Microplastic concentrations, size distribution, and polymer types in the surface waters of a northern European lake

We examined microplastic concentrations, size distributions, and polymer types in surface waters of a northern European dimictic lake. Two sampling methods, a pump sieving water onto filters with different pore sizes (20, 100, and 300 µm) and a common manta trawl (333 µm), were utilized to sample surface water from 12 sites at the vicinity of potential sources for microplastic emissions. The number and polymer types of microplastics in the samples were determined with optical microscopy and μFTIR spectroscopy. The average concentrations were 0.27 ± 0.18 (mean ± SD) microplastics/m(3) in manta trawled samples and 1.8 ± 2.3 (>300 μm), 12 ± 17 (100–300 μm) and 155 ± 73 (20–100 μm) microplastics/m(3) in pump filtered samples. The majority (64%) of the identified microplastics (n = 168) were fibers, and the rest were fragments. Materials were identified as polymers commonly used in consumer products, such as polyethylene, polypropylene, and polyethylene terephthalate. Microplastic concentrations were high near the discharge pipe of a wastewater treatment plant, harbors, and snow dumping site. PRACTITIONER POINTS: Samples were taken with a manta trawl (333 μm) and a pump filtration system (300/100/20 μm). With pump filtration, small 20–300 μm particles were more common than >300 μm particles. The average concentration of manta trawled samples was 0.27 ± 0.18 (mean ± SD) microplastics/m(3.) FTIR analysis revealed PE, PP, PET, and PAN to be the most common polymers.