Quantitative assessment of visual microscopy as a tool for microplastic research: Recommendations for improving methods and reporting

Kotar S, Mcneish R, Murphy-Hagan C, Renick V, Lee CFT, Steele C, Lusher A, Moore C, Minor E, Schroeder J, Helm P, Rickabaugh K, De Frond H, Gesulga K, Lao W, Munno K, Hampton LMT, Weisberg SB, Wong CS, Amarpuri G, Andrews RC, Barnett SM, Christiansen S, Cowger W, Crampond K, Du F, Gray AB, Hankett J, Ho K, Jaeger J, Lilley C, Mai L, Mina O, Lee E, Primpke S, Singh S, Skovly J, Slifko T, Sukumaran S, Van Bavel B, Van Brocklin J, Vollnhals F, Wu C, Rochman CM (2022)

Publication Type: Journal article

Publication year: 2022


Book Volume: 308

Article Number: 136449

DOI: 10.1016/j.chemosphere.2022.136449


Microscopy is often the first step in microplastic analysis and is generally followed by spectroscopy to confirm material type. The value of microscopy lies in its ability to provide count, size, color, and morphological information to inform toxicity and source apportionment. To assess the accuracy and precision of microscopy, we conducted a method evaluation study. Twenty-two laboratories from six countries were provided three blind spiked clean water samples and asked to follow a standard operating procedure. The samples contained a known number of microplastics with different morphologies (fiber, fragment, sphere), colors (clear, white, green, blue, red, and orange), polymer types (PE, PS, PVC, and PET), and sizes (ranging from roughly 3–2000 μm), and natural materials (natural hair, fibers, and shells; 100–7000 μm) that could be mistaken for microplastics (i.e., false positives). Particle recovery was poor for the smallest size fraction (3–20 μm). Average recovery (±StDev) for all reported particles >50 μm was 94.5 ± 56.3%. After quality checks, recovery for >50 μm spiked particles was 51.3 ± 21.7%. Recovery varied based on morphology and color, with poorest recovery for fibers and the largest deviations for clear and white particles. Experience mattered; less experienced laboratories tended to report higher concentration and had a higher variance among replicates. Participants identified opportunity for increased accuracy and precision through training, improved color and morphology keys, and method alterations relevant to size fractionation. The resulting data informs future work, constraining and highlighting the value of microscopy for microplastics.

Involved external institutions

Southern California Coastal Water Research Project US United States (USA) (US) California State University, Bakersfield US United States (USA) (US) University of California, Riverside (UCR) US United States (USA) (US) Orange County Sanitation District (OCSD) US United States (USA) (US) The Metropolitan Water District of Southern California US United States (USA) (US) California State University, Channel Islands (CSUCI) US United States (USA) (US) Norwegian Institute for Water Research (NIVA) NO Norway (NO) Moore Institute for Plastic Pollution Research US United States (USA) (US) Eastman Chemical Company US United States (USA) (US) University of Toronto CA Canada (CA) Barnett Technical Services, LLC US United States (USA) (US) Fraunhofer-Institut für Keramische Technologien und Systeme (IKTS) DE Germany (DE) Université du Québec à Rimouski (UQAR) CA Canada (CA) East China Normal University (ECNU) / 华东师范大学 CN China (CN) BASF (United States) US United States (USA) (US) Environmental Protection Agency (EPA) US United States (USA) (US) Eurofins Environment Testing AU Australia (AU) Eurofins US United States (USA) (US) Jinan University CN China (CN) Pennsylvania State University (Penn State) US United States (USA) (US) HORIBA Instruments Incorporated US United States (USA) (US) Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung (AWI) DE Germany (DE) Eurofins Norge NO Norway (NO) University of Minnesota Duluth (UMD) US United States (USA) (US) NatureWorks LLC US United States (USA) (US) Ministry of the Environment, Conservation and Parks CA Canada (CA) RJ Lee Group US United States (USA) (US) Thermo Fisher Scientific Inc. US United States (USA) (US) Oregon State University (OSU) US United States (USA) (US) Innovations-Institut für Nanotechnologie und korrelative Mikroskopie e.V. (INAM) / Institute for Nanotechnology and Correlative Microscopy DE Germany (DE)

How to cite


Kotar, S., Mcneish, R., Murphy-Hagan, C., Renick, V., Lee, C.-F.T., Steele, C.,... Rochman, C.M. (2022). Quantitative assessment of visual microscopy as a tool for microplastic research: Recommendations for improving methods and reporting. Chemosphere, 308. https://doi.org/10.1016/j.chemosphere.2022.136449


Kotar, Syd, et al. "Quantitative assessment of visual microscopy as a tool for microplastic research: Recommendations for improving methods and reporting." Chemosphere 308 (2022).

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