Method for evaluating ecological risk of microplastics based on population and community indicators

Abstract

The application provides a method for evaluating ecological risk of microplastics based on population and community indexes, and belongs to the technical field of pollutant risk evaluation. The application studies the influence of microplastic concentration and particle size on the filter-feeding speed of Daphnia magna, analyzes the relationship between microplastic intake and algal morphology, and studies the influence of microplastics on the movement ability and filter-feeding of Daphnia magna after the microplastics are taken into the body, so as to evaluate the ecological risk of microplastics at a concentration far below the lethal concentration from the perspective of population and community. It is found for the first time that Daphnia magna will mistake microplastics similar in size to algal cells as food, and after the microplastics are taken into the body, the behavior characteristics of zooplankton will be affected, so that the harm of microplastics to zooplankton is comprehensively evaluated from the perspective of behavior and interspecific relationship. The application provides a new idea for evaluating ecological risk of microplastics from the perspective of population and community, and provides a basis for correctly formulating pollutant emission standards.

Description

Technical Field

[0001] This invention belongs to the field of pollutant risk assessment technology, and in particular relates to a method for assessing the ecological risk of microplastics based on population and community indicators. Background Technology

[0002] As microplastic pollution becomes increasingly serious, assessing the ecological risks of microplastics is gaining growing attention. Microplastics can be ingested by organisms at different trophic levels, adversely affecting their feeding, behavior, growth, development, reproductive capacity, and gene expression, and even causing lethal effects. Furthermore, microplastics have a large specific surface area, enabling them to adsorb microorganisms, organic pollutants, and heavy metals, allowing harmful substances to be transported to more distant locations and placing a heavier burden on ecosystems.

[0003] Among numerous aquatic organisms, phytoplankton and zooplankton occupy the bottom of the food chain in aquatic ecosystems, determining the structure and functional dynamics of these ecosystems. These organisms are small and highly sensitive to environmental pollutants, often serving as model organisms to evaluate the impact of environmental pollutants on aquatic ecosystems. The toxic effects of microplastics on organisms can not only alter the traits of individual organisms but also lead to changes in interspecies relationships through differences in individual responses. Furthermore, the negative impacts can be amplified through food chain transmission, ultimately affecting the structure and function of aquatic ecosystems.

[0004] However, current research on microplastic pollution in water bodies focuses on the toxic effects of microplastic concentrations on individual planktonic organisms, neglecting the fundamental fact that microplastic particle sizes vary widely in the environment. Furthermore, studies at other population and community levels rely primarily on theoretical models for prediction, with almost no direct experimental evidence. Therefore, there is an urgent need to develop a method based on population and community indicators to evaluate the process and harm of microplastic ingestion by Daphnia macrocarpa. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for evaluating the ecological risk of microplastics based on population and community indicators, which comprehensively evaluates the ecological risk posed by microplastics at concentrations far below lethal levels from the perspective of population and community.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for evaluating the ecological risk of microplastics based on population and community indicators, comprising the following steps:

[0008] S1. Microplastic solution, algal solution and large Daphnia are placed in the same system to form an algae-Daphnia system;

[0009] Microplastic solution and algal solution were placed in the same system to form an algal system, which served as a control group;

[0010] Microplastic solution and large daphnia are placed in the same system to form a daphnia system;

[0011] The algae mentioned are one of Chlorella, Scenedesmus tetracauda, ​​and Narrow-shaped fibrous algae;

[0012] S2. Based on the filter-feeding efficiency of the algae-daphnia system and the algae system, the number of microplastic particles filtered in the algae-daphnia system and the algae system is counted, and the ecological risk of microplastics is evaluated.

[0013] S3. Statistically analyze the changes in behavioral indicators of large Daphnia in the Daphnia system to assess the ecological risks of microplastics.

