A method for estimating the amount of microplastics buried in marine sediments

Abstract

This invention provides a method for estimating the amount of microplastics buried in marine sediments, belonging to the field of environmental monitoring technology. The method includes obtaining all microplastics by sample and sediment processing, as well as qualitative and quantitative analysis of microplastics. The estimation method of this invention can accurately calculate the existing amount of microplastics in the environment, providing an effective basis for the control of marine microplastic pollution.

Description

Technical Field

[0001] This invention belongs to the field of environmental monitoring technology, specifically relating to a method for estimating the amount of microplastics buried in marine sediments. Background Technology

[0002] Plastics, with their advantages of being lightweight, inexpensive, chemically stable, and water-resistant, are widely used in the manufacture of various products. However, most plastic products have a short lifespan, and due to the lack of a comprehensive recycling and treatment mechanism, they easily enter the ocean through surface runoff and other pathways. Plastic pollution has become a major global environmental problem, alongside climate change, ozone depletion, and ocean acidification. Plastics can persist in the marine environment for extended periods and break down into microplastics under the influence of ultraviolet radiation, ocean currents, and microorganisms, resulting in a large accumulation of microplastics in the marine environment. Due to the different types of microplastic polymers, their densities vary. On the one hand, microplastics with a density greater than that of seawater will settle into sediments. On the other hand, microplastics with a density less than that of seawater will initially float in the water column, but after interacting with other pollutants, fouling organisms, and organic matter, their density increases, and they will eventually settle into sediments as well. Approximately 99% of microplastics in the marine environment will settle into sediments. Therefore, marine sediments are considered the final sink for microplastics. The current status of microplastic pollution in marine sediments has become a hot topic in the environmental field. However, there are currently few reports internationally on methods for estimating the amount of microplastics buried in sediments. Therefore, establishing a marine sediment environmental monitoring system for microplastics and conducting research on the amount of microplastics buried in sediments are of great significance for protecting the health and sustainable development of the marine environment.

[0003] The abundance of microplastics in sediments is typically 1-3 orders of magnitude higher than in seawater. For example, in Sangou Bay, the largest mariculture area in northern my country, the abundance of microplastics in seawater is 20.06 CFU / L, while it reaches as high as 1674 CFU / kg in sediments. In Da Nang, Vietnam, the Rhine River estuary, and the western Pacific Ocean, the abundance of microplastics in sediments is as high as 9238 ± 2097 CFU / kg and 3300 CFU / kg, respectively. Microplastics in sediments not only have negative effects on benthic organisms, but typhoons and ocean currents can also resuspend microplastics in sediments, further impacting organisms in the water column. Therefore, clarifying the amount of microplastics buried in sediments is a crucial foundation for understanding the fate of microplastics in the ocean. However, there is currently no clear method for calculating the amount of microplastics buried in marine sediments. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for estimating the amount of microplastics buried in marine sediments, wherein the method estimates the amount of microplastics buried in marine sediments through a calculation formula.

[0005] Sediments are considered the most important "sink" for marine microplastics. Microplastics with a density greater than seawater settle into sediments under gravity, while those with a density less than seawater float or remain suspended in the water. However, these microplastics may have microorganisms attached to their surfaces, causing their density to increase, and when their density exceeds that of seawater, they will also settle into the sediments. Once settled in sediments, microplastics will remain buried for a long time if there is no other disturbance on the seabed. Numerous pieces of evidence indicate that sedimentary environments such as deep-sea bottoms, submarine canyons, and nearshore shallow-sea sediments are all "sinks" for microplastics. Marine sediments also possess a significant potential for microplastic enrichment. Scholars estimate that approximately 5.25 trillion plastic particles (weighing about 269 million tons) float in global seawater, 92% of which exist in the form of microplastics. However, the actual observed microplastic content in seawater is only about one percent of the predicted content, indicating that a large amount of microplastics has already settled into sediments. Currently, research on microplastics in marine sediments mainly focuses on analyzing their abundance, lacking comprehensive studies on their burial volume. This invention aims to collect seabed sediments from different marine areas to obtain key parameters such as microplastic abundance, average microplastic size, average microplastic density, and sediment density; to construct calculation formulas applicable to the microplastic burial amount in sediments from different marine areas and nearshore tidal flats; and to obtain the microplastic burial amount in sediments from different marine areas by substituting the aforementioned key parameters into the calculation formulas. This invention can provide technical support for the supervision of microplastic pollution in my country's marine environment and is of great significance for the control of marine microplastic pollution.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for estimating the amount of microplastics buried in marine sediments, the method comprising obtaining all microplastics by sample and sediment treatment, and qualitative and quantitative analysis of microplastics;

