Enzymatic Purification of Microplastics in 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. 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.

Microplastic concentrations, size distribution, and polymer types in the surface waters of a northern European lake

“…Manta samples contained large amounts of algae, insects, and other biological material and particles were selected from the partially digested matrix remains, consisting mainly of chitin. More efficient digestion method, which dissolves also chitin, could ease this problem (Löder et al, ). Additionally, the digestion step made the manta method more prone to contamination than the pump method.…”

Review of Microplastic Pollution in the Environment and Emerging Recycling Solutions

“…The ubiquity of microplastics makes fast sampling methods all the more important. Furthermore, micro-FTIR, micro-Raman (i.e., coupling a microscope with an FTIR/Raman) can be used on small sample masses and isolate a single particle for characterization with the assistance of visual images [14,25,30,32].…”

“…However, these methods could result in some loss of microplastic in the sample and therefore may have a bias towards certain polymers or particle sizes. Thus a new approach, to increase the selectivity of this process, was proposed by Löder et al Their process, called Basic Enzymatic Purification Protocol (BEPP) utilizes a multistep, multi-compound chemical and enzymatic digestion process that raised the selectivity of the process to 84.5 ± 3.3% [25].…”

Microplastics in Aquatic Systems – Monitoring Methods and Biological Consequences

“…Specific enzymes like Proteinase-K and trypsin are very expensive. Technical enzymes, on the other hand, can be used as an inexpensive alternative (Löder and Gerdts 2015;Löder et al 2017;Mintenig et al 2017).…”

“…Enzymatic treatments represent the best choice in terms of being nondestructive to MPs. Several working groups have shown the high effectiveness of enzymatic digestion with different enzymes (Cole et al 2014;Courtene-Jones et al 2017;Karlsson et al 2017;Löder et al 2017;Mintenig et al 2017).…”