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Article

Remote Alpine Lakes and Microplastic Accumulation: Insights from Sediment Analysis of Lake Cadagno

by
Serena M. Abel
1,*,
Colin Courtney-Mustaphi
2,
Maja Damber
2 and
Patricia Burkhardt-Holm
1
1
Man-Society-Environment Program (MGU), Department of Environmental Sciences, University of Basel, Vesalgasse 1, 4051 Basel, Switzerland
2
Geoecology, Department of Environmental Sciences, University of Basel, Klingelbergstrasse 27, 4056 Basel, Switzerland
*
Author to whom correspondence should be addressed.
Microplastics 2025, 4(2), 25; https://doi.org/10.3390/microplastics4020025
Submission received: 13 November 2024 / Revised: 24 February 2025 / Accepted: 27 March 2025 / Published: 7 May 2025
(This article belongs to the Topic Plastic Contamination (Plastamination): An Environmental and Public Health-Related Concern)
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Abstract

:
Microplastic (MP) occurrence is a growing concern in environmental research, with significant attention focused on its presence in various ecosystems worldwide. While much research has centered on large lakes and water bodies, remote alpine lakes remain relatively unexplored in terms of microplastic occurrence. Studying microplastic occurrence in remote alpine lakes is important to understand the global spread of pollution, assess its impact on pristine ecosystems, and inform conservation efforts in these vulnerable environments. This study investigates microplastic presence in the sediment of Lake Cadagno, a remote alpine lake situated in the Piora Valley of southern central Switzerland. The lake has no effluents, and its meromictic nature means that the water on the bottom is not mixed with the water above, which can potentially lead to an enhanced accumulation of microplastics in the sediments that perpetuate in the lake system. Through sediment core sampling and analysis, we aim to identify the sources and deposition trends of microplastics in this pristine alpine environment. Our findings reveal the presence of microplastic within Lake Cadagno: in total, 186 MP particles were extracted from 756 cm3 of processed sediment (0.24 MP/cm3) with an average of 19.5 MP/sample (SD ± 11.8 MP/sample). Our results suggest that microplastics are predominantly attributable to localized sources associated with nearby human activities. The absence of synthetic fibers and the limited polymer types detected suggest a minimal contribution from atmospheric deposition, reinforcing the significance of local anthropogenic influences. Spatial clustering of microplastic particles near potential sources underscores the impact of surrounding land use activities on microplastic distribution. Overall, this study highlights the importance of addressing microplastic contamination even in remote and relatively unmodified ecosystems like Lake Cadagno, to elucidate the need for strict adherence to waste management and correct disposal actions to reduce the impacts of microplastic contamination.

