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Article

Unraveling the Plastic Pollution in the Aquatic Environment of the Croatian Krk Island

by
Maria Râpă
1,
Ecaterina Matei
1,
Elfrida Mihaela Cârstea
2,*,
Cristina Liana Popa
2,
Marta Matić
3,* and
Dejan Kosić
3
1
Faculty of Materials Science and Engineering, National University of Science and Technology Politehnica Bucharest, 060042 Bucharest, Romania
2
National Institute of R&D for Optoelectronics INOE 2000, Atomistilor 409, 077125 Magurele, Romania
3
Ponikve Eco Island Krk Ltd., Vršanska ul. 14, 51500 Krk, Croatia
*
Authors to whom correspondence should be addressed.
Water 2025, 17(6), 785; https://doi.org/10.3390/w17060785
Submission received: 8 February 2025 / Revised: 27 February 2025 / Accepted: 6 March 2025 / Published: 8 March 2025
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Abstract

:
The assessment of plastic pollution due to microplastics (MPs) and nanoparticles (NPs) was performed for the first time on water samples from four natural sites located near the beaches of Krk Island, Croatia, namely Melska, Črnika, rt Šilo, and Zala. MP and NP occurrence was investigated for the water samples collected during December 2022 and June 2023, using the bulk water method followed by filtration using stainless-steel sieves and the digestion process. Factor analysis and Spearman’s correlation revealed that the percentage of MP fragments correlated well with salinity (ρ = 0.76, p < 0.05) and the percentage of filaments correlated well with brown MPs (ρ = 0.80, p < 0.05). The monitoring of MPs throughout the sampling periods generally showed a decrease in abundance as the size increased. The presence of filaments indicated potential contributions from wastewater outlets, particularly from household washing machines, either directly from residents or tourists and abandoned fishing nets. The increased concentration of NPs over time could signify the continuous fragmentation of MPs in water due to natural degradation and biofilm formation on their surface. These findings could potentially be explained by the implemented plastic waste measures along the coast of Krk Island, which on 30 October 2024 was officially declared a zero-waste island.

Graphical Abstract

1. Introduction

Due to physical weathering, photo-oxidation, chemical erosion, biological decomposition, and disintegration, plastic waste from the environment breaks down into fragments smaller than 5 mm [1,2], known as microplastics (MPs), which are usually too small to be seen with the naked eye. MPs originate from both land- and sea based-sources [3]. The main sources of MPs are single-use plastics [4], wastewater treatments [5], plant recycling facilities [6], pontoons and buoys [7], abandoned, lost, or discarded fishing gear (ALDFG) [8], and recreational and tourism activities [9]. The physicochemical degradation of MPs generates smaller plastic particles (typically < 1 µm in size) called nanoplastics (NPs) [10]. The properties of NPs include its small size and large surface area, clumping due to the presence of organic matter or other colloidal substances, high polydispersity with an open structure, and a heterogeneous and irregular shape [11,12]. Their high mobility enables the adsorption of other toxins, particularly trace metals, onto their surface [13].
The contamination caused by MPs is considered irreversible and widespread, posing a threat to ocean health, wildlife, food security, human well-being, coastal tourism, and climate control [14,15]. The concern stems from the durability of plastics, their high surface-area-to-volume ratio, and their chemical surface properties, which enable the absorption of other environmental pollutants. The issue goes beyond floating waste, as stranded plastic debris, particularly in the form of pellets and microplastics, worsens the pollution problem and poses a threat to coastal ecosystems [16]. A study reviewed various key plastic additives and evaluated their prevalence in marine environments [17], concluding that the most commonly used plastic additives include polycyclic aromatic hydrocarbons (PAHs), bisphenol A (BPA), organophosphates (OPEs), phthalates (phthalic acid esters, PAEs), and pharmaceuticals and personal care items [18,19].
These characteristics complicate the detection and measurement of MPs and NPs. Additionally, they lead to cascading impacts on the food chain and ecosystem dynamics. MPs can enter the human body through ingestion, inhalation, and dermal absorption [20]. The presence of MPs (median) in drinking water sources was documented as 2.2 × 103 particles per m3, with the particle sizes typically exceeding 50 µm [21]. The literature data showed that an adult may consume approximately 3.1 billion NPs released from plastic tea bags in a cup of hot water [22]. The intake from inhaled MPs ranges from 0.9 × 10⁴ to 7.9 × 10⁴ particles per year [23]. Recent studies even indicate the presence of MPs in human placental and meconium samples, suggesting widespread exposure among pregnant women and infants [24]. The contaminated MPs can ultimately lead to health problems including atherosclerosis [25], endocrine disruptions affecting immune responses, oxidative stress, inflammation in human intestinal cells (Caco-2 cells) [26], an increased risk of cancer [27,28], and even apoptosis [29,30,31,32]. Consequently, the prolonged impacts of MPs and NPs on the environment and human health emphasize the immediate necessity for worldwide action to reduce this widespread form of plastic pollution [33].
Despite the increase in studies on MPs in the sediment of touristic beaches [34,35,36] and previous investigations of engineered nanoplastics in aqueous systems [22,37,38], there is limited attention on the detection of MPs and NPs collected in seawater in touristic areas. The objectives of this paper are (1) to compare the MPs originating from Melska, Črnika, rt Šilo, and Zala water samples for their relative abundance, color, shape, and size, collected during December 2022 and June 2023 sampling periods; (2) to assess the NP concentration levels in the tested water samples; and (3) to find correlations between MP characteristics and water quality parameters by using the factor analysis and Spearman’s correlation.

