DETERMINING THE ACCUMULATION OF MICROPLASTICS IN LAKE ICE A Case Study of Lake Följesjön, Sweden

Abstract

Microplastics are an emerging pollutant of global concern due to their persistence, widespread distribution, and potential ecological impacts. While the presence of microplastics in marine environments has been extensively studied, knowledge about their accumulation and behavior in freshwater systems, particularly in seasonally ice-covered lakes, remains limited. This thesis investigates the presence, concentration, and characteristics of microplastics in lake ice and water from Lake Följesjön, Sweden, during the winter season of 2024/2025. The results are compared to water samples collected from the same lake during the summer of 2024 to assess seasonal variation and the role of lake ice as a potential sink and source for microplastics. Samples of lake ice, water under the ice, and summer surface water were collected and processed using a combination of size-fractionated sieving, chemical digestion (10% KOH), oil extraction, and μ-Raman spectroscopy for particle identification. Microplastics were detected in all sample types, with concentrations ranging from 51,32 MP/L in the ice sample to 333,33 MP/L for the water under the ice sample. The combined winter concentration (384,65 MP/L) was nearly double that of the total summer concentration (200,00 MP/L), indicating seasonal accumulation. Approximately 13% of the total winter microplastic concentration was incorporated into the ice, suggesting that most particles remain suspended in the water column during ice-covered periods. Particle morphology analysis showed a predominance of small particles with low circularity across all samples. Polyvinyl chloride (PVC) was the most frequently identified polymer in limited range μ-Raman analyses; however, full spectrum analysis revealed a shift toward polyethylene (PE) and uncategorized plastics (UNC), highlighting the importance of spectral range in accurate identification. These findings suggest that lake ice plays a limited but measurable role in microplastic storage and may contribute to seasonal redistribution of microplastics upon melting. The study contributes new knowledge to the underrepresented field of microplastics in seasonally icecovered freshwater lakes and emphasizes the need to better understand microplastic dynamics in ice-covered environments.