阅读说明：本技术 一种基于食物链营养级联效应评价pe微塑料生态危害的方法 (Method for evaluating ecological hazards of PE (polyethylene) micro-plastics based on food chain nutrition cascade effect ) 是由 肖唯衣 田沁东 龙遥跃 金玲 刘丹 潘瑛 于 2021-08-17 设计创作，主要内容包括：本发明提供了一种基于食物链营养级联效应评价PE微塑料生态危害的方法,属于水环境污染监测技术领域。本发明构建二级营养系统和三级营养系统,通过明确微塑料对浮游生物行为、数量等产生影响继而改变食物链营养级联效应来评价微塑料的生态毒性。所述方法采用远低于急性毒性实验的浓度,探讨个体不至死的情况下,低浓度微塑料通过影响自然界广泛存在的物种关系,最终改变群落组成和结构,是更加严谨的评价方法,能够得出更加安全的环境响应浓度,为正确制定污染物排放标准提供了依据。(The invention provides a method for evaluating ecological hazards of PE (polyethylene) micro-plastics based on a food chain nutrient cascade effect, and belongs to the technical field of water environment pollution monitoring. The invention constructs a secondary nutrition system and a tertiary nutrition system, and evaluates the ecological toxicity of the micro-plastics by determining the influence of the micro-plastics on the behavior, the quantity and the like of plankton and then changing the food chain nutrition cascade effect. According to the method, the concentration far lower than that of an acute toxicity experiment is adopted, the species relation widely existing in the nature is influenced by the low-concentration micro-plastic under the condition that an individual is discussed to be not died, the community composition and structure are finally changed, the method is a more rigorous evaluation method, the safer environment response concentration can be obtained, and a basis is provided for correctly formulating a pollutant emission standard.)

1. A method for evaluating ecological hazards of PE (polyethylene) micro-plastics based on food chain nutrition cascade effect is characterized by comprising the following steps:

1) placing the PE micro-plastic, the chlorella algae liquid growing exponentially and the daphnia magna into the same system to form a secondary nutrition system, and meanwhile, setting a contrast secondary nutrition system without the PE micro-plastic;

2) placing PE micro plastic, exponentially growing chlorella algae liquid, daphnia magna and physalis alkekengi larvae into the same system to form a three-level nutrition system, and meanwhile, setting a control three-level nutrition system without the PE micro plastic;

3) respectively counting the cell density of algae in the secondary nutrition system, the tertiary nutrition system, the control secondary nutrition system and the control tertiary nutrition system at the same period;

4) substituting the obtained algae cell density in the secondary nutrition system and the three-level nutrition system into a formula I, calculating a nutrition cascade effect, substituting the algae cell density in the control secondary nutrition system and the control three-level nutrition system into the formula I, and calculating a control nutrition cascade effect;

nutritional cascade effect ═ ln (Np +/Np-) formula I

Wherein Np + represents the cell density of algae in the tertiary nutrient system or the contrast tertiary nutrient system, and the unit is cells mL^-1；

Np-represents the cell density of algae in the secondary nutrient system or the control secondary nutrient system, and the unit is cells mL^-1；

5) Carrying out statistical analysis on the nutrition cascade effect in the step 4) and a contrast nutrition cascade effect, and judging that the PE micro-plastic harms the ecology when the nutrition cascade effect and the contrast nutrition cascade effect are significantly different, otherwise, not generating the harm;

there is no chronological restriction between step 1) and step 2).

2. The method according to claim 1, wherein the initial density of chlorella in the chlorella solution in step 1) or step 2) is 1 x 10⁴～5×10⁴cells·mL^-1。

3. The method according to claim 1, wherein the daphnia magna density in step 1) or step 2) is 100. L^-1；

Pretreating the daphnia magna; the pretreatment method comprises the step of carrying out starvation treatment on the daphnia magna for 4-5 hours before the daphnia magna is placed in the same system.

