Method for the quantitative determination of the total content of micro-nano-plastic in an aquatic environment based on total organic carbon

Abstract

Method for the quantitative determination of the total content of the micro-nano-plastic in the aquatic environment based on total organic carbon, comprising the following steps: (1) filtering a water sample through a first enrichment membrane, and collecting and obtaining a first solid; (2) adding a digestion reagent to the first enrichment membrane carrying the first solid to digest and remove natural organic matter; (3) filtering the mixture obtained in step (2) through a second enrichment membrane to obtain the second solid-supporting second enrichment membrane; and (4) Drying the digested first enrichment membrane and the second solid-supporting second enrichment membrane from step (3), and then determining the total organic carbon value, which is the total organic carbon value of the micro-nano-plastic.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of chemistry for environmental analysis and, more particularly, to a method for quantitatively determining the total content of the micro-nano-plastic in an aquatic environment based on total organic carbon. TECHNICAL BACKGROUND

[0002] Due to the excellent physical and chemical properties of plastics, products made from them are widely used in daily production and everyday life. These plastic products often end up as plastic waste, which enters the environment. A large portion of this plastic waste decomposes under environmental influences such as sunlight, the impact of water flow, and biological degradation, producing micro-nanoplastics. Micro-nanoplastics are also used in industrial raw materials and everyday cosmetic products. During the use of these products, micro-nanoplastics are also released into the environment.

[0003] In recent years, environmental scientists have identified micro-nanoplastics as a new type of pollutant. According to toxicological studies, micro-nanoplastics can be ingested by animals and affect their growth and reproduction. Furthermore, micro-nanoplastics can also adsorb heavy metal ions, organic pollutants, and other contaminants, resulting in complex toxic effects. The toxic effects of micro-nanoplastics are closely related to their concentration level. Therefore, a precise quantitative analysis of micro-nanoplastics is a prerequisite for investigating their pollution level and toxic effects.

[0004] Currently, the weighing method, scanning electron microscopy energy spectroscopy, thermal pyrolysis gas chromatography mass spectrometry, etc., are mainly used for the quantitative analysis of micro-nanoplastics. However, these methods have disadvantages, such as limited application scope (e.g., only suitable for a specific material), time and labor consumption, low sensitivity, and expensive instrumentation. It is difficult to apply these methods to the quantitative analysis of the total content of micro-nanoplastics in actual environmental waters.

[0005] CN 209342492 U discloses a device for the rapid separation and extraction of microplastics in surface water. After the first filtration, the digestion agent is applied to the first filter along with the residue. After two filtrations with two different filters, the second filter is dried and used to determine the amount of microplastics.

[0006] CN 110108629 A discloses a method for detecting microplastic particles in everyday chemical products. After the first filtration, in which microplastic particles above a certain diameter are retained in the filter, the filtrate rather than the filter cake is further processed, so that only microplastic particles below a certain size are relevant for detection. WO 2019 / 171312 A1 discloses a method for extracting and determining microplastics in samples with organic and inorganic matrices. The digestion agent for eliminating the microorganisms is applied before the single filtration. SUMMARY OF THE INVENTION

[0007] To solve the above-mentioned problems, the present invention proposes a method for quantitatively determining the total content of micro-nanoplastics in an aquatic environment based on total organic carbon. Specifically, the present invention provides a method for quantitatively determining the total content of micro-nanoplastics in an aquatic environment based on total organic carbon, the method comprising the following steps: (1) filtering a water sample through a first enrichment membrane, and collecting and obtaining a first solid; (2) adding a digestion reagent to the first enrichment membrane carrying the first solid to digest and remove natural organic matter; (3) filtering the mixture obtained in step (2) through a second enrichment membrane to obtain the second solid-supporting second enrichment membrane; and (4) Drying the digested first enrichment membrane and the second solid-supporting second enrichment membrane from step (3), and then determining the total organic carbon value, which is the total organic carbon value of the micro-nano-plastic. DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram of a method for quantitatively determining the micro-nano-plastic in an aquatic environment in the present invention. Fig. Figure 2 is an electron micrograph of a glass fiber membrane with a nanopore diameter of 300nm in the present invention, which retains and enriches micro-nano plastic particles. Fig.Figure 3 is a graph showing the influence of the volumes of the filtered water samples (100 ml-1000 ml) on the recovery rate of the micro-nanoplastic in the present invention. Fig. Figure 4 is a graph showing the influence of Fenton digestion on the recovery rate of the micro-nanoplastic measured by adding standard material. DESCRIPTION OF THE EMBODIMENTS

[0008] Micro-nanoplastics encompass a wide variety of materials, making quantitative analysis of each type a challenging task. However, micro-nanoplastics are a type of typical carbonaceous particles. Therefore, the total organic carbon content of the micro-nanoplastics can be characterized by the total organic carbon (TOC) value of the micro-nanoplastics. Because a large amount of natural organic matter (NOM) in the natural aquatic environment will interfere with the TOC measurement of micro-nanoplastics, digestion processing is required to eliminate the interference from NOM. The TOC value of a solid sample is generally determined using a catalytic combustion method, in which the solid sample is completely converted into CO2 under the interaction of a catalyst at 900°C and high-purity oxygen.The generated CO2 is introduced into a non-dispersive infrared (NDIR) absorption detector to determine the TOC content. Currently, a method for characterizing the total content of the micro-nanoplastic using TOC or a method for quantitatively determining the total content of the micro-nanoplastic based on TOC has not yet been reported.

