Did you know that, if you wash five pairs of new jeans for the first time, enough microplastic (MP) leaches out to make a plastic bag?
There are a lot of different sources for the intake of MP into the food chain, e.g., car tires, plastic bottles and bags, and even laundry. The reality is, intake sources are everywhere.
MP and — even worse — nanoplastics cannot be filtered out in a water treatment plant and thus find their way into every water resource. From there it flows into our oceans, contaminates the water there and enters directly into the food chain.
Marine litter consists of various materials, of which plastic is considered particularly problematic due to its low degradation rate. In European regions, around 70-80 percent of marine litter consists of plastic. According to recent estimates, approximately 4.8 million tons of plastic waste enter the world's oceans each year. Studies on marine litter often use an internationally agreed protocol (e.g., ICES International Bottom Trawl Survey, IBTS) to record the collected macro litter (>2.5 cm) in a standardized way. In addition to macrowaste, small plastic particles, so-called microplastics (<5 mm), are of particular interest. Microplastics are of particular concern from an ecological point of view, as they are ingested by marine organisms.
However, hazardous additives from the production of the plastic can enter the environment when it decomposes into microplastics (so-called leaching). Plastic particles also absorb persistent organic compounds (POPs), e.g., polychlorinated biphenyls (PCBs). The hydrophobic organic chemicals adhere to the microplastic and concentrations can reach many times — up to 1 million times higher — than that of the surrounding medium (e.g., water). Like additives, POPs can enter and accumulate in organisms through ingestion of the microplastic. Additives and POPs can have hormonal effects, be carcinogenic or toxic.
Figure 1 shows an overview of MP (source FRONTIER LAB).
This blog post will show you an example of a salmon sample. You will learn about the sample preparation — a difficult part of the analysis — pyrolysis in combination with gas chromatography-mass spectrometry (GC-MS) single quadrupole analysis, followed by a detailed search, and quantification in a special pyrolysis software.
There are different technologies available for the identification of MP, however, if it comes to nanoplastic and/or quantification, pyrolysis GC-MS is the best technology that provides proven, detailed and accurate results.
The analysis starts after sample preparation of biota (food samples) with pyrolysis.
FRONTIER LAB has developed a pyrolysis system for the analysis of MP. With a special data analysis software, it is made easy, even for inexperienced analysts to detect and interpretate polymers. The analytical procedure, including the identification, is automated and results can be obtained within about 30 minutes per sample.
For quantification and a system check, it is necessary to use microplastics calibration standards. Those are commercially available from FRONTIER LAB.
Figure 3 shows the composition of the standard diluted in SiO2, as well as the relevant m/z of the quantifier compounds.
Figure 4 shows the total ion chromatogram (TIC) of the MP standard obtained on an ISQ 7610.
The ISQ 7610 MS is controlled by the Thermo Scientific Chromeleon™ Chromatography Data System (CDS). Chromeleon CDS also delivers the data generated by the MS and allows library search versus commercially available libraries and the option for a quantitative analysis. However, this software is made for MS analysis and doesn’t address the specialties of MP analysis, such as background subtraction. Figure 5 shows a pyrolysis cup and a procedure blank in Chromeleon CDS.
This is a clean blank, however, the procedural blank needs to be subtracted before quantification.
After a net.cdf export, the data are loaded into F-SEARCH MPs MPs 2.0, analytical software for microplastic analysis. What does F-SEARCH MPs do?
Step 1 Adjustment of retention index (RI)
RI is created based on the pyrolyzates of MPCS
Step 2 Creating a calibration file (QFL) (e.g. 3 points, n= 5)
Calibration file is created based on pyrograms of MPCS
Step 3 Qualitative/quantitative analysis
of actual MPs analysis data
Step 4 Interpretation/review of results
What do the results look like? This is shown in Figure 6.
The bar graph is a nice feature, showing the amount/composition of different MP in percent (without background subtraction) at a glance.
Watch this video from FRONTIER LAB:
Here we will show an overview of the sample preparation. The samples what have been analyzed have been provided fully prepared and filtered on a glass fiber filter. Details can be found in the master's thesis.