4. The method according to claim 1, wherein the density of the larvae of the Physalis alkekengi in step 2) is 1. L^-1。

5. The method as claimed in claim 1, wherein the statistical method of the cell density of algae in step 3) is as follows:

under a biological microscope with 400 times of the weight, counting the total algae cell density in unit volume by using a phytoplankton counting frame; selecting a diagonal line of a plankton counting frame, counting 10 small squares, sequentially recording the number of algae cells in each small square by using a cell counter, and substituting the number into a formula II to calculate the density of the algae cells;

algal cell density ═ X × 10 × 10 × Y formula II

In the formula: x-total number of algal cells in 10 squares on the diagonal;

y is the dilution multiple of the algae liquid; the unit of the cell density of the algae is cells mL^-1。

6. The method as claimed in claim 1 or 5, wherein the statistical time of the cell density of the algae is 1-5 h after the algae is placed in the same system.

7. The method according to any one of claims 1 to 5, wherein the final concentration of PE micro plastic in the secondary nutrient system in step 1) or the tertiary nutrient system in step 2) is 0.01 to 40 mg/L.

8. The method according to claim 7, wherein the evaluation method of the damage of the PE micro plastic to the ecology further comprises the step of evaluating the evaluation indexes of heartbeat and movement frequency data of daphnia magna, behavior data of the larva of the physalis pubescens and/or the correlation between the movement frequency of the daphnia magna and the attack frequency of the larva of the physalis pubescens.

Technical Field

The invention belongs to the technical field of water environment pollution monitoring, and particularly relates to a method for evaluating ecological hazards of PE (polyethylene) micro-plastics based on a food chain nutrient cascade effect.

Background

In recent years, new pollutant micro-plastics are receiving more and more extensive attention. The micro-plastic is divided into primary micro-plastic and secondary micro-plastic, wherein the primary micro-plastic is a plastic particle industrial product discharged into a water environment through rivers, sewage treatment plants and the like; the secondary micro-plastic refers to plastic fragments and particles with the diameter less than 5mm, which are formed by the plastic products undergoing the actions of friction, collision, weathering, biodegradation and the like in nature. Micro-plastics exist in water, air and soil and are widely spread along with natural factors such as ocean currents, wind power and the like. In water, the micro-plastics are easily swallowed by aquatic organisms such as zooplankton, fish and the like, and generate enrichment effect, thereby generating harm to aquatic ecosystems.

Chlorella (vulgaris) Chlorella genus Purpureal unicellular green algae, a spherical unicellular algae, with a diameter of about 3-8 μm. Daphnia magna (Daphniamagna) belongs to a plankton of arthropoda, has the characteristics of short life cycle, rapid propagation and the like, and is an excellent standard experimental material. The larvae of the physalis pubescens (Ischnurorufostoma belys) are the dominant invertebrate predators in freshwater lakes and are able to attack, capture and digest the daphnia magna.

The existing research mainly focuses on the toxic effect of the micro-plastics on plankton individuals, but the research on the influence of the micro-plastics on the interspecies relationship of downstream organisms and the change of the food chain nutrition cascade effect is still insufficient, and how to evaluate the harm of the micro-plastics and other environmental pollutants from the function change of the food chain is not precedent.

Disclosure of Invention

In view of the above, the present invention aims to provide a method for evaluating ecological hazards of PE micro plastics based on food chain nutrition cascade effect, and comprehensively evaluates risks of micro plastics to aquatic ecosystems from a community perspective.