1. Introduction

Plastic and microplastic (MP) pollution has been documented in nearly every ecosystem globally [1,2]. Environmental studies often focus on identifying the sources and sinks of plastic litter in the environment. Understanding the pathways of plastic litter—how it originates, moves, and accumulates in various environmental sinks—is essential for devising effective measures to prevent and mitigate plastic pollution. Additionally, research examines the transport dynamics that contribute to the ubiquity of MP and the magnitude of its environmental impact [3,4,5]. In freshwater ecosystems, plastic contamination is generally more pronounced in areas with high anthropogenic activity, such as cities and industrial zones, compared to more pristine regions [6,7]. In rivers, specific zones, such as riverbanks and vegetated riparian areas, can influence the deposition and accumulation of plastic litter [1]. Similar patterns have been observed in lakes, where plastic contamination levels vary depending on factors such as tributary rivers and proximity to urban areas [8]. Plastics can enter lake systems from coastlines and terrestrial environments through sources such as domestic waste disposal, landfill redistribution, and industrial activities [9]. The contribution of these sources varies based on a lake’s location and usage. In suburban lakes, primary pollution sources include human activities and river transport. Recreational fishing, for instance, has been identified as a contributor to plastic pollution through the inadvertent loss of plastic devices or synthetic fibers [10]. In alpine and subalpine lakes, which are often more remote, plastic contamination is typically linked to local human activities, such as hiking, camping, and other outdoor recreation, as well as MP runoff and atmospheric transport [11]. However, contamination in these lakes is not solely due to local sources. Atmospheric deposition of MP has been documented in mountain catchments and soils across Switzerland, underscoring the broader scope of pollution [12,13]. Littering not only mars pristine landscapes but also imposes significant costs on local authorities. In the canton of Ticino, which boasts over 130 lakes and attracts approximately 42 million visitors annually, tourism is a major economic driver. However, Switzerland as a whole spends an estimated CHF 200 million annually on clean-up operations (UFAM, 2023). From an environmental perspective, litter fragmentation into MP is a critical issue, accelerated by high UV radiation and other climatic factors in alpine regions [14] Despite extensive research on plastic and MP pollution in suburban lakes—where shore litter surveys, water column analyses, and sediment studies have been conducted—alpine lakes remain largely underexplored [15]. Although often perceived as pristine environments, alpine lakes are not immune to anthropogenic influences. Activities such as hiking, picnicking, skiing, fishing, and gastronomy contribute to plastic contamination. Accidental plastic disposal is a significant driver of littering and subsequent MP generation [6]. Lake Cadagno, a subalpine meromictic lake situated at 1921 m in the Piora Valley of Ticino, Switzerland, exemplifies a remote alpine basin. With a depth of 21 m, the lake is supplied by two primary water sources: a superficial layer fed by snowmelt from spring creeks flowing over granite rocks, and a denser lower layer replenished by subaqueous sulfurous springs through dolomite formations [16,17]. Access to Lake Cadagno is limited, with car access restricted and a funicular operating only during the summer season. Direct access to the lake is strictly regulated, and fishing activities are monitored through seasonal regulations and restrictions on materials used [17]. Despite these controls, littering remains visible in the valley, as is the case with other accessible lakes [18]. This study aims to quantify MP accumulation in the sediment of the Lake Cadagno catchment area. The primary hypothesis is that MP pollution in the lake sediments is predominantly driven by local sources within the catchment area [19], including the weathering of litter along the lake’s shores and in its vicinity. Sediment samples from nine different locations in the lake are analyzed to determine plastic concentrations and detect temporal trends. Elevated MP levels near the surface may indicate increased human activity, providing insights into plastic deposition dynamics over time.

2. Material and Methods

During October 2022, nine sediment cores were collected from Lake Cadagno using a gravity corer with a core base plug (6.3 cm internal diameter; UWITEC, Mondsee, Austria) deployed from an adapted raft [20]. The motorized wooden raft was equipped with a metal support that allowed the core drill to be unhooked and retrieved by means of a steel wire. Further details of the sampling locations are presented in Table 1.
On site, the upper 10 cm of the recovered cores were sliced into 1.5 cm thick layers, which were collected in polytetrafluoroethylene (PTFE) bags and stored in the fridge at 4 °C once back in the laboratory.

