Comparing a picture taken with visible light and a fluorescence picture brings the truth to the fore: The red dots in the latter (picture at the bottom) are microplastic particles in the digestive tract of the animal.

The TDS is well suited for performing serial pyrolysis GC/MS on a small number of samples. When the TDS is fitted with a special module, the PM 1, it can be used for both thermal desorption and pyrolysis on the same sample. When a larger number of samples need to be analyzed by serial pyrolysis GC/MS, the Thermal Desorption Unit (TDU) in combination with the MultiPurpose Sampler (MPS) shown here is the best option.

Material and Environmental Analysis

A Sea of Polymers

Microplastic particles in the marine environment could have a bigger impact than previously thought: To get an idea of the extent of the plastic waste pollution in the marine environment, and of how quickly, if at all, it breaks down, science must rise to the challenge and find ways to determine qualitatively and quantitatively what is floating amongst the aquatic wildlife that makes up a good part of our food supply. Pyrolysis GC/MS has been found to be a useful tool for the characterization of microplastics in environmental samples.

By Guido Deussing

During the International Coastal Cleanup in 2013, 648,015 volunteers worked along a stretch of around thirteen thousand miles of ocean coastline to remove more than 5,500 tons of waste. The top ten waste items were: Cigarette butts (913 tons), paper candy wrapping (794 tons), plastic bottles (426 tons), plastic caps and lids (385 tons), plastic soda straws (252 tons), standard plastic shopping bags (200 tons), glass bottles (179 tons), other plastic bags large and small (176 tons), paper bags (167 tons), and beverage cans (154 tons) [1].

There is no way to correlate the recorded amount of these different types of waste to the total amount of waste released annually into the oceans, but it does paint a grim picture if one considers that we are only looking at the tip of the iceberg. Another large source of pollution is plastic micro beads (less than 5 millimeters in diameter) used in personal care products mostly as exfoliating agents. During use they enter the waste water stream; however, they pass though waste water treatment plants and end up in our water ways and oceans where fish ingest them at an alarming rate. It seems safe to assume that plastics are one of the major sources of environmental pollution. Not just environmental action groups, but also polymer material producers see cause for concern and the need for action as an increasing number of scientific journal papers and reports are referenced in the press documenting the detrimental effects of microplastics on the environment [2]. What then needs to be done – and what can the individual consumer do to avoid contributing to microplastics pollution or even to help improve the situation?

A responsible and sustainable use of polymer materials is a good start for individual consumers, companies and organizations alike. On a grander scale, well organized collection and recycling systems must be available. Various projects have been initiated with the aim of reducing the problem of waste in the oceans [2-6]. In the meantime, inland waterways and water bodies are also becoming the focus of attention since they seem to be impacted significantly as well [7-8].

Obviously, for any long term strategy to have a chance of success, it needs to be built on solid and reliable data. At this time, too little is known about transport routes, transformation processes, as well as effects and whereabouts of polymer residues in the environment. The scientific community is working to close this knowledge gap with a special focus on microplastics [7, 9-12].

The big problem posed by the tiniest particles

Polymer materials are very rugged. Even when exposed to energy-rich solar radiation, chemicals, mechanical force, or microbial attack, they never really seem to degrade or disappear from the environment. Sooner or later, polymer materials become brittle and are ground into ever finer particles until they end up in the microplastics range.

Microplastic particles, due to their small size, ranging from a few micrometers to a few millimeters, and their irregular shape and color, are often mistaken for food and are ingested by aquatic organisms and sea birds.

Increasingly, substantial amounts of polymer fragments are being found in the digestive tracts of dead seabirds. Whether the microplastic particles caused the death of the animals is uncertain. Nevertheless, it is not unreasonable to assume that animals which often ingest plastic material could suffer from malnutrition. Scientists predict that in 2050 we will find plastic residues in around 80 percent of all seabirds. Further, microplastic particles can contain unhealthy or toxic additives as well as pesticides, heavy metals or other toxins that are concentrated in the polymer from the surrounding environment. Since humans are at the top of the food chain this could eventually become a threat to us as well.