The invention provides a method for evaluating ecological hazards of PE (polyethylene) micro-plastics based on a food chain nutrition cascade effect, which comprises the following steps of:

1) placing the PE micro-plastic, the chlorella algae liquid growing exponentially and the daphnia magna into the same system to form a secondary nutrition system, and meanwhile, setting a contrast secondary nutrition system without the PE micro-plastic;

2) placing PE micro plastic, exponentially growing chlorella algae liquid, daphnia magna and physalis alkekengi larvae into the same system to form a three-level nutrition system, and meanwhile, setting a control three-level nutrition system without the PE micro plastic;

3) respectively counting the cell density of algae in the secondary nutrition system, the tertiary nutrition system, the control secondary nutrition system and the control tertiary nutrition system at the same period;

4) substituting the obtained algae cell density in the secondary nutrition system and the three-level nutrition system into a formula I, calculating a nutrition cascade effect, substituting the algae cell density in the control secondary nutrition system and the control three-level nutrition system into the formula I, and calculating a control nutrition cascade effect;

nutritional cascade effect ═ ln (Np +/Np-) formula I

In the formula, Np + represents the cell density of algae in a tertiary nutrition system or a contrast tertiary nutrition system, and the unit is cells/mL;

np-represents the density of algae cells in the secondary nutrition system or the contrast secondary nutrition system, and the unit is cells/mL;

5) carrying out statistical analysis on the nutrition cascade effect in the step 4) and a contrast nutrition cascade effect, and judging that the PE micro-plastic harms the ecology when the nutrition cascade effect and the contrast nutrition cascade effect are significantly different, otherwise, not generating the harm;

there is no chronological restriction between step 1) and step 2).

Preferably, the initial density of chlorella in the chlorella solution in step 1) or step 2) is 1 × 10⁴～5×10⁴cells/mL。

Preferably, the density of daphnia magna in the step 1) or the step 2) is 100. L^-1；

Pretreating the daphnia magna; the pretreatment method comprises the step of carrying out starvation treatment on the daphnia magna for 4-5 hours before the daphnia magna is placed in the same system.

Preferably, the density of the physalis pubescens larvae in the step 2) is 1. L^-1。

Preferably, the statistical method for the cell density of algae in step 3) is as follows:

under a biological microscope with 400 times of the weight, counting the total algae cell density in unit volume by using a phytoplankton counting frame; selecting a diagonal line of a plankton counting frame, counting 10 small squares, sequentially recording the number of algae cells in each small square by using a cell counter, and substituting the number into a formula II to calculate the density of the algae cells;

algal cell density ═ X × 10 × 10 × Y formula II

In the formula: x-total number of algal cells in 10 squares on the diagonal;

y is the dilution multiple of the algae liquid; the unit of the cell density of the algae is cells mL^-1。

Preferably, the statistical time of the cell density of the algae is 1-5 hours after the algae are placed in the same system.

Preferably, the final concentration of the PE micro plastic in the secondary nutrition system in the step 1) or the tertiary nutrition system in the step 2) is 0.01-40 mg/L.

Preferably, the evaluation method of the damage of the PE micro plastic to the ecology further comprises the step of evaluating by taking the heartbeat and movement frequency data of the daphnia magna, the behavior data of the physalis pubescens larvae and/or the correlation between the movement frequency of the daphnia magna and the attack frequency of the physalis pubescens larvae as evaluation indexes.

The invention provides a method for evaluating ecological hazards of PE (polyethylene) micro-plastics based on a food chain nutrition cascade effect. The invention proves that even if the concentration is far lower than the acute toxicity concentration, the structure and the function of a food chain can be finally changed by influencing the interspecies relationship of environmental pollutants such as the micro-plastics, and provides a method guide for more comprehensively evaluating the ecological risk of the micro-plastics. Meanwhile, the method provided by the invention has the characteristics of strong operability, simplicity, good reproducibility, small harm to aquatic organisms, convenience and rapidness in evaluation, more natural practice-conforming evaluation result and the like.

Drawings

FIG. 1 shows the influence of micro-plastics on the heartbeat frequency of daphnia magna under the condition of existence of a physalis pubescens larva;

FIG. 2 is the influence of micro-plastics on the movement frequency of daphnia magna under the condition of existence of a physalis pubescens larva;

FIG. 3 is the effect of survival rate of daphnia magna in microplastic in the presence of a larva of a physalis pubescens;

FIG. 4 is a graph of the effect of micro-plastics on the nutrient cascade in the chlorella system.

