https://orcid.org/0000-0003-3504-767X
Figures
Abstract
Cigarette butts are one of the most abundant litter items on beaches and represent an emerging source of microplastic pollution due to the degradation of their cellulose acetate filters. When improperly discarded on beach sand, cigarette butts release chemical contaminants and undergo physical and photo-oxidative fragmentation, generating persistent fiber-type microplastics in coastal environments. This study assessed the presence and characteristics of microplastics (MPs) associated with cigarette butt (CB) and cigarette butt fiber (CBF) residues in beach sand at a pilot tourist site. Monthly sampling was conducted across 16 campaigns between 2021 and 2022 to evaluate temporal trends in microplastic categories. Triplicate samples of CBs, CBFs, and beach sand were collected from usage-based zones and analyzed using Fourier-transform infrared spectroscopy (FTIR) to identify functional groups and polymeric composition. The results indicated that 44% of the CB-related functional groups reported in the literature were detected in the service area, with 36% associated with cellulose acetate degradation. The correspondence between functional groups identified in CBs and those detected in fiber-type MPs in sediments suggests that cigarette butts constitute a relevant source of hazardous MP fibers in beach environments. These findings support the need for improved waste management strategies and policy measures aimed at reducing CB pollution in coastal areas.
Citation: Díaz-Mendoza C, Mouthon-Bello J, Botero CM, Valdelamar Villegas J, Gutiérrez L, Martinez-Villadiego K (2026) Functional group analysis of cigarette butts in beach sand and their association with microplastics: Bocagrande Beach, Cartagena, Colombia. PLoS One 21(3): e0345311. https://doi.org/10.1371/journal.pone.0345311
Editor: Zhi Zhou, Purdue University, UNITED STATES OF AMERICA
Received: July 14, 2025; Accepted: March 4, 2026; Published: March 20, 2026
Copyright: © 2026 Díaz-Mendoza et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All relevant data are within the manuscript and its Supporting information files.
Funding: The author(s) received no specific funding for this work.
Competing interests: The authors have declared that no competing interests exist.
1. Introduction
CB are primarily composed of cellulose acetate (CA) fibers and certain binding agents. Due to chemical alterations in the polymer, these butts have limited capacity for natural degradation. Additionally, fiber compaction and the presence of plasticizers in conventional cigarettes hinder their decomposition. These conditions make CBs a source of toxic issues for the environment [1]. The biodegradation of potentially biodegradable plastics typically requires a specific environment, making it challenging to ensure complete biodegradation in settings with multiple variables and unknown life cycle [2].
CA has low degradability in aquatic environments; therefore, being present in cigarette butts and due to their constant improper disposal, it can be claimed that these elements are a growing source of long-lasting microfibers in coastal environments [3].
The CA forming the core of CBs undergoes photochemical degradation by wavelengths shorter than 280 nm, but it has limited photodegradability in sunlight due to the lack of chromophores to absorb UV light. This holds true only when not considering other factors such as air, water, and contaminations [4]. Therefore, CBs discarded on beach sand may undergo degradation processes distinct from those deposited in the marine environment. The degradation of cigarette butts, including heavy metal release and fragmentation into MPs, is governed by multiple environmental factors, with physical degradation processes playing a key role. Wave action, tides, and precipitation promote the mechanical breakdown of cigarette materials and facilitate heavy metal mobilization [5]. In addition, exposure to environmental conditions intensifies these processes, as ultraviolet (UV) radiation accelerates filter degradation and enhances the release of associated metals [6].
The disintegration of CBs is hindered due to the highly intertwined network of fibers and the reinforcing effect of the plasticizer (acetin) used to bind the fibers. This explains the persistence of CBs in the marine environment for many years. Research has shown that the combination of photodegradation and biodegradation allows for synergy that enhances the overall degradation rate of CA. This synergy is attributed to photodegradation causing the formation of pits, thereby increasing the material’s surface area, and improving biodegradation. In this regard, environmental conditions strongly influence the degradation rate of CA [4].