2. Materials and Methods

2.1. Sample Locations

In this study, the investigation of MPs and NPs from aqueous media was performed in Melska, Črnika, rt Šilo, and Zala beaches located next to Risika village, Krk town, Omišalj municipality, and Stara Baška village, respectively, from Krk Island (Figure 1). The island of Krk is the largest island in Croatia, located in the northern Adriatic Sea within the Kvarner Bay, just 30 km from the city of Rijeka. This island is a renowned tourist hotspot, known for its temperate Mediterranean climate, advantageous geographical location, and wealth of natural and cultural attractions. Historically, it has been referred to as “the golden island”. The main factor in selecting these particular beaches for water sampling was their different geolocation with regard to the cardinal directions, allowing for the inclusion of beaches influenced by different winds and waves. Melska beach, at the east of the island, faces the mainland, and the bora wind brings a lot of marine litter with winter storms. Črnika beach is situated in the southwest of the island, closest to the inhabited area. rt Šilo, its toponym being cape Šilo, is the beach located in the wider area of Omišalj municipality, located at the northwest of the island near the Krk bridge, a site not frequently visited due to its view of the mainland industrial area. Zala beach is situated in the southern part of the island and is popular during the summer. It is the only beach with a beach bar on-site, which gathers families during the day and hosts occasional beach parties on the weekend. These four beaches were also monitored every 6 months from 2020 till 2023 during the InNoPlastic Project [39] for the removal of marine debris.

2.2. Methodology

The methodology for the assessment of MPs and NPs was established by Cecchi et al. [40] as a participation in the HORIZON 2020—InNoPlastic Project [39]. In summary, the water matrix was removed from samples by filtering through a 32 µm mesh sieve in the case of water sampling performed on December 2022 and a cascade configuration of stainless-steel sieves with 250 µm, 125 µm, 90 µm, 32 µm, and 20 µm mesh sizes for those sampled on June 2023, followed by digestion using a 30% hydrogen peroxide Suprapur (H2O2) solution (Merck KGaA, Darmstadt, Germany), filtration by vacuum, and characterization. The filtrates resulted from the MP processing were used for the NP investigation after filtration through a 1 µm mesh sieve and digestion. This approach enabled the detection of small-mesh-size MPs and the quantification of all nanoparticles (plastics, dissolved organic matter, metal oxides, and clay) found in water samples.
For each monitoring location (Figure 1), three water samples each of 6.5 L in volume were collected at a depth of 50–70 cm in plastic bottles. Prior to usage, the bottles were rinsed three times with seawater. The choice of plastic bottles emerged because glass bottles exhibited higher MP contamination compared to other types of bottles [41]. During both collection periods, the temperature during transit was maintained between 4.7 °C and 7.5 °C. Upon arrival at the testing laboratory, the exterior of the sealed sample bottles was washed with distilled water multiple times before any additional handling. This procedure eliminated any contaminants that might have been introduced during transportation.
To avoid contamination from the laboratory setting, all the personnel wore white cotton lab coats and nitrile gloves during sample handling. The filtration tool and work surfaces were disinfected with 70% ethanol and subsequently rinsed three times with distilled water before commencing work. All working solutions (distilled water, ethanol, oxidizing agent) were pre-filtered using mixed cellulose ester filter papers (47 mm, white gridded, with pore sizes of 0.45 μm or 0.22 μm) to eliminate possible microplastic contamination. Blank controls (n ≥ 3) were performed simultaneously during each analytical procedure. Upon completion, the filter papers were examined for MPs using an optical microscope. Any MPs detected on the filter papers through optical microscopy were excluded from the sample of interest.
The main physico-chemical parameters of water samples were measured using a CONSORT C831 multi-parameter analyzer (Consort, Turnhout, Belgium) (for pH), a Consort C862 multi-parameter analyzer (for evaluation of total dissolved solids (TDS), salinity (SAL), and an electrical conductivity (EC)) meter (Consort, Turnhout, Belgium), while the content of chloride ions was assessed using the titration method.
The identification of MPs was performed using an optical microscope (Olympus BX 51 M, Olympus Corporation, Tokio, Japan, Stream Essential 1.9.3 software), which enables image detection at 50×, 100×, and 200× magnifications, as well as the measurement of MP length using a polyline ruler. The shape and color of the MPs were also documented during this analysis.
Nanoparticles from the natural aqueous environment were measured by using a nanoparticle tracking analysis (NTA) system (Nanosight NS300, Malvern Panalytical, Worcestershire, UK), which carried out five replicates. NTA offers the evaluation of nanoparticle size in a liquid sample, with a lower maximum resolution of 10–30 nm [42].