2.1. Sample Preparation and Processing

Several preparatory steps were conducted to extract MP from the sediment matrix prior to micro-FTIR analysis. This included a density-based separation followed by an organic matter digestion and sample filtration.
For the density-based separation [3], 12 cm3 (wet weight) (the water content expressed in % of each sample is given in Table 1) was subsampled from each sediment layer down the core (7 samples per core) and transferred into glass culture media bottles with a straight neck (300 mL Duran), using a PTFE measuring cup. The bottles were filled to 2.5 cm below the brim with a sodium bromide (NaBr) solution (density 1.53 g cm−3) (>99% purity, Carl Roth GmbH+Co. KG, Berlin, Germany) and covered with aluminum foil. The samples were stirred at 400 rmp (Heidolph MR3000. Faust AG, Berlin, Germany) until completely suspended (for up to 1h). Then, the external walls of the bottles were rinsed with 0.22 μm filtered Milli-Q ultrapure water (Milli-Q water) and placed into glass Petri dishes (Ø = 150 mm) individually under a horizontal flow cabinet (HFX.180BS SKAN AG, Basel, Switzerland) to let the sediment to settle ≤ 24 h or until the solution appeared clear and the sediment was completely settled.
Subsequently, the upper layer was extracted via overflow: 90 mL of NaBr solution was added to each sample by using glass syringes, 7 cm below the surface (50 mL, Carl Roth GmbH+Co. KG, Berlin, Germany), in two steps with a settling time of 10 min between injections. The overflow procedure was repeated after a second stirring step of about 5 min and another overnight settling to maximize the extraction of MP. During this time, the already extracted fraction was stored in glass bottles with PTFE lids (250 mL, Schott). The samples were filtered onto stainless steel filters with a 25 µm mesh size (47 mmØ Wolftechnik Filtersysteme GmbH & Co.KG, Berlin, Germany) and manually flushed with 250 mL of Milli-Q water.
A Fenton reaction was performed by adding 20 mL of iron sulfate and 40 mL of H2O2 directly to the particulate material concentrated in the stainless steel filters. The detailed procedure according to the protocols suggested by [3,21] is described in the Supplementary Materials.
The digested material was then divided in two size classes via vacuum filtration onto PTFE filters with a 500 µm mesh size (47 mmØ, Sefar AG, Basel, Switzerland). The filtrate containing particles <500 µm was transferred onto 25 µm mesh stainless steel filters. The material filtered onto the stainless steel filter was resuspended in Milli-Q water and subsequently filtered onto aluminum-oxide filters (Anodisc, 0.2 μm pore size, 25 mmØ, Whatman, Berlin, Germany). Both the PTFE filters and the Anodisc filters were placed into Petri dishes and stored in a desiccator cabinet for a minimum of 12 h (PureLab flex, Labtec Servicies, Berlin, Germany) until spectroscopic analysis.

2.2. Microplastic Identification

Putative large MPs (L-MPs) [22,23] were manually sorted from the >500 μm sample fraction using a stereomicroscope set at 100–400× magnification and applying the identification characteristics defined by [22,24]. All the visually sorted putative L-MPs, including fibers [25] and particles, were transferred to glass Petri dishes for further analysis. They were photographed and measured for length and width dimensions under a stereo microscope (Olympus SZ61) equipped with a digital camera (Olympus SC50), Germany and image analysis software (CellSens, Olympus), Germany. Subsequently, each particle and fiber underwent individual polymer identification using an attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectrometer (Bruker Alfa coupled to a diamond platinum ATR unit, Bruker Optik GmbH, Germany). The infrared spectra were collected in the range of 400–4000 cm−1 and compared against a reference library [3,21]. Particles exhibiting a match score of at least 700 out of 1000 were deemed effectively identified. For particles with a match score between 600 and 700, manual comparison with database spectra was conducted, as well as a visual evaluation, followed by re-evaluation for confirmation or rejection. Particles with a match score below 600 were categorized as undefinable and excluded from further analysis.
For the lower size class (S-MPs: small microplastics) (25–500 µm), the particle analysis was conducted via micro-FTIR (Lumos, Bruker Optics GmbH. Billerica, MA, USA). Within the controlling software OPUS, provided by Bruker Optics GmbH, each filter underwent imaging, with only particles exceeding a major length of 50 μm selected for further automated scanning, while others were excluded from subsequent analysis, as the image resolution of the smaller particles images was not sufficient for an accurate size measurement.
For scanning, the particles were subjected to a transmission mode with a 50 μm × 50 μm aperture, covering the spectral range between 4000 and 1200 cm−1, at a resolution of 4 cm−1, and a total of 64 coadded scans. Data extraction from OPUS files into individual spectrum CSV spreadsheet files was achieved using a custom MATLAB script (R2021a Update 4), retaining data within the range of 3300 to 1300 wavenumber cm−1. Synthetic polymer particles were measured in their widest and narrowest part within OPUS. Library searches involved preprocessing raw data through smoothing and baseline correction, following the specifications of [21]. Processed spectra were then compared against the libraries of [3,26]. Simultaneously, searches were conducted using the first derivative of the spectra to highlight peak positions. Matches with a Pearson correlation coefficient > 0.7 were considered. Additionally, each selected match to a synthetic polymer underwent visual assessment by two researchers independently. Afterwards, the accepted matches were grouped into polymer groups [21,27].

