Microplastic extraction from water, sediment, soil, and atmospheric deposition samples

This document is the Ecohydrology Research Group (ERG) standard operating procedure (SOP) for separating microplastics (MPs) from sediment, soil, atmospheric deposition, and water samples. It applies to aqueous samples, such as atmospheric bulk deposition, surface water grab samples, and pore water, wet sediment or soil, and dry sediment or soil. The procedure includes the following major steps: spiking and preliminary separation (Steps 1 and 2), density separation (Step 3), organic matter removal (Step 4), manual counting (Step 5), and particle identification (Step 6). While not strictly required, we recommend spiking samples with known amounts of MP standards to assess recovery efficiencies. The sample, spiked or not, is sieved through a 500 μm sieve and collected on a 20 μm sieve. The next step consists of a density separation using a 60% ZnCl₂ solution, a broadly accepted technique to separate MPs from sediment by flotation (Prata et al., 2019). The Fenton oxidation reaction is then used to remove organic matter from the MP surfaces, before characterising and counting the MP particles with Laser Direct Infrared (LDIR) spectroscopy. The steps described in this SOP were optimized by extensive laboratory testing at ERG, University of Waterloo, as part of the “Microplastics fingerprinting at the watershed scale: from sources to receivers” project supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) under the program “Plastics science for a cleaner future” (Alliance grant ALLRP 558435 – 20).