The interest in researching cigarette butts waste on beaches and in aquatic ecosystems has been increasing, especially because they have proven to be potentially toxic to different species such as cultured benthic foraminifera, including Rosalina globularis, a species with perforated calcareous shells; Quinqueloculina spp., a species with imperforate calcareous shells; and Textularia agglutinans, a species that forms agglutinations. In this study, it was found that at concentrations of 4 CBs per liter of water, the calcareous genera experienced shell decalcification and the death of most individuals, except for the agglutinated species, which proved to be more resistant. These findings suggest that leachate from cigarette butts could cause harm due to the reduction of pH and the release of toxic substances, especially nicotine, leading to physiological disturbances and, in many cases, cell death [7].
The effects of CBs on aquatic life can be more severe compared to their impact on land-based organisms. Most aquatic studies have primarily focused on invertebrates (such as crustaceans, mollusks, and freshwater insect larvae) and vertebrates (including fish and amphibians), with only a limited number of investigations involving microorganisms, algae, and plankton. Exposure to leachate from CBs has been shown to disrupt population dynamics, species interactions, and overall ecosystem functioning. This disruption is evident in various ways, including alterations in the movement patterns of marine and freshwater gastropods. Additionally, marine polychaetes and freshwater bivalves may exhibit delayed burrow creation, with the latter forming shallower burrows [8]. Another example of how improper disposal of CBs leads to disruptions in soil species is the species Eisenia fetida, which was used as a test organism. The study confirmed avoidance behavior, lethality, body weight loss, and severe damage to the surface tissues and intestinal structures [9].
In addition to the interest in impacts on biological species and the potential to induce contamination through trophic networks, studies have also been conducted that link the decomposition of CBs to MPs. The study by [3] found that smoked cigarette filters release approximately 100 small MP fibers (<0.2 mm) per day. In a rough estimate, around 0.3 million tons of potential MP fibers could be entering aquatic environments annually from this source.
The quantity of microplastics originating from laundered clothing is comparable to that released by discarded CBs. However, this issue has not received the same attention as other types of microplastics in the scientific community. Discarded cigarette butts contaminating the environment can further break down, increasing the number of released MPs, thereby raising the risk for organisms exposed to this chemical and microplastic pollution. Therefore, it is crucial to delve deeper into the MP fibers released by cigarette butts and their impact on the surrounding environment [10].
MPs could act as vectors for the transport and release of toxic substances in marine organisms, as the hydrophobic properties of microplastics enable them to absorb contaminants such as Bisphenol-A, alkylphenols, PAEs, phthalates, organobromines, styrene, and heavy metals on their surface while in seawater and release these contaminants when entering a biotic system [11]. Cigarette waste acts as a point source of metal contamination, as the rapid leaching of these elements may induce acute toxic effects in coastal and marine organisms [12]. CBs contain heavy metals such as Na, As, Mg, Pb, Cr, Mn, Cu, and Hg, which pose risks to human health and aquatic ecosystems; in particular, Hg and Pb represent potential sources of contamination in coastal environments, while As, Cr, Ni, and Cd have been causally linked to cancer development in humans [13].
In the study conducted by [3], FTIR spectra were analyzed, comparing smoked and non-smoked filters. No differences were found between the smoked and non-smoked samples analyzed, indicating that the smoking process does not alter the chemical structure of the filter or make it more photodegradable. Processes such as deacetylation and reduction of molecular weight in CBs are expected to increase the hydrophilicity of the films due to the rise in the number of free hydroxyl groups [2].
Smoked filters subjected to conditions of humidity and natural solar radiation for 18 months in the study by [3] did not show chemical changes. For these reasons, it can be concluded that CA has very low degradability in aquatic environments. Therefore, microscopic fibers released from cigarette filters can be considered as microplastics and, consequently, may persist in the environment for a long time.