2.3. Sedimentological Analysis

To determine the organic material content and water content in the sediment, LOI (loss on ignition) analysis was performed on 1 cm3 for every sediment layer. For this, the sediment was heated up to 105, 550, and 950 °C samples to remove organic matter and volatile compounds, leaving behind the inorganic components (see Supplementary Materials Table S1). The weight loss after heating was measured and used to calculate the percentage of organic matter in the sediment [28] and the water content, showing that the volume of layers was represented mostly by sediment.

2.4. Data Processing and Statistical Analysis

For core intercomparison, the MP concentrations were standardized to a 12 cm3 volume (standardization at 12 cm3 overcomes the raw data manipulation necessary for comparative purposes) [29]. A Shapiro–Wilk test (significance level 5%) was performed to assess whether MP distribution in the sediment column followed a normal distribution. To investigate any correlation of the MP abundance with the distance from the shore or the lake depth, the Spearman correlation coefficient was calculated [29] (software: Origin Pro2023b).

2.5. QA/QC

During the sampling campaign and laboratory analysis, contamination was monitored by field and procedural blanks. In all the steps, the researchers were wearing cotton clothes and 100% cotton lab coats. To exclude fiber contamination, subsamples of clothing were taken and categorized according to color and material (measured via ATR). In the laboratory, the analysis was performed in a horizontal flow cabinet. Dustboxes (Lufttechnik GmbH Type 1000, Berlin, Germany) equipped with HEPA filters, which continuously filtered the laboratory air. All labware was made of stainless steel and PTFE and was rinsed with Milli-Q, and all chemicals were filtered through glass fiber filters prior to use.
To avoid water signals, a dehumidifier was active in the laboratory during spectroscopic analysis, keeping the humidity below 40% [5,30].

3. Results

In total, out of 74,000 analyzed particles, 176 were identified as MPs (50–500 µm), while for the >500 µm fraction, 9 out of 282 analyzed particles were made of synthetic polymers (Figure 1).
In all the cores, MPs were found and ranged between 6 (CAD9) and 48 (CAD6) particles per 12 cm−3. By visual assessment, 21 particles where reassigned to “organic material” due to incongruences in the spectra matches. Most of these materials were identifies as “cellulose” and “cellulose with silicate”.
Overall, the S-MP particle size ranged between 50 and 457.87 µm (mean size: 146.6 µm), while the L-MP size range was between 882 µm and 1000 µm (mean size: 541.7 µm). By checking the image of the plastic particle on the Anodiscs and the PTFE filters, no particles with an elongated shape (such as fibers) were detected.
The cores adjacent to the mountain (slope that ends in the lake CAD 6 and CAD7) showed the highest MP numbers (48 and 26 MP/12 cm3, respectively), while the cores located close to the shore that is not easily accessible by tourists (CAD4, CAD5, and CAD9) presented the lowest MP loads (12, 7, and 6 MP/12 cm3), respectively. Finally, in CAD1, CAD2, CAD3, and CAD8, 19 MP/12 cm3, 20 MP/12 cm3, 22 MP/12 cm3, and 16 MP/12 cm3 were detected. Statistical tests revealed no significative correlation between MP abundance and core depth or distance from the shore.
A total of six polymer types were identified, with polyethylene terephthalate (PET) comprising 58% of the polymer diversity, followed by polyethylene (PE;25%) and polypropylene (PP, 11%). Together, the remaining polymers (polystyrene (PS), acrylic, and polyvinylchloride (PVC)) accounted for the other 6%. No visible vertical distribution pattern was observed along the sediment column within an intralayer and interlayer comparison of polymer type distribution or MP abundance (Figure 2).

4. Discussion

The detection of 185 MP particles from 756 cm3 (corresponding to 737g of processed sediment) of sediment in Lake Cadagno underscores a relatively high MP accumulation in this remote alpine environment, especially when considering its small catchment area (0.26 km2) [31] The lake is near a headwater system and has limited anthropogenic use pressure when compared to downstream environments. Our results are useful for quantifying upstream section models of plastic accumulation and stocks. In fact, this environment, often thought to be less impacted, may act as a reservoir or conduit for MPs.

