Development of Sampling and Analytical Methods for Measuring Microplastics with Sizes Greater than 20 μm in Tap Water

Abstract

A novel sampling method with an analysis for microplastics (MPs) with sizes greater than 20 μm in tap water was developed to reveal their occurrence characteristics, such as their concentrations, polymer compositions and size distributions, with high precision. Micro-Fourier transform infrared spectroscopy followed by density separation could recover 91.0% of MP particles in tap water. Large amounts of water could make the standard deviations of detected MP concentrations much smaller, and the coefficient of variation decreased to 14.9% when the sampling volume was 1000 L. The sampling method for MPs under faucets with unused plankton nets outside collected 16.7 ± 6.4 particles by dry deposition from the atmosphere, but the coverage by lids could reduce the level of deposition. Finally, MPs in 1000 L of tap water originating from groundwater were analyzed. Twelve polymers were detected and their total concentrations ranged from 78 ± 10.4 to 2130 ± 358 particles m⁻³. Polyethylene, alkyd resins and polymethyl methacrylate were dominant and their total concentrations contributed 56.5 to 94.0% to the total MP concentrations. The median sizes of MPs observed in all samples ranged from 30.1 to 60.4 μm and their dominant shape was of the fragment type.