Detailed Description

The invention provides a method for evaluating ecological hazards of PE (polyethylene) micro-plastics based on a food chain nutrition cascade effect, which comprises the following steps of:

1) placing the PE micro-plastic, the chlorella algae liquid growing exponentially and the daphnia magna into the same system to form a secondary nutrition system, and meanwhile, setting a contrast secondary nutrition system without the PE micro-plastic;

2) placing PE micro plastic, exponentially growing chlorella algae liquid, daphnia magna and physalis alkekengi larvae into the same system to form a three-level nutrition system, and meanwhile, setting a control three-level nutrition system without the PE micro plastic;

3) respectively counting the cell density of algae in the secondary nutrition system, the tertiary nutrition system, the control secondary nutrition system and the control tertiary nutrition system at the same period;

4) substituting the obtained algae cell density in the secondary nutrition system and the three-level nutrition system into a formula I, calculating a nutrition cascade effect, substituting the algae cell density in the control secondary nutrition system and the control three-level nutrition system into the formula I, and calculating a control nutrition cascade effect;

nutritional cascade effect ═ ln (Np +/Np-) formula I

In the formula, Np + represents the cell density of algae in a tertiary nutrition system or a contrast tertiary nutrition system, and the unit is cells/mL;

np-represents the density of algae cells in the secondary nutrition system or the contrast secondary nutrition system, and the unit is cells/mL;

5) carrying out statistical analysis on the nutrition cascade effect in the step 4) and a contrast nutrition cascade effect, and judging that the PE micro-plastic harms the ecology when the nutrition cascade effect and the contrast nutrition cascade effect are significantly different, otherwise, not generating the harm;

there is no chronological restriction between step 1) and step 2).

According to the invention, PE micro-plastic, exponentially growing chlorella algae liquid and daphnia magna are placed in the same system to form a secondary nutrition system, and a contrast secondary nutrition system without the PE micro-plastic is arranged; placing PE micro plastic, exponentially growing chlorella algae liquid, daphnia magna and physalis pubescens larva in the same system to form a three-level nutrition system, and simultaneously setting a control three-level nutrition system without PE micro plastic

In the present invention, the PE micro plastic preferably comprises a body of water containing the PE micro plastic. The culture solution in the same system is preferably a combo medium. The formulation of the combo medium is not particularly limited in the present invention, and a combo medium formulation well known in the art may be used. In the examples of the present invention, the formulation of the combo medium is as follows:

in the present invention, the initial density of chlorella in the chlorella solution is preferably 1 × 10⁴～5×10⁴cells/mL, more preferably 1X 10⁴～2×10⁴cells/mL. The source of the chlorella is not particularly limited in the present invention, and chlorella known in the art may be used. The density of the daphnia magna is preferably 100. L^-1. Pretreating the daphnia magna; the pre-treatment method is preferably to pre-starve the daphnia magna for 4-5 hours before the daphnia magna is placed in the same system, so as to ensure the foraging activity of the daphnia magna on the chlorella. The density of the physalis pubescens larva is preferably 1. L^-1. The method comprises the following steps of preferably putting the physalis pubescens larvae which are healthy and active and have no significant difference in weight into different systems. The physalis pubescens larvae serve as predators of daphnia magna and serve as the top of the food chain.

In the present invention, the final concentration of PE micro-plastic in the secondary or tertiary nutrient system is preferably 0.01E40mg/L, more preferably 10 to 20 mg/L. The final concentration of the PE micro plastic is far lower than the lethal concentration (57.3 mg.L) of the PE micro plastic reported in the prior art^-1). The invention discusses how the low-concentration micro-plastic finally changes community composition and structure by influencing species relationship widely existing in the nature, can obtain safer environment response concentration, and provides basis for correctly formulating pollutant emission standard.