Chemicals: PDF page 28
Method: PDF page 29-31 (“optimized protocol 1”; 24 h incubation with orbital agitation at 125 rpm, 40 °C, using KOH and detergents in a saline buffer solution)
75 g of salmon for the sample preparation
Note: Bones were removed from the salmon tissue, because they can present a problem when calculating digestion efficiencies. Thus, we experience fewer organic contaminants on the filter for analysis.
An overview of the sample preparation is shown in Figure 7.
Figure 8 shows a TIC of a salmon sample and the picture of a filter before pyrolysis. Since only one sample was available, the filter was cut into two pieces before putting into the pyrolysis cup. It must be taken into consideration, that only 75 g of salmon were used. The normal serving size of a piece of salmon in a restaurant is 200 g, so, the intake into the human body is much higher. Due to the sample preparation, there are limits in the amount of sample that can be used. Otherwise, big reactors that exceed the size of a normal lab would be needed.
Figure 9 shows the EICs (m/z 82 to detect hydrocarbons) of the procedural blank and lowest calibration level 1 in FSEARCH MPs.
Microplastics polyethylene (PE) is not included, or only in a very small amount. The blank must be subtracted in F-SEARCH MPs for correction of the results. This is a very important feature and, in some cases, necessary, however it’s not an automated function.
Figure 10 shows the calibration curves for some of the polymers found in the salmon sample. This is the base for the following quantification of MP in the real sample.
Figure 11 shows results in F-SEARCH MPs. The bar graph allows a rough overview of the MP contained and the amount by percent. On the right side of the figure, the result is shown with and without background correction. Also impressive is the library match, which was set to a minimum of 80 percent. All identified polymers had a greater match then 90 percent.
What we see here is traces in the µg range. The total amount of the microplastics on the filter is around 7.5 µg in 75 g of salmon muscle meat. But, as mentioned, only 75 g of salmon was used. Knowing the amount of salmon that is consumed allows the analyst to conclude how much MP enters the human body. Just by interpolation, if 200 g were consumed, we could reach a level of 20 µg of MP.
This example shows the necessity of a fully automated workflow for the analysis of polymers.
Thermo Fisher Scientific offers — together with Frontier Laboratories — a system that allows the sensitive detection of MP in food samples. Since pyrolysis is sometimes considered as a “dirty” technique, a big advantage is the Vacuum-Probe-Interlock (VPI) on the ISQ 7610, that allows to exchange the ion source after contamination without breaking the vacuum.
There are already many systems that include autosamplers from FRONTIER LAB in the market, for fully automated pyrolysis.
The ISQ 7610 provides the necessary sensitivity to detect µg of MP in food samples. FRONTIER LAB provides the standards, the library and the F-SEARCH MPs software, to perform MP analysis without compromises.
This blog post shared only one example of microplastic analysis in food. There are many more foods that are contaminated. In a later blog post this year, we will show the challenges with Fleur de Sel (a rare type of sea salt) as sample matrix. And as many matrices are out there, just as many sample preparations are needed. In general, a conclusion might be made, that the sample preparation is the most time-consuming step compared to the analysis itself. And unfortunately, there is not one single solution for all kind of biota.
The pyrolysis followed by GC-MS analysis is a proven standard for microplactics analysis. When the sample comes on a filter, it doesn’t matter whether it comes from water (environmental) or is a biota sample. Well, biota have their own challenges, but you will learn more about that in Pyrolysis Part 2 in June of 2023.
Mark your calendar for the upcoming webinar "Pyrolysis GC-MS for the analysis of microplastic in biota samples."
May 11, 2023: Pyrolysis GC-MS for the analysis of microplastic in biota samples
May 9, 2023: Auf Deutsch -- Pyrolyse-GC-MS für die Analyse von Mikroplastik in Biota-Proben
I would like to thank Dr. Michael Soll, European Business Development Manager, Frontier Laboratories, Essen, Germany, and Dr. Klaus Schrickel, Senior Application Scientist GC and GC-MS, Thermo Fisher Scientific, Dreieich, Germany, for their help and input on the project.
Many thanks for an interesting post!
Well there goes my desire to eat fish for dinner! Also, we need hemp - not plastics!! Thanks for sharing this post.
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.