A method for degrading PPCPs in water by using root exudates of aquatic plants

Abstract

The present invention provides a method for degrading PPCPs, a pollutant in water, by using root secretions of aquatic plants. The steps are as follows: selecting Myriophyllum or Vallisneria as target aquatic plants, and placing their seedlings in a plexiglass tank for hydroponics; after culturing for 25 to 40 days, taking out water samples and filtering them to obtain root secretions of aquatic plants; putting the root secretions into a polluted water body and adding 365nm UV-LED light; under the irradiation environment of the root secretions, PPCPs in the water body are degraded. The present invention uses the root secretions of Myriophyllum and Vallisneria during their life cycle as research objects, and diphenhydramine and cimetidine as target pollutants, to explore the changes in the physical and chemical properties of the root secretions during the growth of Myriophyllum and Vallisneria, the generation of photoactive substances, and the degradation of PPCPs, and based on this, a method for efficiently degrading PPCPs, a pollutant in water, is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and in particular to a method for degrading water pollutants PPCPs by utilizing root secretions of aquatic plants. Background Art

[0002] In recent years, with the continuous increase in drug production and consumption, a large amount of drug residual pollutants have entered the water environment, posing risks to the ecological environment and human health.

[0003] PPCPs (Pharmaceutical and Personal Care Products) are an emerging class of organic pollutants, including various antibiotics, synthetic musks, analgesics, antihypertensive drugs, contraceptives, hypnotics, diet pills, hair sprays, hair dyes, and fungicides. Many PPCP components exhibit strong biological activity, optical rotation, and polarity, and most are present in trace concentrations in the environment. Veterinary and agricultural pharmaceuticals, human medications, and cosmetics are the primary routes of their introduction into the environment.

[0004] In order to adapt to environmental changes, the roots of aquatic plants continuously secrete substances to the outside world. These substances constitute an important component of dissolved organic matter (DOM) in natural water environments. Studies have found that the secretions of aquatic plant roots can absorb photon energy under light to generate excited triplet states ( 3 DOM * ), singlet oxygen ( 1 O2) and hydroxyl radicals ( · OH) and other active substances that can oxidize organic matter, thereby removing organic pollutants from water. However, as aquatic plants change their growth stages, their roots' ability to secrete substances also changes. This leads to constant changes in the composition of root secretions in the water, affecting their photochemical activity and ultimately affecting the efficiency of pollutant degradation.

[0005] Therefore, it is necessary to explore the secretion of root secretions during the growth of aquatic plants and the degradation mechanism of PPCPs, and based on this, obtain a method that can efficiently degrade PPCPs pollutants in water. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for degrading PPCPs, a pollutant in water, by utilizing root secretions of aquatic plants. This method can efficiently degrade PPCPs, an organic pollutant in water.

[0007] The present invention adopts the following technical solutions to solve the above technical problems:

[0008] A method for degrading PPCPs in water using aquatic plant root secretions comprises the following steps:

[0009] (1) Select Myriophyllum or Vallisneria as target aquatic plants and place their seedlings in a plexiglass tank filled with ultrapure water for hydroponics;

[0010] (2) After culturing for 25 to 40 days, water samples are taken from the hydroponic system and filtered using a water filter membrane to obtain the desired aquatic plant root secretions;

[0011] (3) adding the aquatic plant root secretions obtained in step (2) into the polluted water body and adding 365nm UV-LED light; the root secretions degrade the target pollutant PPCPs in the water body under the 365nm UV-LED irradiation environment.

[0012] As one of the preferred embodiments of the present invention, in step (1), Myriophyllum or Vallisneria seedlings with intact root systems and good condition are selected, and the seedlings are first rinsed with tap water until there is no impurities on the surface, and then rinsed with ultrapure water; then, the rinsed seedlings are placed in a plexiglass tank filled with ultrapure water for hydroponics, and the roots of the plants are fixed with clean quartz sand; during the hydroponics period, the plants are placed in a ventilated indoor environment and supplemented with light every day.

