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Comparison of microplastic isolation and extraction methods for marine sediment
Citation:
Ho, K., M. Cashman, S. Robinson, S. Russo, T. Bovinng, AND R. Burgess. Comparison of microplastic isolation and extraction methods for marine sediment. 2019 SETAC North America Fall Meeting, Toronto, Ontario, CANADA, November 03 - 07, 2019.
Impact/Purpose:
Microplastics (MP)are a growing concern in our environment. Methods to extract and isolate MP from environmental matrices (sediment, water tissues) are necessary to understand the effects of these persistent, ubiquitous particles. Methods are not yet standardized in this young and rapidly growing field of study. This research helps to standardize methods for sediment extraction of MP and point out some of the difficulties of this type of analysis.
Description:
Microplastics are a growing concern in our environment. Methods for the isolation and extraction of these small particles (1- 1000 microns) from environmental media vary widely and prevent meaningful comparison among reported environmental concentrations. As microplastics become biofouled and aggregate in the water column, sediments become their ultimate sink. We quantified recovery among five commonly used extraction/isolation methods for sediments that were chosen to represent a wide range of approaches in the literature. We tested each of the five methods with five poylmers: polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate fiber (PET) and polypropene (PP) rope in a variety of shapes and sizes including flakes, fibers and spheres ranging from 40-700 m. All combinations of methods and plastics were tested in two marine sediment types (i.e., sandy and silty). In addition to the five tested methods, we used Nile Red staining post extraction on all methods to determine if the stain increased recovery of spiked plastics. Mean recoveries of microplastics ranged from 0-87%, depending on method, polymer and sediment type. No one method recovered all plastics with the same efficacy, and all methods had mean recoveries <70% per plastic type. As expected, denser plastics were not recovered by lower density salt solutions. Organic matter present in silty sediments increased the complexity of recovery and probably reduced method success. The Nile Red stain increased the fluorescence background in complex, organically rich samples further confounding recovery. Lessons from this investigation provide valuable information for developing a hybridized method for the isolation and extraction of MPs from marine sediments (see Cashman et al. 2019 poster). In addition, we recommend using a standardized mixture of weathered microplastics to quantify method performance.