Enzymatic Purification of Microplastics in Environmental Samples

TLDR

Micro‑FTIR and Raman spectroscopy can identify microplastics, but low environmental concentrations require large sample volumes that coenrich organic matter, and conventional density separation cannot remove this organic fraction without risking polymer degradation by strong acids or bases. The study aims to purify microplastics from organic material before spectroscopic analysis. An enzymatic purification protocol (BEPP) employing technical‑grade enzymes was developed and refined for universal application to water, wastewater, sediment, biota, and food samples compatible with FPA‑based micro‑FTIR. BEPP removed 98.3 % of the sample matrix in surface water, achieved an 84.5 % recovery rate, and successfully quantified microplastics ranging from 0.05 to 4.42 items m⁻³ in North Sea environmental samples.

Abstract

Micro-Fourier transform infrared (micro-FTIR) spectroscopy and Raman spectroscopy enable the reliable identification and quantification of microplastics (MPs) in the lower micron range. Since concentrations of MPs in the environment are usually low, the large sample volumes required for these techniques lead to an excess of coenriched organic or inorganic materials. While inorganic materials can be separated from MPs using density separation, the organic fraction impedes the ability to conduct reliable analyses. Hence, the purification of MPs from organic materials is crucial prior to conducting an identification via spectroscopic techniques. Strong acidic or alkaline treatments bear the danger of degrading sensitive synthetic polymers. We suggest an alternative method, which uses a series of technical grade enzymes for purifying MPs in environmental samples. A basic enzymatic purification protocol (BEPP) proved to be efficient while reducing 98.3 ± 0.1% of the sample matrix in surface water samples. After showing a high recovery rate (84.5 ± 3.3%), the BEPP was successfully applied to environmental samples from the North Sea where numbers of MPs range from 0.05 to 4.42 items m-3. Experiences with different environmental sample matrices were considered in an improved and universally applicable version of the BEPP, which is suitable for focal plane array detector (FPA)-based micro-FTIR analyses of water, wastewater, sediment, biota, and food samples.