Comparison of two pump-based systems for sampling small microplastics (>10 μM) in coastal waters

Microplastics (MPs) have emerged as an important research topic due to their ubiquity in the environment and their potentially harmful effects on aquatic biota. However, our knowledge of the abundance and characteristics of the smaller fraction of MPs (<300 μm) in marine waters remains limited. This study aims to compare two different filter pump devices: AAU-UFO (Universal Filtering Object) pump and KCD (KC Denmark's Micro Plastic Particle) pump for sampling small MPs (>10 μm). Coastal waters from six sites in the Gulf of Bothnia (Baltic Sea) were sampled with both devices. The concentration and composition of the collected MPs were analyzed by FPA-μFTIR imaging. The median concentrations were 117 MP/m³ with a median mass of 118 μg/m³ and 162 MP/m³ with a median mass of 117 μg/m³, for the UFO pump and KCD pump, respectively. The predominant MP shape was fragment, and the most abundant polymers were polyester, polyethylene, and polypropylene. MPs smaller than 300 μm represented more than 90% of the MPs in the samples. The recorded microplastic concentrations were several orders of magnitude higher than those previously reported using a Manta net in this area, highlighting the importance of analyzing MPs smaller than 300 μm. No significant differences in MP concentrations were found between samples from the two filter pumps, indicating that both devices are comparably effective systems for sampling MPs (>10 μm) in coastal waters. Overall, our findings contribute to harmonizing sampling methodologies for small MPs in aquatic systems, which is crucial for establishing effective monitoring programs and ensuring accurate risk assessments.