International efforts to learn more

The European Commission’s Marine Strategy Framework Directive (MSFD) [13] focuses on protecting the seas and on managing natural marine resources efficiently. According to the MSFD, the type and composition of micro particles, and microplastic particles in particular, need to be characterized. This is exactly what researchers at the Universities of Osnabruck and Darmstadt, both located in Germany, have set out to do. As part of their research [10, 11], Professor Elke Fries and her colleagues investigated marine microplastic particles, which they had extracted from sand samples collected on the North Sea Island of Norderney, Germany. In order to determine the material composition of the microplastic particles collected as well as any additives used or pollutants that had been absorbed by the particles, Prof. Fries and her colleagues turned to pyrolysis-GC/MS as the first scientists ever to do so for this type of sample [10-12]. Previously, mainly spectroscopic methods had been used to establish the structure and composition of polymers, Fries et al. wrote, and organic additives were extracted using supercritical fluid extraction or Soxhlet extraction. For polymer particles that are not easily dissolved, extracted or hydrolyzed, pyrolysis GC/MS can be a highly useful complementary technique.

Pyrolysis GC/MS serves to provide structural information about macromolecules based on the fragments formed in a controlled thermal decomposition process [14].

Serial pyrolysis is performed in two or more steps. Initially, volatile compounds are thermally extracted from the sample at a relatively low temperature. The technique is referred to as thermal desorption. Following the first step, the same sample is pyrolyzed at a higher temperature; ideally both steps are performed without the need to reconfigure the instrument. By collecting GC/MS data for both steps, organic additives and pyrolysis breakdown products can be determined during a single sample run. As Prof. Fries et al. note, this is a very efficient means of gathering information on both polymer type and the additives it contains.

For their work, the researchers used a 7890 GC (Agilent Technologies) equipped with a Cooled Injection System, PTV-type inlet (GERSTEL CIS) and a Thermal Desorption System (GERSTEL TDS) fitted with a Pyrolysis Module ( GERSTEL PM 1). This instrument combination is well suited for performing pyrolysis and serial pyrolysis manually. If a larger number of samples need to be analyzed, the process can readily be automated using the GERSTEL MultiPurpose Sampler (MPS) in combination with a GERSTEL Thermal Desorption Unit (TDU) and the GERSTEL PYRO module.

Technical and application details

Fries et al. performed the analysis as follows: A microplastic particle was placed in a pyrolysis sample tube and transferred to the PM 1. The PM 1 was then inserted into the TDS and sealed using the cone locking mechanism. The TDS temperature was set to 40 °C and heated at a rate of 10 °C/min to 350 °C (10 min); during this period, volatile compounds were thermally extracted from the matrix and cryofocused in the CIS at -50 °C; subsequently, the CIS was heated from -50 °C at a rate of 12 °C/min to 280 °C (3 min) and the analytes transferred to the GC column (30 m HP 5MS with 250 μm ID and 0.25 μm film thickness). The GC oven temperature program used was 40 °C initial temperature; 15 °C/min to 180 °C; 5 °C/min to 300 °C (12 min). Helium carrier gas was used. After the GC/MS run for the volatile compounds had been completed, the sample was pyrolyzed as follows: The TDS was set to a starting temperature of 60 °C (1 min) and heated at a rate of 180°C/min to 350 °C. Pyrolysis was then performed in the PM 1 at 700 °C (1 min).

The pyrolysis fragments formed were transferred to the CIS and cryofocused using liquid nitrogen. Following the pyrolysis step, the fragments were then transferred from the CIS to the GC column using a temperature program as described above. Mass selective detection followed using a MS 5975C from Agilent Technologies. In addition to the chromatogram of the volatile compounds, the pyrogram containing the pyrolysis products was collected.

Obtaining valuable information efficiently

Based on mass spectral libraries as well as comparison of retention times and mass spectra of analyzed standards, Fries et al. were able to identify a variety of plastic additives in the microplastic particles found on the North Sea island of Norderney. Among these were plasticizers, including the phthalates DEHP, DBP, DEP, DIBP and DMP, the antioxidant 2,4-di-tert-butylphenol, and aromatic compounds such as benzaldehyde, which is added as fragrance to cosmetics and to polymers directly.

