A Paraffin Microtomy Method for Improved and Efficient Production of Standardized Plastic Microfibers.

Microfibers are one of the most abundant microplastic particle types found in the environment, where they cause negative impacts on organisms and possibly on human health. Microfibers should be included in a wide range of laboratory studies; however, microfibers for scientific studies are not commercially available. Current methods to make microfibers generally create particles with large size ranges and poor precision, and efficient production of particles ≤100 µm is difficult. Laboratory studies of the biological and toxicological effects and chemical interactions of microfibers require uniform, small microfibers in sufficient numbers for environmentally relevant experiments. We developed a novel fiber embedding technique and modified a seminal cryomicrotomy method to produce precise microfibers in quantities suitable for environmentally relevant concentrations. Polyethylene terephthalate (PET) and nylon fibers were strategically wound onto a spindle, embedded in paraffin wax, and sectioned using a standard paraffin microtome. After processing with a suitable organic solvent to remove the wax, microfiber size distributions were assessed. The small microfibers (10-42 µm) were accurate to the target lengths with excellent precision and a production rate ≥13.5 times higher than previous methods. As a proof of application, three lengths of manufactured PET fibers were stained with Nile red and exposed to eastern oyster larvae (Crassostrea virginica) for 24 h. Larvae ingested the smaller fiber lengths (14 and 28 µm), and the Nile red-stained fibers were visible and distinguishable in the guts of the larvae. This experiment was the first to demonstrate ingestion of plastic particles other than microspheres by oyster larvae. The present method facilitates the use of small microfibers in laboratory experiments, allowing for a more complete understanding of microplastic effects in the environment. Environ Toxicol Chem 2022;41:944-953. © 2021 SETAC.