beaches in 2017 and 2019.
Figure 3. Quantity of microplastics found on the studied beaches in 2017 and 2019.
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Figure 4. Photomicrographs of the different types of microplastics found in the sands of the beaches studied in Limón on the southern Caribbean coast of Costa Rica.
Figure 4. Photomicrographs of the different types of microplastics found in the sands of the beaches studied in Limón on the southern Caribbean coast of Costa Rica.
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Figure 5. Size (A), morphology (B), and colors (C) of the microplastics analyzed on the studied beaches. In (B), other microplastics corresponded to styrofoam, film, fiber, and plastic foams. Figure (A) legend: yellow < 2 mm, red 2 > 5 mm, blue > 5 mm.
Figure 5. Size (A), morphology (B), and colors (C) of the microplastics analyzed on the studied beaches. In (B), other microplastics corresponded to styrofoam, film, fiber, and plastic foams. Figure (A) legend: yellow < 2 mm, red 2 > 5 mm, blue > 5 mm.
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Figure 7. Microplastics on Airport (A,B) and Cieneguita (C) beaches, where the highest concentrations of pellets, fragments, and styrofoam were identified. Bananito Beach with many tree trunks after heavy rains in 2019 (D). Photos: André Silva in 2017 (C) and 2019 (A,B,D).
Figure 7. Microplastics on Airport (A,B) and Cieneguita (C) beaches, where the highest concentrations of pellets, fragments, and styrofoam were identified. Bananito Beach with many tree trunks after heavy rains in 2019 (D). Photos: André Silva in 2017 (C) and 2019 (A,B,D).
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Table 1. Quantity of microplastics per square meter and per kilogram.
Table 1. Quantity of microplastics per square meter and per kilogram.
SectorItems.m−2Items.kg−1
2017Northwestern8142.6
Southeastern5516.9
2019Northwestern471235.5
Southeastern4014.2
Total in 201713632.3
Total in 2019511106.4
Total (2017 and 2019)64770.3
Source: authors.
Table 2. Amount of particles found in the different types of microplastics collected on the studied beaches.
Table 2. Amount of particles found in the different types of microplastics collected on the studied beaches.
BeachesMicroplastics
20172019
FoamFiberFilmFragmentPelletStyrofoamFoamFiberFilmFragmentPelletStyrofoamTotal
Northwestern coastCieneguita-1-11729411176116235338
Airport-5-1841-313173-208
Bananito-3-2---1----6
Southeastern coastManzanillo 1366206----1--42
Manzanillo 2-2-51--1-27-18
Gandoca 1---3---31---7
Gandoca 2--3----3-157-28
Total (type)3179591830422198234935647
Grand total136511
Source: authors.
Table 3. Concentration of microplastics on certain beaches around the world and methods of sampling and extraction in the laboratory.
Table 3. Concentration of microplastics on certain beaches around the world and methods of sampling and extraction in the laboratory.
LocationAreaSampling MethodMicroplastics ExtractionItems.kg−1Mean (Items·m2)Reference
PhilippinesBayTransect 1 × 1 m (surface)Sieving and filtration-17.8 items·m2[72]
ChinaSheltered beachesSurfaceDensity (saturated sodium chloride solution)1.3–14,712.5. kg−19.07 items·m2[71]
ColombiaExposed beachesTransect 1 × 1 m (surface)Density (saturated sodium chloride solution)1109 items.kg−1-[44]
Puerto RicoIsland beachesTransect 0.5 × 0.5 m (surface)Density (saturated sodium chloride solution)3–17 items.kg−152–432 items·m2[46]
GuatemalaExposed beachesTransect 0.5 × 0.5 m (surface)Density (saturated sodium chloride solution)30 items.kg−1279 items·m2[35]
ColombiaExposed beachesTransect 0.5 × 0.5 m (surface)Sieving-112 ± 103 items·m–2[40]
ColombiaExposed and island beachesTransect 0.5 × 0.5 m (surface)Density (hypersaline solution)-318 ± 314 items·m2[41]
PanamaExposed and sheltered beachesTransect 0.5 × 0.5 m (surface)Density (saturated sodium chloride solution)-294 ± 316 items·m2[33]
BrazilBayTransect 0.5 × 0.5 m (surface)Density (saturated sodium chloride solution)166.50 items.kg− 1543 items·m− 2[1]
BrazilBayTransect 1 × 1 mDensity (saturated sodium chloride solution)-12–1300 items·m−2[65]
BrazilExposed beachTransect 988 cm2 (surface)Sieving and filtration -0.29 items·cm−2[73]
PeruExposed beachesTransect 0.5 × 0.5 m (surface)Density (saturated sodium chloride solution)-89.7 ± 143.5 items·m−2[74]
DubaiBayTransect 0.5 × 0.5 m (surface)Density (potassium iodide solution)59.71 items.kg−1-[75]
PortugalExposed beachesTransect 0.5 × 0.5 m (surface)Density (saturated sodium chloride solution)-666 ± 2642 items·m−2[76]
IndiaBayTransect 0.5 × 0.5 m (surface)Density (saturated sodium chloride solution)7.49 items.kg−168.83 items·m−2[77]
TaiwanSheltered beachesTransect 0.5 × 0.5 m (surface)Density (saturated sodium chloride solution)0.771 items.gr0.0125 items·m3[78]
Costa RicaExposed beachesTransect 1 × 1 m (surface)Density (saturated sodium chloride solution)70.3 items.kg−1647 items·m−2Present study
Source: authors.
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MDPI and ACS Style

Madureira, E.A.L.; da Silva, A.L.C.; Barrantes-Castillo, G.; de Araújo, F.V. Occurrence and Distribution of Microplastics on the Beaches of Limón on the Southern Caribbean Coast of Costa Rica. Micro 2025, 5, 1. https://doi.org/10.3390/micro5010001

AMA Style

Madureira EAL, da Silva ALC, Barrantes-Castillo G, de Araújo FV. Occurrence and Distribution of Microplastics on the Beaches of Limón on the Southern Caribbean Coast of Costa Rica. Micro. 2025; 5(1):1. https://doi.org/10.3390/micro5010001

Chicago/Turabian Style

Madureira, Emanuelle Assunção Loureiro, André Luiz Carvalho da Silva, Gustavo Barrantes-Castillo, and Fábio Vieira de Araújo. 2025. "Occurrence and Distribution of Microplastics on the Beaches of Limón on the Southern Caribbean Coast of Costa Rica" Micro 5, no. 1: 1. https://doi.org/10.3390/micro5010001

APA Style

Madureira, E. A. L., da Silva, A. L. C., Barrantes-Castillo, G., & de Araújo, F. V. (2025). Occurrence and Distribution of Microplastics on the Beaches of Limón on the Southern Caribbean Coast of Costa Rica. Micro, 5(1), 1. https://doi.org/10.3390/micro5010001

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