Microplastics Identification in Remote Aquatic Environments Using Raman Spectroscopy: A Case Study for Mt. Tymfi's Alpine Lake

ABSTRACT Water samples from the alpine lake of Mt. Tymfi (Dragon Lake) in Greece were analyzed for microplastics (MPs) using optical microscopy and Raman microspectroscopy. The alpine lake of Tymfi (Dragon Lake) represents a pristine environment with few anthropogenic interventions. A total of 4770 ± 637 L of the lake's surface water was analyzed as part of an expedition of the LiMnADs project in 2023—post‐tourism. Volume‐reduced sampling (large water volumes filtered via a plankton net), oxidative digestion with Fenton reagent, stereoscopy, and Raman spectroscopy (RS) were carried out in the samples to detect the presence of microplastics. Stereoscopy revealed 100 MPs (0.021 MP/L) larger than 150 μm, with fibers being the most abundant (66%), followed by fragments (34%). Fibers were predominantly blue (95%) and long > 1000 μm (~70%), whereas fragments were mainly transparent (73%) and < 500 μm (97%). A nondestructive Raman investigation was then performed on a random subsample of 70/100 microparticles directly on the filters without further treatment. Eighty‐three percent (83%) of them were Raman active. Polymers identified were PE fragments, PET fibers, and PA (nylon) fibers. Several analytical challenges such as (1) strong fluorescence, (2) pigments obscuring the polymer peaks, and (3) weathering of the material by UV irradiation led to highly complex and demanding processes regarding the polymer identification, highlighting the analytical challenges in such environmental samples. The MPs in the alpine lake of Tymfi could originate from human activities; the low level of degradation of some synthetic fibers could indicate recent exposure. The pretreatment of the samples before Raman analysis also proved to be crucial. This work contributes to the literature on the detection of MPs in Greece, proposes a method for MPs extraction in remote environments, and takes a step forward in MP analysis by Raman spectroscopy.