Comprehensive Comparison of Various Microplastic Sampling Methods in Sea Water: Implications for Data Compilation

The problem of plastic and microplastic (MP, <5 mm in size) pollution has received widespread attention globally, with its widespread presence being reported in various environmental media. However, a lack of standard sampling and analysis methods is making it difficult to compare data across studies and understand the source and fate of plastics and MPs. Common sampling strategies used in studies of MP in natural waters include Manta net and pump filtering using different mesh sizes, but the impact of these sampling technologies on the final MP abundance and characteristics is not well understood. This study used common sampling devices, including a Manta trawl net, shallow-water plankton pump (SPP), deep-water plankton pump (DPP), and submersible pump with on-site filtration using 50 and 330 µm aperture size meshes, to sample MP in natural coastal water. The results showed that while Manta trawl and plankton pumps produced similar MP abundance (2.0–6.0 n/m3), the MP characterization was significantly different, with fibers being the dominant MP in plankton samples (>70%) and only 14.2% in Manta trawl samples. Submersible pump sampling using a 50 µm mesh retained a higher percentage of fibers, with a two magnitude higher abundance of MPs (357 ± 119 and 553 ± 19 n/m3 for 330 µm and 50 µm mesh, respectively) attributed to the floating debris encountered during sampling and the shallower sampling depth as well as smaller sampling volume. This study highlights the key factors that impact MP abundance and characteristics as well as the challenges to harmonizing MPs sampling methods in aquatic environments, which is also helpful for data compilation across studies.