High-resolution NMR spectroscopic approaches to quantify PET microplastics pollution in environmental freshwater samples

Abstract

Reliable identification and precise quantification of microplastics pollution of the environment are essential prerequisites to comprehend the impact of microplastics on Earth’s ecosystems. In this study, we propose a workflow to examine polyethylene terephthalate (PET) contamination of environmental surface waters by applying high-resolution nuclear magnetic resonance (NMR) spectroscopic approaches. The detection of PET by high-resolution NMR spectroscopy enables the unambiguous identification and - at the same time - precise quantification at atomic resolution independent from the size of the particles obtained from surface waters. Monitoring the properties of translational diffusion and relaxation of PET chains present in the samples obtained from Lake Constance water by filtration (‘Manta trawls’), extraction and dissolving, hints towards a rather heterogeneous distribution in length of the PET chains. The workflow developed here achieved a limit of detection of 192.2 ng PET and a recovery rate of 88 ± 25% for PET microplastics that was spiked to the Manta trawls. The NMR driven analysis led to a concentration determination of 335 ± 200 ng PET per cubic meter of Lake Constance water. The workflow developed here offers not only a simple and reliable quantitative determination of the mass of PET in environmental samples independent of particle size but is additionally providing insights into the inherent polymeric features of PET, which are not accessible through other established methods of microplastics detection. Therefore, a broad application of the NMR spectroscopic approach presented here can be assumed.