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A comprehensive pyrolysis-gas chromatography/mass spectrometry analysis for the assessment of microplastics in various salts
Summary
Scientists measured microplastic contamination in different types of edible salt using advanced chemical analysis and found that sea salt contained the most microplastics, roughly 17 times more than rock salt. Polyethylene, polypropylene, and PET made up the vast majority of particles found, and some contamination came from the salt packaging itself. Based on average salt consumption, a person using sea salt could be exposed to over 2,300 micrograms of microplastics per year through salt alone.
Analytical pyrolysis-gas chromatography/mass spectrometry(Py-GC/MS) was chosen to quantify microplastics(MPs) in edible salts: sea salt(SS), deep-sea salt(DSS), rock salt(RS), and lake salt(LS). Samples were filtered by two-step using 20 μm(MPs20) and 1 μm(MPs1) filters. Two Py-GC/MS methods with split ratios of 100/1 for high-level and 10/1 for low-level MPs were used. Quality control measures were taken to avoid pre-contamination. Methods showed high linearities (R > 0.995) and recoveries (84.2-118.1 %) for standards, polyethylene(PE), polypropylene(PP), polystyrene(PS), and polyethylene terephthalate(PET). SS showed highest MPs concentration (584.5 ± 204.4 μg/kg), followed by RS(34.2 ± 16.7 μg/kg) and LS(6.2 μg/kg). Over 7.2 % of detected MPs in SS and RS were smaller than 20 μm. PE, PP, and PET comprised 98.4 % of MPs in SS and 88.1 % in RS. MPs contamination from packaging materials was experimentally confirmed by the presence of similarly shaped PS particles in RS. MPs annual exposure was highest in SS(2304 μg/person), followed by RS(135 μg/person), and LS(24 μg/person), indicating substantial variation in exposure based on salt type.