Bocagrande Beach was selected as the study site due to its relevance as a high-use tourist area and previous evidence of significant accumulation of cigarette-related waste. A pilot study conducted across five tourist beaches in Latin America reported a high abundance of cigarette butt–derived fibers, with particularly elevated values at beaches in Peró Beach, Brazil (0.77 CBF/m²), and at Bocagrande Beach, Colombia (0.27 CBF/m²) [14]. However, that study was limited to establishing a statistical correlation between the presence of CBs and MP fibers, without conclusively demonstrating a common origin or chemical correspondence between the fibers identified in beach sand and the constituent materials of CBs. In this context, Bocagrande represents a strategic pilot site to advance the chemical identification of fiber-type MPs using Fourier-transform infrared spectroscopy (FTIR) and to assess their potential direct relationship with CB degradation, thereby addressing a relevant knowledge gap in coastal pollution research.
2. Materials and methods
2.1. Study area
The study was conducted at Bocagrande Beach, located in Cartagena, Colombia (75° 33′ 42.0″ W, 10° 28′ 56.7″ N). The selection of this site was based on evidence from previous research documenting significant solid waste accumulation on beach sand between 2010 and 2016 within the framework of the ICAPTU project, as well as elevated abundance and density of CBs and CBFs reported during 2021–2022 through the PROPLAYAS Network international collaboration project. The geographic location of the study area is presented in Fig 1.
The map was produced by the authors using open-source geographic information from OpenStreetMap. Base map and data from OpenStreetMap and OpenStreetMap Foundation.
Furthermore, the pilot beach possesses urban characteristics, hosting diverse commercial services, accommodations, and facilities. In such areas, recreational considerations often take precedence over conservation values [15].
The beach’s sand is predominantly fine sandy (80% of the analyzed samples are sands with particle sizes of 150 µm), featuring a microtidal range around 0.2 m [16] and a mixed diurnal tide type. The selected sampling area covered a beach length of 500 meters, three study areas were identified based on the activities conducted in each, considering the recreational and tourist nature of the beaches under investigation.
The following considerations were applied to the project. A) Active area: along the coastline, around the waterline; intended for sports and recreational activities such as walking, running, beach soccer, and beach volleyball. This area allows access to the bathing zone. B) Rest area: designated for the relaxation and rest of visitors, equipped with umbrellas, chairs, and other services. C) Service area: occupies the innermost part of the beach, where tourist and support services like bars, restaurants, and souvenir shops are located [14,17]. The active, rest, and service use zones were selected as sampling areas because the presence of cigarette butts in beach sand varies according to space use. These zones differ in user traffic and residence time, availability of shaded areas, and exposure to environmental factors such as solar radiation and wind, which may influence CB degradation and the generation and distribution of fiber-type MPs. This zonation enabled a comparative assessment of the relationship between beach use patterns, cigarette butt degradation, and microplastic presence in sediments.
2.2. Sample collection
For the recovery of sand samples for MPs determination, monitoring was carried out in the period between September 2021 and December 2022 (16 months of sampling), which included both the rainy and summer seasons. At the study beach, a transect measuring 100 meters in length by 1 meter in width was established area with high abundance of CBs and CBFs [14]. Sand samples were collected every 10 m along the zone of maximum height of the intertidal line, at a depth of 5–7 cm, using a metal spoon or garden trowel. Samples were preserved in glass containers to prevent cross-contamination from plastic materials and transported to the laboratory for processing within a maximum period of 48 hours.
For FTIR analysis, July was selected as a representative sampling month due to peak tourist activity and the high abundance of CBs observed during this period. In each beach use zone (active, rest, and service areas), triplicate samples of beach sand, CBs, and CBFs were collected for chemical characterization. In addition, triplicate sand samples were collected in each zone to determine MP abundance. The CBs and CBFs used as virgin references for FTIR analysis were selected based on previous studies conducted at the same beach, which identified 24 commonly discarded brands and a consistent dominance of specific brands (Chesterfield, Luchies, Marlboro, and Rothmans) [18]. These results were consistent with observations from the 16 monitoring campaigns (2021–2022). Therefore, the most frequently occurring brands were selected as virgin reference samples to ensure representativeness.
