DE102019106806A1 - Method for determining the microplastic content in environmental samples - Google Patents

Abstract

A method for determining a microplastic content of an environmental sample, comprising: providing a particle fraction of the environmental sample; Providing a pyrolysis gas by heating the particle fraction in a defined temperature interval at a defined heating rate, the particle fraction being heated in an inert gas atmosphere; Burning the pyrolysis gas in an oxygen-containing atmosphere and determining a total heat release (THR) during the burning of the provided pyrolysis gas; and assigning the determined total heat release to a microplastic content of the environmental sample.

Description

Technical area

The invention is in the field of environmental analysis and relates to stakeholders in the field of microplastics, in particular users of routine methods for estimating and / or determining the microplastic content in environmental samples, for example for environmental measurement technology in water, waste and environmental engineering.

Prior art

The presence of microplastics, i.e. plastic particles smaller than 5 mm, is increasingly being observed in the environment [1]. Microplastic particles are used as a product additive e.g. B. in cosmetic articles introduced directly into the environment or arise from larger plastic fragments or products during chemical, physical, biological or mechanical degradation. In this context, a plastic particle is understood to mean both a flat structure, for example a fragment of a film or a thin-walled molded part, a synthetic or semi-synthetic fiber or the fragment of a fiber, but also a spherical and an irregularly shaped, e.g. polyhedral particle or fragment of a Molded part, comprising a material consisting predominantly of semi-synthetic or synthetic thermoplastic, thermosetting or elastomeric polymer materials. The size specification “less than 5 mm” refers to the longest dimension of the particle. Corresponding particles are typically obtained from a corresponding sample using a sieve with a mesh size of 5 mm and smaller. A mean arithmetic diameter of the particles of the particle fraction is thus typically below 5 mm. In particular, a maximum geometrical expansion of the particles of the particle fraction examined is 5 mm. The term plastic used here includes not only synthetic thermoplastic and thermosetting polymer materials, but also modified natural polymers (e.g. natural rubber, cellophane, viscose), as well as products that are predominantly based on polymers (e.g. synthetic textiles, tires, paints). Microparticles can be created from these materials, which are identified as polymers and are all colloquially referred to as microplastics or MP for short. So far, the risks for humans, animals and the environment caused by MP are still unclear and are discussed controversially [2].

Known processes for the detection of MP from complex environmental samples (water, solids, air, biota) are based on the analysis of filtrates or directly obtained solid samples. Mainly spectroscopic (microscopic) methods are used, in which specific, spectroscopic structural features of the MP are assigned to different types of polymer [3]. MP particle numbers, sizes and geometries can be determined depending on a defined sample volume (e.g. water filtrate or air sample) or on a defined solid mass (e.g. sediment, soil or compost sample). However, it is not possible to determine the mass contents of MP in an environmental sample. It is also disadvantageous that these methods, depending on the environmental matrix, require several time-consuming sample preparation steps, which extend over days to weeks per measurement in order to reduce organic and inorganic components of the environmental matrix in the interests of meaningful results. The identification of the particles can be automated, but the analytical recording of representative filter surfaces or sample fractions is still very time-consuming. It typically requires several hours per measurement and includes the handling and evaluation of very large amounts of data.

Thermal-analytical methods are also known [4]. Here, specific decomposition products of the MP or the synthetic polymers are recorded and assigned to the MP content in the sample. MP Particle numbers, sizes and geometries cannot be determined using this detection method, but the mass content of MP in an environmental sample can be determined. Depending on the sampling and sample preparation, these can be assigned to specific size classes and thus allow an assessment of the size classes that occur. Reliable identification and quantification requires around 2-4 hours per measurement. In view of the large number of samples produced during environmental monitoring, however, this period is also clearly too long.

There are also initial efforts to derive MP by means of balancing methods based on an elemental analysis with regard to carbon, nitrogen, oxygen and sulfur, but a prior separation of the organic matter is absolutely necessary, for example for the analysis of water samples. As can be seen, an automatic sample analysis can only be implemented with great effort.

Against this background, the use of the techniques described above in routine processes is at least questionable or completely ruled out. So there are no standardized test methods in environmental analysis, including sampling, preparation and MP detection, for the reliable and rapid detection of MP in environmental samples that meet the requirements mentioned. However, the ubiquitous findings to be observed require a systematic and reliable recording of MP. Only in this way can MPs' entry paths into the environment and its whereabouts be traced, and the necessary measures to curb its spread can be initiated.

It is therefore the object of the present invention to provide a method which enables a quantitative determination of the mass content of MP in environmental samples, reduces the time and costs for this compared to previously known methods, and which can be automated.

Summary of the invention

This object is achieved by a method according to claim 1. Further embodiments, modifications and improvements emerge from the following description and the appended claims.

• - Bereitstellen einer Partikelfraktion der Umweltprobe;
• - Bereitstellen eines Pyrolysegases durch Heizen der Partikelfraktion in einem definierten Temperaturintervall mit einer definierten Heizrate, wobei das Heizen der Partikelfraktion in einer Inertgasatmosphäre erfolgt;
• - Verbrennen des Pyrolysegases in einer sauerstoffhaltigen Atmosphäre und Bestimmen einer totalen Wärmeabgabe (THR) während des Verbrennens des bereitgestellten Pyrolysegases; und
• - Zuordnen der bestimmten totalen Wärmeabgabe zu einem Mikroplastikgehalt der Umweltprobe.

In particular, a method for determining a microplastic content of an environmental sample is proposed. The procedure includes:

• - providing a particle fraction of the environmental sample;
• - providing a pyrolysis gas by heating the particle fraction in a defined temperature interval at a defined heating rate, the particle fraction being heated in an inert gas atmosphere;
• - Burning the pyrolysis gas in an oxygen-containing atmosphere and determining a total heat release (THR) during the burning of the pyrolysis gas provided; and
• - Assignment of the determined total heat emission to a microplastic content of the environmental sample.

The use of the method described above for the analysis of environmental samples to determine their MP content is also proposed. In particular, it is proposed to use the determination of the heat of combustion by means of a Pyrolysis Combustion Flow Calorimeter (PCFC) or a suitable micro-combustion calorimeter (MCC) in order to determine the MP content of an environmental sample, in particular a filtrate of a water or air sample, or a solid sample ( e.g. soil, compost, sewage sludge, sediment, biota, human and animal waste).

It is also proposed that the Pyrolysis Combustion Flow Calorimeter (PCFC), or micro-combustion calorimeter (MCC) suitable for this purpose, for determining the MP content of environmental samples, in particular the filtrate of a water or air sample, or a solid sample (soil, Compost, sewage sludge, sediment, biota, human and animal waste).

PCFC is a method for measuring the heat release rate of samples on a milligram scale, or a specially developed micro-combustion calorimeter (MCC). PCFC or MCC designate devices that work according to an identical measuring principle. Both terms can be used and denote the same device type, in the further course of the text the term PCFC is used. The method allows the solid-state and gas-phase processes of flaming combustion to be mapped separately in a non-flaming test by rapidly controlled pyrolysis in an inert gas stream, followed by high-temperature oxidation (combustion) of the volatile pyrolysis products in excess of oxygen. The volatile pyrolysis products are burned (high-temperature oxidation) in a separate combustion chamber (combustor). These devices and the measuring methods based on them have so far been used exclusively for research and development of refractory or fire-reducing materials. [5] No temperature intervals limited by upper and lower values are used to determine the effective heat of combustion. In the present case, in the original sense of the word, an interval is a closed, i.e. continuous, understood as the range between two fixed values.