[0013] As one of the preferred embodiments of the present invention, when the target aquatic plant is specifically Myriophyllum, the hydroponic temperature is 20-30° C., and 100 W of simulated sunlight is supplemented for 8-10 hours every day.

[0014] As one of the preferred embodiments of the present invention, when the target aquatic plant is specifically Vallisneria, the hydroponic temperature is 28-32° C., and 100 W of simulated sunlight is supplemented for 5-8 hours every day.

[0015] As one of the preferred embodiments of the present invention, in step (2), when hydroponically cultivating Myriophyllum, after culturing for 25 days, a water sample is taken out from the hydroponic system and filtered to obtain the desired Myriophyllum root secretions.

[0016] As one of the preferred embodiments of the present invention, in step (2), when hydroponically cultivating Vallisneria lappa, after culturing for 40 days, water samples from the hydroponic system are taken out and filtered to obtain the desired Vallisneria lappa root secretions.

[0017] As one of the preferred embodiments of the present invention, in step (2), when filtering the water sample, a 0.45 μm water filter membrane is used; thereafter, the water sample is stored in a brown reagent bottle and placed in a 4° C. refrigerator for standby use.

[0018] As one of the preferred embodiments of the present invention, in step (3), under the 365nm UV-LED irradiation environment, the root secretions of Myriophyllum and Vallisneria lappa photosensitize and degrade diphenhydramine DIP and cimetidine CIM in the polluted water.

[0019] As one of the preferred embodiments of the present invention, during the process of photosensitizing the degradation of target pollutants by the root secretions of Myriophyllum and Vallisneria, 3 DOM * and 1 O2 is the photoactive species that degrades DIP and CIM, and With f TMP 、、 and All have good correlation.

[0020] As one of the preferred embodiments of the present invention, during the DIP photosensitization degradation process, 3 DOM * Degradation occurs through electron transfer with nitrogen atoms in DIP;

[0021] During the CIM photosensitized degradation process, 1 O2 degrades CIM molecules by attacking oxidation reactions and attacking the CS bonds in the CIM molecules.

[0022] The advantages of the present invention over the existing technology are: the present invention takes the root secretions of Myriophyllum and Vallisneria during their life cycle as the research objects, and takes diphenhydramine (DIP) and cimetidine (CIM), two typical PPCPs, as the target pollutants, to explore the changes in the physical and chemical properties of the root secretions during the growth of Myriophyllum and Vallisneria, the generation of photoactive substances, and the degradation of PPCPs, revealing the general law of the changes in the photoactivity of the root secretions during the growth of aquatic plants, and based on this, obtaining a method for efficiently degrading the pollutants PPCPs in water. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a diagram of the hydroponic apparatus for Myriophyllum and Vallisneria in Experimental Example 1;

[0024] Figure 2 1 is a graph of the UV-visible absorption spectra of the root secretions of Myriophyllum and Vallisneria during their growth in Experimental Example 1 (Figure a is Myriophyllum, and Figure b is Vallisneria);

[0025] Figure 3 This is a three-dimensional fluorescence spectrum of the root secretions of Myriophyllum in Experimental Example 1 during its growth;

[0026] Figure 4 This is a graph of the fluorescent components of the root exudates of Myriophyllum in Experimental Example 1;

[0027] Figure 5 This is a three-dimensional fluorescence spectrum of the root exudates of Vallisneria during its growth in Experimental Example 1;

[0028] Figure 6 This is a graph of fluorescent components of Vallisneria root exudates in Example 1;

[0029] Figure 7 The results of the 365nm UV-LED irradiation in Experimental Example 1 show that the root secretions of Myriophyllum and Vallisneria are 1 EPR spectra of O2 (in the figure, a is Myriophyllum, b is Vallisneria);

[0030] Figure 8 This is the EPR spectrum of ·OH in the root secretions of aquatic plants under 365nm UV-LED irradiation in Experimental Example 1 (Figure a is Myriophyllum, and Figure b is Vallisneria);