[0014] Preferably, the method for calculating the filter efficiency is as follows:

[0015] The algal cell density in the algae-daphnia system and the algae system were counted separately, and the number of Daphnia macrocarpa in the algae-daphnia system was counted. Then, the filter feeding efficiency of Daphnia macrocarpa during the filter feeding process was calculated by substituting the data into Formula I.

[0016] Formula I: GR = V[In(C0) – In(C1)] / Nt

[0017] In the formula, GR is the filter feeding efficiency, in mL / animal·h; V is the culture volume, in mL; C0 is the algal cell density at the end of the algae system experiment, in cells / mL; C1 is the algal cell density at the end of the algae-daphnia system experiment, in cells / mL; N is the number of Daphnia macrocarpa; and t is the duration of the experiment, in h.

[0018] Preferably, the behavioral indicators include the heart rate and stroke rate of the giant daphnia.

[0019] Preferably, the final concentration of the microplastic solution is 0–10 mg / L; and the particle size of the microplastic solution is 5–32 μm.

[0020] Preferably, the initial density of the algal solution is 1×10⁻⁶. 5 ~4×10 5 cells / mL.

[0021] Preferably, the density of the large daphnia is 45-55 daphnia / L.

[0022] Preferably, before placing them in the same system, the domestication and cultivation of Daphnia and algae are also included.

[0023] In steps S2 and S3, the statistical time is 2 to 6 hours after the system is placed in the same system.

[0024] Preferably, the method for calculating the algal cell density is as follows:

[0025] When counting, select one diagonal of the plankton counting frame, and 10 squares on the counting line. Observe and record the number of algal cells using a counter. After recording the raw data, calculate the algal cell density according to Formula II:

[0026] Algal cell density in algal solution = A × 10 × 10 × B (Formula II)

[0027] In the formula, A represents the total number of algal cells in the 10 diagonal squares; B represents the dilution factor of the algal solution; and the unit of algal cell density in the algal solution is cells / mL.

[0028] Preferably, the particle size of the microplastic solution is 5–20 μm, 20–27 μm, and 27–32 μm; the final concentration gradient of the microplastic solution is 0 mg / L, 0.4 mg / L, 2 mg / L, and 10 mg / L.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] This invention provides a method for evaluating the ecological risk of microplastics based on population and community indicators. The invention studies the effects of microplastic concentration and particle size on the rate at which *Daphnia macrocarpa* filters algae, analyzes the relationship between microplastic ingestion and algal morphology, and investigates the impact of microplastic ingestion on the motility and filter-feeding ability of *Daphnia macrocarpa*. It evaluates the ecological risk posed by microplastics at concentrations far below lethal levels from the perspectives of population and community. This invention is the first to discover that *Daphnia macrocarpa* ingests microplastics similar in size to algal cells, revealing a potential mechanism for microplastic ingestion. After ingestion, microplastics affect the behavioral characteristics of zooplankton, reducing their ability to filter-feed phytoplankton. This provides a comprehensive evaluation of the harm of microplastics to plankton from behavioral and interspecific perspectives. The method of this invention is simple, easy to operate, convenient, and quick, with minimal harm to aquatic organisms, and the results are accurate and reliable. It provides a new approach to assessing the ecological risk of microplastics at the population and community levels and also provides a basis for the correct formulation of pollutant emission standards. Attached Figure Description

[0031] Figure 1 Particle size distribution of a 10 mg / L microplastic solution;

[0032] Figure 2 A schematic diagram showing the number of microplastic particles of different sizes and concentrations ingested by large Daphnia magna;

[0033] Figure 3 A schematic diagram showing the effect of microplastic solution concentration and particle size on the filter feeding efficiency of large Daphnia magna;

[0034] Figure 4 This is a schematic diagram showing the effects of microplastic concentration and particle size on the heartbeat and paddling frequency of Daphnia macrocarpa under algae-free conditions. Detailed Implementation

[0035] This invention provides a method for evaluating the ecological risk of microplastics based on population and community indicators, comprising the following steps:

[0036] S1. Microplastic solution, algal solution and large Daphnia are placed in the same system to form an algae-Daphnia system;

[0037] Microplastic solution and algal solution were placed in the same system to form an algal system, which served as a control group;

[0038] Microplastic solution and large daphnia are placed in the same system to form a daphnia system;

[0039] The algae mentioned are one of Chlorella, Scenedesmus tetracauda, ​​and Narrow-shaped fibrous algae;

[0040] S2. Based on the filter-feeding efficiency of the algae-daphnia system and the algae system, the number of microplastic particles filtered in the algae-daphnia system and the algae system is counted, and the ecological risk of microplastics is evaluated.

[0041] S3. Statistically analyze the changes in behavioral indicators of large Daphnia in the Daphnia system to assess the ecological risks of microplastics.

[0042] In this invention, before placing them in the same system, the process includes acclimatizing and culturing Daphnia macrocarpa and algae to select Daphnia macrocarpa in similar states and algae with similar growth rates. The method for acclimatizing and culturing Daphnia macrocarpa in this invention involves culturing Daphnia macrocarpa in COMBO medium for 10–14 hours, then transferring it to a light box for further cultivation, adding 0.5 × 10⁻⁶ ppm of the medium to the beaker daily. 5 ~1.5×10 5 The algae were cultured at a concentration of cells / mL, with the culture medium changed regularly (every 2 days). The method for acclimatizing and culturing the algae was as follows: *Chlorella vulgaris*, *Scenedesmus tetracauda*, and *Stenoptera fibrousa* were cultured separately in COMBO medium for 10–14 h, and then transferred to a light-controlled shaker. The preferred conditions for the light chamber and light-controlled shaker were: temperature 25 ± 1 °C, light cycle 14 h:10 h, and light intensity 120 μmol·m⁻¹. -2 s -1 The rotation speed is 30 rpm. In this invention, the COMBO culture medium needs to be sterilized in an autoclave at 121°C and 0.1 MPa for 30 minutes, then placed in a sterile laminar flow hood for cooling, and the pH of the COMBO culture medium is adjusted to 7.8. This invention does not have a special limitation on the source of the COMBO culture medium; products known in the art or commercially available products can be used.

[0043] As a preferred embodiment, after domesticating and culturing Daphnia macrocarpa and algae, Daphnia macrocarpa that is 1-3 days old and algae that have been cultured for 3-5 days are selected. The preferred method for selecting Daphnia macrocarpa is to pick out the larvae after they enter the reproductive period and expand their culture. From the cultured larvae, individuals of the same age, similar body length, and vigorous vitality are selected and subjected to appropriate starvation treatment. The preferred starvation treatment time is 1-3 hours. The preferred method for selecting algae is to use a phytoplankton classification fluorescence instrument (PHYTO-PAM) to measure the chlorophyll a concentration of Chlorella, Scenedesmus tetracauda, ​​and Narrow-spotted fibrous algae, plot algal growth curves to determine the algal growth status, and select well-grown pure cultures of algae with a growth time of 3-5 days after inoculation as the test algal species.

[0044] The Chlorella vulgaris, Scenedesmus quadricauda, ​​and Ankistrodesmus angustus used in this invention are preferably Chlorella vulgaris (FACHB–32), Scenedesmus quadricauda (FACHB–1297), and Ankistrodesmus angustus (FACHB–453), which have different cell sizes. The cell sizes of Chlorella vulgaris, Scenedesmus quadricauda, ​​and Ankistrodesmus angustus are shown in Table 1.