2.3. Statistical Analysis

Factor analysis was performed with GNU PSPP v2.0.0 software, and correlations were made using Real Statistics Resource Pack [43] and Past 5.0.2 software [44]. Factors were extracted using the principal axis factors with quartimax rotation. Components with little variability were removed from the factor analysis. Four factors were chosen with eigenvalues over 1.0. The distribution of the data is significantly non-normal (Shapiro–Wilk test, W = 0.42–0.98, p < 0.001). The statistical significance of differences between data was determined using the Kruskal–Wallis H test followed by the Nemenyi test (p < 0.05).

3. Results and Discussion

3.1. Physico-Chemical Parameters

Table 1 shows the physico-chemical parameters such as total dissolved solids (TDSs), salinity (SAL), electrical conductivity (EC), pH, and chloride (Cl) content measured for the water samples.
As a general rule, the water samples had EC and TDS values which decreased in the summer, while the pH values increased (Table 1). The highest means for EC and TDS recorded in Krk Island were in Krk/Črnika (55.9 ± 0.26 mS/cm and 34.96 ± 0.32 g/L, respectively, in the winter season. Electrical conductivity is directly correlated with salinity. In this study, salinity ranged between 33‰ and 36‰, values typically characteristic of seawater. It was documented that the salinity increases the refractive index of seawater, which leads to the decrease in UV light and consequently signifies a low degradation [45]. In addition, the Cl ions inhibit the photo-oxidation process. Based on the data reported in Table 1, it was expected that the degree of fragmentation would decrease in winter for Krk/Črnika, Omišalj/rt Šilo, and Stara Baška/Zala samples. A slow increase in the pH values was observed in the water samples collected during the summer season. This means that the surface of MPs was negatively charged and tended to adsorb toxic heavy metals through electrostatic interaction [46].
No significant differences were found between the two collection periods for most of the measurements. Only the pH values of Risika/Melska samples presented significant differences between 2022 and 2023 (p < 0.05). However, significant differences were found between locations. TDS showed significant differences between Risika/Melska and Krk/Črnika (p < 0.05). EC presented significant differences between Risika/Melska and Krk/Črnika (p < 0.01) and Omišalj/rt Šilo and Stara Baška/Zala (p < 0.05), while salinity values showed significant differences between Risika and Črnika beaches (p < 0.01).