2.3. Microplastic analysis
Following the methodology of [19,20], the samples were dried in an oven at a temperature of 60ºC for 48 hours. Subsequently, 50 grams of soil per sample were taken and placed in agitation in 200 ml of concentrated Sodium Chloride (NaCl) solution. Each sample was agitated for 1 minute and left to settle for 6 hours. After 6 hours, the supernatant solution was filtered through a 90 mm – 65 g/m2 filter. The MPs counted on the filters were examined using a Binocular Stereomicroscope SMZ 171 -Bled, identifying microplastics such as fibers, granules, fragments, and films.
2.4. FTIR analysis
A total of 30 samples were analyzed using Fourier Transform Infrared Spectroscopy (FTIR) with an IRAffinity-1 spectrometer (SHIMADZU, Series A213749) operating in transmission mode using KBr pellets. Spectra were acquired in the mid-infrared range (4000–450 cm ⁻ ¹) at a resolution of 4 cm ⁻ ¹ with 32 scans per sample. Spectroscopy-grade KBr was dried prior to use to minimize moisture interference. For each analysis, approximately 1–2 mg of sample was homogenized with ~100–200 mg of dry KBr in an agate mortar and compressed to form transparent pellets. The analyzed samples comprised 9 CB samples, 9 CBF samples, 9 beach sand samples, and 3 virgin composite reference samples, including two CB composites from different brands and one CBF composite. Prior to pellet preparation, all samples were rinsed with distilled water to remove adhering particles, dried at ≤40 °C to constant weight, and manually fragmented to obtain representative portions. FTIR spectra were processed using OriginPro software (OriginLab Corporation, USA) for baseline correction, peak identification, and spectral visualization. The identification of functional groups was based on characteristic absorption bands within established wavenumber ranges reported in the literature.
2.5. Statistical analysis
The statistical analysis included the calculation of relative frequencies and the estimation of measures of central tendency (mean) and dispersion (standard deviation) for the microplastic content present across the three beach zones. Comparisons of mean microplastic density among the three beach zones (active, rest, and service) were performed using one-way analysis of variance (ANOVA), followed by pairwise comparisons using Tukey’s post hoc test. Prior to the analyses, the assumptions of data normality were assessed using the Shapiro–Wilk test, homogeneity of variances was evaluated using Bartlett’s test, and independence of residuals was verified using the Durbin–Watson test. All statistical analyses were conducted at a 95% confidence level. Data estimation and graphical representation were performed using R version 4.5.2 [21] and the ggplot2 package [22], as well as GraphPad Prism version 8.0.2 [23].
In addition, a network analysis was conducted to identify the degree of connectivity (connectance) among the different functional groups identified in the sand, cigarette butts (CB), and cigarette butt fibers (CBF) matrices across the different beach zones. This analysis was performed using the computational software Gephi version 0.10.1 [24].
3. Results
3.1. Microplastics identified at the study beach
In the research conducted on Bocagrande Beach in Cartagena to determine the presence and types of MPs in the sand, an average of approximately 916.63 microplastics per kilogram of dry soil (kg d.w) was found, including fibers, fragments, films, and granules.
The sand samples collected at the study beach, during the period from September 2021 to December 2022, were analyzed, revealing the percentage distribution according to the identified forms such as fibers, granules, films, and fragments per month of monitoring, as indicated in Fig 2.
The percentage distribution indicates that fiber-type MPs are the most abundant in all monitoring periods, ranging from 38.3% to 79.30%, with an average of 534.5 fibers per kg dry weight. High values were observed in December, May, June, and January, coinciding with storm surges and rainfall during sampling. This pattern aligns with findings in the study [25], where four forms of MPs (fibers, pellets, fragments, and foam) were found on the study beaches Among these forms, MP fibers were observed in all beaches, representing 83% of the total, with an average of 866 MPs per kilogram.
