6 Materialchemie
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While plastics have become indispensable in our daily lives over the last decades, the input into the environment has been increasing concurrently. Plastics often end up in the environment because of intensive use and poor waste management practice. They are subjected to aging and fragmentation and finally be deposited as microplastic particles or in short microplastics (MP). MP are defined as particles originating from synthetic polymers between 1 µm and 5 mm.
Although the pervasive abundance of MP in aquatic environments has been demonstrated comprehensively, less is known about the occurrence and fate of MP in terrestrial ecosystems. It is still unclear if soil functions as a MP source or a sink for aquatic environments. MP can either be transported into water bodies by soil erosion or be retained in soils. The few studies published are not comparable because of non-existent harmonized and standardized methods for sampling, sample preparation, and analysis.
For an assessment of a potential exposure situation of MP, the determination of a mass content in the soil is crucial. Consequently, spectroscopic methods like Raman or FTIR are not suitable, as they deliver information about the shape and size of individual particles. Therefore, we show the application of ThermoExtractionDesorption-GasChromatography-MassSpectrometry (TED-GC-MS) for MP analysis in the soil. In this method, the soil sample is heated up to 600 °C in a nitrogen atmosphere. The decomposition gases are sorbed on a solid phase, then transferred to a GS-MS system where they are desorbed, separated and identified. The method allows the rapid identification of individual polymers through the detection of specific decomposition products, but also the quantitative determination of the MP mass. Besides thermoplastics, elastomers originated from tire abrasion, can be detected.
In the present study, several terrestrial ecosystems in south-west Germany were systematically sampled. Subsequent sample preparation included sieving in fractions of 5-100 µm, 100-1000 µm, and 1-5 mm. MP were extracted by density separation using ZnCl2 solutions. The detection was done by TED-GC-MS measurements. Data of agricultural areas and floodplains are presented exemplarily. A quantitative assessment of highly occurring MP from littering as well as tire abrasion is conducted.
The talk is about microplastics in soil. Some results were presented with mainly state of the art according to microplastics in standardization.
Plastics and rubber are used in many applications, such as packaging, building, construction and mobility. Due to their favourable properties like light weight, flexible processing and low costs their production and consequently their input into the environment has increased significantly over the last decades. In the environment, oxidation processes and mechanical abrasion lead to the decomposition of these plastics into small fragments, called microplastic (< 5 mm). By definition, microplastics only involve thermoplastics and duroplastics but elastomers made out of synthetic polymers (e. g. styrene butadiene rubber), modified natural polymers (e. g. natural rubber) and products of synthetic polymers (e. g. tires) are also part of the current microplastic discussion. The main entry pathway of rubber into the environment is the wear of used tire treads in road traffic. Lassen et al. showed that 60 % of the microplastic emissions in Denmark into the environment come from secondary microplastics generated by tires. Rain events can cause microplastic and rubber to get from the street into the street inlets. Depending on the sewage system, these waters are sometimes not cleaned in the sewage treatment plants and reach the surface waters untreated.
To analyse microplastic particles in samples, mainly FTIR or Raman spectroscopic methods are applied at present. Rubber or tire particles in environmental samples cannot be analysed by these methods, because the added carbon black leads to annoying absorption and fluorescent effects.
We developed a thermoanalytical method, the so-called TED-GC-MS (thermal extraction desorption gas chromatography mass spectrometry), which allows the simultaneous detection of microplastic and tire wear with almost no sample preparation in about 2.5 h. The TED-GC-MS is a two-step analytical method which consists of a thermobalance and a GC-MS system. Up to 50 mg of an environmental sample is heated up to 600 °C in a nitrogen atmosphere. During pyrolysis, between 300 and 600 °C polymer-specific decomposition products are produced and collected on a solid phase. Afterwards the substances are desorbed, separated and analysed using the GC-MS.
The aim of the present work is to present the TED-GC-MS as a time efficient screening method to quantify the industrial most relevant polymers in street run-off samples. Analytical challenges in the determination of polyethylene (PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET) and polyamide (PA), polymethyl methacrylate (PMMA) and styrene-butadiene-rubber (SBR) as a component of tire wear are honestly discussed.
The study area is a 200 m long section of the Clayallee in Berlin, a representative typical urban catchment area. The road run-off in this section flows through the gullies directly into a sample chamber, which directs the runoff in an open channel to the rainwater sewer of this area. The sample chamber allows a sample to be taken directly from the road run-off without mixing with the run-off from other areas. The sample chamber is equipped with an automatic sampler. The automatic sampler is controlled by a conductivity sensor to detect the storm event at an early stage. The sensor gives the sampler a signal to start the sampling program when it gets in contact with water and reaches a certain conductivity threshold. The capacity of the sample container is 100 l and the maximum delivery of the automatic sampler is 2.8 l/min.
Afterwards, the water was pumped through various stainless-steel sieves with a diameter of approximately 20 cm and mesh widths of 500, 100, 50 μm. The obtained solids were steam sterilized, freeze-dried and measured with the TED-GC-MS.
The results of the TED-GC-MS-measurements are summarized in Figure 1. It shows the polymers which were detected in 1 mg of the dry masses of various street run off samples obtained during a period of 1.5 years. We detected PMMA, PS, PP, PE and SBR, as a component of tire wear in the samples. The quantification of the polymers leads to amounts of PS, PP, PE and SBR between 0 µg and 10 µg. PMMA was only detected in traces.