Preliminary investigation of microplastics in the production process of sea salt sourced from the Bohai Sea, China, using an optimised and consistent approach.

In this study, we present a preliminary investigation of the characteristic changes in microplastic during the production process of sea salt in China. Five representative samples, including seawater, saturated brine, crude salt, coarse salt, and refined salt were successively collected from the production process of sea salt sourced from the Bohai Sea in China. The pretreatment method of microplastics was optimised and evaluated by the recovery rates of particle references. Microplastic characteristics in the five samples were investigated using consistent pretreatment, microscopic, and spectroscopic analyses. Results indicated that microplastics were present in every stage of sea salt production. During the "journey" of microplastics in salt production from seawater-to-seawater evaporation, to salt crystallisation, and external force processing, the abundance of microplastics with size ranging from 18 μm to 4936 μm increased substantially from 23 ± 8 to 413 ± 61 particles kg, while the proportion of larger microplastics (≥1000 μm) decreased from 33% to 9%. The results illustrate the effect of the production process on microplastic contamination of sea salt.