Furthermore, the determination of the MP content of an environmental sample by determining the effective heat of combustion of a pyrolysis gas detected when the environmental sample is heated within a temperature interval is proposed.

Detailed description

According to one embodiment, a method previously only used to investigate the flammability and the burning behavior of materials - the pyrolysis combustion flow calorimetry, or the use of a corresponding measuring device - a pyrolysis combustion flow calorimeter (PCFC) or a micro-combustion calorimeter (MCC) - proposed for the determination of the MP content of environmental samples.

• - Bereitstellen einer Partikelfraktion der Umweltprobe;
• - Bereitstellen eines Pyrolysegases durch Heizen der Partikelfraktion in einem definierten Temperaturintervall mit einer definierten Heizrate, wobei das Heizen der Partikelfraktion in einer Inertgasatmosphäre erfolgt;
• - Verbrennen des Pyrolysegases in einer sauerstoffhaltigen Atmosphäre und Bestimmen einer totalen Wärmeabgabe (THR) während des Verbrennens des bereitgestellten Pyrolysegases; und
• - Zuordnen der bestimmten totalen Wärmeabgabe zu einem Mikroplastikgehalt der Umweltprobe.

In particular, a method for determining a microplastic content of an environmental sample is proposed. The procedure includes:

• - providing a particle fraction of the environmental sample;
• - providing a pyrolysis gas by heating the particle fraction in a defined temperature interval at a defined heating rate, the particle fraction being heated in an inert gas atmosphere;
• - Burning the pyrolysis gas in an oxygen-containing atmosphere and determining a total heat release (THR) during the burning of the pyrolysis gas provided; and
• - Assignment of the determined total heat emission to a microplastic content of the environmental sample.

A continuous transfer of the pyrolysis gas released from the particle fraction with the aid of an inert gas into a separate combustion chamber, for example with an inert gas stream, typically takes place simultaneously with the heating. The pyrolysis gas is burned directly in the combustion chamber with a defined supply of oxygen or synthetic air, the amount of oxygen used for combustion being assigned to the defined temperature range, i.e. the temperature interval in which the burned pyrolysis gas was obtained through heating.

The heating and thus the pyrolysis and the provision of the pyrolysis gas advantageously take place under temperature-identical conditions, in particular at a constant heating rate. The method can advantageously be carried out using a commercially available device, in particular a PCFC or an MCC device. According to typical embodiments, the combustion takes place at a constant temperature in that the temperature of the combustion chamber is kept constant. For example, the temperature of the combustion chamber can be set to a constant 900 ° C. The particle fraction never comes into contact with oxygen during heating; only the pyrolysis gas released within the defined temperature range is burned in an oxygen-containing atmosphere. This enables an increased precision of the MP determination, for example also because solid phase oxidation processes possibly contained in the particle fraction, humic substances, sugars or amino acids cannot falsify the result.

According to a further embodiment, the temperature interval comprises a temperature range that extends over 100 to 300 K or over 100 to 200 K, a corresponding temperature window is 100, 150, 200, 250 or up to 300 degrees wide. For example, the temperature window in which the total heat release rate is determined can also only be 100, 125, 150, 175 or 200 degrees wide.

Advantageously, the pyrolysis of individual MP grades does not extend over a significantly broader range. The temperature window can typically be narrowly defined if the type of MP expected, for example PE, PS or PP, is known and only a concentration of the relevant polyolefin is to be monitored. A typical application scenario is, for example, the monitoring of industrial wastewater from a specific polluter or the monitoring of water treatment systems that are downstream of industrial processes.

According to a further embodiment, the selected temperature interval comprises the temperature range from 300 to 600 ° C, 350 to 550 ° C, or 350 to 500 ° C.

The pyrolysis of polymers typically found as microplastics (polyolefins such as PE, PS and PP and elastomers) advantageously takes place within this temperature range. It should be noted, however, that - depending on the heating rate used in accordance with the method - the pyrolysis of MP can also start at lower temperatures. A heating rate significantly lower than 1 K / s, for example a heating rate of 30 K / min (0.5 K / s) or 15 K / min (0.25 K / s), can trigger pyrolysis at temperatures as low as 200 ° C of olefins. Against this background, the temperature interval can also be lower Temperatures include and, for example, be selected from the temperature range of 200-450 ° C, the range of 250-450 ° C or the range of 275-500 ° C.

According to a further embodiment, the mass of the particle fraction provided is between 1 μg and 1 kg, in particular a mass between 1 mg and 10 g, or even 1 mg and 30 mg.

The specified masses advantageously correspond to the microplastic contents found in the environmental analysis of solid and liquid samples.

According to a further embodiment, the combustion takes place in a combustion chamber with, preferably continuous, supply of oxygen or a mixed gas or synthetic air with a known oxygen concentration.

The proposed method enables the selection of a separate combustion chamber with a defined gas supply. Typically, the spatial shape of the combustion chamber is fluidically adapted so that no dead volumes are formed at the flow speeds used for the carrier gas or oxygen.

According to a further embodiment, the determination of the total heat emission comprises determining an amount of oxygen consumed in the combustion of the pyrolysis gas.

For example, a lambda probe or a paramagnetic sensor can be used to determine oxygen. Advantageously, conclusions can be drawn about the oxygen consumption and thus the heat release from the oxygen content determined in the exhaust gas flow and the known oxygen supply. This is based on the fact that 1 kg of oxygen consumed corresponds to a heat quantity of 13.1 MJ.

According to a further embodiment, the pyrolysis gas burned when determining the total heat release is provided in an interval of the temperatures reached during heating between 350 to 550 ° C. or between 375 to 525 ° C., for example at a constant heating rate in each case.

This advantageously allows the MP content of environmental samples to be determined quickly, since e.g. Typical MP grades like PE, PP, PS and various elastomers can be pyrolyzed in this temperature range. While these polymers are characterized by heat of combustion of approx. 40 MJ / kg, the relevant environmental matrix - i.e. other sample components - is characterized in the relevant temperature window by a specific heat of combustion of only approx. 1-2 MJ / kg. The former can thus be distinguished from the latter.

According to a further embodiment, the determined oxygen consumption and / or the determined total heat emission is assigned using an MP calibration curve.

The calibration curve can advantageously be adapted to expected or respectively relevant MP contents.

• - mit definierten Probengemischen umfassend eine Umweltmatrix und einen der Umweltmatrix zugesetzten Masseanteil Mikroplastik;
• - mit der Partikelfraktion der Umweltprobe zugesetzten Masseanteilen Mikroplastik oder eines synthetischen Polymers; oder
• - an Hand eines Erwartungswertes einer spezifischen Verbrennungswärme definierter Massen des synthetischen Polymers.

According to a further embodiment it is proposed to create the calibration curve as an alternative:

• - With defined sample mixtures comprising an environmental matrix and a mass fraction of microplastic added to the environmental matrix;
• - The mass fractions of microplastics or a synthetic polymer added to the particle fraction of the environmental sample; or
• - on the basis of an expected value of a specific heat of combustion of defined masses of the synthetic polymer.