3.2. Occurrence and Distribution of MPs

Figure 2 revealed the shape, color, and size of some MPs examined through optical microscopy.
Although the optical microscopy helps to easily detect MPs, some errors related to the recognition of MPs can occur.
Figure 3 shows the concentration of MPs from investigated water samples through normalization to 1 L.
Generally, low levels of MP pollution were detected for the four different sampling locations on Krk Island. Among the tested samples, a high content of MPs per L was observed for the water samples collected from Risika/Melska (2.97 ± 3.16) and Krk/Črnika (2.87 ± 1.09) in December 2022 and Stara Baška/Zala (1.43 ± 0.37) in June 2023. The high number of MPs recorded at Risika/Melska in winter and Stara Baška/Zala in summer could be explained by their locations being directly along the path of the Bora wind coming from the east. In addition, the Zala location is also most exposed to the Jugo wind (south wind). The low concentration of MPs detected at the Krk/Črnika and Omišalj/rt Šilo sites in summer may be attributed to Črnika being shielded from the Bora wind, while the rt Šilo is sheltered from the Bura wind.
In a similar study performed in winter 2022 concerning the MPs present in the Venice Lagoon, concentration values of 0.83 MPs/L, 2 ± 1.01 MPs/L, and 1.57 ± 0.91 MPs/L were identified for the Venice–Lido port inlet, Rialto Bridge, and Saint Marc water samples [40]. Another study reported high concentrations of the floating MPs (230–3320 MPs/L) by analyzing 1 L of seawater collected from various locations spread between Southern Italy and the United States of America from 2019 to 2022 [47]. Other authors reported that at low temperatures, the plastic fragmentation is more pronounced compared to that in the summer season [48]. Therefore, an abundance of MPs between 473 ± 34 and 3605 ± 497 particles/L was reported for natural water when using the bulk method to collect a 1 L volume of sample in the winter period (November 2017–January 2018) [49]. A similar finding was reported on the beaches of the Niterói Oceanic Region in Rio De Janeiro, Brazil, when 85% of MPs was collected during winter compared to 73% in summer [50]. This finding is not in agreement with other authors, who stated that in popular tourist destinations, the summer season contributes to 75% of the annual waste production, with tourists typically generating 10% to 15% more waste compared to the local residents [51].
The lowest abundance of MPs per L was recorded in Omišalj/rt Šilo (0.51 ± 0.10) in June 2023. It is possible that the high occurrence of phytoplankton in summer may lead to a poor identification of MPs. The low content of MPs detected in the samples collected from Krk Island sites during the summer of 2023 could be a result of the plastic waste management measures implemented during 2012. Despite the considerable obstacles posed by the stress of tourism during the summer, when the resident population on the island increases by five times, the municipalities on Krk Island have accomplished 58% individual waste sorting and reduced mixed waste by 22% per person compared to the national mean, introduced various educational and waste minimization strategies, and developed the necessary infrastructure for efficient community waste handling. The company Ponikve Eco Island Krk Ltd. has been actively involved in waste management (waste collection and door-to-door waste collection system), succeeding in collecting up to 70% of waste directly from citizens, already separated into fractions by type (paper, plastic, glass, biowaste, a.s.o.) [52]. On the island of Krk, the amount of communal waste collected increases by 65–70% during the tourist season. The island implements a separate waste collection system, which shows an increase of 300% of the collected plastic fraction during the summer months [52]. This refers only to the plastic collected separately, not the total amount of plastic in the garbage, as the amount of “mixed” litter also increases significantly in the summer season. This is due to tourists and non-permanent residents (seasonal workers) having poorer discipline in following recycling guidelines. These strategies contributed to the achievement of the zero-waste island certification as of October 30th 2024. Krk Island is the first island in Croatia and the second worldwide to become a zero-waste island.

