Microplastics in the commercial seaweed nori

Microplastics have been reported to attach to the marine macroalgae which act as the vector for microplastic transfer in the marine food web. In this study, the edible seaweed nori (Pyropia spp.) was chosen as a target species. The microplastic contaminant situations in nori were analyzed in both its final commercial products and the intermediate products across different processing stages. The abundance of microplastics ranged from 0.9 to 3.0 items/g (dw) among 24 brands of commercially packaged nori samples. With the development of nori processing stages, an enlarged size fraction of greater microplastics (1-5 mm) was observed. Compared with commercially packaged nori samples, the proportions of polypropylene, polyethylene and poly (ethylene-propylene) copolymers increased, whereas that of polyester decreased in factory-processed nori. Additionally, we further simulated and quantified the number of fluorescent polyester fibers (concentrations: 0, 1000, 5000, 10,000 fibers/L) attach to the algal pieces of Pyropia yezoensis under laboratory conditions. The average abundance of microfibers on the nori was positively and quantitatively related to their abundances in seawater (p < 0.01). To our best knowledge, this is the first work that shows the prevalence of microplastics in the commercial seaweed nori and relates to their potential sources during the processing phase.