A calibration curve established in the former way can be advantageous for the monitoring of a certain type of environmental sample, e.g. Water samples, sewage or soil samples can be applied to MP. The identification of MP from a certain type of environmental sample (e.g. Raman, FTIR, TED-GC-MS), for example supported by spectroscopy or thermal analysis, and the graded addition of this MP fraction to an environmental sample of the same origin but with an unknown MP content allows a high level of precision to determine the unknown MP levels for precisely this type of environmental sample. The calibration curve created in the last-mentioned way can be used universally and is particularly suitable for monitoring process wastewater.

According to a further embodiment, the proposed method further comprises detecting a loss of mass of the weighed-in particle fraction during the pyrolysis of the particle fraction, at least during the pyrolysis of a part of the particle fraction.

This advantageously offers the possibility of checking whether the MP content determined on the basis of the heat of combustion of pyrolysis gases is reliable or whether a falsification, e.g. due to high fat content. In this case, a chemical extraction of the fats could be carried out before the implementation of the method, so that the method then additionally includes a fat extraction step. Highly volatile organic solvents and processes with which such a fat extraction can be carried out are familiar to the person skilled in the art.

According to a further embodiment, the heating rate is selected from a value between 1 K / min and 100 K / min. It is, for example, 1 K / min, 5 K / min, 10 K / min, 20 K / min, or even 1 K / s or more.

This advantageously increases the precision of the specific heat output.

According to one embodiment, the use of the method according to at least one of the embodiments described above for the determination of an MP content of a filtered water or air sample (filtrate), or on a solid sample (soil, compost, sewage sludge, sediment, biota, human and / or animal excrement).

Advantages arise from the shortening of the time required for each analysis and the automation of the analyzes.

According to one embodiment, the use of a Pyrolysis Combustion Flow Calorimeter (PCFC) for a characteristic temperature interval for determining an MP content of an environmental sample is proposed. The environmental sample can be selected from a filtrate from a water or air sample, a solid sample selected from a soil, compost, sewage sludge or sediment sample and from various biological samples. Biological samples are, for example, samples comprising an animal or a plant, its tissue or organs, a body part, a body fluid, a stomach content sample, a fecal sample, a blood sample from an animal (so-called animal sample); a plant sample (e.g. a crop) or a product intended for further processing. The process described can of course also be used for foodstuffs and intermediate products.

Pyrolysis Combustion Flow Calorimeters (PCFC) are advantageously commercially available and can thus be included in the basic equipment of corresponding analysis laboratories for environmental monitoring and / or food hygiene testing.

According to one embodiment, the MP content of an environmental sample is determined by determining the effective heat of combustion of a pyrolysis gas captured or captured when the environmental sample is heated and converting it into MP content using the specific heat of combustion of synthetic polymers typical for MP (e.g. PE, PS, or PP and other polyolefins or other anthropogenic polymers).

Advantages of this embodiment have already been mentioned: the method enables MP-selective determination of MP contents with high resolution in environmental samples, offers significantly better quality of the analysis compared to previously known methods. The proposed method and its use, as well as the use of known PCFC devices and enables simple and reliable determination of MP contents in environmental samples, considerably reduces the time required for each analysis compared to previously known methods and can also be automated.

According to a further embodiment, the selected temperature interval comprises a temperature range that is 100 to 200 K wide and / or falls within a temperature range of 300 to 600 ° C, 350 to 550 ° C, or 350 to 500 ° C.

The pyrolysis of polymers typically found as microplastics (polyolefins such as PE, PS and PP and elastomers) advantageously takes place within this temperature range. It should be noted here, however, that - depending on the heating rate used according to the method - the pyrolysis of MP can also start at lower temperatures. A significantly lower heating rate than 1 K / s, For example, a heating rate of 30 K / min (0.5 K / s) or 15 K / min (0.25 K / s) can induce the pyrolysis of olefins even at temperatures around 200 ° C. Against this background, the temperature interval can also include lower temperatures and, for example, be selected from the temperature range from 200-450 ° C., the range from 250-450 ° C. or the range from 275-500 ° C.

The embodiments described above can be combined with one another as desired. However, the invention is not limited to the specifically described embodiments, but can be modified and modified in a suitable manner. It is within the scope of the invention to suitably combine individual features and feature combinations of one embodiment with features and feature combinations of another embodiment in order to arrive at further embodiments according to the invention.

• - Einwiegen einer Partikelfraktion der Umweltprobe, d.h. Erhalten einer Einwaage der Partikelfraktion der Umweltprobe;
• - Heizen der eingewogenen Partikelfraktion bei einer Heizrate, die ausgewählt ist unter einer Heizrate zwischen 5-200 K/min, sodass eine Pyrolyse der eingewogenen Partikelfraktion erfolgt, wobei das Heizen und die Pyrolyse unter Ausschluss von Sauerstoff erfolgen;
• - Pyrolysieren der eingewogenen Partikelfraktion in einem Inertgas, beispielsweise in einem Gasstrom eines inerten Trägergases, umfassend Stickstoff, Argon, und/oder Helium;
• - Überführen eines beim Pyrolysieren gebildeten Pyrolysegases in einen Verbrennungsraum;
• - Unmittelbares Verbrennen (parallel zur Pyrolyse) des in den Verbrennungsraum überführten Pyrolysegases;
• - Bestimmen einer Wärmeabgaberate (HRR, heat release rate) während des Verbrennens des Pyrolysegases, das innerhalb eines durch kontinuierliches Heizen erreichten Temperaturintervalls freigesetzt wurde und/oder Erfassen einer von einem verbrennenden Pyrolysegas insgesamt abgegebenen Wärmemenge als totale Wärmeabgabe (THR, total heat release), wobei das Pyrolysegas in einem definierten Temperaturintervall bereitgestellt wurde, und wobei das Temperaturintervall für die Pyrolyse und/oder Verbrennung synthetischer organischer Polymere charakteristisch ist,
• - Bestimmen einer Masse eines gegebenenfalls nach dem Heizen und Pyrolysieren verbliebenen Rückstands und Bilden einer absoluten Massendifferenz zur ursprünglichen Einwaage, beispielsweise durch Rückwiegen eines Probentiegels mit dem gegebenenfalls verbliebenen Rückstand;
• - Ermitteln einer effektiven Verbrennungswärme (THE, total heat evolved) durch Division der totalen Wärmeabgabe (THR) durch die absolute Massendifferenz; wobei nur die für das definierte Temperaturintervall bestimmten und ermittelten Werte berücksichtigt werden; und
• - Ermitteln des MP-Gehaltes der Einwaage aus der bestimmten effektiven Verbrennungswärme und der spezifischen Verbrennungswärme eines synthetischen Polymers, wobei das Ermitteln des Mikroplastik-Gehalts an Hand einer Kalibrierkurve mit definierten Probengemischen umfassend eine Umweltmatrix und einen der Umweltmatrix zugesetzten Masseanteil Mikroplastik, an Hand von weiteren Einwaagen der Umweltprobe zugesetzten Masseanteilen Mikroplastik oder Masseanteilen des synthetischen Polymers, oder an Hand eines Erwartungswertes der spezifischen Verbrennungswärme definierter Massen des synthetischen Polymers erfolgt.