[0009] The present invention discloses a method for quantitatively determining the total content of the micro-nano-plastic in the aquatic environment based on the total organic carbon, comprising the following steps: (1) filtering a water sample through a first enrichment membrane, and collecting and obtaining a first solid; (2) adding a digestion reagent to the first enrichment membrane carrying the first solid to digest and remove natural organic matter; (3) filtering the mixture obtained in step (2) through a second enrichment membrane to obtain the second solid-supporting second enrichment membrane; and (4) Drying the digested first enrichment membrane and the second solid-supporting second enrichment membrane from step (3), and then determining the total organic carbon value, which is the total organic carbon value of the micro-nano-plastic.

[0010] In step (2) in some embodiments of the present invention, the pH of the digestion reagent is less than 3.

[0011] In step (2) in some embodiments of the present invention, the digestion temperature is 25 to 60 °C, and the digestion time is 0.5 to 2 hours.

[0012] In step (2) in some embodiments of the present invention, the digestion reagent comprises a Fenton's reagent.

[0013] In step (4) in some embodiments of the present invention, the drying temperature in the drying step is 60 to 190°C.

[0014] In step (4) in some embodiments of the present invention, the drying time in the drying step is 0.5 to 6 hours.

[0015] In step (4) in some embodiments of the present invention, in the drying step, the first enrichment membrane and the second enrichment membrane are placed directly in a sample boat and dried.

[0016] In step (4) in some embodiments of the present invention, the instrument used in the step of determining the total organic carbon value of the micro-nano-plastic comprises a total organic carbon analyzer equipped with a solid-state accessory, wherein the detector of the total organic carbon analyzer is a non-dispersive infrared detector, wherein the carrier gas in the total organic carbon analyzer contains oxygen, the carrier gas flow rate is 400 to 500 ml / min, the pressure is 190 to 200 kPa, and the reaction furnace temperature is 900 to 1200°C.

[0017] In some embodiments of the present invention, the first enrichment membrane and the second enrichment membrane both comprise a glass fiber membrane, an alumina membrane, or a quartz membrane.

[0018] In some embodiments of the present invention, the pore diameter of the glass fiber membrane is 1 to 1000 nm.

[0019] In an exemplary embodiment, the method for quantitatively determining the total content of the micro-nano-plastic in environmental waters according to the present invention comprises the following steps: Filtering an environmental water sample through a glass fiber membrane to capture and enrich the micro-nano-plastic in the water sample; Removal of the natural organic matter (NOM) on the membrane with the enriched micro-nanoplastic by digestion with a Fenton's reagent; filtering the digestion fluid through a new glass fiber membrane, and drying the two membranes (namely glass fiber membranes) at 60°C-190°C for 0.5-6 hours; and Determining the TOC value by a TOC meter equipped with a solid-state accessory to represent the total content of the micro-nano-plastic by the TOC value.

[0020] Here, TOC is used as a parameter to quantitatively represent the total content of the micro-nano-plastic.

[0021] Here, the membrane for retention and enrichment is a glass fiber membrane. Here, the method for NOM removal is Fenton digestion, and the digestion reagent is Fenton's reagent. The Fenton's reagent is prepared by mixing a 30% (w / v) H2O2 solution and a 0.05 mol / L Fe 2+ Solution with equal volumes was obtained.

[0022] Here is Fe 2+ FeSO4·7H2O or another iron salt with a divalent iron ion, while the digestion condition with Fenton's reagent is pH <3.

[0023] Here, the two membranes are placed directly in a sample boat and dried. The TOC value is measured after drying.

[0024] Here, the membranes containing the retained and enriched micro-nanoplastic are treated with Fenton digestion to remove NOM and simultaneously remove inorganic carbon (IC). The measured total carbon (TC) value is then the TOC value.

[0025] Here the two membranes are dried for 0.5-6 hours at 60°C-190°C.

[0026] The purpose here is to remove the water on the membrane without destroying the micro-nanoplastic. Temperatures between 60 and 190°C will not affect the measurement of the micro-nanoplastic.