[0045] Table 1. Cell sizes of Chlorella, Scenedesmus tetracauda, ​​and Narrow-spotted Fiber Algae

[0046]

[0047] In this invention, filter-feeding and behavioral experiments were conducted to investigate the effects of microplastic concentration and particle size on the behavior of *Daphnia macrocarpa* at the population and community levels. The final concentration of the microplastic solution is preferably 0–10 mg / L; the particle size of the microplastic solution is preferably 5–32 μm. More preferably, the particle sizes of the microplastic solution are 5–20 μm, 20–27 μm, and 27–32 μm; the final concentration gradient of the microplastic solution is 0 mg / L, 0.4 mg / L, 2 mg / L, and 10 mg / L. The microplastic solution of this invention requires the use of a dispersant, Tween 80, to ensure uniform dispersion in the culture medium. The concentration of the microplastic solution in this invention is far lower than the lethal concentration of microplastics reported in the prior art. The effects of microplastic concentration and particle size on the filter-feeding rate of *Daphnia macrocarpa* on algae were investigated, and the relationship between microplastic ingestion and algal morphology was analyzed, resulting in safer environmental concentrations and particle sizes, providing a theoretical basis for the correct formulation of pollutant emission standards.

[0048] In this invention, the initial density of the algal solution is preferably 1 × 10⁻⁶. 5 ~4×10 5The cells / mL density of large daphnia is preferably 45-55 cells / L, and the statistical time is preferably 2-6 hours after the cells are placed in the same system.

[0049] In this invention, the preferred method for calculating the filter efficiency is as follows:

[0050] The algal cell density in the algae-daphnia system and the algae system were counted separately, and the number of Daphnia macrocarpa in the algae-daphnia system was counted. Then, the filter feeding efficiency of Daphnia macrocarpa during the filter feeding process was calculated by substituting the data into Formula I.

[0051] GR = V[In(C0) – In(C1)] / Nt Formula I

[0052] In the formula, GR is the filter feeding efficiency, in mL / animal·h; V is the culture volume, in mL; C0 is the algal cell density at the end of the algae system experiment, in cells / mL; C1 is the algal cell density at the end of the algae-daphnia system experiment, in cells / mL; N is the number of Daphnia macrocarpa; and t is the duration of the experiment, in h.

[0053] In this invention, the preferred method for calculating algal cell density is as follows:

[0054] When counting, select one diagonal of the plankton counting frame, and 10 squares on the counting line. Observe and record the number of algal cells using a counter. After recording the raw data, calculate the algal cell density according to Formula II:

[0055] Algal cell density in algal solution = A × 10 × 10 × B (Formula II)

[0056] In the formula, A represents the total number of algal cells in the 10 diagonal squares; B represents the dilution factor of the algal solution; and the unit of algal cell density in the algal solution is cells / mL.

[0057] In this invention, when determining the algal cell density in the algal solution, 1 mL of algal solution is taken each time and 10 μL of Lugol's reagent is added to stain and fix the algal sample.

[0058] In this invention, the preferred behavioral indicators include the heart rate and stroke rate of the large daphnia. The heart rate is captured under a microscope using biological microscope imaging software for 1 minute. The stroke rate is observed using a camera, placed vertically 20 cm above a beaker and shielded from light with a black cloth. Recordings are taken at 2, 4, and 6 hours of the experiment, each lasting 5 minutes.

[0059] This invention first explores the effects of microplastic concentration and particle size on the rate of microplastic filter-feeding by *Daphnia macrocarpa*, and analyzes the relationship between microplastic ingestion and algal morphology. It preliminarily reveals that microplastic ingestion by *Daphnia macrocarpa* is an active process, resulting from the misingestion of microplastics as phytoplankton of similar size. Therefore, the impact of microplastics of varying sizes on zooplankton filter-feeding of phytoplankton differs. The more similar the size of microplastics to the potential phytoplankton in the environment, the more likely they are to be mistakenly ingested by zooplankton. This provides a new explanatory mechanism for understanding the microplastic ingestion process of *Daphnia macrocarpa*.