In other words and described in more detail, a method for determining a MP content of an environmental sample is proposed, which has the following process steps:

• - Weighing in a particle fraction of the environmental sample, ie obtaining an initial weight of the particle fraction of the environmental sample;
• Heating the weighed-in particle fraction at a heating rate which is selected from a heating rate between 5-200 K / min, so that pyrolysis of the weighed-in particle fraction takes place, the heating and pyrolysis taking place with the exclusion of oxygen;
• Pyrolyzing the weighed-in particle fraction in an inert gas, for example in a gas stream of an inert carrier gas comprising nitrogen, argon and / or helium;
• - Transferring a pyrolysis gas formed during pyrolysis into a combustion chamber;
• - Immediate burning (parallel to pyrolysis) of the pyrolysis gas transferred into the combustion chamber;
• - Determination of a heat release rate (HRR, heat release rate) during the burning of the pyrolysis gas, which was released within a temperature interval achieved by continuous heating and / or recording of a total amount of heat released by a burning pyrolysis gas as total heat release (THR, total heat release), wherein the pyrolysis gas was provided in a defined temperature interval, and wherein the temperature interval is characteristic of the pyrolysis and / or combustion of synthetic organic polymers,
• - Determination of a mass of a residue that may have remained after heating and pyrolysis and formation of an absolute mass difference to the original weight, for example by reweighing a sample crucible with the possibly remaining residue;
• - Determination of an effective heat of combustion (THE, total heat evolved) by dividing the total heat emission (THR) by the absolute mass difference; only the values determined and determined for the defined temperature interval are taken into account; and
• - Determination of the MP content of the initial weight from the determined effective heat of combustion and the specific heat of combustion of a synthetic polymer, the determination of the microplastic content on the basis of a calibration curve with defined sample mixtures comprising an environmental matrix and a mass fraction of microplastic added to the environmental matrix, on the basis of others Weighing in the mass fractions of microplastics or mass fractions of the synthetic polymer added to the environmental sample, or based on an expected value of the specific heat of combustion of defined masses of the synthetic polymer.

When determining the effective combustion values, the explanations given at the beginning are taken into account, in particular that 1 kg of oxygen consumed corresponds to a heat quantity of 13.1 MJ.

According to developments of this embodiment, the heating takes place at a heating rate that is selected between 5-200 K / min, for example at a heating rate of 1 K / s. Independently of this, a volume flow of the inert carrier gas can be 100-200 ml / min, for example 150 ml / min. The temperature range used when determining the heat release rate HRR, when recording the total heat release THR, and when determining the effective heat of combustion THE typically comprises 100 to 200 K and covers a temperature range that is characteristic of the pyrolysis and / or combustion of synthetic polymers of anthropogenic origin. For example, the THE can be determined using a defined sample mixture (environmental matrix with added defined masses of microplastics) using an addition of defined MP masses to the present environmental sample or using an expected value for a pure Polymer obtained calibration curve take place. Such a calibration curve shows a dependency of the THE and / or the THR on the mass of a synthetic polymer or a polymer mixture, or a MP content in a specific environmental matrix.

According to typical embodiments, the particle fraction provided (initial weight) is continuously heated at the same heating rate during pyrolysis. Alternatively, the heating rate can also be increased and is only constant from a lower value of the temperature interval (temperature window). The HRR is recorded over the entire heating period. The temperature window mentioned above is only used for the evaluation for determining microplastics. If a lower value of the selected temperature range (temperature window) is reached during heating, for example a value of 350 ° C, then the recording of the integral of the heat release rate (HRR) during the combustion of the pyrolysis gases released within this temperature window is started. When an upper value of the selected temperature range is reached, for example when 500 ° C is reached, or when 550 ° C is reached, the integral of the heat release rate when burning the pyrolysis gases in the temperature range from 350 ° C to 500 (550) ° C is recorded completed. The MP content is measured by determining the oxygen consumed in the combustion chamber (combuster). It is assumed that 1 kg of oxygen consumed corresponds to a heat quantity of 13.1 MJ. The heating rate typically selected between 1 to 100 K / min can, for example, 1 K / min; 5 K / min; 10 K / min; 15 K / min; 20 K / min; 25 K / min; 30 K / min; 35 K / min; 40 K / min; 45 K / min; 50 K / min; 55 K / min; 60 K / min; 65 K / min; 70 K / min; 75 K / min; 80 K / min; 85 K / min; 90 K / min; 95 K / min; 100 K / min; but also 105 K / min; 110 K / min; 115 K / min; 120 K / min; 125 K / min; 130 K / min; 135 K / min; 140 K / min; 145 K / min; 150 K / min; 155 K / min; 160 K / min; 165 K / min; 170 K / min; 175 K / min; 180 K / min; 185 K / min; 190 K / min; 195 K / min or 200 K / min. Dynamic sample heating leads to a clearer signal compared to isothermal heating.

Advantages of these embodiments and their further developments result from the ability of the method described to be able to analyze MP in a reproducible manner with a considerably reduced time requirement per sample. While the synthetic polymers most frequently found in environmental samples, polyethylene (PE), polypropylene (PP), polystyrene (PS) and elastomers (for example in the form of abrasion from automobile tires) are characterized by particularly high specific heat of combustion of approx. 40 MJ / kg Environmental matrix - i.e. other sample components - characterized in the analyzed temperature window by a specific heat of combustion of only approx. 1-2 MJ / kg. Even if it is not possible to differentiate between the different polymers within a measurement, the determination of an increased effective heat of combustion still allows conclusions to be drawn unambiguously about the presence and mass content of MP in the relevant sample. The, as shown, clear difference in the specific heat of combustion (factor 3 -30, depending on the comparison with natural polymers or the typical values for different environmental matrices) enables the selective determination of MP and the high sensitivity, i.e. a good resolution of the proposed method compared to all previously known methods.

In order to clarify some terms, the following explanation is given. The terms calorific value and calorific value always refer to combustion in oxygen. The present case is a pyrolysis, which takes place with the exclusion of oxygen, and a subsequent combustion of the pyrolysis gases, the amount of oxygen required for the combustion of the pyrolysis gases being precisely recorded. The formation of water is taken into account as an integral part because the measurement is based on the determination of the oxygen consumption.

To determine the heat of combustion, a dried substance is burned under pressure with excess oxygen in a calorimeter (see https://de.wikipedia.org/wiki/Kalorimeter). This creates gaseous carbon dioxide as combustion products and water as condensate (which is liquid under the prevailing pressure conditions). These values are referenced to 25 ° C as standard in tables.

The gross calorific value (see https://de.wikipedia.org/wiki/Brennwert) is identical to the absolute amount (see https://de.wikipedia.org/wiki/Betragsfunktion) of the standard enthalpy of combustion Δ _V given with a negative sign H ° of general thermodynamics (see https://de.wikipedia.org/wiki/Standardverbrenntenthalpie). In terms of heating technology, this means that the water content (from product moisture residues, supply air moisture and the oxidized hydrogen atoms in the fuel) is not in vapor form in this calculation, but in liquid form before and after combustion. The term condensing technology used for heating systems also relates to this (https://de.wikipedia.org/wiki/Brennwerttechnik): The enthalpy of evaporation bound in the water vapor is also used effectively here. For heating purposes, the calorific value (more precisely: the upper calorific value) is the better parameter because when using the (lower) Due to the fact that it does not take into account the use of the enthalpy of evaporation of the water, apparently physically nonsensical degrees of utilization of over 100% can occur.

The calorific value of a substance cannot be determined directly by experiment. It refers to a combustion that produces only gaseous combustion products. For the calculation, the evaporation enthalpy of the water is subtracted from the calorific value, provided hydrogen atoms are contained in the fuel, so the calorific values of such fuels are approx. 10% below their calorific values.