In the invention, the reference secondary nutrition system means that chlorella algae liquid containing exponential growth and daphnia magna are placed in the same system. The contrast of the third-level nutrition system is that the chlorella algae solution containing exponential growth, the daphnia magna and the physalis pubescens larva are placed in the same system.

After the culture, the invention respectively counts the cell density of algae in the secondary nutrition system, the tertiary nutrition system, the control secondary nutrition system and the control tertiary nutrition system at the same period.

In the present invention, the statistical method of the algal cell density is preferably as follows:

under a biological microscope with 400 times of the weight, counting the total algae cell density in unit volume by using a phytoplankton counting frame; selecting a diagonal line of a plankton counting frame, counting 10 small squares, sequentially recording the number of algae cells in each small square by using a cell counter, and substituting the number into a formula II to calculate the density of the algae cells;

algal cell density ═ X × 10 × 10 × Y formula II

In the formula: x-total number of algal cells in 10 squares on the diagonal;

y is the dilution multiple of the algae liquid; the unit of the cell density of the algae is cells mL^-1。

In the invention, the statistical time of the algae cell density is preferably 1-5 h, more preferably 2-4 h, and most preferably 3h after the algae cell density is placed in the same system. After the plants are placed in the same system, the secondary nutrition system and the tertiary nutrition system prey on low-grade organisms by high-grade organisms, for example, the larval of the physalis alkekengi starts to prey on the daphnia magna, and meanwhile, the daphnia magna prey on the chlorella.

After the algae cell density data of each system is obtained, the algae cell densities in the obtained secondary nutrition system and the obtained tertiary nutrition system are brought into a formula I, the nutrition cascade effect is calculated, the algae cell densities in the control secondary nutrition system and the control tertiary nutrition system are brought into the formula I, and the control nutrition cascade effect is calculated;

nutritional cascade effect ═ ln (Np +/Np-) formula I

In the formula, Np + represents the cell density of algae in a tertiary nutrition system or a contrast tertiary nutrition system, and the unit is cells/mL;

np-represents the cell density of algae in the secondary nutrient system or the control secondary nutrient system in cells/mL.

And (3) obtaining a nutrition cascade effect, carrying out statistical analysis on the nutrition cascade effect and a contrast nutrition cascade effect, judging that the PE micro-plastic harms the ecology when the nutrition cascade effect and the contrast nutrition cascade effect have significant difference, and otherwise, not generating harm.

In the present invention, by setting a system of only chlorella and PE micro plastic, the result shows that the density of chlorella does not change with the change of the concentration of PE micro plastic, whereas in the secondary nutrition system, the density of chlorella increases with the increase of PE concentration, but the density of chlorella is always lower than that of the system of only algae. This indicates that the presence of PE micro-plastic in the secondary nutrient system affects the feeding of the chlorella by the daphnia magna. In the tertiary nutrient system, the density of algae is always higher than that of the secondary nutrient system without the added physalis pubescens larvae, the change trend of the density of algae is similar to that of the secondary nutrient system, the density of algae is increased along with the increase of the concentration of PE, but the increase of the density of algae in the system is more obvious. This indicates that the nutritional cascade effect is significantly affected by the PE concentration and continuously increases with the increase in the PE concentration, so the ecological hazard of PE microplastics is evaluated with the nutritional cascade effect as a judgment index.

In the invention, in order to clarify the influence of the PE micro plastic on the behavior of the daphnia magna, the behavior of the daphnia magna larvae and the relationship between the movement frequency of the daphnia magna and the attack frequency of the daphnia magna larvae, the heartbeat and movement frequency of the daphnia magna in the secondary nutrition system and the tertiary nutrition system, the survival rate of the daphnia magna in the tertiary nutrition system are further determined, the behavior of the daphnia magna larvae (three behavior frequencies of orienting, attacking and capturing the daphnia magna) is observed, and the correlation between the movement frequency of the daphnia magna and the attack frequency of the daphnia magna larvae is analyzed. The result shows that the concentration of the PE micro plastic is negatively related to the heartbeat and the movement frequency of the daphnia magna, negatively related to the survival rate of the daphnia magna and positively related to the behavior of the physalis pubescens larvae. Therefore, the evaluation method of the damage of the PE micro plastic to the ecology also preferably comprises the step of evaluating by taking the heartbeat and movement frequency data of the daphnia magna, the behavior data of the physalis pubescens larvae and/or the correlation between the movement frequency of the daphnia magna and the attack frequency of the physalis pubescens larvae as evaluation indexes.

