Microplastics & Environment


Identification of microplastics in environmental samples

Two scientists sitting in front of a computer talking to each other Copyright: © Peter Winandy

Microplastics have been detected in various environmental media such as seas, rivers, soils, sediments, sludge and composts. Microplastic particles have even been measured by atmospheric deposition in ice samples far from human civilization. Often there are only a few particles that can be detected in a very heterogeneous and complex matrix. To do this, a representative sample with a sufficient amount of analytes must first be taken. In the case of slightly polluted waters such as groundwater or drinking water, between 0.5-5,000m3 of water should be enriched on a filter in order to be able to detect even the smallest amounts of microplastic particles. In aqueous samples or solids with a high content of solids, the isolation of the microplastic particles from a much larger amount of other organic and inorganic solid particles is the greatest difficulty.

The aim of the planned examinations must be specified before the analysis. For example, is the focus on balances or loads of microplastics from sewage treatment plants or in water sediments or measurement data for ecotoxicological studies? Furthermore, the question of the dimension and type of the desired measurement results must be clarified. A distinction is made here between the number of particles or the mass in an environmental medium. The environmental medium and the available analytics determine the sample preparation and the sample volume before the analytical examination. Bulky polymers commonly found in the environment include polypropylene, polyethylene, polystyrene, polyvinyl chloride, polyethylene terephthalate, and polyamide.

In the early days of microplastic analysis, only manual microscopic examinations were used after extensive sample preparation, for example using acids, alkalis or oxidizing substances, to remove the matrix from organic material and then separate the minerals, such as sand and clays, by density separation. This method has the disadvantage that the manual counting or the identification of potential plastic fragments based on color and shape is subjective. However, a distinction can be made here between primary microplastics - such as pellets and microbeads - and secondary microplastics in the form of fragments and fibers.

At the Chair of Geology, Geochemistry and Deposits of Crude Oil and Coal and at the Institute for Urban Water Management, spectroscopic, thermoanalytical and chemical analysis methods are used to examine microplastics in environmental samples. In addition to the number of particles, the type of polymer can also be determined with the spectroscopic methods.

Further information can be found in the science magazine RWTH THEMEN on the subject of “Plastic and the Environment”. Professor Volker Linnemann from the Institute for Urban Water Management and Professor Jan-Claudius Schwarzbauer from the Chair of Geology, Geochemistry and Deposits of Crude Oil and Coal show in their text "Identifying microplastics in environmental samples" the advantages and disadvantages of spectroscopic, thermoanalytical and chemical analysis.