3.3. Shape, Size, and Color Distribution of MPs

In Krk Island, in this study, the morphology of detected MPs is classified as filaments, foils, and fragments (Figure 4a,b).
Filaments are the most prevalent for all locations, ranging from 92% to 100% independent of the collection periods. Foils were observed in 2% of the cases for Risika/Melska samples collected in winter (Figure 4a), while fragments accounted for 7% of the cases in samples collected from the Krk/Črnika site in summer (Figure 4b). A significant number of filaments potentially originated from wastewater outlets, particularly from household washing machines, as the existing filters and biofilters on the island of Krk are not sufficient to capture MPs and NPs coming from clothing. Also, filaments could have originated from abandoned fishing nets, which generally account for 32% of the total plastic waste [53]. Fragment MPs were prevalent in the offshore waters at a 3–10 km distance from the coasts of the Central Adriatic Sea [54].
It is challenging to compare and monitor MP contamination data when consistent protocols are not followed, while the geomorphological environment, anthropogenic activities, and land- and sea-based sources are different from other coastal locations [55,56]. When the Neuston Manta net was used for sampling of water from the Salento peninsula (Apulia, Italy), concentrations of 0.09 and 2.33 MP/m3 in autumn 2020 and spring 2021, respectively, were found [57]. For water sampling in the summer of 2022 from coastal ecosystems of Shenzhen, China, performed with a catamaran trawl with a net mouth, an abundance of 2.40 ± 2.48 items/m3 was revealed [58]. A total of 10.1 ± 3.10 and 8.52 ± 3.92 items/100 L was detected for other coastal areas in Bangladesh (Cox’s Bazar and Kuakata) [59] and 12.7 ± 14.9 items/m3 for the southern coast of the Buenos Aires province, Argentina [60]. High amounts of MPs, 30,670.8 ± 15,094.9 items/m3 (ranging from 15,579 to 58,772 items/m3), were detected in a tourist beach in Bohai Bay, North China [56]. In addition, it was proven that residual seawater currents could significantly affect the abundance of MPs [56,61]. For instance, an average concentration of 119 ± 40 MPs microfibers/L was identified in the water samples collected from Lake Superior, Lake Michigan, and northern Lake Huron in the United States using a Niskin bottle followed by filtration with a 0.45 µm pore size filter [62].
The size range distribution of MPs detected in samples from the island of Krk are depicted in Figure 5a,b.
Overall, in this study, the abundance of MPs detected in the examined water samples decreased with the size increase. Figure 5a shows that all studied samples exhibited MPs with sizes ranging from <500 µm to 501–1000 µm. Particles smaller than 500 µm could be easily ingested by marine organisms. These miniscule particles can be mistaken for food by filter-feeding organisms or may be unintentionally ingested when present in the water column. This can lead to the accumulation of plastic particles within the food chain.
Over 80% of the MPs detected in seawater, marine sediments, and corals were smaller than 2 mm [63]. Approximately 40–60% of the total MPs were released by water treatment plants, and their size ranged from 1 to 5 μm [49]. This presents potential ecological and health hazards for marine life and, ultimately, for humans who consume seafood.
As evidenced in Figure 5b, for all water samples collected in June 2023, most of the MPs have sizes between 501 µm and 1000 µm for Risika/Melska (44.4%), Krk/Črnika (21.4%), and Omišalj/rt Šilo (50%). Stara Baška/Zala water samples showed the majority of MPs with sizes ranging between 1001 and 2000 µm (35.7%). However, due to the collection method, the size of MPs observed from the selected locations did not exceed 5000 µm.
Figure 6a,b shows the percentage of MP colors identified in water samples from the island of Krk.
Figure 6a,b reveals that a black color was predominantly observed in the case of Risika/Melska (62% in winter and 44% in summer) and Stara Baška/Zala (80% in winter) samples. Black and blue were the main colors of MPs found in Krk/Črnika and Omišalj/rt Šilo samples in both sampling periods. Colorless MPs were the second most frequently detected in water sampled from Risika/Melska in December 2022 (12%) and Krk/Črnika in June 2023 (14%). Reported data indicate that the colorless or transparent particles are a result of weathering that bleaches polymers, suggesting that these particles are more likely to be consumed by marine creatures [64]. Furthermore, red, brown, green, yellow, and purple MPs were detected in almost all water samples from Krk Island but less frequently compared to other colors of MPs. The abundance of yellow or black MPs denotes the degree of degradation in the aquatic environment [65].