Example: The enthalpy of evaporation of water is 45.1 kJ / mol (0 ° C), 44.0 kJ / mol (25 ° C) or 40.7 kJ / mol at 100 ° C (see also “Heat of evaporation” or cf. . https://de.wikipedia.org/wiki/Verdampfungsw%C3%A4rme).

The MP determination method proposed here is significantly faster than all the methods previously used for this purpose, as measuring a sample only takes about 20 minutes. On the basis of the proposed method, MP levels in environmental samples can thus be determined efficiently and cost-effectively in routine operation.

According to one embodiment, the weighing is heated in a temperature range of 100 ° C - 800 ° C and the effective heat of combustion is determined within a specially selected temperature range, which is typically 100 to 350 ° C, preferably within a temperature range that extends over 150 degrees within the temperature range from 100 ° C to 800 ° C, for example within the temperature range from 100 ° C to 600 ° C or between 300 to 600 ° C or between 350 to 550 ° C.

The selection of the temperature interval, actually a measuring window that is only 100 to 350 degrees wide, for example 110, 120, 130, 140, 150, 160, 170, 180, 190, or 200 degrees wide, allows reliable measurement of the To distinguish the measurement values generated by the combustion of pyrolysis products of synthetic polymers (the amount of oxygen required for complete oxidation of the pyrolysis products) from the significantly lower measurement values that occur during the combustion of pyrolysis products of organic components or naturally occurring polymers from the environmental matrix. The MP content contained in the relevant environmental sample can thus advantageously be inferred, even if the environmental sample and the particle fraction obtained from it contain polymers of natural origin, such as cellulose, lignin or chitin. Advantageously, polyolefins, especially PE, PS and PP, are 100% pyrolyzed and have higher heat of combustion than the environmental matrix, while the environmental matrix - which is in particle form and is therefore to be found in the particle weights examined for MP - does not. Thus, the pyrolysis preceding the combustion of pyrolysis gases and a separate (selective) combustion of the pyrolysis gases allow a high accuracy of the MP determination.

According to one embodiment, the proposed method further comprises recording a total loss of mass of the weighed-in particle fraction as a result of the pyrolysis, for example by weighing a sample crucible before and after the measurement, but also continuously during heating or for the selected temperature interval (decomposition temperature window).

This advantageously allows a pyrolytic and inorganic residue of the weighed-in particle fraction to be recorded before and after the pyrolysis.

According to one embodiment, the heating rate for heating the weighed-in particle fraction is selected in the range between 1K / min and 100 K / min, for example below: 1.5 K / s (90 K / min); 1.25 K / s (75 K / min); 1.0 K / s (60 K / min); 0.5 K / s (30 K / min) and 0.25 K / s (15 K / min). The heating rate is advantageously adapted to the expected MP fraction in the sample.

A faster heating rate allows the generation of a high pyrolysis gas concentration and thus high signal intensities in a small temperature interval. However, rapid heating rates can also bring about a broadening of the pyrolysis temperature over a broader temperature range, so that the preferred heating rate is adapted to the polymer typically present as MP, especially for monitoring industrial wastewater flows to an expected type of MP.

According to one embodiment, the mass of the weighed-in sample is selected from a mass between 1 μg and 1 kg, in particular a mass between 1 mg and 30 mg for thermoanalytical apparatus and between 0.5 g and 10 g for larger weights of the environmental matrix in a device specially adapted for the determination of MP in environmental samples.

MP components extracted from samples with low levels of contamination and / or from comparatively small volumes of water can also advantageously be detected or, if necessary, also in larger sample volumes. While conventional devices are primarily adapted for the investigation of micro-quantities of the corresponding materials, the method is adapted for the investigation of larger sample quantities, which for example can be rich in organic contents (including biota, natural polymers) or are rich in inorganic contents (including sediment, carbonates, salts). Nevertheless, it is possible to detect the enriched MP fraction.

According to typical embodiments, the combustion of the gas transferred into the combustion chamber takes place with the supply of defined concentrations of oxygen or synthetic air, so that from each within a unit of time - the at a constant heating rate / possibly. offset in time / corresponds to a defined temperature range, a heat of combustion of the pyrolysis gas can be determined.

The intrinsic CO ₂ release from the environmental matrix (e.g. from carbonates, carboxylic acids and esters), which cannot be ruled out, can advantageously be used to determine the oxygen consumed to burn the pyrolysis gases (1 kg of oxygen consumed corresponds to an amount of heat of 13.1 MJ) do not falsify.

According to one embodiment, the heat of combustion of the pyrolysis gases emitted when the sample is burned is determined in a selected temperature interval that spans only 150 K, for example between 350 to 550 ° C or between 375 to 525 ° C at a constant heating rate, for example at a heating rate of 1K / s.

The reliable differentiation between pyrolysis products of synthetic polymers and natural organic compounds and thus the MP-selective determination is advantageously achieved in the specified temperature intervals.

According to one embodiment, the microplastic content is determined by determining the effective heat of combustion of the weighed-in particle fraction of the environmental sample and the specific heat of combustion of at least one pure synthetic polymer.

Surprisingly, it turned out that the heat release, which is about 3 to 30 times higher than that of naturally occurring polymers and other sample components of natural origin, during pyrolysis and combustion of synthetic polymers of anthropogenic origin is suitable for detecting and quantifying MP in environmental samples. The measurement accuracy of the method is further increased if the measurement of the effective heat of combustion is carried out within a defined temperature interval.

Figure list

• 1 zeigt Ergebnisse der Thermogravimetrischen Analyse (TGA) von Schwebstoffen.
• 2 zeigt Ergebnisse der Thermogravimetrischen Analyse (TGA) der verwendeten Polymermaterialien.
• 3 zeigt einen Ausschnitt der Ergebnisse aus 1 für 300 bis 550 °C.
• 4 zeigt einen Ausschnitt der Ergebnisse aus 2 für 300 bis 550 °C.
• 5 zeigt PCFC Ergebnisse der HRR der vier Einzelmaterialien.
• 6 zeigt einen hinsichtlich der HRR gespreizten Ausschnitt aus 5.
• 7 zeigt PCFC Ergebnisse (HRR) für drei Wiederholungen einer Schwebstoffprobe (ca. 5 mg)
• 8 zeigt PCFC Ergebnisse (HRR) für drei Wiederholungen einer Schwebstoffprobe mit zugesetztem 1 % PE (ca. 5 mg Probe gesamt)
• 9 zeigt PCFC Ergebnisse (HRR) für drei Wiederholungen Schwebstoffprobe mit zugesetztem 3 % PE (ca. 5 mg Probe gesamt)
• 10 zeigt PCFC Ergebnisse (HRR) für drei Wiederholungen Schwebstoffprobe mit zugesetztem 5 % PE (ca. 5 mg Probe gesamt)
• 11 zeigt PCFC Ergebnisse (HRR) für drei Wiederholungen Schwebstoffprobe mit zugesetztem 1 % PE und 1 % PS (ca. 5 mg Probe gesamt)
• 12 zeigt PCFC Ergebnisse (HRR) für drei Wiederholungen Schwebstoffprobe mit zugesetztem 3 % PE und 3 % PS (ca. 5 mg Probe gesamt)
• 13 PCFC Ergebnisse (HRR) für drei Wiederholungen Schwebstoffprobe mit zugesetztem 5 % PE und 5 % PS (ca. 5 mg Probe gesamt)
• 14 zeigt ein Korrelation der effektiven Verbrennungswärme (THE) gegenüber der PE Einwaage in den Schwebstoffproben
• 15 zeigt ein Korrelation der effektiven Verbrennungswärme (THE) gegenüber der MP Einwaage in den Schwebstoffproben

The accompanying figures illustrate embodiments and, together with the description, serve to explain the principles of the invention.