[0060] The present invention further explores the effects of microplastic ingestion on the locomotion and filter feeding of large Daphnia magna. It confirms that inadvertent ingestion of microplastics can impair zooplankton behavior and further reduce the efficiency of zooplankton filter feeding on phytoplankton. Zooplankton behavior and filter feeding are bridges linking other individual and community characteristics; for example, zooplankton filter feeding is directly related to individual growth and development, while locomotion is related to zooplankton's ability to avoid predators at higher trophic levels. Therefore, by inhibiting zooplankton locomotion and reducing phytoplankton filter feeding efficiency, microplastics can further harm zooplankton growth, development, and survival, and transfer more microplastics to higher trophic levels, ultimately harming the entire ecosystem. This invention provides a new approach to assessing the ecological risk of microplastics at the population and community levels.

[0061] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0062] In the following embodiments, *Daphnia magna* was purchased from the Guangdong Provincial Institute of Laboratory Animal Monitoring. *Chlorella vulgaris* (FACHB–32), *Scenedesmus quadricauda* (FACHB–1297), and *Ankistrodesmus angustus* (FACHB–453) were purchased from the Freshwater Algae Culture Bank of the Wuhan Institute of Hydrobiology, Chinese Academy of Sciences.

[0063] Analysis of significant differences: SPSS software was used to test the homogeneity of variance for all data, and the significance level was set at P < 0.05. The effect of microplastic concentration or particle size on biological indicators was analyzed by one-way ANOVA; the effect of phytoplankton species, microplastic concentration and particle size on indicators of some organisms was analyzed by three-way ANOVA; the effect of microplastic concentration or particle size on biological indicators was analyzed by repeated measures ANOVA.

[0064] Example 1

[0065] A method for assessing the ecological risk of microplastics based on population and community indicators, comprising the following steps:

[0066] (1) Preparation of experimental materials

[0067] COMBO medium was sterilized in an autoclave at 121°C and 0.1 MPa for 30 minutes, then placed in a sterile laminar flow hood for cooling. After cooling for 12 hours, the pH was adjusted to 7.8 with 1 mol / L NaOH and HCl reagent to obtain sterilized COMBO medium.

[0068] Weigh the corresponding weight of microplastic powder using a 1 / 10000 electronic balance, and prepare microplastic solutions with corresponding concentrations of 0 mg / L, 0.4 mg / L, 2 mg / L, and 10 mg / L. Place the microplastic solutions on a magnetic stirrer and stir for 2 minutes, then place them in an ultrasonic cleaner and sonicate for 2 hours.

[0069] Microplastic solutions with different particle sizes at the above concentrations (0.4 mg / L, 2 mg / L, 10 mg / L) were prepared respectively, wherein the particle sizes of the microplastic solutions were 5–20 μm, 20–27 μm, and 27–32 μm.

[0070] Figure 1 This is a particle size distribution diagram for a 10 mg / L microplastic solution.

[0071] (2) Domestication and cultivation of algae and Daphnia macrocarpa

[0072] Chlorella, Scenedesmus tetracauda, ​​and Narrow-spotted fibrous algae were cultured separately in 1L Erlenmeyer flasks containing sterile COMBO medium and placed in a light shaker with a photothermal temperature of 25±1℃, a photoperiod of 14h:10h, and a light intensity of 120μmol·m⁻¹. -2 s -1 The algal solution was collected at 30 rpm every 24 hours and its chlorophyll a concentration was measured using PHYTO-PAM. Algae with good growth and pure culture 3-5 days after inoculation were selected as test algae.

[0073] Forty large Daphnia were transferred to 1L beakers containing 600mL of sterile COMBO medium and placed in a light incubator with a photoperiod of 25±1℃, a photoperiod of 14h:10h, and a light intensity of 120μmol·m⁻¹. -2 s -1 Rotation speed 30 rpm, daily concentration 1×10 5 Any of the above-mentioned algae with cells / mL were used as food, and dead individuals were removed using Pasteur tubes. The culture medium was changed every 2 days, and individuals of the same age, similar body length, and vigorous vitality were selected for future use.