[0008] The specific steps for the qualitative and quantitative analysis of microplastics are as follows:

[0009] ① Composition: Determine the compositional characteristics of microplastics;

[0010] ② Shape: Divided into granular / spherical, fibrous, and thin-layered forms;

[0011] ③ Sizes: Divided into 1 μm-0.5 mm, 0.5-1 mm, 1-2 mm, 2-3 mm, 3-4 mm, and 4-5 mm;

[0012] ④ Average volume of microplastics :

[0013] ;

[0014] , , The average volumes of granular / spherical, fibrous, and thin-layer microplastics are respectively; The average diameter of granular or spherical microplastics; The average diameter of the cross-section of the fibrous microplastic; The average length of the thin-layered microplastics; The average width of the thin-layered microplastics; The average thickness of the thin-layered microplastics; , , These represent the percentages of particulate / spherical, fibrous, and thin-layer microplastics in the total number of microplastics; , , These represent the quantities of granular / spherical, fibrous, and thin-layered microplastics, respectively. This represents the total number of microplastics. denoted as the average volume of the microplastics, and h as the average length of the fibrous microplastics.

[0015] ⑤ Average density of microplastics ρ:

[0016] ;

[0017] , The percentage of microplastics of different components in the total number of microplastics; The number of microplastics in different components; and The density of microplastics with different compositions.

[0018] ⑥ Microplastic content in sediments The current stock of microplastics in marine sediments is calculated using the following formula:

[0019]

[0020]

[0021] In the formula The number of representative sea areas, This indicates the number of microplastics buried in sediments in different regions. Indicates the abundance of microplastics in sediments from different regions. Indicates the area of ​​different sea areas. Indicates the depth of sediment sampling. The density of sediments in different regions is calculated using the ring sampler method; symbol These represent different areas, including coastal waters, the center of the bay, and the mouth of the bay; This indicates the amount of microplastics buried in sediments from different regions. This represents the average volume of microplastics. This indicates the average density of microplastics.

[0022] The sediment was processed to obtain all microplastics: ① The wet density of the sediment was determined using the ring cutter method, and then the sediment was placed in an oven at 60°C to dry. After it was completely dried, it was weighed again in a glass beaker. 250 ml of saturated sodium chloride solution was added and stirred. After standing for 6 h, the upper liquid was sucked out using a vacuum suction device. This was repeated 3 times to ensure that all microplastics were suspended in the upper liquid. The upper liquid was then passed through a 30 μm stainless steel sieve.

[0023] ② Mark and weigh a clean, dry container, accurate to 0.1 mg; transfer all the solids from the 30 μm stainless steel sieve to the container, rinse the sieve with distilled water; dry the container;

[0024] ③ Wet hydrogen peroxide oxidation method: Add 30% H2O2 by volume and let stand; place a stir bar and cover with a watch glass; heat at 75°C for 30 min; if organic matter can be observed, add another 30% H2O2 by volume; repeat the above steps until all organic matter is digested; add NaCl solid according to the remaining liquid volume until saturation.

[0025] ④ Density separation: Transfer all the solution from step ③ to a separatory funnel; allow it to settle overnight; observe whether there are microplastics in the precipitated solid. If so, remove the precipitated solid from the separatory funnel and take out the microplastics; discard the precipitated solid; collect all the floating solids onto a 30μm stainless steel sieve for microscopic observation.

[0026] The advantages of this invention compared to existing technologies are as follows: Although scholars have conducted extensive research on the sample collection, pretreatment, qualitative and quantitative analysis of microplastics, this invention aims to establish a method for estimating the burial flux of microplastics in marine sediments based on previous research methods. Sediments from different sea areas are then collected, and the physicochemical characteristics of microplastics are obtained. By accurately calculating the average volume and average density of microplastics and substituting them into a formula, the burial amount of microplastics in the sediments can be obtained. This estimation method can accurately calculate the existing amount of microplastics in the environment, providing an effective basis for the remediation of marine microplastic pollution. Attached Figure Description

[0027] Figure 1 Sampling station location map (May 2023);

[0028] Figure 2 Microscopic characterization of different microplastics;

[0029] Figure 3Fourier transform infrared spectra of different microplastics: A. cellulose, B. polyethylene, C. polystyrene, D. polypropylene. Detailed Implementation

[0030] The present invention is described below by way of example only to show that the invention can be repeatedly implemented and can achieve outstanding substantial effects, but does not constitute a limitation on the present invention.

