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Here I will describe how I examined in the laboratory the presence of microplastics in the collected snow samples. Basically, the whole procedure consists of three main steps:
– filtration of samples
– electron microscope examination
– Raman microscope examination (spectroscopy)
Of course, all these concepts are explained in more detail later in this article.
But let’s start from the beginning …
I collected snow samples for testing in four locations:
– Mount Kilimanjaro in Africa,
– Kitzsteinhorn ski resort in Austria,
– Valley of the Five Polish Ponds in the High Tatras,
– Hornsund fjord area in southern Svalbard (read about my expedition).
I collected snow into previously washed glass bottles with a capacity of 330 to 1000 ml. Why glass? To avoid secondary microplastic contamination in the sample.
I have always collected a thin, top layer of snow cover from the largest possible surface.
This step was to separate all solids from the sample. For this I used the appropriate laboratory equipment and cellulose filters with a pore diameter of 0.45 μm (very small, 0.00045 mm). That is, all particles larger than 0.45 μm remained on the filter.
The filtration procedure itself is not difficult, but it is also not very interesting and entertaining. I will briefly present its course, but I will also not be offended if you jump to the next paragraph now.
Stages of the filtration process:
• I took the samples to the water laboratory and thawed them (they were previously stored in a refrigerator);
• I have installed a cellulose filter on the filtering device;
• I sealed it tightly with a vessel into which, after shaking, I poured the tested water with sediment;
• I started the apparatus. As a result of the generation of negative pressure (pressure difference), the water was seeping through the filter, leaving all solid particles on it.
• after filtering, remove and protect the cellulose filter.
• I repeated these activities for all tested samples (there were eleven of them);
• after filtering, the samples were transported for drying.
Visualization and chemical analysis of the sediment using an electron microscope
The next step in the analysis of samples is scanning electron microscopy. It allows you to view the tested elements under a very high and precise magnification. The microscope used is a Quanta 250 by Thermo-Fisher. The procedure for searching for microplastic particles was as follows:
– I brought dried samples on cellulose filters to the laboratory,
– I prepared special tables with a carbon base for the electron microscope. The carbon backing is responsible for the black background in the photos. This makes it easier to distinguish the test molecules.
– I put the tables on the samples. The material under test then sticks to them.
– I placed the tables with the tested material in an electron microscope.
– I closed it tightly and started the apparatus.
– I looked at each sample under magnification for potential microplastic particles.
– After finding promising elements, I took a photo of them.
– I repeated the activity until I found at least two microplastic particles in each of the eleven samples.
Below are some photos of potential microplastic particles found:
Raman radiation measurements
What is Raman Spectroscopy? It is an analytical technique where a spectrum is obtained as a result of the interaction of electromagnetic radiation.
Translating into a simpler language. The laser beam excites the particles which start to vibrate. Each element has a different excitation range. From the chart obtained, you can “decode” the composition of the molecule.
Spectroscopy gives information about the interconnection of atoms in a molecule. This enables the identification of chemical compounds, i.e. learning what the tested element is made of. A great advantage of this method is the non-destructive analysis of the sample.
I examined only three selected elements. Below I present the test procedure and photos of sample charts.
• the samples were transferred to the Raman Spectroscopy laboratory;
• I installed the selected sample under the microscope;
• a previously identified MP molecule was found optically;
• Raman spectroscopy study was carried out on the selected molecule;
• I repeated the activities for selected samples.
After the research was completed, the most important part of the work awaited. Collecting the results as a whole, analysing them and making conclusions.