[0031] Figure 9 This is the degradation result of TMP in the root secretions of Myriophyllum and Vallisneria under 365nm UV-LED irradiation in Experimental Example 1 (Figure a is Myriophyllum, Figure b is Vallisneria);

[0032] Figure 10 This is the degradation rate constant of TMP in the root exudates of Myriophyllum and Vallisneria in Experimental Example 1 (Figure a is Myriophyllum, and Figure b is Vallisneria);

[0033] Figure 11 This is the degradation result of FFA in the root secretions of Myriophyllum and Vallisneria under 365nm UV-LED irradiation in Experimental Example 1 (Figure a is Myriophyllum, and Figure b is Vallisneria);

[0034] Figure 12 is the degradation rate constant of FFA in the root exudates of Myriophyllum and Vallisneria under 365 nm UV-LED irradiation in Experimental Example 1 (Figure a is Myriophyllum, and Figure b is Vallisneria);

[0035] Figure 13 This is the production of hTPA in the root secretions of Myriophyllum and Vallisneria under 365nm UV-LED irradiation in Experimental Example 1 (Figure a shows Myriophyllum, and Figure b shows Vallisneria);

[0036] Figure 14 is the degradation rate constant of hTPA in the root exudates of Myriophyllum and Vallisneria under 365 nm UV-LED irradiation in Experimental Example 1 (Figure a is Myriophyllum, and Figure b is Vallisneria);

[0037] Figure 15 is f in Experiment 1 TMP and Φ·OH The correlation analysis results (Figure a is 1 O2, b figure is ·OH);

[0038] Figure 16 This is the degradation result of DIP in the root secretions of aquatic plants under 365nm UV-LED irradiation in Experimental Example 1 (Figure a is Myriophyllum, Figure b is Vallisneria);

[0039] Figure 17 is the degradation rate constant of DIP in the root exudates of aquatic plants under 65 nm UV-LED irradiation in Experimental Example 1 (Figure a is Myriophyllum, Figure b is Vallisneria);

[0040] Figure 18 This is the degradation result of CIM in the root secretions of aquatic plants under 365nm UV-LED irradiation in Experimental Example 1 (Figure a is Myriophyllum, Figure b is Vallisneria);

[0041] Figure 19 is the degradation rate constant of CIM in the root exudates of aquatic plants under 365 nm UV-LED irradiation in Experimental Example 1 (Figure a is Myriophyllum, Figure b is Vallisneria);

[0042] Figure 20 In Experiment 1 and Correlation analysis. DETAILED DESCRIPTION

[0043] The following embodiments of the present invention are described in detail. These embodiments are implemented based on the technical solutions of the present invention, and detailed implementation methods and specific operating procedures are given. However, the scope of protection of the present invention is not limited to the following embodiments. At the same time, the reagents and experimental methods used in the following examples are conventional reagents or methods in the art unless otherwise specified, and will not be repeated here.

[0044] Example 1

[0045] A method of utilizing root secretions of Myriophyllum spurge to degrade PPCPs in water comprises the following steps:

[0046] (1) Select foxtail algae seedlings with intact root systems and good condition, first rinse the seedlings with tap water until there is no impurity on the surface, and then rinse them with ultrapure water several times; then, place the rinsed seedlings in a plexiglass tank filled with ultrapure water for hydroponics, and fix the roots of the plants with clean quartz sand; during the hydroponics period, the foxtail algae plants are placed in a ventilated indoor culture at a temperature of 25℃, and are supplemented with 100W simulated sunlight for 9 hours every day.

[0047] (2) After culturing for 25 days, water samples were taken from the hydroponic system and filtered using a 0.45 μm water filter membrane to obtain the target Myriophyllum root secretions. The secretions were then stored in a brown reagent bottle and placed in a 4°C refrigerator for later use.

[0048] (3) adding the root secretions of Myriophyllum obtained in step (2) into the polluted water body and adding 365nm UV-LED light; under the 365nm UV-LED irradiation environment, the root secretions of Myriophyllum are photosensitized and degraded to target pollutants DIP and CIM in the water body.