The polymer type was determined by the researchers by comparing pyrograms from the collected microplastic particles with those from standard polymers. They identified polyethylene (PE), polypropylene (PP), polystyrol (PS), polyamide (PA) as well as chlorinated and chlorosulfonated PE.

Overlay pyrograms enable easy comparison of standard polymers (Purple: Standard low density Polyethylene [LDPE]) with those found in environmental samples (black: Polyethylene C.).

Concerning their method for the determination of organic polymer additives, the researchers came to the following verdict: Compared with traditional solvent extraction based methods, the serial pyrolysis method offers the advantage of determining both the volatile compounds in the material, including additives, and the type of polymer in a single process step – without having to use solvents and without background contamination from the material. The pyrogram is free of interfering compounds that offer no structural information since these have been removed in the thermal desorption step.

Final words from the researchers

Serial pyrolysis GC/MS has sufficient sensitivity to determine plasticizers, antioxidants, and fragrances in microplastic particles with a mass of less than 350 μg. This makes it possible to determine the chemical, toxicological or endocrine disrupting risk potential of such particles. According to Fries et al., Serial pyrolysis could be used for the implementation of the Marine Strategy Framework Directive (MSFD) by enabling the determination of the chemical composition of microplastic particles. Just for good measure, in addition to the organic compounds, the researchers also determined the following inorganic polymer additives: Titanium oxide, as well as barium-, sulfur- and tin compounds [10].

References

[1] http://www.oceanconservancy.org/our-work/marine-debris/iccdata-2014.pdf (14.11.2015)
[2] Marine litter solutions (www.marinelittersolutions.com, 14.11.2015)
[3] Marine Debris Solutions (www.marinedebrissolutions.com, 14.11.2015)
[4] Fishing for litter (www.nabu.de/themen/meere/plastik/fishingforlitter, 14.11.2015)
[5] The Ocean Cleanup (www.theoceancleanup.com, 14.11.2015)
[6] E. R. Zettler, T. J. Mincer, L. Amaral-Zettler, Life in the „Plastisphere“: Microbial Communities on Plastic Marine Debris, Environmental Science Technology 47 (2013) 7137-7146
[7] H. K. Imhof, N. P. Ivleva, J. Schmid, R. Niessner, C. Laforsch, Contamination of beach sediments of a subalpine lake with microplastic particles, Current Biology 23 (2013) 867-868
[8] M. Wagner, C. Scherer, D. Alvarez-Muñoz, N. Brennholt, X. Bourrain, S. Buchinger, E. Fries, C. Grosbois, J. Klasmeier, T. Marti, S. Rodriguez-Mozaz, R. Urbatzka, A. D. Vethaak, M. Winther-Nielsen, G. Reifferscheid, Microplastics in freshwater ecosystems: what we know and what we need to know. Environmental Sciences Europe 26 (2014) 12
[9] A. Lechner, H. Keckeis, F. Lumesberger-Loisl, B. Zens, R. Krusch,M. Glas, M. Tritthart, E. Schludermann, The Danube so colourful: a potpourri of plastic litter outnumbers fish larvae in Europe’s second largest river, Environmental Pollution 188 (2014) 177- 181
[10] E. Fries et al., Identification of polymer types and additives in marine microplastic particles using pyrolysis-GC/MS and scanning electron microscopy, Environmental Science: Processes Impacts 15 (2013) 1949-1956
[11] J. Willmeyer, Analysis of marine plastic debris using thermodesorptionpyrolysis-gas chromatography/mass spectrometry (TD-Pyr-GC/MS), Bachelor-Arbeit, Institut für Umweltsystemforschung, Universität Osnabrück, September 2012
[12] J. Henning Dekiff, Occurrence and spatial distribution of microplastics and organic additives in sediments from the Island Norderney, Master-Arbeit, Institut für Umweltsystemforschung, Universität Osnabrück, November 2012
[13] Marine Strategy Framework Directive, http://ec.europa.eu/environment/marine/eu-coast-and-marine-policy/marine-strategy-framework-directive/index_en.htm
[14] E. Kleine-Benne, B. Rose, Versatile automated pyrolysis GC combining a filament type pyrolyzer with a thermal desorption unit, GERSTEL Application Note 11/2011 (www.gerstel.de/pdf/p-gc-an-2011-04.pdf)

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