[0027] Here, the TOC value of the micro-nano-plastic on the glass fiber membranes is measured using a TOC meter equipped with a solid-state accessory.

[0028] Here, the detector is a non-dispersive infrared detector (NDIR), the carrier gas is high-purity oxygen, and the flow rate is 400-500 ml / min, and the pressure is 190-200 kPa, and the TC reaction furnace temperature is 900-1200°C.

[0029] The technical solutions of the present invention are further explained below through specific examples in combination with the drawings. It should be noted that the following specific embodiments are merely illustrative, and the scope of the present invention is not limited thereto.

[0030] The chemicals and raw materials used in the following examples are all commercially available or are manufactured in-house using known manufacturing processes.

[0031] This example provides a method for the quantitative determination of micro-nano-plastics in an aquatic environment. As shown in Fig.1, the method included the following steps: (1) Filtering the water sample to be tested through a glass fiber membrane with nanopores so that the micro-nano-plastic particles were retained and enriched on the glass fiber membrane; (2) Removal of the natural organic matter (NOM) on the membrane enriched with micro-nano-plastic particles by digestion treatment with a Fenton's reagent; (3) Filtration through another new glass fiber membrane, and washing the container wall three times with ultrapure water (18.3 MΩ), and drying the two membranes at 60°C-190°C for 0.5 to 6 hours; (4) Determine the TOC value at the end by a TOC meter connected to a solid-state accessory to represent the total content of the micro-nano-plastic by the TOC value.

[0032] In step (1), a glass fiber membrane with a nanopore diameter (1-1000 nm) is used. The glass fiber membrane is made of carbon-free glass fiber, so it does not interfere with the TOC measurement. A dense fiber structure is conducive to the retention and enrichment of micro-nano-plastic particles. As described in Fig. As shown in Figure 1, the micro-nanoplastic is retained and enriched in the dense glass fiber membrane structure. The dense glass fiber membrane structure plays a role in the enrichment of the micro-nanoplastic.

[0033] As in Fig. In Figure 2, the arrow points to the micro-nanoplastic. The plastic particles are retained on the glass fiber membrane.

[0034] As in Fig.Figure 3 shows the influence of the volume of the filtered water sample on the recovery rate of the micro-nanoplastic. Several types of micro-nanoplastic with different carbon contents are added as standard materials to 100 to 1000 mL of ultrapure water. The recovery rates measured by adding the standard materials are between 84% and 99%. It is found that with a filtered water sample volume of 1000 mL, the recovery rate of the micro-nanoplastic measured by adding the standard material is not significantly reduced, and the membrane is not completely blocked or penetrated. As shown in Fig. As shown in Figure 3, the recovery rate of the micro-nanoplastic does not decrease significantly when the volume of the filtered water sample is increased from 100 ml to 1000 ml.

[0035] In step (2), a large amount of NOM is present in the natural environmental water body. When such a natural environmental water body is filtered with a membrane, a portion of NOM will inevitably be retained on the membrane. If this portion of NOM is not treated, the TOC measurement will be disturbed. A digestion treatment with Fenton's reagent (H2O2 (5 ml, 30% (w / v)) and Fe 2+ (5 ml 0.05 mol / L)) is performed to eliminate the interference of NOM. As in Fig.Figure 4 shows the recovery rates of the micro-nanoplastics measured without digestion for water samples spiked with standard materials and two different matrices (river water and seawater). The recovery rates of the micro-nanoplastics measured after digestion by adding standard materials were 119% to 206% for river water and 124% to 218% for seawater. The recovery rates of the micro-nanoplastics measured after digestion by adding standard materials were 90% to 96% for river water and 95% to 111% for seawater. This shows that Fenton's reagent can very effectively eliminate the interference of NOM and does not affect the recovery rate of the micro-nanoplastics. Fig. As shown in Figure 4, the recovery rates of the micro-nanoplastic without Fenton digestion are well over 100%, regardless of whether the matrix is ​​river water or seawater. After digestion, the recovery rates of the micro-nanoplastic are close to 90%.

[0036] In step (3), the purpose of washing three times with ultrapure water is to transfer the micro-nano-plastic adsorbed on the container wall to the film as much as possible, and the purpose of drying the two membranes at 60°C-190°C for 0.5 to 6 hours is to remove the moisture for subsequent TOC measurement, and temperature control at 60°C has no influence on the micro-nano-plastic.

[0037] In step (4), the two membranes to be tested are placed directly into the ceramic sample boat without any additional treatment. When the micro-nanoplastic is sufficiently exposed to high-purity oxygen at high temperature and under catalytic conditions, it can completely convert to CO2.

[0038] Under the above-mentioned optimal experimental conditions, the micro-nanoplastic measured by the method of the present invention has a linear range of 0.02 - 3.6 mg C (correlation coefficient 0.998), and the detection limit thereof is 14 - 19 µg C / L. Example 1

[0039] Quantitative measurements of micro-nano-plastic in water bodies with different matrices were carried out.