[0031] Example 1

[0032] (1) Sample collection: The sampling location was near the Laoshan shoreline in Jiaozhou Bay; the sampling time was March 2023 (spring). Sediments were successfully sampled from 8 sites, such as... Figure 1 Eight sites are shown. A Van Veen sampler from HYDRO-BIOS (Germany) was used to obtain approximately 5 cm of top sediment. The sediment samples were then transferred to aluminum foil bags using a stainless steel scraper and stored at -20°C until analysis.

[0033] (2) Separation of microplastics from sediments: In the laboratory, distilled water and solutions were filtered through a 45 μm filter, and all equipment was rinsed with distilled water to ensure no plastic contamination during the experiment. Each sample was weighed approximately 300 g, dried in an oven, and weighed again in a glass beaker. Then, 250 ml of saturated NaCl solution was added and stirred for 2 minutes to ensure suspension of microplastics. After standing for 12 hours, the supernatant was filtered through a 30 μm membrane using a vacuum suction device and repeatedly washed with distilled water to remove NaCl. The material on the membrane was transferred to a glass beaker, and 30% H2O2 (v / v) was added in the presence of Fe(II) catalyst to remove organic matter, followed by suspension with saturated NaCl solution. The supernatant was filtered through a 30 μm membrane and washed with distilled water to remove NaCl. Finally, the membrane was placed in a glass petri dish for analysis.

[0034] (3) Observation and identification: Microplastics were counted and photographed using an optical microscope (Olympus BX-51, Japan). Microplastics were classified into six size grades: <0.5 mm, 0.5-1 mm, 1-2 mm, 2-3 mm, 3-4 mm, and 4-5 mm; their shapes were classified as granular / spherical, fibrous, and lamellar. Figure 2 As shown, the composition of the suspected plastics was identified using Fourier transform infrared microscopy (micro-FTIR; ThermoFisher Nicolet iN10, USA). Each sample was analyzed using Fourier transform infrared spectroscopy at 4000 and 650 cm⁻¹. -1 Between, the resolution is 8cm -1 Using a 3-second collection time, 16 total scans were performed. For example... Figure 3As shown, each spectrum was compared with the OMNIC standard spectral library. Suspicious particles were identified as microplastics when the match was greater than 70%. The actual number of microplastics was recalculated based on the number of previous works. The abundance of microplastics was determined by dividing the number of identified microplastics by the dry weight of the sediment (cells / kg dw).

[0035] (4) Estimating the amount of microplastics buried in sediments: The calculation of the amount of microplastics buried in sediments is divided into three steps.

[0036] The first step involved determining the sediment density in different sea areas using the ring cutter method. The sediment densities at the eight stations were 1690.69 kg / m³. 3 1749.36 kg / m 3 1720.35 kg / m 3 1688.12 kg / m 3 1698.25 kg / m 3 1710.97kg / m 3 1682.69 kg / m 3 1759.36 kg / m 3 The second step involved determining the quantity and abundance of microplastics through steps (2) and (3). The number of microplastics in the sediments from the eight stations were 9, 11, 4, 7, 8, 10, 3, and 6, respectively. The abundance of microplastics in the sediments from the eight stations were 27.70 / kg, 34.48 / kg, 10.87 / kg, 22.01 / kg, 25.72 / kg, 28.41 / kg, 9.06 / kg, and 17.54 / kg, respectively. The third step involved determining the physicochemical properties of the microplastics. A total of 58 microplastics were detected in all samples, including 19 granular / spherical microplastics, 31 fibrous microplastics, and 8 thin-layered microplastics. The proportion of particles / spheres in the total quantity was 32.76%. The proportion of fibrous material was 53.45% of the total. Thin-layered particles accounted for 13.79% of the total. Average radius of particles / spheres. It is 30 μm; the average length of the fibrous structure is 170μm, cross-sectional radius 5 μm; average length of thin film It is 120μm in diameter and has an average width. It is 80μm in diameter and has an average thickness of [missing information]. It is 10 μm; calculated according to the formula. The average volume of microplastics was obtained. It is 5.74 -8 cm 3The composition includes 13 polystyrene components, 12 polyethylene components, 26 polypropylene components, and 7 cellulose components. Polystyrene (PS) accounts for 22.41% of the total, with a density of 1.05 g / cm³; polyethylene (PE) accounts for 20.69%, with a density of 0.95 g / cm³; polypropylene (PP) accounts for 44.83%, with a density of 0.90 g / cm³; and cellulose (CE) accounts for 12.07%, with a density of 1.55 g / cm³. According to the formula...

