BayCEER Workshop 2022

A novel approach to extract, purify, and fractionate microplastics from environmental matrices by isopycnic ultracentrifugation

The increasing accumulation of microplastics (MP) in the environment is considered one of the most important global challenges of our time. Reliable extraction and detection methods for MP in environmental samples are essential for determining the extent of pollution and assessing ecological risks. However, extraction of MP from complex environmental matrices such as soils remains a difficult task. Today, density-based extractions with saturated salt solutions are a widely applied practice. Nevertheless, current extraction approaches do not allow fractionation of different MP particle types according to their specific polymer densities. Here, we present a novel isopycnic ultracentrifugation approach for the simultaneous extraction and fractionation of MP mixtures based on the particle-specific buoyant densities. In this proof-of-concept, diffusion-based density gradients were prepared using caesium chloride media, covering a density range between 1.1 and 1.5 g mL^-1, sufficient to resolve many common polymer densities. We selected MP particles with a low (PA66), medium (PBAT), and high (PET) density to validate the separation performance. Pristine MP mixtures and particles pre-incubated in soil showed a clear banding pattern at expected buoyant densities after isopycnic separation. µFTIR imaging of subsamples collected from resolved MP fractions exhibited a polymer-specific separation of ≥ 87.6 %. In addition, our workflow provided quantitative MP recoveries between 86-99%. Further, the potential of our approach to preserve the MP-associated biofilms was also assessed. Soil-incubated MP particles were inspected by fluorescence microscopy before and after isopycnic separation, indicating a preservation of extracellular polymeric substances and microbes. Hence, isopycnic ultracentrifugation offers a powerful novel approach for polymer-specific extraction and resolution of MP particles with wide potential for applications in MP research.