[0040] First, water samples of 100 to 1000 ml containing various matrices were passed through glass fiber membranes with a pore diameter of 300 nm. The micro-nanoplastic particles were retained and enriched on the glass fiber membrane. The glass fiber membrane was transferred to a glass container. Digestion was carried out with Fenton's reagent (H2O2 (5 ml, 30% w / v)) and Fe 2+(5 ml 0.05 mol / L)) was performed to eliminate the interference of NOM. The digested solution was then filtered through another membrane and washed with ultrapure water (18.3 MΩ) three times. Then, the two membranes were transferred to a sample boat and dried at 60°C–190°C for 0.5–6 hours to remove water. Finally, TOC was measured using a TOC meter connected to a solid-state accessory. The total content of micro-nanoplastics was represented by the TOC value. The results are shown in Table 1. Micro-nanoplastics were not found in the water samples from Daliaohe River, Luanhe River, and Bohai Sea 2. This means that there was no micro-nanoplastic in these samples, or the concentration of micro-nanoplastics was much lower than the detection limit of this method.In the samples from Bohai Sea 1, Bohai Sea 3, Bohai Sea 4 and Bohai Sea 5, 17 to 67 µg C / L were detected, indicating that this method can be used to determine the micro-nanoplastic at a low concentration level in the environment. Table 1 The measurement results of the total content of the micro-nano-plastic in actual environmental water bodies using the present method sample TOC (µg C / L, mean ± standard deviation, n=3) Daliaohe River ND* Luanhe River ND Bohai Sea 1 17 ± 3 Bohai Sea 2 ND Bohai Sea 3 67 ± 3 Bohai Sea 4 38 ± 1 Bohai Sea 5 31 ± 5 ND*: below the detection limit

[0041] According to the above specific embodiments, the method for quantitatively determining the total content of the micro-nano-plastic in an aquatic environment based on the total organic carbon of the present invention has at least one of the following advantages over the prior art. 1. In the present invention, the TOC value of micro-nanoplastics is used to represent the total content of micro-nanoplastics. Measurements of the total content of micro-nanoplastics can be performed at the µg C / L level. This method has already been applied to accurately determine the total content of micro-nanoplastics in actual water samples. 2. The sensitivity is high, and the detection limit of the method is 14-19 µg C / L. 3. The operation is simple and the operating cost is low.

[0042] The specific embodiments described above further describe the purpose, technical solutions, and advantageous effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modification, equivalent replacement, and improvement, etc., within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims

[1] Method for the quantitative determination of the total content of the micro-nano-plastic in the aquatic environment based on the total organic carbon, comprising the following steps: (1) filtering a water sample through a first enrichment membrane, and collecting and obtaining a first solid; (2) adding a digestion reagent to the first enrichment membrane carrying the first solid to digest and remove natural organic matter; (3) filtering the mixture obtained in step (2) through a second enrichment membrane to obtain the second solid-supporting second enrichment membrane; and (4) Drying the digested first enrichment membrane and the second solid-supporting second enrichment membrane from step (3), and then determining the total organic carbon value, which is the total organic carbon value of the micro-nano-plastic. [2] Method according to claim 1, characterized by that the pH of the digestion reagent in step (2) is less than 3. [3] Method according to claim 1, characterized by that in step (2) the digestion temperature is 25 to 60 °C and the digestion time is 0.5 to 2 hours. [4] Method according to claim 1, characterized by that the digestion reagent in step (2) comprises a Fenton's reagent. [5] Method according to claim 1, characterized by that the drying temperature in the drying step in step (4) is 60 to 190°C. [6] Method according to claim 1, characterized bythat the drying time in the drying step in step (4) is 0.5 to 6 hours. [7] Method according to claim 1, characterized by that in the drying step in step (4) the first enrichment membrane and the second enrichment membrane are placed directly in a sample boat and dried. [8] Method according to claim 1, characterized by that the instrument used in the step of determining the total organic carbon value of the micro-nano-plastic in step (4) comprises a total organic carbon analyzer equipped with a solid-state accessory, wherein the detector of the total organic carbon analyzer is a non-dispersive infrared detector, wherein the carrier gas in the total organic carbon analyzer contains oxygen, the carrier gas flow rate is 400 to 500 ml / min, the pressure is 190 to 200 kPa, and the reaction furnace temperature is 900 to 1200°C. [9] Method according to claim 1, characterized by that the first enrichment membrane and the second enrichment membrane both comprise a glass fiber membrane, an alumina membrane or a quartz membrane. [10] Method according to claim 9, characterized by that the pore diameter of the glass fiber membrane is 1 to 1000 nm.

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