The method for evaluating the ecological hazard of PE micro-plastics based on food chain nutrition cascade effect provided by the invention is described in detail in the following with reference to the examples, but the method cannot be understood as limiting the protection scope of the invention.

Example 1

In 20 days 11 and 2020, a specific experiment was carried out in Yunnan university of Kunming, Yunnan province, and the steps were as follows:

(1) preparing a combo culture medium for daphnia magna.

(2) Selecting a suitable subject: exponentially growing chlorella were selected for the experiments, all algae having initial densities of 5 × 10⁴cells·mL^-1Randomly selecting young daphnia as experimental material with age of 24-48 h and similar body size before experiment, and then starving for 4h to ensure foraging activity of herbivore in experiment, wherein the density of daphnia magna is 100. L^-11 healthy and active physalis pubescens of similar body length was placed in each treatment (1L volume system).

(3) Experiment design:

in the algae only system, samples were taken at experiments 1, 3 and 5h and observed for changes in algae density.

In the algae-daphnia secondary nutrition system, algae samples are taken in experiments 1, 3 and 5h, heartbeat and motion videos of daphnia magna are shot at the same time, and changes of behaviors of daphnia magna of herbivores are observed.

In the algae-daphnia-physalis pubescens larva three-level nutrition system, algae samples are taken in experiments 1, 3 and 5 hours, the survival number of daphnia magna is recorded, and rows of daphnia magna and physalis pubescens larva are shotAnd recording the heartbeat video of the daphnia magna at the end of the experiment. Shooting heartbeat and movement frequency videos of the daphnia magna, observing and analyzing, wherein when the heartbeat frequency videos of the daphnia magna are shot, 5 daphnia magna are randomly selected from each experiment beaker and placed in a circular plankton counting frame, then shooting heartbeat processes of the daphnia magna through image software under a biomicroscope of 5 times, and recording time is 1 min. And (3) watching the video at 0.5 times of speed by using image processing software Potplayer at the later stage of the experiment, and recording the heartbeat frequency of each daphnia magna for 1 min. When the movement frequency of the daphnia magna is observed, a tripod is placed on a laboratory table, a camera (FDR-AX 30; Sony, Japan; spatial resolution, 3840 x 2160pixels) is arranged on the laboratory table, two cameras are vertically placed at a position 20cm away from the projection plane of the beaker, and the horizontal and vertical behaviors of the daphnia magna are recorded simultaneously under the condition of uniform illumination. Starting the experiment, mechanically oscillating the beaker to allow daphnia magna to adapt to the experiment environment for 10min, and treating for 1, 3, and 5h at 50frame s^-1The video recording is carried out at the frame rate of (2), and the recording time is 5 min. After the recording is finished, the video is watched at 0.5 times speed by using image processing software Potplayer at the later stage of the experiment, 5 daphnia magna are randomly selected in each experiment beaker, and the jump frequency of 5min is respectively read (the jump is defined as that a second antenna under the antenna of the daphnia magna is pushed downwards and returns to the initial position).

(4) Video was recorded, with the following data analysis performed once:

analyzing daphnia magna data: heartbeat and movement frequency analysis

As a result: both heart beat frequency and movement frequency decreased with increasing concentration of PE microplastic, especially after 1 hour exposure and throughout the experiment, exposure to 5, 40 and 160 mg.L^-1After 1 hour, the heartbeat rate of the PE micro plastic is respectively reduced by 5.88 percent, 9.26 percent and 11.18 percent; the hopping frequency was reduced by 4.02%, 10.26 and 25.35%, respectively, and the experimental data are shown in fig. 1 and fig. 2.