[0037] ;

[0038] The average density of microplastics was obtained It is 1.022 g / cm³ 3 The water area surrounding the 8 stations Press 4.5 10 6 m 2 Calculation. Based on the formula for calculating the quantity buried. calculate,

[0039] .

[0040] The total amount of microplastics in nearshore sediments from Maidong Bay to Shazikou Bay was determined. It is 6.77 10 Quantity calculated according to the formula for the number of buried items. calculate, 6.77 10 1.022g / cm 3 5.74 -8 cm 3 The results showed that the amount of microplastics buried in the nearshore sediments from Maidong Bay to Shazikou Bay was 3.96 kg.

[0041] The method of this invention is used to process samples from different sea areas, and to statistically analyze information such as sediment density, microplastic abundance, microplastic composition, average volume and average density of microplastics in different sea areas; a calculation formula applicable to the amount of microplastics buried in sediments of different sea areas and nearshore tidal flats is constructed; the above key parameters are substituted into the calculation formula to obtain the amount of microplastics buried in sediments of different sea areas.

Claims

1. A method for estimating the amount of microplastics buried in marine sediments, characterized in that, The method includes obtaining all microplastics and qualitative and quantitative analysis of microplastics by processing samples and sediments. The specific steps for the qualitative and quantitative analysis of microplastics are as follows: ① Composition: Determine the compositional characteristics of microplastics; ② Shape: Divided into granular or spherical, fibrous, and thin-layered forms; ③ Size: Divided into 1μm-0.5 mm, 0.5-1 mm, 1-2 mm, 2-3 mm, 3-4 mm, and 4-5 mm; ④ Average volume of microplastics : ； , , The average volumes of granular / spherical, fibrous, and thin-layer microplastics are respectively; The average diameter of granular or spherical microplastics; The average diameter of the cross-section of the fibrous microplastic; The average length of the thin-layered microplastics; The average width of the thin-layered microplastics; The average thickness of the thin-layered microplastics; , , These represent the percentages of particulate / spherical, fibrous, and thin-layer microplastics in the total number of microplastics; , , These represent the quantities of granular / spherical, fibrous, and thin-layered microplastics, respectively. This represents the total number of microplastics. The average volume of the microplastics. h The average length of the fibrous microplastics; ⑤ Average density of microplastics ρ : ； ； , The percentage of microplastics of different components in the total number of microplastics; The number of microplastics in different components; and Density of microplastics with different compositions; ⑥ Microplastic content in sediments The current stock of microplastics in marine sediments is calculated using the following formula: ； ； In the formula The number of representative sea areas This indicates the number of microplastics buried in sediments in different regions. Indicates the abundance of microplastics in sediments from different regions. Indicates the area of ​​different sea areas. Indicates the depth of sediment sampling. The density of sediments in different regions is calculated using the ring sampler method; symbol These represent different areas, including coastal waters, the center of the bay, and the mouth of the bay; This indicates the amount of microplastics buried in sediments from different regions. This represents the average volume of microplastics. This indicates the average density of the microplastics. The treatment of the sediment to obtain all microplastics: ① The wet density of the sediment was determined by the ring cutter method, and then the sediment was placed in an oven to dry. After it was completely dried, it was weighed again in a glass beaker; saturated sodium chloride solution was added and stirred, and the sediment was allowed to stand. The upper liquid was then sucked out using a vacuum suction device to ensure that all microplastics were suspended in the upper liquid. The upper liquid was then passed through a 30μm stainless steel sieve. ② Mark and weigh a clean and dry container; transfer all the solids from the 30μm stainless steel sieve in step ① into the container, rinse the sieve with distilled water; dry the container; ③ Wet hydrogen peroxide oxidation method: Add 30% H2O2 by volume and let stand; place a stir bar and cover with a watch glass; heat at 75℃ for 30 min; if organic matter can be observed, add another 30% H2O2 by volume; repeat the above steps until all organic matter is digested; add NaCl solid according to the remaining liquid volume until saturation. ④ Density separation: Transfer all the solution from step ③ to a separatory funnel; allow it to settle overnight; collect all floating solids onto a 30μm stainless steel sieve for microscopic observation.

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