3.4. Quantification of NPs

The evaluation of NPs was performed by measuring the average size, undersize (D10, D50, and D90), and particle concentration per mL (Figure 7 and Figure 8). The water samples were filtered using a 1 µm syringe filter, and the concentration of nanoparticles in the control sample was subtracted from each tested water sample.
An increase in NP concentration from December 2022 to June 2023 could be observed for the water samples collected from Risika/Melska, Omišalj/rt Šilo, and Stara Baška/Zala locations (Figure 7). This indicated the ongoing fragmentation of MPs. Water samples collected from Omišalj/rt Šilo beach recorded the lowest concentrations of NPs (0.55 × 107 ± 0.41 × 107 NPs/mL in winter and 2.09 × 107 ± 5.15 × 106 NPs/mL in summer) compared to other investigated sites from Krk Island. This trend was also observed in the case of MPs (Figure 3). Since the rt Šilo beach is really not visited by many people, this suggested that the anthropogenic activities play a pivotal role in the occurrence of plastic pollution. The low concentrations of NPs found in the water samples collected in the winter season from Omišalj/rt Šilo (0.55 × 107 ± 0.41 × 107 NPs/mL) and Stara Baška/Zala (0.72 × 107 ± 0.55 × 107 NPs/mL) are correlated with the highest values of salinity recorded (Table 1).
Fragmentation prevalence is dependent on time and the thickness of the MPs and can occur due to the exposure to different factors such as temperature, light, wind, the shear stress of waves [66,67,68], and the specific physico-chemical parameters measured in the water samples. Laboratory-induced UV irradiation showed that 57.9% of PP nanoparticles with an average size of 435 ± 250 nm are generated after 68 days of exposure [69]. Another paper revealed that after 25 weeks of weathering in water, 90% of the fragments were >1 mm with very similar shapes to the ones presented in this study [70]. Other possible origins of ongoing MP fragmentation in natural aquatic habitats involve the development of biofilm on the surface of MPs [71], oxidative breakdown [72], and biological processes [73]. The decrease in MP dimensions generates the production of nanoparticles and induces the leaching of toxic chemical compounds into the marine environment [74].
The physical dynamics of the water sampling sites can determine the entrapment or concentration of MPs. Seawater parameters such as salinity, riverine plumes, wave action, tides, and wind speed, as well the geographical location of the ecosystem and the extent of anthropogenic activities, can influence the accumulation and concentration of MPs in coastal areas [64]. For example, high winds and rough seas typically generate strong surface currents, which [66,67,68] create turbulence in the water. This turbulence allows surface waters to mix with deeper layers of the sea, causing a widespread occurrence of MPs.
The lowest mean size of NPs was detected at the Krk/Črnika location (150.9 ± 92.4 nm), while the highest mean size was recorded for the water samples collected from Omišalj/rt Šilo (319.1 ± 17.2 nm), with both collection campaigns being undertaken in winter (Figure 8a). The water samples showed no significant variations for D10, D50, and D90 parameters between the two time periods. Only the water sample originating from the Omišalj/rt Šilo site and collected during summer showed reduced sizes for D10, D50, and D90 parameters compared with those measured during winter. The tiny size of nanoparticles (50–200 nm) is linked to their harmful effects on hepatocytes, while larger particles (500–5000 nm) lead to apoptotic cell death or an inflammatory reaction based on the length of exposure [32].

3.5. Factor Analysis and Correlation of Parameters

Factor analysis (Table 2) and Spearman’s correlation (Figure 9) were used to determine the relationships between individual components.
Four factor solutions (F1–F4) with positive (exceeding 0.5) and negative (below −0.5) loadings are shown in Table 2. These factors explained a variance of 88.9% from the data total variance. Factor loadings over 0.9 were considered as very strong, between 0.9 and 0.7 as strong, and between 0.5 and 0.7 as moderate.
Factor F1 explains 34.9% of the total variance. The water quality parameters, electrical conductivity, salinity, and total dissolved solids showed the strongest loadings. Fragment MPs showed a strong loading, while blue MPs showed moderate loading. Negative moderate loadings were observed for filament MPs, chloride content, and brown MPs. The percentage of fragments correlated well with salinity (ρ = 0.76, p < 0.05) and the percentage of filaments correlated well with brown MPs (ρ = 0.80, p < 0.05). The association between fragments and salinity potentially indicates the influence of salinity on MP fragment characteristics, as past studies [75,76] showed that salinity affected the transport and interaction of MPs in marine environments.
Factor F2 explains 21.8% of the total data variance. Mean size showed the strongest loading, while pH showed moderate loading. Strong negative loadings were observed for yellow MPs and abundance of MPs. Yellow MPs presented a highly significant negative correlation with mean size (ρ = −0.91, p < 0.01), indicating that small-size MPs were yellow-colored. However, more studies are needed to determine the chemical composition of the MPs and identify a potential source.
Factor F3 contains the dominant MP color components that explain 17.40% of the data variance. Red MPs presented a very strong loading, while black MPs showed a very strong negative loading. Moderate loading was observed for blue MPs. No correlation was observed between these components and the other parameters.
Factor F4 explains 14.8% of the total data variance. The concentration of NPs presented a very strong loading and colorless MPs a strong loading, while brown MPs and filaments showed moderate loadings, similar to factor F1. The concentration of NPs showed significant negative correlation with brown MPs (ρ = −0.84, p < 0.05) and filaments (ρ = −0.79, p < 0.05). These results potentially indicate that different sources of plastic pollution contribute to the sampling sites.

