Selecting Membrane Filters to Detect Microplastics in High-Particulate Environmental Matrices

Analyzing Microplastics in the Environment
Oral Presentation

Prepared by L. Lozeau1, R. Muralidharan2, K. Sydlowski1
1 - MilliporeSigma, 400 Summit Drive, Burlington, MA, 01803, United States
2 - Sigma-Aldrich, Inc., P.O. Box 14508, St. Louis, MO, 63178, United States


Contact Information: [email protected]; 781-496-5656

ABSTRACT

The development of analytical methods to detect microplastics—plastic particles, 1 µm to 5 mm in size—in the environment is an increasing priority due to mounting evidence of their negative impacts on human health. However, sample preparation and downstream analytical methods for isolating and studying microplastics are as heterogenous as the particles themselves. Protocols are even more varied for high-particulate matrices, such as wastewater and soils, where non-standardized digestion and separation steps are required. While most of these methods involve one or more membrane filtration step(s) and may even use a filter as a substrate, each analytical workflow, from GC-pyrolysis to FTIR and microscopy, has different requirements for the best filter choice.

In order to create a standard guide for choosing the best filter for each characterization technique, the properties of various filter materials and pore sizes, including polycarbonate, aluminum oxide, glass fiber, mixed cellulose ester, and quartz fiber were studied for their suitability in isolation protocols involving (1) salt/density separation, (2) oil separation, (3) chemical digestion and (4) enzymatic digestion. “Suitability” was determined by filter handleability, chemical and temperature compatibility, morphology, and filter functionality during the protocol. Then, a vacuum workflow was devised to isolate, quantify and identify model microplastic particles in high-particulate matrices after separation and digestion using the most suitable filters. Lastly, an example case study was implemented using the most suitable filters as substrates to quantify microplastics in sand from three to New England beaches using microscopy, FTIR spectroscopy and GC-pyrolysis. Comparing the results on multiple filter types and analytical methods provided valuable insights on how to choose membrane filters for the accurate isolation, identification, analysis and characterization of microplastics in high-particulate environmental matrices.