• 1 shows the results of the thermogravimetric analysis (TGA) of suspended solids.
• 2 shows the results of the thermogravimetric analysis (TGA) of the polymer materials used.
• 3 shows a section of the results 1 for 300 to 550 ° C.
• 4th shows a section of the results 2 for 300 to 550 ° C.
• 5 shows PCFC results of the HRR of the four individual materials.
• 6th shows a section that is expanded with regard to the HRR 5 .
• 7th shows PCFC results (HRR) for three repetitions of a suspended matter sample (approx. 5 mg)
• 8th shows PCFC results (HRR) for three repetitions of a suspended matter sample with added 1% PE (approx. 5 mg sample total)
• 9 shows PCFC results (HRR) for three repetitions of suspended solids sample with added 3% PE (approx. 5 mg sample total)
• 10 shows PCFC results (HRR) for three repetitions of suspended matter sample with added 5% PE (approx. 5 mg sample total)
• 11 shows PCFC results (HRR) for three repetitions of suspended matter sample with added 1% PE and 1% PS (approx. 5 mg total sample)
• 12th shows PCFC results (HRR) for three repetitions of suspended solids sample with added 3% PE and 3% PS (approx. 5 mg total sample)
• 13 PCFC results (HRR) for three replicates suspended matter sample with added 5% PE and 5% PS (approx. 5 mg sample total)
• 14th shows a correlation between the effective heat of combustion (THE) and the PE weight in the suspended matter samples
• 15th shows a correlation of the effective heat of combustion (THE) versus the MP initial weight in the suspended matter samples

In summary, according to the proposed exemplary embodiments, MP contents are determined on the basis of the effective heat of combustion of their pyrolysis products and the specific heat of combustion of pure polymers. In the pyrolytic decomposition, organic compounds are only broken down by the action of temperature with the exclusion of oxygen. The complex environmental samples are pyrolyzed in a temperature range typically from 100 to 800 ° C under inert conditions. The evaluation is carried out for pyrolysis gases recorded in a defined temperature interval, for example between 350 and 550 ° C. The selection of the temperature interval is adapted to the respective heating rate so that that temperature range is enclosed in which the synthetic polymers are pyrolyzed at the selected heating rate. The pyrolysis range of plastics is known to be dependent on the heating rate. The interval is therefore selected so that the respective temperature range of the pyrolysis of synthetic polymers is included. Heating rates of 5-200 K / min, in particular 1 K / s, for example, and an inert carrier gas flow (nitrogen, argon, helium) of 100-200 ml / min (device-dependent size) are used to transport the gases released during pyrolysis . The gases formed are transferred to a spatially separate combustion chamber (combustor), in which the heat of combustion of the pyrolysis gases is then determined. The heat of combustion of the non-pyrolyzed residue under the conditions in the PCFC is not taken into account in the proposed method. The detection of the heat of combustion of the pyrolysis gases can be determined, for example, via the oxygen consumption required for this. The consumption of one kilogram of oxygen releases 13.1 MJ of heat. This means that the possible intrinsic CO ₂ release from the environmental matrix (eg carbonates, carboxylic acids and esters) is not taken into account and cannot falsify the measurement data.

Overall, the proposed method is recommended for the routine measurement of environmental samples for the presence of MP. It is fast, simple, sensitive, precise and therefore suitable as a quick routine procedure. It is based on the determination of the high effective heat of combustion of pure polymers, the low amount of residue and the evaluation of characteristic temperature intervals, which typically include the pyrolysis of synthetic polymers and thus MP.

The use of existing thermo-analytical methods, e.g. Thermogravimetry with coupled or downstream analysis of the volatile products is already comparatively fast, but this relatively expensive and complex method also requires very good training on the part of the user. Until now, there was no inexpensive, fast method with a simple and reliable evaluation for routine analysis. The proposed use of the analytical technique in environmental analysis, which has hitherto been known exclusively from fire protection research, for the determination of MP levels in environmental samples is new and was completely alien to the expert in the field of environmental analysis, since questions relating to the investigation of the burning behavior of polymers for environmental analysis, in particular with regard to the MP content of water samples are of no importance.

Practical embodiment

According to a practical embodiment, the described method was used to quickly determine the MP content by measuring the effective heat of combustion of the pyrolysis products in characteristic decomposition temperature ranges for the analysis of an exemplary water filtrate sample from surface water (suspended matter), the added MP content PE, PP and PS (commercially available polymers without function-specific additives). As explained below on the basis of the results obtained, the results obtained show that samples rich in organic matter (organic content of ~ 20% by weight) with a sample weight of only 5 mg (MP quantities with up to 50 µg in 5 mg environmental matrix correspond to real finds in surface waters or sewage treatment plant processes) MP contents <1% by weight can be reliably analyzed. In addition to the short measurement time, the simple linear relationship between MP content and heat dissipation in the characteristic temperature range enables the simple and quick routine determination of MP.

A TG / DTA 220 device from Seiko Instruments Inc. was used for the measurements described. Sample weights of 5 mg each were heated in aluminum oxide crucibles at a heating rate of 10 K / min. For the temperature range from 25 ° C to 600 ° C, the sample chamber was flushed with 200 ml / min nitrogen, and for the temperature range from 600 ° C to 1000 ° C with 200 ml / min synthetic air. Calorimetric measurements to determine the effective heat of combustion were carried out with a Combustion Flow Calorimeter (PCFC) or micro-combustion calorimeter (MCC) (Fire Testing Technology Ltd., UK) specifically designed for determining the heat of combustion of plastics.

To determine characteristic parameters of the components present in the examined sample, the suspended solids, PE particles, PP particles and PS particles used were individually thermogravimetrically examined. The results of the thermogravimetric analysis (TGA) are shown as a function of the relative sample mass as a function of the temperature, usually at a constant heating rate. The differentiation of the measured values obtained during this process provides the temperature- and heating-rate-dependent rate of mass loss, which is also known as differential thermogravimetry (DTG).

1 shows the results of the TGA of suspended solids. The mass losses achieved at the respective temperature are plotted against the left ordinate in% by mass, while the right ordinate with DTG shows the first derivative of these values, corresponding to differential thermogravimetry in µg / min. The loss of mass due to thermal decomposition and combustion at temperatures between 350 and 550 ° C is striking.

2 shows the results of the TGA of the three polymers examined here as examples: polyethylene (PE), polypropylene (PP) and polystyrene (PS). It can be seen that the polymers are completely thermally decomposed in the temperature range between 350 ° C and 520 ° C. From the 3 and 4th it can be seen that in the temperature range from 350 to 550 ° C a complete pyrolysis can be observed for all polymers, while a mass loss of only approx. 4.5% occurs with the suspended solids.