In the present study, the comparison of microplastic density across the three beach zones (active, rest, and service) using one-way ANOVA is shown in Fig 3. The results indicate that fibers, in addition to exhibiting the highest mean density, were the only microplastic category that showed statistically significant differences among beach zones, with higher values observed in the active and service zones compared to the rest zone. Despite this, the same figure shows a slight decreasing trend in the density of granules and films from the active zone toward the service zone, a pattern that was not observed for fibers and fragments. Additionally, the abundance was analyzed in the same usage zones by recovering 10 samples per zone. The average abundance was found to be 1414 kg d.w. in the active zone, 1192 kg d.w. in the rest zone, and 1524 kg d.w. in the service zone. These data are of interest because they can be related to the processes of MP fragmentation, not only due to the influence of waves and sedimentation processes but also to parameters such as temperature and the transport of materials towards dune areas located in the service zones. Therefore, promoting further studies considering these parameters on other beaches is necessary.
Different letters above the bars indicate statistically significant differences at the 95% confidence level.
As analyzed so far, there is a significant abundance of MPs present in beach sand with varied sources. Additionally, it has been widely identified that a residue with high abundance and persistence in the sand is CBs, composed of CA. In their decomposition process, they could contribute to the load of MPs, especially fiber types, found in the sand.
3.2. Functional groups of CBs and CBFs identified at the study beach
Table 1 provides a synthesis of the peaks identified in the literature for CBs studies related to the set of peaks resulting from the tests conducted in this study. For better understanding, an alphabetical categorization is applied, denoting with letters from A to Y the set of identified peaks.
In Table 1, it is observed that, for each peak category described in the literature, a series of peaks are grouped, showing shifts that can be attributed to changes generated in the CBs and CBFs material over time of persistence in the sand and various environmental variables such as temperature, humidity, wind or rain erosion, sand granulometry, and organic material content.
To analyze the presence of peaks and functional groups in CBs, CBFs, and sand for each usage zone, the previously identified code will be employed, as shown in Fig 4. The results obtained in the FTIR test are described for each sample.
The analysis of Fig 4 shows that the relative frequency of functional groups in each analyzed matrix varies across beach zones. In the Active zone, 85% of the functional groups (22 out of 26) were present, with groups D, K, P, R, and W being absent. In the Rest zone, the presence increased to 92% (24 out of 26), with absences limited to group P and potentially one additional group according to the notation. The Service zone exhibited the highest coverage, with 96% of the functional groups present (25 out of 26), with only group D absent. Overall, a clear increasing trend in the relative occurrence of functional groups is observed from the Active zone toward the Service zone, where nearly all groups are represented at some frequency.
Among the indicators of plastic-derived compounds, group E stands out due to its association with the presence of polyethylene glycol, a compound that, although generally considered to have low toxicity, can form derivatives such as mPEGA-480 that are highly toxic at low concentrations. These derivatives can trigger oxidative stress processes in living cells through the generation of reactive oxygen species (ROS) and the depletion of reduced glutathione (GSH), leading to an imbalance in intracellular redox status and ultimately to cellular apoptosis [26]. Such toxicological effects have been documented in aquatic organisms, including the zebrafish (Danio rerio), where adverse impacts—particularly during early developmental stages—have been reported. These effects include malformations such as tail and spinal deformities, edema, and pigmentation alterations, as well as changes in heart rate that may result in high mortality rates, especially at elevated concentrations of this compound [27].
Other functional groups of relevance were groups A and H, which indicate the presence of cellulose acetate. According to the scientific literature, cellulose acetate exhibits significant initial toxic effects and may continue to pose long-term environmental risks due to the formation of new toxic compounds during its degradation [28,29].
Additionally, group G, an indicator of anhydroglucose—a polymer associated with nanocellulose—was detected at relatively high frequencies. Nanocellulose has been reported to induce adverse effects in animal cells, including cytotoxicity, oxidative stress, inflammation, and genotoxicity; however, these effects are generally associated with extremely high concentrations or specific surface modifications [30].
According to data reported in the literature, 25 different types of peaks corresponding to functional groups have been identified in CBs. For the present study, two composite samples of freshly smoked cigarette butts (Virgin CBs) were taken into consideration because they are the brands identified most regularly in the monitoring conducted during the project (14 functional groups related to those shown in the literature were identified in these samples). Fibers from filters without contact with sand (Virgin CBFs) were also sampled, and 8 functional groups related to the literature were identified in these samples.
