Removing microplastics from table salt solutions using high-surface biochars

The pollution of the aquatic environment by microplastics has been extensively studied; however, data on their presence in commercial salts widely consumed around the world remain limited. Most people consume foods containing a significant amount of salt throughout their lifetime. Therefore, its consumption is a long-term route of exposure of microplastics to the human body, and it can lead to negative health effects. Previous studies have shown that 94% of the salt products tested worldwide contain microplastics, with fragments and fibers being the prevalent types of particles and polypropylene (PP), polyethylene (PE) and polyethylene terephthalate (PET) being the most abundant polymer types. Therefore, this study focuses on the presence of microplastics in table salt products purchased in Greece. Samples from various brands and sources were analyzed using a combination of metallic sieves and stereomicroscopy to assess particle size, color, and morphology. Blank analyses were conducted to eliminate the possibility of internal cross-contamination. Furthermore, microplastic types were identified using chemical pretreatment and advanced spectroscopic techniques, including Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy. Then, batch experiments were employed to study the removal of PE with a diameter of 10 μm from water using different types of biochars. In particular, the results indicated that biochar synthesized from grape seed exhibits better microplastic removal than biochar derived from rice husk. This improved removal process is attributed to the enhanced porosity and surface area of the grape seed biochar.