Six Microplastics Analysis in Bottled Water, Purified Tap Water and Branded Table Salt by Double-Shot Pyrolysis–Gas Chromatography/Mass Spectrometry

The quantification analysis of microplastics (MPs) in bottled water, purified tap water and branded table salt was executed by double-shot pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS), and the concentration was expressed as a mass concentration, which was more suitable for the data comparison. MPs including polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polycarbonate (PC), polypropylene (PP), polystyrene (PS) and polyethylene (PE) were separated by filtration with glass fiber filter membranes. After being folded, the whole glass filter membrane containing MPs was transferred into a pyrolysis cup directly to avoid the sample loss during transfer. The characteristic pyrolysates were used to identify and quantify PMMA, PET, PC, PP, PS and PE. The linear relationships were found between the polymer weight amount and peak areas of each characteristic pyrolysates with the correlation coefficients larger than 0.993. The intra-day precisions of the pyrolysates for peak areas were 0.56–18.94%, and the inter-day variability was 8.47–19.88%. The recovery values of the spiked standards were in a range of 81.5–114.5%. MPs in bottled water, purified tap water and branded table salt samples were successfully quantified by the proposed Py–GC/MS method. For four brands of bottled water samples, 0.088 μg/L PET was found in one sample. PP was detected in all purified tap water samples from five brands with the concentrations between 0.028 and 0.489 μg/L, and PE was detected in purified tap water samples from two brands with the concentrations between 0.194 and 1.26 μg/L. As for nine table salt samples, PP were found in a range of 4.00–182.80 μg/100 g salt in eight table salt samples. Due to the high content of MPs in purified tap water samples and large daily consumption, the estimated daily intake (EDI) of MPs from purified tap water was calculated. The estimated daily intakes (EDIs) for adults are 2.57 ng PP/kg/d and 4.17 ng PE/kg/d from purified tap water; the EDIs for children are 5.63 ng PP/kg/d and 9.11 ng PE/kg/d from purified tap water.