In Fig 5a, 5b, 5c, the FTIR results for the samples taken in the zones are shown, where samples of CBs, CBFs, and sand were collected. In the active zone, nine functional groups (C, F, G, J, L, M, T, V, and X) were identified in CBs samples; twelve functional groups (A, B, C, F, G, L, J, M, N, T, V, and X) were present in CBFs samples, and six functional groups (A, B, E, H, J, V) were identified in the sand. It’s important to note that this area is exposed to wind, has higher humidity being closer to the water, and is a zone where users regularly transit to enter the sea.
In the resting zone, sixteen functional groups (A, B, C, D, E, F, G, H, J, K, L, M, T, V, W, and X) were identified in the CBs sample; thirteen functional groups were present in the CBFs sample (B, C, F, G, L, J, M, N, T, R, V, X, and Y), and six functional groups (A, B, E, H, J, V) were identified in the sand. It’s important to note that the functional groups identified in the sand are the same as those in the active zone, with the particularity that in the resting area, there is furniture such as tents, umbrellas, and chairs that create more shaded areas in the sand.
Finally, in the services zone, twenty functional groups (A, B, C, E, F, G, J, L, M, N, O, P, Q, R, T, U, V, W, X, and Y) were identified in the CB sample; twenty functional groups were present in the CBFs sample (A, B, C, F, G, H, J, L, M, N, O, P, Q, R, T, U, V, W, X, and Y), and eleven functional groups (A, B, E, G, H, N, O, Q, U, V, and Y) were identified in the sand. In the services zone, the highest number of functional groups was reported in both CBs and CBFs, and the sand also exhibited a higher number of peaks associated with the decomposition processes of CBs. In this area, there is a noticeable increase in the temperature of the sand compared to the other two zones.
3.3. Description of identified functional groups (FTIR)
Table 2 summarizes the functional groups identified by FTIR analysis in cigarette butts, cigarette butt–derived fibers, and sand samples. The comparison of characteristic absorption bands reveals shared chemical features among the three matrices, particularly those associated with cellulosic polymers and plastic additives. The detection of similar functional groups in fibers and sand indicates progressive fragmentation and chemical alteration of cigarette butts, supporting a direct link between butt degradation processes and the release of fiber-type microplastics into the surrounding environment.
4. Discussion
The literature was reviewed for the report of different functional groups identified and described as variations of cellulose acetate, polyethylene glycol, acetyl groups, ashes, hydrocarbons, triacetin (plasticizer) reported as cigarette compounds. Additionally, around 130 chemicals are present in cigarette filters, and many more chemicals (between 40,000 and 100,000) have been identified in cigarette smoke, some of which could potentially be retained in these filters, including aromatic and heterocyclic amines, carbonylated compounds, phenols, and polycyclic aromatic hydrocarbons [44].
In tourist beaches, the presence of various types of solid waste is common, including the frequent occurrence of discarded plastics in the sand. Research has drawn attention to the presence of primary or secondary MPs in beach sand. Due to their low degradation, they exhibit high persistence in this environment, potentially leading to contamination [45]. The study conducted on 22 beaches along a distance of >4600 km on the coast of Brazil reveals the identification of 10 types of plastic waste, of which approximately 2% corresponds to cigarette butts. This reaffirms the significance of this emerging waste on beaches. The study emphasizes the color classification, describing CBFs as “no color” due to variations in shades attributed to different forms of exposure to the environment [46].
Other studies in the literature have reported varying MP abundances on different beaches worldwide. For instance, Claromeco Beach in Argentina recorded an average of 330−410 items kg-1 of MPs, featuring findings of Cellulose, PA, PMDS, PET [47]. The study conducted on seven beaches along the East Coast of India reported variations ranging from 1 to 6 MP items per kilogram of dry soil, presenting microplastics in various colors, including red, white, blue, black, and yellow, in the form of films, fragments, and filaments [45]. In the beach sand study carried out in Rayong, Thailand, six sites were sampled, revealing abundances ranging from 20 to 1160 particles per kilogram of dry weight, with an average microplastic abundance of 338.89 ± 264.94 particles per kilogram of dry weight [48]. In the study conducted in the Red Sea to assess microplastic pollution along the Egyptian coasts, out of the 17 evaluated beaches, 3 meet the conditions of having fine sandy beaches and a tourist nature, located in the Suez area. They had concentrations of 120.0 ± 96.4, 110.0 ± 17.3, and 146.7 ± 60.3 MPs/kg dry weight. This indicates a low presence of MPs compared to the coasts of the Mediterranean region of Egypt [49].