4. Conclusions

Generally, a low level of MP pollution was detected for the four different sampling locations from island of Krk. Among these samples, a high MP concentration per L was observed for water samples collected from Risika/Melska (2.97 ± 3.16), Krk/Črnika (2.87 ± 1.09) in December 2022, and Stara Baška/Zala (1.43 ± 0.37) in June 2023. All studied samples have the MPs’ class sizes ranging from < 500 µm to 501–1000 µm. Most of the MPs were filaments, foils accounted for 2% of the MPs detected in Risika/Melska samples during winter, while fragments represented 7% of MPs in Krk/Črnika water samples during summer. It can be concluded that the decrease in MP occurrence is due to the protective measures implemented on the beaches from the island of Krk, requiring a collaborative effort among people, companies, and municipalities. The waste management strategies employed have led to the island of Krk achieving a zero-waste status, serving as an inspiration for other coastal regions in the fight against plastic pollution.
Future research is still needed to better understand plastic pollution in aqueous ecosystems, including the sampling of more locations over shorter time periods, identifying the source of small plastic pollutants, and exploring the relationship between MP abundance and water quality factors.

Author Contributions

Conceptualization, M.R.; data curation, E.M. and D.K.; formal analysis, E.M.; investigation, M.R., E.M.C. and M.M.; methodology, M.M.; software, C.L.P.; supervision, D.K.; validation, M.R.; writing—original draft, M.R.; writing—review and editing, M.R., E.M., E.M.C., C.L.P., M.M. and D.K. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by EU Horizon 2020 (InNoPlastic) G.A. no. 101000612.

Data Availability Statement

The data presented in this study are available upon request from the corresponding authors.

Acknowledgments

E.M. Carstea and C.L. Popa acknowledge the support of the Ministry of Research, Innovation and Digitalization and the Romanian Ministry of European Investment and Projects through projects Core Program OPTRONICA VII PN23 05 (11N/2023) and 152/2016, SMIS 108109.

