Sampling the aquatic environment for microplastic concentration is inherently difficult because of variations in microplastic concentration, shape, and density and the potential for contamination. We present an assessment of a method for microplastic sampling that uses a peristaltic pump to pump water through a series of in-line stainless-steel mesh filters. Following filtration, the stainless-steel filters were treated using previously published methods to isolate microplastics, adjusted for the stainless-steel mesh filters. Microplastics were identified using micro-Fourier Transform Infrared (µFTIR) spectroscopy in transmission mode. This method was tested in the laboratory using standard polyethylene beads and was applied to two sample sites at the Las Vegas Wash in Nevada. The results showed 70% of the polyethylene beads were recovered after the peristaltic pump and laboratory steps with minimal blank contamination. The advantages of the peristaltic pump sampling method are it (1) supports a range of sample volumes, (2) reduces sample handling, (3) reduces the potential for contamination, (4) provides flexibility in sampling locations, and (5) supports a variety of filter types. Using stainless-steel mesh filters allows for (1) streamlined and direct field-to-laboratory sample processing, (2) µFTIR transmission mode analysis of filter-mounted microplastics, and (3) reduced filter and sample processing costs.

A  Microplastic polymer type was identified using a Thermo Nicolet iN10 MX instrument housed at DRI. We analyzed the SS mesh mounted samples in transmission mode using the imaging detector MCT cooled array with an aperture size of 25 µm x 25 µm and 25 µm step size, spectral resolution of 8 cm^-1 (from 4000 to 715 cm^-1), and 64 scans. Background spectra using the same settings were automatically collected every 60 minutes. Results were corrected for baseline drift and data were exported and processed using siMPle^40–42 The publicly available standard dataset⁴³ was imported into siMPle and was used to compare and identify the collected spectra. We tested the siMPle program using known standard plastic materials and adjusted the threshold match accordingly (Supplementary Table S2). One randomly selected area of the VMPS25 standard (Table 1) with PE beads was analyzed for method testing and two randomly selected areas of each LVW SS filter were analyzed.