4.1. MP Accumulation Trends

Understanding this accumulation improves predictions of plastic transport and distribution across broader ecosystems, aiding in more accurate environmental management strategies. The unique characteristics of the lake, extensively studied for its meromixis, sediment composition, and microbiological communities, provide a valuable context for understanding the dynamics of MP accumulation [32]. Sediments act as environmental archives, providing valuable insights into historical conditions and processes within aquatic ecosystems. With a sedimentation rate of 2.5–5.5 mm per year, each layer analyzed in this study captures roughly 27 to 60 years of sediment accumulation [33]. The sediment cores represent a time span of approximately 189 to 420 years. The cores were sampled up to this age range to verify that no MPs would be present below the estimated depth limit, as plastic production began only in the 1950s. Based on this timeline, MPs were expected to be confined to the upper 2 to 4.5 cm, corresponding to the first three layers (L1 to L3). However, as shown in Figure 2, MPs were unexpectedly detected in deeper layers (L7 in six out of nine cores), suggesting earlier or deeper plastic contamination than initially presumed. Moreover, MP abundance throughout the core shows no evidence of correlation with depth: if the MP abundance in the environment is demonstrated to increase over the years, this trend also should be observed in MP accumulation [34]. Even considering that patchiness of MP distribution in the environment could partially screen this abundance decrease with depth, only one core (CAD2) out of nine shows this trend. The reasons for this sedimentation trend can be multiple, as factors such as bioturbation and recasting events can affect the accuracy for age determination in upper sediment layers [3,35]. Also, the sampling event itself can contribute to the intralayer mixing, which is enhanced by fine-grained sediment that can easily get resuspended [3]. Finally, as highlighted by [33] turbidite layers were detected in the first cm of the sediment column. However, the layering model of the study is not defined in such detail as the layering in this study (the different purpose of the study and different analysis require different sampling models, such as the core depth). Despite this, turbidites in the sediment column fraction investigated in this study can be assumed, and they explain the transport of MPs in the deeper sediments. We conclude that in the samples of non-compacted sediment, the presence, absence, or abundance of MPs cannot be used as indicators of MP deposition trends over time.
Despite the lack of statistically supported evidence, the data visualization revealed the spatial clustering of MP particles in certain areas of the lake, particularly in close proximity to potential sources, such as the shores that are most exploited for fishing and the site where the runoff of the mountain slope enters the lake (as reported in the fishing guidelines of the canton). These observations suggest a potential linkage between MP distribution and the surrounding land use activities. For example, CAD6 and CAD7 were the cores showing the highest MP numbers (48 and 26 MP/12 cm3, respectively). These cores are located directly at the end of the slope through which meltwater enters the lake system, and with it also sediment and MPs. Furthermore, the cores located close to the shore that is not easily accessible by tourists (CAD4, CAD5, and CAD9) presented the lowest MP loads (12.7 and 6 MP/12 cm3), respectively. This observation supports the hypothesis of MP source vicinity and MP abundance in the lake sediment.