[0074] (3) Experiment on the effects of microplastic concentration and particle size on macrophytes:

[0075] a. Select Daphnia macrocarpa that is 1-2 days old from the Daphnia macrocarpa cultured in step (2) as experimental material and starve them for 2 hours. Calculate the density of the three types of algae cultured for 3-5 days, and calculate the algal cell density according to the following formula:

[0076] Algal cell density (cells / mL) in 1 mL of algal solution = A × 10 × 10 × B

[0077] Note: A represents the total number of algal cells in the 10 diagonal squares; B represents the dilution factor of the algal solution.

[0078] b. The experiment included three microplastic solution particle sizes (5–20 μm, 20–27 μm, 27–32 μm), four microplastic solution concentrations (0 mg / L, 0.4 mg / L, 2 mg / L, 10 mg / L), two groups with and without algae, and two groups with and without Daphnia macrocarpa. Each treatment had six replicates.

[0079] Based on the set initial algal concentration of 2×10 5 Cell / mL: Add the above microplastic solution and algal solution (one of Chlorella, Scenedesmus tetracauda, ​​and Narrow-spotted fibrous algae) sequentially to the beaker, mix thoroughly, and then add 50 Daphnia magna (1-2 days old) per L to form an algae-Daphnia system. Place all beakers in an artificial climate chamber to begin the experiment.

[0080] Based on the set initial algal concentration of 2×10 5 The microplastic solution and algal solution (one of Chlorella, Scenedesmus tetracauda, ​​and Narrow-shaped fibrous algae) are added sequentially to a beaker at a cell / mL ratio and mixed thoroughly to form an algal system.

[0081] Add the above microplastic solution to a beaker in sequence, then add 50 large daphnia (1-2 days old) per liter, mix thoroughly to form a daphnia system.

[0082] Algal samples were extracted and the behavioral capabilities of large Daphnia were assessed at 2, 4, and 6 hours during the experiment.

[0083] Based on the algae-daphnia system and the algal cell density within the algae system, and by counting the number of Daphnia macrocarpa in the algae-daphnia system, the filter-feeding efficiency of Daphnia macrocarpa during the filter-feeding process is calculated using Formula I:

[0084] GR = V[In(C0) – In(C1)] / Nt Formula I

[0085] In the formula, GR is the filter feeding efficiency, in mL / animal·h; V is the culture volume, in mL; C0 is the algal cell density at the end of the algae system experiment, in cells / mL; C1 is the algal cell density at the end of the algae-daphnia system experiment, in cells / mL; N is the number of Daphnia macrocarpa; and t is the duration of the experiment, in h.

[0086] At the end of the experiment, the algae-daphnia system and the large daphnia in the daphnia system were washed with distilled water and pressed into tablets. The number of microplastic particles in the tablets was observed and counted under a biological microscope.

[0087] The heart rate and stroke rate of large daphnia in the daphnia system were statistically analyzed. The heart rate was captured under a microscope using biological microscope imaging software for 1 minute. The stroke rate was observed using a camera. The camera was placed vertically 20 cm above a beaker and shielded from light with a black cloth. Recordings were taken at 2, 4, and 6 hours of the experiment for 5 minutes each.

[0088] Figure 2 Data shows that the ingestion of microplastics by Daphnia macrocarpa is an active process. In systems containing Chlorella and Scenedesmus tetracauda (small-sized algae), Daphnia macrocarpa filters more small-sized (5-20 μm) microplastics; conversely, in systems containing narrow-shaped fibrous algae (large-sized algae), Daphnia macrocarpa filters more large-sized (27-32 μm) microplastics.

[0089] Figure 3 Data shows that in the algae-daphnia system, regardless of the particle size, the rate of large daphnia filter-feeding algae decreases with increasing microplastic concentration. In the Chlorella and Scenedesmus systems, the rate of large daphnia filter-feeding Chlorella decreases more significantly with increasing small-sized microplastic concentration, while in the narrow-fiber algae system, the filter-feeding efficiency decreases more significantly with increasing large-sized microplastic concentration.

