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Polymers found in seabirds’ stomachs: Comprehensive analysis applying FTIR and EDX technology

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  • Published: Nov 1, 2015
  • Source: Shimadzu Europa GmbH
  • Categories: Infrared Spectroscopy
thumbnail image: <font size=3>Shimadzu Europa</font><br />Polymers found in seabirds’ stomachs: Comprehensive analysis applying FTIR and EDX technology

Albert van Oyen1, Marion Egelkraut-Holtus2, Jan Andries van Franeker3

1Carat GmbH, Harderhook 20, 46395 Bocholt, Germany
2Shimadzu Europa GmbH, Spectroscopy, Duisburg, Germany
3IMARES Wageningen UR, Landsdiep 4 't Horntje, Texel, Netherlands

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While polymers contribute to the convenience of modern life, they also threaten the environment and life, particularly in oceans, as plastic waste. Polymers decompose very slowly. Through physical impact they reduce in size and degrade into fragments of oxidized polymers. Such fragments are found “everywhere” today. The ideal grinder of polymers is the sea with its permanent activity and movement on beaches, in water and on the ocean ground - it is quite simply a huge mill.

The effect of maritime animals or birds picking up polymer fragments of all sizes is well recognized all over the world. Especially fish are victims of human waste, but also seabirds, such as fulmars from, in this case, the North Sea region [1, 2], which carry plastic waste in their stomachs.

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Figure 1: A young Fulmar bird’s stomach and its content. It was analyzed at IMARES Fulmar Workshop (Institute for Marine Resources & Ecosystem Studies) in October 2014 on the island of Texel, Netherlands.

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Figure 1 shows the content of the two stomachs of a fulmar. The fulmar pre-digests in the large part of its stomach (proventriculus), and hard parts are ground in the smaller stomach (gizzard). In the smaller stomach a variety of polymer particles and harder particles from different sources were found. Figure 2 shows a comparison of the polymer content from a fulmar stomach with the equivalent amount for a human stomach.

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Figure 2: Comparison of the average content of plastics in a fulmar’s stomach and a human stomach. On the left:
0.31 g plastics in the stomach of a 0.7 kg bird. Right from the tweezers: the extrapolated volume of more than 30 g of plastics in a 70 kg human’s stomach.

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Analysis of particles and techniques in use

The plastic content of one fulmar’s stomach was identified using three techniques:

  • Visual and stereo-microscopy
  • FTIR-ATR and identification with software
  • EDX-RF, element analysis and RoHS quantification (Cd, Pb, Hg, Cr and Br)

All three techniques are non-destructive and fast. The stereo-microscope visualizes the surface whereas FTIR-ATR penetrates the surface by approx. 1 to 2 µm; EDX penetrates even more deeply into polymers, on the scale of millimeters.

Due to its two separate optical paths with two objectives and eyepieces, the stereo-microscope provides a three-dimensional visualization of the sample being examined.

Using the FTIR infrared spectroscopic measuring technique, all types of materials and their appearances can be measured. Combined with a single-reflectance ATR unit (Quest™), the sample can be measured directly.

With EDX-RF it is possible to screen for the presence of any elements and some of the heavy metals (Cd, Pb, Hg, Cr), and halogen bromine can be quantified.

Measurements with stereo-microscope

The stereo-microscope helps to carry out a visual inspection of the particle, its color, size and dimension, and further characteristics. The analysis of two samples from the fulmar stomach content are shown in Figure 3. The size of the particles is in the lower millimeter range. The grid in the background shows a scale sized 1 by 1 mm. The color of the pieces is greenish and cream-white. The shapes of the particles are different. The surfaces are rough. The details of the observation are described on the right hand sides of the pictures in Figure 3.

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Figure 3: Microscope images from two samples and the visual inspection results.

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Stereo-microscopy allows the classification of the samples. Such analysis is helpful to differentiate between meso- and micro-plastics (> 5 mm versus < 5 mm). On the surface of some plastic fragments micro-plastics were found. It is not always possible to conclude that the additional micro-plastics are stomach content or from a different source, for instance clothing. Another phenomenon was the obvious fragmentation of samples. One fragment can possibly break up into a large number of smaller pieces.