4.2. Polymeric Composition of Detected Plastic

Overall, six polymer types were detected (Figure 1).
The polymer composition matches with the composition of certain application groups: PE, PP, PET, and PVC are the most common polymer types that are utilized for the manufacture of food and beverage packaging ([34,36]).
The provenance of MP fraction particles could not be determined due to their small size. However, stereomicroscopic analysis of L-MPs revealed shapes indicative of abrasion from hard plastic objects and textures resembling synthetic fabrics. These items are a source of MPs in the lake environment [37]. In fact, the particular environmental conditions of high-altitude alpine lakes can contribute to an enacted weathering effect of the litter plastic fraction with the consequent production of secondary MPs [14]. As proven from several studies, the weathering of plastic material is accelerated by high-UV radiation, which increases with increasing altitude. The cleavage of weaker C-H bonds from tertiary carbons, which are present in PP and PS for instance, is particularly favorable to photooxidation [38]. Additionally, in cold climates, the impact intensifies for polymer composite materials that harbor moisture within capillaries, pores, and microvoids [39]. The presence of accumulated water within polymeric materials during sub-zero temperatures leads to heightened levels of internal stresses [40].
A second interesting observation is that no systemic fibers were detected. The causes of the absence of fibers can be attributed to fiber loss due to the size limitation of the analysis and/or negligible contribution of atmospheric fiber transport. While proving the absence of atmospheric deposition over time is out of the scope of our analysis, the methodological limitations are known. In this study, the lower size limit for MP characterization was set at 50 µm. Smaller particles were not measured; therefore, there is the potential for the underestimation of small-sized MPs, transported by wind and rain. The lower size limit was due to insufficient resolution of the spectra quality of the smaller particles, the high background noise, and scattering. Accordingly, a characterization of very small particles was not possible [41]. Another potential underestimation is a consequence of the extraction method applied: density separation-based extraction methods of MPs from sediments are not capable of extracting particles denser than the brine solution that is used as separation fluid [42]. This means that particles with a polymer mix, such as tire and road wear particles (TRWP), cannot be extracted or measured. Moreover, the TRWPs complex composition [43], carbon black interference with spectroscopic analysis in the infrared radiation range [44], and the difficulty involved in their extraction from sediment via density extraction [45,46] make it challenging to characterize them with the methods applied in this study.
Overall, it was not possible to distinguish between atmospheric and local MP sources. However, it is also difficult to quantify what still has no unanimous definition in the literature: atmospheric MPs. This MP “category” does not have a consistent definition that includes size ranges, shapes, and sources. In fact, its definition is quite broad, as it includes particles and fibers in a size range from 13 ± 4 μm [47] to 358 μm [48]. Moreover, the definition includes a wide range of different sources [49] that require a certain level of transport and are influenced by the typology of the MP (size and shape) [50]. Thus, the particles detected in the lake sediment, between 50 and 358 μm, cannot be identified with absolute certainty as a source of contamination.
Potentially, the presence of atmospheric MPs cannot be excluded as a contamination source of the lake system, and all these factors—environmental, methodological, and definition limitations—should be considered when it comes to the estimation of MPs, as they eventually lead to underestimations of MPs.