Behavior analysis of the larva of the physalis pubescens: for carnivorous predator physalis alkekengi larvae, in a tertiary trophic level system, the influence of the frequency of three behaviors of orientation, attack and capture of daphnia magna is increased along with the increase of the PE concentration in the experiment. In addition, in the whole experiment process, the survival rate of daphnia magna is obviously reduced along with the increase of the PE concentration, and the survival rate is also obviously reduced along with the increase of the experiment time, and the result is shown in figure 3.

Analyzing the movement frequency of the daphnia magna and the attack frequency of the predator physalis pubescens larva: the result shows that the moving frequency of the daphnia magna is reduced along with the increase of the PE concentration, the behavior frequency of the larva of the physalis pubescens is increased, and the survival rate of the daphnia magna is reduced.

Response analysis of algae density and nutrition cascade strength to micro-plastics: the total algal cell density per unit volume was counted under a 400-fold biomicroscope (Olympus BX43 with a DP27 imaging system, Olympus, Tokyo, Japan) using a phytoplankton counting box. The specific operation is as follows: selecting a diagonal line of the plankton counting frame, counting 10 small squares, and sequentially recording the number of algae cells in each small square by using a cell counter. After recording all raw data, algal cell density was calculated by the following formula II:

algal cell Density (cells. mL) in 1mL sample liquid^-1) Formula II of X × 10 × 10 × Y

In the formula: x-total number of algal cells in 10 squares on the diagonal;

y is the dilution factor of the algae liquid.

In algae-only systems, chlorella cell density is not affected by PE concentration, while in secondary nutrient systems, algae density increases with increasing PE concentration, but is consistently lower than algae-only systems. In the tertiary nutrient system, the density of algae is always higher than that of the secondary nutrient system without the added physalis pubescens larvae, the change trend of the density of algae is similar to that of the secondary nutrient system, the density of algae is increased along with the increase of the concentration of PE, but the increase of the density of algae in the system is more obvious. The above experimental results show that the effect of the nutrient cascade is significantly affected by the PE concentration and the experimental time, and continuously increases with the increase of the PE concentration and the experimental time, as shown in fig. 4.

Analyzing the influence factors of the micro-plastic on the nutrition cascade effect: the method of calculating the nutritional cascade effect is a logarithmic ratio transformation method to estimate the intensity of the top-down cascade effect of predators on primary productivity.

Nutritional cascade effect ═ ln (Np +/Np-) formula I

In the formula: np + -there are physalis pubescens larvae, i.e., the density of algae (cells. mL) in the algae-daphnia magna-physalis pubescens larva system^-1)；

Np-Doudou larva, namely algae density (cells. mL) in algae-daphnia magna system^-1)。

And (4) conclusion: in a three-level nutrition level system, the influence of the micro-plastics on the nutrition cascade effect and the survival rate of the daphnia magna are in obvious negative correlation.

From the above examples, it can be seen that the targeting, attacking and trapping frequency of the myrtle larvae increases with increasing PE concentration at each observation time throughout the experiment. Therefore, with increasing PE concentration, the risk of predation of daphnia magna increases and the survival rate drops significantly. In this case, with the increase of PE concentration, the density and filter feeding efficiency of daphnia magna decreases, eventually leading to a sharp increase in algae density, with a concomitant increase in the nutritional cascade effect. Specifically, 20 mg.L^-1The PE micro-plastic can obviously influence the function of an ecosystem, and the concentration of the PE micro-plastic is far lower than the safe dose range (57.3 mg.L) obtained by the research of acute toxicity experiments or individual experiments^-1) (Short-term expression with high consistency of primer microplastic particles leads to immunological analysis of Daphnia magna, Saskia Rehs, Werner Kloas, Christiane Zarfl,2016), fully illustrates the necessity and stringency of the method of the invention.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.