The literature review of peer-reviewed scientific studies published in English, providing quantitative measurements of MPs with a diameter less than 5 mm in sediments or beach sand, spans the period of studies conducted between 2017 and 2022. A total of 21 studies were identified, reporting data on the abundance of MPs in terms of the number of MPs per kilogram of dry sand or per square meter of sand. The study locations included India, Hong Kong, Brazil, China, the Baltic Sea, Australia, Viet Nam, Europe, Thailand, Portugal, Bangladesh, Spain, Dubai, and the United States. The study noted that Adelaide Beach in South Australia reported the lowest abundance of MPs, ranging from 0.5 to 2.2 microplastics per kilogram of sand, while the sediments off the coast of Da Nang, Vietnam, exhibited the highest levels of MPs, reaching 9238 ± 2097 elements per kilogram of dry weight [50].
In the literature, there is a reported study conducted along the coasts of the Metropolitan City of Mugla, located in southwestern Turkey, surrounded by the Mediterranean Sea to the south and the Aegean Sea to the west. The study focused on tourist beaches, revealing that 61.07% of all MPs detected in both summer and winter seasons were fibers, followed by fragments (32.12%), expanded polystyrene particles (2.49%), films (2.38%), and pellets (1.94%), respectively [51]. In Argentina, sampling was conducted on three beaches to analyze factors contributing to the presence of MPs, with a focus on tourism and other recreational activities such as artisanal fishing. Additional factors, including MP pollution transported by seawater through littoral drift, were also considered. On average, a concentration of 1133.3 ± 811.3 elements per kilogram of dry weight (d.w.) was recorded, with fibers and films of less than 1 mm being the most prevalent particles [52].
In this study, MPs were analyzed and classified into fibers, fragments, pellets, and films. Across all land-use zones, fibers were the dominant category, accounting for 1090 fibers kg ⁻ ¹ dry soil (77.1% of total MPs) in the active zone, 774 fibers kg ⁻ ¹ dry soil (64.9%) in the resting zone, and 1138 fibers kg ⁻ ¹ dry soil (74.7%) in the service zone. These values are comparable to those reported in the literature and represent a particularly relevant finding in the Colombian context, where fiber-type MPs potentially associated with CB degradation have not been previously reported.
The high abundance of fibers observed in the services zone may be driven by several interacting factors, particularly the elevated density of CBs (0.874 CBs m ⁻ ²) recorded in this area compared with the resting zone (0.188 CBs m ⁻ ²) and the active zone (0.134 CBs m ⁻ ²). This spatial pattern is consistent with the distribution of CBFs, which also exhibited the highest density in the services zone (0.066 CBFs m ⁻ ²), followed by the resting zone (0.024 CBFs m ⁻ ²) and the active zone (0.006 CBFs m ⁻ ²). Furthermore, previous research conducted at the site in 2022 reported a marked tendency toward CB disposal and accumulation in the services zone, as well as higher sand surface temperatures. These conditions may enhance the degradation rate of CA in CBs, thereby promoting the release of fiber-type MPs [53].
It is important to mention that the abundance of discarded cigarette butts in the environment is very high, even in developed countries. Approximately 75% of cigarette butts are estimated to be discarded in the soil, contributing to 340–680 million kg of CB waste annually, causing significant environmental impacts, especially in coastal marine ecosystems [35].