After the mass loss had been determined, the heat release rate (HRR) was determined in the Pyrolysis Combustion Flow Calorimeter (PCFC). Corresponding results are in the 5 and 6th and summarized in Table 1 below. The 5 and 6th prove that in the temperature range from 350 to 550 ° C clear heat release peaks can be observed for all polymers, while only a broad, unspecific signal can be determined for the suspended matter. Table 1: Effective heat of combustion (THE) of the sample components determined in the Combustion Flow Calorimeter (PCFC). sample THE in kJ / g PE 41.2 ± 0.2 PP 43.5 ± 0.2 PS 40.7 ± 0.1 Suspended solids 6.7 ± 0.6

In addition to the values listed in Table 1, it should be added that when the THE values are determined, they refer to the mass loss measured over the entire temperature range from 25 to 600 ° C, as the device currently does not allow mass loss determination in a small selected temperature range. However, it is possible to use the mass loss determined in the TGA within the temperature interval.

The measurement curves of the 7th to 13 show the course of the heat release rates (HRR) determined by means of PCFC for model samples consisting of suspended matter and different contents of different types of MP. The exact compositions of the samples are summarized in Table 2. Table 2: Overview of the composition of the model samples measured in the Combustion Flow Calorimeter (PCFC) Sample designation Suspended matter [mg] PE [mg] PS [mg] wt .-% PE wt .-% PS Suspended matter 1 5.006 0 0 Suspended matter_2 4,997 0 0 Suspended matter_3 5.001 0 0 1wtPE_1 4,956 0.049 0 0.98 0.00 1wtPE_2 4,954 0.052 0 1.04 0.00 1wtPE_3 4,954 0.053 0 1.06 0.00 3wtPE_1 4.851 0.152 0 3.04 0.00 3wtPE_2 4.857 0.148 0 2.96 0.00 3wtPE_3 4,848 0.151 0 3.02 0.00 5wtPE_1 4,745 0.251 0 5.02 0.00 5wtPE_2 4,746 0.251 0 5.02 0.00 5wtPE_3 4,746 0.255 0 5.10 0.00 1PE_1PS_1 4,898 0.051 0.059 1.02 1.18 1PE_1PS_2 4.896 0.049 0.064 0.98 1.28 1PE_1PS_3 4.891 0.052 0.054 1.04 1.08 3PE_PS_1 4,699 0.148 0.163 2.95 3.25 3PE_PS_2 4.697 0.151 0.153 3.02 3.06 3PE_PS_3 4.702 0.15 0.152 3.00 3.04 5PE_PS_1 4,508 0.25 0.245 5.00 4.90 5PE_PS_1 4.493 0.256 0.262 5.11 5.23 5PE_PS_1 4,507 0.25 0.251 4.99 5.01

The 14th and 15th correlate the polymer concentrations in the sample against the determined effective heats of combustion (THE). They demonstrate the linear relationship between the MP content of a sample and the heat of combustion (THE) of the products released during pyrolysis.

In conclusion, in view of the practical examples, it becomes clear that, on the one hand, the high effective heat of combustion of pure polymers compared to suspended solids opens up the possibility of determining the MP content of a sample of unknown composition with improved sensitivity and resolution. The additional definition of characteristic temperature intervals (decomposition temperature intervals) further increases the MP selectivity and the sensitivity of the measurements. Overall, the results were shown to be very repeatable. There is a linear relationship between the MP content and THE. The measurement uncertainty of the method is achieved below 1 mass% MP in a sample. The ones in the 14th and 15th The straight lines shown can be used to calibrate the proposed method. But they also prove the determination of MP levels.

1. 1. Verfahren zur schnellen Bestimmung des MP-Gehalt, insbesondere mit Messmethoden, die auf konstanten Heizraten zwischen 5 K/min und 200 K/min beruhen, wobei eine konstante Heizrate ausgewählt ist unter 10 K/min, 20 K/min, und 1 K/s;
2. 2. Verfahren zur Bestimmung des MP-Gehalt in komplexen Umweltproben;
3. 3. Verfahren zur Bestimmung des MP-Gehalt in Probenmengen zwischen 1 Mikrogramm und 1 kg, insbesondere zwischen 1 mg und 30 mg oder zwischen 0,5 g und 10 g;
4. 4. Verfahren zur Bestimmung des MP-Gehalt mittels Messung der effektiven Verbrennungswärme der anaeroben Pyrolyse, gekoppelt mit der Verbrennung von gasförmigen Zersetzungsprodukten in einem Combustor mit daran anschließender Bestimmung der Wärmeabgabe durch die Sauerstoffverbrauchsmethode;
5. 5. Verfahren zur Bestimmung des MP-Gehalt mittels Messung der effektiven Verbrennungswärme der jeweiligen Pyrolyseprodukte in charakteristischen Zersetzungstemperaturbereichen, z.B. in den Bereichen 300 bis 600°C beispielsweise bei einer Heizrate von 1K/s, wobei die Temperaturbereiche typischerweise in Abhängigkeit von einer Probenmenge und einer jeweils gewählten Heizrate ausgewählt sind.

Aspects of the proposed method therefore concern:

1. 1. Method for the rapid determination of the MP content, in particular with measurement methods based on constant heating rates between 5 K / min and 200 K / min, with a constant heating rate selected from 10 K / min, 20 K / min, and 1 K / s;
2. 2. Procedure for determining the MP content in complex environmental samples;
3. 3. Method for determining the MP content in sample quantities between 1 microgram and 1 kg, in particular between 1 mg and 30 mg or between 0.5 g and 10 g;
4. 4. Method for determining the MP content by measuring the effective heat of combustion of anaerobic pyrolysis, coupled with the combustion of gaseous decomposition products in a combustor with subsequent determination of the heat output by the oxygen consumption method;
5. 5. Method for determining the MP content by measuring the effective heat of combustion of the respective pyrolysis products in characteristic decomposition temperature ranges, e.g. in the ranges 300 to 600 ° C, for example at a heating rate of 1K / s, the temperature ranges typically depending on a sample amount and a selected heating rate are selected.

In summary, a method for determining the microplastic content of an environmental sample is proposed. The method comprises the steps of: providing a particle fraction of the environmental sample; Providing a pyrolysis gas by heating the particle fraction in a defined temperature interval at a defined heating rate, the particle fraction being heated in an inert gas atmosphere; Burning the pyrolysis gas in an oxygen-containing atmosphere and determining a total heat release (THR) during the burning of the provided pyrolysis gas; and assigning the determined total heat release to a microplastic content of the environmental sample.

While specific embodiments have been shown and described herein, it is within the scope of the present invention to appropriately modify the shown embodiments without departing from the scope of the present invention. The following claims represent a first, non-binding attempt to generally define the invention.