4.3. Literature Comparison and Challenges in Microplastic Investigation

As mentioned in the previous sections, the number of studies investigating the presence of plastic and MP in Swiss alpine lakes is limited. Concerning the accumulation of MP in the sediments of alpine lakes in the Swiss realm, a similar study was conducted in Lake Sassuolo (Ticino). Velasco et al., [51] report an accumulation of 33 MP particles per kg of sediment. These concentrations are far less than those found in Lake Cadagno (185 MP in 737 g analyzed sediment). Nevertheless, the comparison might lead to a wrong interpretation of the MP load of the two basins. In fact, Velasco et al., [51], the MPs ranging between 5 mm and 125 μm; this study investigates particles down to 50 μm. As 48% of all the MPs in Lake Cadagno are smaller than 125 μm, an underestimation of the MP load in Lake Sassuolo cannot be excluded. Nevertheless, both of the investigation outcomes suggest a significantly lower level of MP contamination in remote lakes compared to MP concentrations along the shores of suburban Swiss lakes, such as Lake Lugano and Lake Maggiore (located in the same canton as Lake Cadagno) and other larger Swiss lakes (Zürich, Konstanz, Geneva, Neuchâtel, and Brienz) [52,53]. Although the reported data refer to shore contamination, with MP abundance reported per m2 and a larger size range (0.3–500 mm), the concentration can still be considered higher (max concentration detected in Lake Lugano with 3063 ± 2566 (mean ± SD particles/m2).
The polymer richness was also comparable to the findings in other lakes (seven matching polymers in Lake Lugano versus six in Lake Cadagno). In Lake Lugano, the low polymer number might be attributed to underestimation (among other reasons) given the non-match of 8% of the analyzed particles with reference spectra [52,53]. In Lake Cadagno, the low polymer richness of the identified particles implies limited and mostly localized sources. However, this assumption must be maintained, as it cannot be assumed that it applies to all alpine lakes that may have varied degrees of anthropogenic use pressures. In fact, the complex diversity of the alpine ecosystems poses a challenge for an overall quantification of MP contamination in this realm [54,55]. Effective comprehension of MP contamination in alpine environments necessitates meticulous, site-specific investigations tailored to the unique attributes of the area. In fact, the representativeness of an area and the analysis effectiveness depend on many factors, such the size and type of sample matrix, the MP size class target, and the sampling design [3]. Notably, the analysis of sediments from Lake Cadagno presented distinct advantages for reliably assessing MP contamination in remote locales.
First, the lake does not have effluents; so, sedimented MP most likely remains in the lake system. The risk of the resuspension of MPs in the upper water layer and their potential exit from the lake system is considerably lower due to the meromictic nature of the lake, which mitigates the mixing of the two water layers [16] and the consequent resuspension of material from the lower to the upper layer. This leads to a faithful accumulation quantification over time, as “what is in the system, stays in the system”: there is an unlikely particle loss of MPs in the sediment consequent to the loss of particles from the lake system.
Moreover, MP sources in this environment can be broadly categorized into two main types: those originating from the weathering and fragmentation of larger plastic items linked to local human activities, and atmospheric MP deposition. This can facilitate the investigation of potential sources and the understating of deposition trends, allowing a focus on the mitigation of the sources of contamination that contribute the most to the total MP budget.
Furthermore, the oligotrophic water conditions and the characteristic moorland around the lake lead to the reduced presence of recalcitrant organic material, such as lignin and cellulose, which is derived from wood and leaf runoff, in the analyzed sediment (LOI results in Supplementary Materials show the total amount of organic material). This facilitates the sample analysis [56]. During the organic material digestion processes, in this case Fenton’s treatment, the oxidation may not be as effective on particular complex and recalcitrant organic compounds, such as lignin or chitin [57,58].

5. Conclusions

Addressing the environmental challenges posed by the ever-increasing tourism in the Swiss Alps requires a comprehensive approach involving collaboration between government agencies, local communities, tourism industry stakeholders, and the visitors themselves. By promoting responsible tourism practices, improving infrastructure, enforcing regulations, and conducting research, it is possible to strike a balance between economic development and environmental conservation. Sustainable tourism not only preserves the natural beauty of the Swiss Alps for future generations but also ensures the long-term viability of the tourism industry itself [59,60]. The challenges inherent in MP investigation, such as defining sources, as well as the heterogenicity of the alpine realm, highlight site-specific nature of contamination in remote alpine lakes. The oligotrophic conditions of Lake Cadagno, coupled with its meromictic nature, provide advantages for assessing MP contamination and understanding deposition trends. However, they also underscore the need for comprehensive approaches to mitigate sources of contamination and preserve these pristine environments. The correlation between tourism increase and environmental impact is evident, raising awareness of the need for sustainable tourism practices.
In conclusion, the study of MP contamination in Lake Cadagno underscores the importance of understanding and mitigating the impacts of human activities on remote alpine ecosystems. By adopting a comprehensive approach to address these challenges, we can ensure the preservation of these less-impacted environments for future generations while sustaining the socioeconomic benefits derived from local human activities.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/microplastics4020025/s1, Table S1: LOI Analysis of the sediment cores, subdivided in layers from one to seven.

Author Contributions

Conceptualization, S.M.A.; Methodology, S.M.A.; Validation, C.C.-M.; Formal analysis, S.M.A. and C.C.-M.; Investigation, S.M.A. and M.D.; Data curation, S.M.A.; Writing—original draft, S.M.A.; Supervision, C.C.-M. and P.B.-H.; Funding acquisition, P.B.-H. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

The study did not require ethical approval.

Informed Consent Statement

Informed consent was obtained from all subjects involved in the study.

Data Availability Statement

The original contributions presented in this study are included in the article/Supplementary Materials. Further inquiries can be directed to the corresponding author.

