Polski
Science, Issue 17/2025
Microplastics in Greece’s lakes and lagoons. What hides under the surface of the water?
Dec
Most previous studies of microplastics in inland waters have focused solely on the near-surface layer. This approach only captured light, floating particles, creating only
Why is it necessary to look within?
The results of the study, published December 3, 2025 in the scientific journal Water, suggest that microplastic pollution is dynamic. Its distribution changes under the influence of seasonal stratification, wind, plankton blooms or biofilm loading, which can cause particles to fall. A growing body of research confirms that much of the microplastic ends up in deeper water and in bottom sediments, often reaching concentrations there that are higher than those observed at the surface. The study’s authors emphasize that failure to consider the vertical profile leads to a serious underestimation of the actual load on ecosystems.
Ecosystems studied – from deep lakes to shallow lagoons
The study was conducted in seven different ecosystems in western Greece: five lakes and two lagoons differing in depth, trophicity, level of human pressure and nature of use. The lakes, such as Trichonis and Ziros, are Natura 2000 protected areas, while Pamvotis and the lagoons of Etoliko and Amphilochia are directly adjacent to towns, farmland and tourist destinations. This diversity makes it possible to assess how morphometrics and anthropogenic impacts affect pollution.
Microplastics are ubiquitous
Analysis of 40 surface samples and 19 from the water column profile revealed the presence of microplastic particles at all points tested. The samples were definitely dominated by fibers – they accounted for 84 percent of all PET particles. This trend continued both on the surface and in the vertical profile. A total of 4428 fibers and 825 microplastic fragments were collected.
Average fiber contents in the near-surface layer ranged from 0.47 units perm3 (n/m3) in Lake Ziros to 19.27 n/m³ in Lake Pamvotis. For fragments, the range was from 0.08
Surprisingly, higher concentrations were recorded in samples from the vertical profile – fibers from 5.14 n/m3 (Ziros) to as much as 149.38 n/m3 (Pamvotis), and fragments 2.33 to 9.17 n/m3. This means that microplastics are more likely to accumulate throughout the water column rather than just at the surface.
What does microplastic look like? Colors, shapes and types of polymers
Nine colors of microplastic particles were distinguished in the samples. On the surface, blue fibers predominated (31-67.6 percent), while the vertical samples had the most transparent fibers (29.4 percent), but red and black fibers also stood out.
The fibers ranged from 0.3 to 15 mm in length, and more than half of the finds in all samples were in the 2-3 mm range. The fragments had varied shapes, with as many as 71.5-75 percent of them being particles described as hard flattened, i.e. fragments with flat and hard surfaces and very thin thickness (thin fragments of plastic). The vast majority of the fibers consisted of PET (84.3 percent), with fragments from PET (39.4 percent) and PP (33.8 percent). The PA and PVC particles most likely came from fisheries and wastewater.
Man as key driver of pollution
Statistical analysis showed that neither the area occupied by the lake, nor its depth or catchment size were significantly related to pollution levels. The only factor showing a clear correlation was anthropogenic pressure (expressed by the relative anthropogenic pressure(RAP) index), positively related to the concentration of fibers and fragments.
Lake Pamvotis – which is in direct contact with a city of 65,000 people, intensive tourism, a fleet of 14 boats operating more than 7,000 times a year, and numerous sources of sewage inflow – turned out to be the most loaded with microplastics. The cleanest was Lake Ziros, located in the forest, far from development and without significant human activity nearby.
The distance from the nearest buildings correlated with the concentration of fibers in the water column – the farther away from the cities, the lower the load.
Why do different studies give different results? The problem of lack of standardization
The authors discuss extensively the key problem of microplastic research – the lack of uniform methods for sample collection, processing and analysis. The volume reduction method (meshes with pores of 20-500 μm) allows hundreds of cubic meters of water to be pumped, but allows smaller particles to pass through. The bulk method, on the other hand, is more precise, but covers a minimal area, generating high variability in results. These differences make it very difficult to compare studies between countries and ecosystems.
The authors emphasize the urgent need for global standards for data collection, processing and presentation, in order to eliminate errors and misunderstandings in interpreting the scale of pollution.
Microplastic is not a water surface problem – it’s a problem for the entire ecosystem
The study reveals that:
- Microplastics can be found in any type of inland water, regardless of its trophy or size;
- Fiber is the dominant form, which agrees with global trends;
- The content of microparticles is often higher in the water column than on the surface;
- Anthropopression is the most important factor explaining pollution levels;
- the cleanest are ecosystems far from cities, not exposed to intensive human activity.
The researchers stress that a full understanding of microplastic distribution requires comprehensive sampling of vertical profiles and standardization of survey methods. Only then will it be possible to realistically assess ecological risks and plan effective conservation measures for inland waters.
Source:
Kehayias, G.; Kanellopoulou, P.; Kechagias, A.; Giannakas, A.E.; Salmas, C.E.; Maimaris, T.N.; Karakassides, M.A.. Comparative Distribution of Microplastics in Different Inland Aquatic Ecosystems. Water 2025, 17, 3432. https://doi.org/10.3390/w17233432
