A novel, density-independent and FTIR-compatible approach for the rapid extraction of microplastics from aquatic sediments

Microplastics have been detected in aquatic sediments around the world, highlighting the propensity of this matrix to serve as a sink for these structural pollutants. More reliable and reproducible extraction protocols for microplastics would facilitate comparisons across studies. A number of different extraction techniques are currently used to separate microplastics from sediment and almost exclusively employ density-based separations, which take advantage of the inherent densities of plastic particles. Some of these techniques are cost-effective but fail to fully recover all plastic types. Other techniques may recover most plastic types, but are more costly and/or hazardous to human or environmental health. We present here a novel, cost-effective oil extraction protocol (OEP) that provides an alternative to density-based approaches by taking advantage of the oleophilic properties of microplastics. Using this technique, we counted microplastic particles in spiked sediment samples using light microscopy and observed 96.1% ± 7.4 recovery for total microplastics, with recovery rates of 92.7% ± 4.3 for fibers and 99% ± 1.4 for particles. Subsequent analysis with Fourier-Transform Infrared Spectrometry (FTIR) revealed that the oil interfered with the FTIR spectrum of microplastics, but that an additional, post-extraction clean-up step using ethyl alcohol (90%) removed residual traces of oil and eliminated the FTIR spectral interference. The application of this new technique to shoreline sediment samples collected from sites in urban Vancouver, British Columbia, Canada, and a remote beach on Vancouver Island, as well as bulk seawater, demonstrated that the oil extraction protocol is effective for environmental samples. This novel OEP represents a cost-effective and reliable alternative to leading density-based techniques.