Analysis of the effect of salt processing on microplastic residues in crushed and washed sea salt

This study focused on issues related to sea salt processing caused by marine microplastic pollution and investigated the effect of crushed and washed sea salt (CWSS) processing on microplastics (MPs) residues for the first time. Thirteen MPs contaminants were identified in the crude salts derived from seawater crystallization, with relative abundance of 256 ± 26 particles/10 g detected. After CWSS processing there were a total of 6 ± 5–112 ± 30 particles/10 g abundance in the final product. The results confirmed that the CWSS process had a significant impact on the abundance distribution of MPs in sea salt (p-value = 0.00147 < 0.01), and CWSS processing removed between 56.25% and 97.66% of microplastic particles from the crude material. The most prominent MP contaminants in both crude salt and commercial salt were PA (polyamide) and PU (polyurethane). It was found that PP (polypropylene) was mainly introduced during CWSS processing, in particular when packaging the salt. In addition, There was no significant difference for CWSS processing in the MPs removal between 0 and 140 μm (p-value = 0.098 > 0.05).