[0090] Figure 4 The results showed that, without the addition of algae, regardless of the microplastic particle size, the heart rate and number of strokes of Daphnia macrocarpa decreased with increasing microplastic concentration, and these values ​​were significant throughout the entire experimental period.

[0091] In summary, the ingestion of microplastics by Daphnia macrocarpa is an active process, stemming from its misidentification of microplastics as phytoplankton. This misidentification is based on the similarity in size between the microplastics and the phytoplankton. Specifically, Daphnia macrocarpa cannot distinguish microplastics that are similar in size to its edible algae. Furthermore, microplastic ingestion restricts and inhibits the motility of zooplankton and reduces their filter-feeding efficiency; this effect is primarily related to the concentration of ingested microplastics.

[0092] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for evaluating ecological risk of microplastics based on population and community indicators, characterized in that, It comprises the following steps: S1. Put the microplastic solution, algal liquid and daphnia into the same system to form an algae-daphnia system; Put the microplastic solution and algal liquid into the same system to form an algae system as a control group; Put the microplastic solution and daphnia into the same system to form a daphnia system; The algae is one of Scenedesmus quadricauda and Cladophora sp. S2. According to the filtering efficiency of the algae-daphnia system and the algae system, the number of microplastic particles filtered in the algae-daphnia system and the daphnia system is counted by filtering, and the ecological risk of microplastics is evaluated; S3. The behavioral index change of daphnia in the daphnia system is counted to evaluate the ecological risk of microplastics; The calculation method of the filtering efficiency is as follows: The algal cell density in the algae-daphnia system and the algae system is counted respectively, and the number of daphnia in the algae-daphnia system is counted, and then formula I is used to calculate the filtering efficiency of daphnia in the filtering process; GR=V[In(C0)–In(C1)] / Nt Formula I In the formula, GR is the filtering efficiency, unit mL / each·h; V is the culture volume, unit mL; C0 is the algal cell density at the end of the algae system experiment, unit cells / mL; C1 is the algal cell density at the end of the algae-daphnia system experiment, unit cells / mL; N is the number of daphnia; t is the duration of the experiment, unit h; The behavioral index includes the heartbeat frequency and the swimming frequency of daphnia; The particle size of the microplastic solution is 5-20 μm, 20-27 μm and 27-32 μm; and the final concentration gradient of the microplastic solution is 0 mg / L, 0.4 mg / L, 2 mg / L and 10 mg / L; In the system with Scenedesmus quadricauda, daphnia filter more small size microplastics, and the small size is 5-20 μm; On the contrary, in the Cladophora sp. system, daphnia filter more large size 27-32 μm microplastics; In the Scenedesmus quadricauda system, the filtering rate of daphnia decreases more significantly with the increase of the concentration of small size microplastics, while in the Cladophora sp. system, the filtering efficiency decreases more obviously with the increase of the concentration of large size microplastics; The daphnia is 1-3 days old.

2. The method of claim 1, wherein, The initial density of the algal broth is 1 x 10 5 ~ 4 x 10 5 cells / mL.

3. The method of claim 1, wherein, The daphnia density is 45-55 per liter.

4. The method of claim 1, wherein, Before being put into the same system, the daphnia and algae are domesticated and cultured.

5. The method of claim 1, wherein, In steps S2 and S3, the counting time is 2-6 h after being put into the same system.

6. The method of claim 1, wherein, The calculation method of the algal cell density is as follows: When counting, one diagonal line of the plankton counting frame is selected, 10 squares on the counting line are observed, and the number of algal cells is recorded with a counter. After recording the original data, the algal cell density is calculated according to formula II: Algal cell density in algal liquid=A×10×10×B Formula II In the formula, A is the total number of algal cells in 10 squares on the diagonal line; B is the dilution multiple of the algal liquid; and the unit of the algal cell density in the algal liquid is cells / mL.

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