Acknowledgments

Fieldwork was supported by Gabriel Erni Cassola and Centro Biolgia Alpina Piora. Thanks to Kirstie Starr, Sara Stäubli, Nicole Daniela Seiler-Kurth, Laura Fritschi, Ruben Niebling, and Heidi Schiffer for the laboratory work and great support. Finally, we thank Clara Leistenschneider for the proofreading.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Map of Lake Cadagno, Quinto (Ticino, Switzerland), and detected microplastics. The pie hart size displays the microplastic abundance (size fraction: 50–500 µm) and the polymer composition; the cylinders display number and polymer composition of large microplastic particles (>500 µm; only detected in cores of CAD3 and CAD 6). PE: polyethylene, PP: polypropylene, PET: polyethylene terephthalate, PVC: polyvinylchloride, PS: polystyrene.
Figure 1. Map of Lake Cadagno, Quinto (Ticino, Switzerland), and detected microplastics. The pie hart size displays the microplastic abundance (size fraction: 50–500 µm) and the polymer composition; the cylinders display number and polymer composition of large microplastic particles (>500 µm; only detected in cores of CAD3 and CAD 6). PE: polyethylene, PP: polypropylene, PET: polyethylene terephthalate, PVC: polyvinylchloride, PS: polystyrene.
Microplastics 04 00025 g001
Microplastics 04 00025 g002
Figure 2. (a) Distribution of number of microplastic particles in the core’s (CAD1 to CAD9) layers (L1 to L7), the dots represent plastic particles > 500 µm. (b) Size distribution of the detected microplastic particles. The small box plot shows the size distribution of particles > 500 µm (CAD3 and CAD6). PET: polyethylene terephthalate, PE: polyethylene PP: polypropylene, PS polystyrene, PVC: polyvinylchloride.
Figure 2. (a) Distribution of number of microplastic particles in the core’s (CAD1 to CAD9) layers (L1 to L7), the dots represent plastic particles > 500 µm. (b) Size distribution of the detected microplastic particles. The small box plot shows the size distribution of particles > 500 µm (CAD3 and CAD6). PET: polyethylene terephthalate, PE: polyethylene PP: polypropylene, PS polystyrene, PVC: polyvinylchloride.
Microplastics 04 00025 g002
Table 1. Sample ID core depth, coordinates, and water content of the samples.
Table 1. Sample ID core depth, coordinates, and water content of the samples.
Sample ID Depth (m)Latitude NLongitude EWater Content (%)
CAD121.746°55′059″87°11′70″9.0
CAD214.446°55′012″87°14′10″8.5
CAD313.246°54′996″87°08′93″9.1
CAD45.746°54′891″87°12′32″9.4
CAD510.646°55′012″87°15′19″8.7
CAD63.546°55′166″87°13′76″9.0
CAD720.346°55′128″87°11′47″9.1
CAD81146°55′060″87°08′63″9.2
CAD98.146°54′876″87°09′61″8.3
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Abel, S.M.; Courtney-Mustaphi, C.; Damber, M.; Burkhardt-Holm, P. Remote Alpine Lakes and Microplastic Accumulation: Insights from Sediment Analysis of Lake Cadagno. Microplastics 2025, 4, 25. https://doi.org/10.3390/microplastics4020025

AMA Style

Abel SM, Courtney-Mustaphi C, Damber M, Burkhardt-Holm P. Remote Alpine Lakes and Microplastic Accumulation: Insights from Sediment Analysis of Lake Cadagno. Microplastics. 2025; 4(2):25. https://doi.org/10.3390/microplastics4020025

Chicago/Turabian Style

Abel, Serena M., Colin Courtney-Mustaphi, Maja Damber, and Patricia Burkhardt-Holm. 2025. "Remote Alpine Lakes and Microplastic Accumulation: Insights from Sediment Analysis of Lake Cadagno" Microplastics 4, no. 2: 25. https://doi.org/10.3390/microplastics4020025

APA Style

Abel, S. M., Courtney-Mustaphi, C., Damber, M., & Burkhardt-Holm, P. (2025). Remote Alpine Lakes and Microplastic Accumulation: Insights from Sediment Analysis of Lake Cadagno. Microplastics, 4(2), 25. https://doi.org/10.3390/microplastics4020025

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