The study conducted by [3] demonstrated that CBs are a potential source of MP contamination, estimating 0.3 million tons of microfibers ending up in aquatic ecosystems annually. The study in the Southwest Atlantic (Argentina) identified CBs as the most abundant mesoplastic residue, with 1080 units out of 2461 counted. It is suggested that these types of residues can be transported by natural factors such as wind and water, may undergo variable frictional wear according to different sand granulometries, and can be affected by anthropogenic factors depending on the intensity of recreational beach use. Therefore, these various factors may be responsible for the MPs found in the sand [54].
Approximately three quarters of CBs are improperly discarded, leading to their widespread accumulation in coastal environments and the release of substantial amounts of microfibers into aquatic systems [3]. In this context, the findings of the present study provide empirical support for these concerns, as functional groups characteristic of CBs and CBFs were identified in sand samples, together with a high abundance of fiber-type MPs across all surveyed zones. These results confirm that CBs function not only as visible litter but also as a source of secondary MPs, reinforcing their classification as an underestimated yet environmentally relevant contaminant in coastal ecosystems. Accordingly, there is a clear need for stricter control over the distribution and disposal of CBs in the environment, supported by robust legislative action, innovation in product design, and increased public awareness to mitigate long-term environmental and human health risks [55].
In the study of CA degradation processes resulting from homogeneous or heterogeneous acetylation of cellulose, it should be noted that the properties of CA depend on the degree of substitution (DS). DS is the average value of acetyl groups replacing hydroxyl groups in the anhydroglucose units (AGU) of cellulose. CA with a low DS value has a greater potential for biodegradation, while a high DS value indicates more acetyl groups that disrupt the ordered structure of cellulose, resulting in CA with higher acetylation levels and lower crystallinity. It’s important to note that an increase in temperature favors acetylation [56]. The above-described findings are consistent with the CA functional groups reported in the literature and identified in the sand, CB, and CBF samples from the study beach.
This study provides baseline evidence that supports future research aimed at expanding the understanding of cigarette butt–derived MP pollution in coastal environments. Further investigations should incorporate a larger number of samples and complementary analytical techniques beyond FTIR, while integrating environmental variables such as temperature, wind speed, humidity, solar radiation, sediment granulometry, and tidal variability in the active zone. Extending the temporal coverage to include additional sampling months would also improve the assessment of spatial and seasonal dynamics influencing MP generation and distribution.
5. Conclusions
This study demonstrates a clear predominance of fiber-type MPs on the study beach, with fibers representing the most abundant category across all usage zones and sampling periods. Based on 160 sand samples collected over 16 months, fiber-type MPs were dominant in 87.5% of the samples, followed by fragments and films, indicating a stable and persistent contamination pattern. Higher fiber abundances in the active and services zones suggest that environmental conditions such as wave action, humidity, and elevated sand temperatures may enhance plastic degradation and microfiber generation.
A key contribution of this study is the identification of functional groups associated with CBs and CBFs in sand samples using FTIR analysis. Approximately 24% of the functional groups reported in the literature for CBs were detected in the sand, including bands linked to cellulose acetate and its degradation products. The presence of characteristic peaks (e.g., 460.99, 692.44, 1083.99, and 1161.15 cm ⁻ ¹) across active, resting, and services zones provides chemical evidence supporting the role of discarded cigarette butts as a secondary source of fiber-type MPs in coastal environments.
Despite these findings, this study has limitations that should be acknowledged. Potential sources of uncertainty include the limited control of environmental variables such as temperature, solar radiation, wind dynamics, and tidal variability, as well as the diversity of cigarette brands and filter compositions present in the environment.
Overall, this research provides baseline evidence relevant to understanding cigarette butt–derived MP pollution in tropical coastal environments. Future studies should expand the number of analyzed samples, incorporate additional analytical techniques beyond FTIR, and explicitly evaluate environmental drivers such as sediment granulometry, meteorological conditions, and seasonal variability. Such approaches will improve the assessment of degradation mechanisms and strengthen the understanding of the environmental and public health implications of cigarette butt pollution.
Supporting information
S1 File. Characteristic FTIR peaks (cm ⁻ ¹) of cigarette butts (CBs) and beach sand according to beach use zones.
https://doi.org/10.1371/journal.pone.0345311.s001
(XLSX)
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