Conflicts of Interest

Authors Marta Matić and Dejan Kosić were employed by the company Ponikve Eco Island Krk Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Water 17 00785 g001
Figure 1. Location of the four sampling points along the coast of Krk Island, Croatia, for MP and NP investigation during December 2022 and June 2023. Risika/Melska GPS coordinates: latitude: 45.100624 and longitude: 14.661386; Krk/Črnika GPS coordinates: latitude: 45.012987 and longitude: 14.561584; Omišalj/rt Šilo GPS coordinates: latitude: 45.244462 and longitude: 14.554328; and Stara Baška/Zala GPS coordinates: latitude: 44.948901 and longitude: 14.699455.
Figure 1. Location of the four sampling points along the coast of Krk Island, Croatia, for MP and NP investigation during December 2022 and June 2023. Risika/Melska GPS coordinates: latitude: 45.100624 and longitude: 14.661386; Krk/Črnika GPS coordinates: latitude: 45.012987 and longitude: 14.561584; Omišalj/rt Šilo GPS coordinates: latitude: 45.244462 and longitude: 14.554328; and Stara Baška/Zala GPS coordinates: latitude: 44.948901 and longitude: 14.699455.
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Water 17 00785 g002aWater 17 00785 g002b
Figure 2. Representative images of MPs visualized by optical microscopy. (a) Risika/Melska, (b) Krk/Črnika, (c) Omišalj/rt Šilo, and (d) Stara Baška/Zala.
Figure 2. Representative images of MPs visualized by optical microscopy. (a) Risika/Melska, (b) Krk/Črnika, (c) Omišalj/rt Šilo, and (d) Stara Baška/Zala.
Water 17 00785 g002aWater 17 00785 g002b
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Figure 3. Abundance of MPs detected in water samples from Krk Island during December 2022 and June 2023. Parameters that present the same letter are not significantly different at p < 0.05.
Figure 3. Abundance of MPs detected in water samples from Krk Island during December 2022 and June 2023. Parameters that present the same letter are not significantly different at p < 0.05.
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Figure 4. Morphology of the collected MPs in the studied water samples in (a) December 2022 and (b) June 2023.
Figure 4. Morphology of the collected MPs in the studied water samples in (a) December 2022 and (b) June 2023.
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Figure 5. Stacked bar chart showing the MP sizes detected in water samples from island of Krk in (a) December 2022 and (b) June 2023.
Figure 5. Stacked bar chart showing the MP sizes detected in water samples from island of Krk in (a) December 2022 and (b) June 2023.
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Figure 6. Chromatic MPs detected in water samples from island of Krk in (a) December 2022 and (b) June 2023.
Figure 6. Chromatic MPs detected in water samples from island of Krk in (a) December 2022 and (b) June 2023.
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Figure 7. Abundance of nanoparticles in water samples from island of Krk during December and June 2023. Parameters that present the same letter are not significantly different at p < 0.05.
Figure 7. Abundance of nanoparticles in water samples from island of Krk during December and June 2023. Parameters that present the same letter are not significantly different at p < 0.05.
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Figure 8. Nanoparticle size represented for water samples collected from Risika/Melsa, Krk/Črnika, Omišalj/rt Šilo, and Stara Baška/Zala locations during December 2022 and June 2023. (a) Mean size and (b) D10, D50, and D90. Parameters that present the same letter are not significantly different at p < 0.05.
Figure 8. Nanoparticle size represented for water samples collected from Risika/Melsa, Krk/Črnika, Omišalj/rt Šilo, and Stara Baška/Zala locations during December 2022 and June 2023. (a) Mean size and (b) D10, D50, and D90. Parameters that present the same letter are not significantly different at p < 0.05.
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Figure 9. Spearman’s rank correlation coefficients (red shades—negative correlations, blue shades—positive correlations). Values in boxes represent significant correlation at p < 0.05.
Figure 9. Spearman’s rank correlation coefficients (red shades—negative correlations, blue shades—positive correlations). Values in boxes represent significant correlation at p < 0.05.
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Table 1. Variation in the main physico-chemical parameters during December 2022 and June 2023 for water samples from Risika/Melska, Krk/Črnika, Omišalj/rt Šilo, and Stara Baška/Zala.
Table 1. Variation in the main physico-chemical parameters during December 2022 and June 2023 for water samples from Risika/Melska, Krk/Črnika, Omišalj/rt Šilo, and Stara Baška/Zala.
Risika/MelskaKrk/ČrnikaOmišalj/rt ŠiloStara Baška/Zala
20222023202220232022202320222023
TDS, g/L32.56 ± 1.1732.23 ± 0.1534.96 ± 0.32 33.63 ± 0.1534.8 ± 0.4333.13 ± 0.1134.53 ± 0.2033.56 ± 0.05
EC, mS/cm51.73 ± 0.5551.86 ± 0.1555.9 ± 0.2653.93 ± 0.2355.56 ± 0.7553.13 ± 0.0555.13 ± 0.3753.80 ± 0
pH7.90 ± 0.018.43 ± 0.058.06 ± 0.0098.43 ± 0.058.12 ± 0.018.4 ± 08.11 ± 0.0098.4 ± 0
SAL, ‰33.73 ± 0.3034.2 ± 0.336.86 ± 0.2535.80 ± 0.2036.93 ± 0.2034.16 ± 1.7936.43 ± 0.2035.56 ± 0.11
Cl−, g/L24.43 ± 0.5823.42 ± 0.2122.79 ± 0.7523.67 ± 0.2123.55 ± 0.3723.55 ± 023.29 ± 0.5824.61 ± 0.50
Table 2. The four factor solutions provided by the factor analysis.
Table 2. The four factor solutions provided by the factor analysis.
Percentage of Variance
34.90%21.80%17.40%14.80%
Factor
F1F2F3F4
ComponentLoadingComponentLoadingComponentLoadingComponentLoading
EC0.96Mean size0.86Red 1.01Concentration0.92
Salinity0.96pH0.61Blue0.57Colorless0.76
TDS0.95Yellow−1.02Black−0.91Brown−0.65
Fragment 0.75Abundance−0.78 Filament−0.62
Blue 0.55
Filament−0.67
Cl−0.63
Brown−0.62
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Râpă, M.; Matei, E.; Cârstea, E.M.; Popa, C.L.; Matić, M.; Kosić, D. Unraveling the Plastic Pollution in the Aquatic Environment of the Croatian Krk Island. Water 2025, 17, 785. https://doi.org/10.3390/w17060785

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Râpă M, Matei E, Cârstea EM, Popa CL, Matić M, Kosić D. Unraveling the Plastic Pollution in the Aquatic Environment of the Croatian Krk Island. Water. 2025; 17(6):785. https://doi.org/10.3390/w17060785

Chicago/Turabian Style

Râpă, Maria, Ecaterina Matei, Elfrida Mihaela Cârstea, Cristina Liana Popa, Marta Matić, and Dejan Kosić. 2025. "Unraveling the Plastic Pollution in the Aquatic Environment of the Croatian Krk Island" Water 17, no. 6: 785. https://doi.org/10.3390/w17060785

APA Style

Râpă, M., Matei, E., Cârstea, E. M., Popa, C. L., Matić, M., & Kosić, D. (2025). Unraveling the Plastic Pollution in the Aquatic Environment of the Croatian Krk Island. Water, 17(6), 785. https://doi.org/10.3390/w17060785

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