Prevalence of microplastic fibers in the marginal sea water column off southeast China

Microplastic (MP) fibers are present in all environmental media, yet little is known about their distribution, sources, and transport in the water column of marginal seas. In this study, we conducted an intensive sampling campaign in the marginal sea water column off southeast China, which is an area that is greatly influenced by high MP emissions. We found that hydrological effects largely regulated the spatial variations of MP fiber distribution and that MP fibers likely were not entering the South China Sea through terrestrial input from southeast China during the summer monsoon. Polyethylene terephthalate (PET) fibers were pervasive in the surface water (SW) (89.47%), subsurface chlorophyll maximum layer (SCML) (92.65%), and bottom water (BW) (94.29%) of the water column during the sampling period. Approximately 32% of MP fibers in the samples were smaller than 330 μm. The abundance of MP fibers in SW was significantly lower than that in the SCML and BW. Based on this observation, we estimated the inventory of MP fibers in the SW, SCML, and BW of the sampling area to be 1.377–1.378, 2.820–2.825, and 2.627–2.629 metric tons, respectively. These results improved our understanding of the source-to-sink process of MP fiber contamination in the water column of marginal seas.