References

• [1] Horton, AA, Walton, A., Spurgeon, DJ, Lahive, E. and Svendsen, C. (2017) Microplastics in freshwater and terrestrial environments: Evaluating the current understanding to identify the knowledge gaps and future research priorities. Science of The Total Environment 586, 127-141 . Li, JY, Liu, HH and Chen, JP (2018) Microplastics in freshwater systems: A review on occurrence, environmental effects, and methods for microplastics detection. Water Research 137, 362-374 . Wagner, S., Huffer, T., Klockner, P., Wehrhahn, M., Hofmann, T. and Reemtsma, T. (2018) Tire wear particles in the aquatic environment - A review on generation, analysis, occurrence, fate and effects. Water Research 139, 83-100.
• [2] Koelmans, AA, Besseling, E., Foekema, E., Kooi, M., Mintenig, S., Ossendorp, BC, Redondo-Hasselerharm, PE, Verschoor, A., van Wezel, AP and Scheffer, M. (2017 ) Risks of Plastic Debris: Unraveling Fact, Opinion, Perception, and Belief. Environmental Science & Technology 51 (20), 11513-11519 .
• [3] Käppler, A., Fischer, D., Oberbeckmann, S., Schernewski, G., Labrenz, M., Eichhorn, K.-J. and Voit, B. (2016) Analysis of environmental microplastics by vibrational microspectroscopy: FTIR, Raman or both? Analytical and Bioanalytical Chemistry, 408 (29) 8377-8391 . Ivleva, NP, Wiesheu, AC and Niessner, R. (2017) Microplastic in Aquatic Ecosystems. Angewandte Chemie International Edition 56 (7), 1720-1739 .
• [4] Dümichen, E., Eisentraut, P., Bannick, CG, Barthel, A.-K., Senz, R. and Braun, U. (2017) Fast identification of microplastics in complex environmental samples by a thermal degradation method . Chemosphere 174, 572-584. Elert, AM, Becker, R., Duemichen, E., Eisentraut, P., Falkenhagen, J., Sturm, H. and Braun, U. (2017) Comparison of different methods for MP detection: What can we learn from them, and why asking the right question before measurements matters? Environmental Pollution 231 (Part 2), 1256-1264. Fischer, M. and Scholz-Böttcher, BM (2017) Simultaneous Trace Identification and Quantification of Common Types of Microplastics in Environmental Samples by Pyrolysis-Gas Chromatography-Mass Spectrometry. Environmental Science & Technology 51 (9), 5052-5060 .
• [5] Lyon, RE and Walters, RN (2004) Pyrolysis combustion flow calorimetry. Journal of Analytical and Applied Pyrolysis 71 (1), 27-46 .

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Non-patent literature cited

• Horton, A.A., Walton, A., Spurgeon, D.J., Lahive, E. and Svendsen, C. (2017) Microplastics in freshwater and terrestrial environments: Evaluating the current understanding to identify the knowledge gaps and future research priorities. Science of The Total Environment 586, 127-141 [0088]
• Li, J.Y., Liu, H.H. and Chen, J.P. (2018) Microplastics in freshwater systems: A review on occurrence, environmental effects, and methods for microplastics detection. Water Research 137, 362-374 [0088]
• Wagner, S., Huffer, T., Klockner, P., Wehrhahn, M., Hofmann, T. and Reemtsma, T. (2018) [0088]
• Koelmans, A.A., Besseling, E., Foekema, E., Kooi, M., Mintenig, S., Ossendorp, B.C., Redondo-Hasselerharm, P.E., Verschoor, A., van Wezel, A.P. and Scheffer, M. (2017) Risks of Plastic Debris: Unraveling Fact, Opinion, Perception, and Belief. Environmental Science & Technology 51 (20), 11513-11519 [0088]
• Käppler, A., Fischer, D., Oberbeckmann, S., Schernewski, G., Labrenz, M., Eichhorn, K.-J. and Voit, B. (2016) Analysis of environmental microplastics by vibrational microspectroscopy: FTIR, Raman or both? Analytical and Bioanalytical Chemistry, 408 (29) 8377-8391 [0088]
• Ivleva, N.P., Wiesheu, A.C. and Niessner, R. (2017) Microplastic in Aquatic Ecosystems. Angewandte Chemie-International Edition 56 (7), 1720-1739 [0088]
• Elert, A.M., Becker, R., Duemichen, E., Eisentraut, P., Falkenhagen, J., Sturm, H. and Braun, U. (2017) [0088]
• Fischer, M. and Scholz-Böttcher, B.M. (2017) Simultaneous Trace Identification and Quantification of Common Types of Microplastics in Environmental Samples by Pyrolysis-Gas Chromatography-Mass Spectrometry. Environmental Science & Technology 51 (9), 5052-5060 [0088]
• Lyon, R.E. and Walters, R.N. (2004) Pyrolysis combustion flow calorimetry. Journal of Analytical and Applied Pyrolysis 71 (1), 27-46 [0088]

Claims (16)

A method for determining a microplastic content in an environmental sample, comprising: - providing a particle fraction of the environmental sample; - providing a pyrolysis gas by heating the particle fraction in a defined temperature interval at a defined heating rate, the particle fraction being heated in an inert gas atmosphere; - Burning the pyrolysis gas in an oxygen-containing atmosphere and determining a total heat release (THR) during the burning of the pyrolysis gas provided; and - Assignment of the determined total heat emission to a microplastic content of the environmental sample. Procedure according to Claim 1 , wherein the heating of the particle fraction, the provision of the pyrolysis gas and the burning of the pyrolysis gas take place simultaneously in that the pyrolysis gas is transferred with an inert gas into a combustion chamber. Procedure according to Claim 1 or 2 , wherein the temperature interval comprises a temperature range of 100 to 200 K. Procedure according to Claim 3 , wherein the temperature range is from: 300 to 600 ° C, 350 to 550 ° C, or 350 to 500 ° C. Method according to at least one of the Claims 1 to 4th , wherein a mass of the provided particle fraction is selected from a mass between 1 μg and 1 kg, in particular a mass between 1 mg and 10 g, or 1 mg and 30 mg. Method according to at least one of the Claims 1 to 5 wherein the combustion takes place in a combustion chamber, and oxygen or synthetic air of a defined oxygen concentration is continuously supplied to the combustion chamber. Procedure according to Claim 6 wherein the determination of the total heat emission comprises determining an amount of oxygen consumed in the combustion of the pyrolysis gas. Method according to at least one of the Claims 1 to 7th , the heating taking place in the temperature interval between 350 to 550 ° C. or between 375 to 525 ° C., for example in each case at a constant heating rate. Method according to at least one of the preceding claims, wherein the assignment takes place on the basis of a calibration curve. Procedure according to Claim 9 , the calibration curve being created: with defined sample mixtures comprising an environmental matrix and a mass fraction of microplastic added to the environmental matrix; - Mass fractions of microplastics or mass fractions of a synthetic polymer added to the particle fraction of the environmental sample; or - on the basis of an expected value of a specific heat of combustion of defined masses of the synthetic polymer. The method according to at least one of the preceding claims, further comprising: - Detecting a loss of mass of the weighed in particle fraction during a pyrolysis of the particle fraction. Method according to at least one of the Claims 1 to 11 , whereby the defined heating rate is between 1 and 100 K / min. Use of a method according to at least one of Claims 1 to 12th for the determination of a microplastic content in a filtrate of a water or air sample, or in a solid sample, selected from: soil, compost, sewage sludge, sediment, biota, human and / or animal excretions. Use of a Pyrolysis Combustion Flow Calorimeter (PCFC) to determine the microplastic content of an environmental sample, in particular in a filtrate of a water or air sample, or on a Solid sample selected from: a soil, compost, sewage sludge or sediment sample, in biota, in human and / or in animal excrement. Determination of the microplastic content of an environmental sample by determining the heat of combustion of a pyrolysis gas detected when the environmental sample is heated within a temperature interval Determination after Claim 15 , wherein the temperature interval comprises a temperature range from 100 to 200 K or temperatures from: 300 to 600 ° C, 350 to 550 ° C, or 350 to 500 ° C.

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