A Basis for Standardization: Optimizing Sampling Methods and Quantities for Accurate Microplastic Assessment in a Marine Environment

The presence and persistence of microplastics (MPs) in the marine environment pose increasing threats to marine organisms and ecosystem health. Environmental monitoring of MPs facilitates assessment of their potential impacts on ecosystems and biota. Although numerous studies have confirmed the widespread presence of MPs pollution in the marine environment, there are still significant differences in the sampling methods and sample quantities used for MPs monitoring. To address these issues, this study investigated the influence of different sampling methods and quantities on the survey results of MPs in the marine environment. The impact of different sample mass on the detection of MPs abundance in sandy and muddy beach sediments of the supratidal, intertidal, and subtidal zones was examined. And the effects of different seawater MPs collection methods (trawl sampling, water collector sampling, and pump sampling) and quantities on MPs abundance detection in seawater were also explored. Results show that the most suitable sample mass for detecting MPs in beach sediments is at least 30 g. Additionally, comprehensive sampling and monitoring of the supratidal, intertidal, and subtidal zones should be conducted to ensure accurate assessment of MPs abundance. Seawater samples were collected via trawl, water collector sampling, and pump sampling to evaluate effects of methods, sample quantities, filter aperture, and sampling depth on the monitoring abundance of MPs. Results show that the optimal sampling parameters are trawl durations at least 10 min and water collector sampling volumes at least 10 L. In the water collector sampling method, the total abundances of MPs after filtration through 48 and 330 μm filters are at the same order of magnitude, indicating that the filtration pore size has no significant effect on the total abundance of MPs. However, the size ranges of retained MPs differ significantly between the two pore sizes. Furthermore, while no significant difference is observed in MPs abundance among different water layers in Leizhou Bay, variations are found in polymer composition and MPs size distribution. This research is helpful in improving the accurate monitoring of MPs in the marine environment.