A comprehensive pyrolysis-gas chromatography/mass spectrometry analysis for the assessment of microplastics in various salts

Abstract

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 (R2 > 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.