Measurements with FTIR-ATR

Whereas stereo-microscopy helps to classify the fragments, FTIR-ATR identifies the particles or fragmentations. Depending on their sizes, a decision has to be made between infrared microscopy for particles measuring micrometers or the ATR technique for particles measuring millimeters. The ATR technique is a surface identification method, the penetration depth of the infrared radiation into the sample surface is about 2 µm (tables with more precise values for specific wave numbers, incident angle and crystal material are available). In this case, a diamond window was part of the single-reflection ATR unit.

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Figure 4: Graph of the FTIR-ATR technique showing the penetration depth of infrared radiation into the sample surface and the calculation formula (a) for the penetration depth. The depth depends on the refractive index and incident angle of the crystal window used for the application (45° incident angle and diamond crystal in this application).

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The FTIR-ATR spectra were identified using standard library software. Modern FTIR-ATR software uses mathematical algorithms for comparison to identify the unknown samples. From a series of particles and fragments, one was selected for the presentation of the infrared result (see Figure 5).

A micro-plastic named FAE-2011-X86-005 with a size smaller than 5 mm was analyzed.

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Figure 5: Stereo-microscope analysis of sample FAE-2011-X86-005 and result of visual analysis.

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Figure 6: Search result in a polymer library for the maritime micro-plastics.

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The “standard” library is based on industrial samples. However, the surface of plastics in the environment or fulmar stomach can differ from clean industry pellets and products. In addition, the theoretical results from a library can differ from practice. Figure 6 shows that a polyethylene was found as the first match for the most intense signals, which is correct. A more precise analysis finally showed a good match with EVA (ethylene vinyl acetate copolymer).

For a correct analysis, water and protein as well as fat are needed to obtain a full identification of weak or strong additional signals which can occur in the FTIR spectra. Regarding the EVA result it has to be stated that EVA (ethyl-vinyl acetate) is mainly used in glues. It is a coupling agent and has a high VA content. It is found in items with the recycling label LDPE (No. 4). Pure EVA film is used in the solar industry. EVA with a low VA content is used in plastic sheets.

Measurements with EDX

With EDX-RF, it is possible to screen the sample for elements. Smaller or light elements (< 13 Al) are not detected. After complex calibration (plastic yields other results than e.g. metals) it is possible to quantify the elements, such as Cd, Pb, Hg, Cr and Br (restrictions in the electronic EU RoHS directive 2011/65). In the past, cadmium (highly toxic) was found in beach pellets and fulmar stomach fragments. In the analyzed stomach, lead was found in a plastic fragment (FAE-2011-x86-001); the concentration: 130 ± 20 ppm. RoHS restricts lead in electronics to a concentration of > 1000 ppm. At present, the hazard potential of a plastic fragment (130 ± 20 ppm) in a fulmar stomach is unknown.

Conclusion

Real-life samples rather than just theoretical samples were analyzed using stereo-microscopy, FTIR-ATR, and EDX-RF. The combination of these three methods provides a comprehensive overview of an unknown sample of which neither the source is known nor the effects to the polymer’s lifespan. Stereo-microscopy provides a 3D impression of the sample, FTIR-ATR penetrates the surface by approx. 1 to 2 µm, and EDX radiation penetrates even deeper into the sample being examined. Applying FTIR-ATR and EDX-RF, most of the polymers and elements are identified.

Literature

[1] Fulmar litter EcoQO monitoring in the Netherlands – Update 2012 and 2013, J. A. van Franeker, S. Kühn, E.L. Bravo Rebolledo & A. Meijboom, Report number C122/14, IMARES Wageningen UR.

[2] Tierwelt leidet an Plastikabfällen, FTIR-Analyse von Polymeren in Mägen von Eissturmvögeln; LABO 01.04.2015, S. 18, Dr. J. A. van Franeker, Albert van Oyen, Marion Egelkraut-Holtus.

Shimadzu Europa GmbH
Albert-Hahn-Str. 6–10, 47269 Duisburg, Germany
www.shimadzu.eushimadzu@shimadzu.eu

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