[0049] Example 2

[0050] The method of using root secretions of Myriophyllum to degrade PPCPs in water in this embodiment is basically the same as that in Example 1, with the main difference being that in step (1), during the hydroponic culture period, the Myriophyllum plants are placed in a ventilated indoor environment at a temperature of 20°C and are supplemented with 100W of simulated sunlight for 8 hours every day.

[0051] Example 3

[0052] The method of using root secretions of Myriophyllum to degrade PPCPs in water in this embodiment is basically the same as that in Example 1, with the main difference being that in step (1), during the hydroponic culture period, the Myriophyllum plants are placed in a ventilated indoor culture at a temperature of 30°C and supplemented with 100W simulated sunlight for 10 hours every day.

[0053] Example 4

[0054] A method of using Vallisneria root secretions to degrade PPCPs in water includes the following steps:

[0055] (1) Select Vallisneria serrata seedlings with intact root systems and good condition, first rinse the seedlings with tap water until there is no impurity on the surface, and then rinse with ultrapure water several times; then, place the rinsed seedlings in a plexiglass tank filled with ultrapure water for hydroponics, and fix the roots of the plants with clean quartz sand; during the hydroponics period, the Vallisneria serrata plants are placed in a ventilated indoor culture at a temperature of 30°C, and are supplemented with 100W simulated sunlight for 6 hours every day.

[0056] (2) After culturing for 40 days, water samples were taken from the hydroponic system and filtered using a 0.45 μm water filter membrane to obtain the desired Vallisneria root secretions; the secretions were then stored in a brown reagent bottle and placed in a 4°C refrigerator for later use.

[0057] (3) adding the root secretions of Vallisneria lappa obtained in step (2) into the polluted water body and adding 365nm UV-LED light; under the 365nm UV-LED irradiation environment, the root secretions of Vallisneria lappa photosensitize and degrade the target pollutants DIP and CIM in the water body.

[0058] Example 5

[0059] The method of using root secretions of Vallisneria salsa to degrade PPCPs in water is basically the same as that of Example 4, with the main difference being that in step (1), during the hydroponic culture, the Vallisneria salsa plants are placed in a ventilated indoor environment at a temperature of 28°C and are supplemented with 100W of simulated sunlight for 5 hours every day.

[0060] Example 6

[0061] The method of using root secretions of Vallisneria salsa to degrade PPCPs in water is basically the same as that of Example 4, with the main difference being that in step (1), during the hydroponic culture period, the Vallisneria salsa plants are placed in a ventilated indoor environment at a temperature of 32°C and are supplemented with 100W of simulated sunlight for 8 hours every day.

[0062] Experimental Example 1

[0063] This experimental example is used to explore the changes in the physical and chemical properties of root secretions, the generation of photoactive substances, and the degradation of PPCPs during the growth of aquatic plants.

[0064] 1. Changes in the physical and chemical properties of root secretions during the growth of aquatic plants

[0065] 1. Experimental plants:

[0066] Two aquatic plants: foxtail algae and Vallisneria.

[0067] 2. Experimental methods:

[0068] Purchase Myriophyllum and Vallisneria seedlings with intact root systems in good condition, rinse with tap water until there is no impurity on the plant surface, and then rinse with ultrapure water several times; 20 Myriophyllum and Vallisneria seedlings that have been rinsed clean are placed in a plexiglass jar filled with 30L ultrapure water for hydroculture, and the plant roots are fixed with clean quartz sand; Myriophyllum and Vallisneria are placed in a ventilated indoor culture at the same time, and the culture conditions are referred to Examples 1 and 4, respectively. The culture device is as follows: Figure 1 shown.

[0069] From the start of incubation, water samples were collected from the Myriophyllum hydroponic system on days 1, 5, 10, 15, 25, 40, 60, 80, and 110. Water samples were collected from the Vallisneria hydroponic system on days 1, 5, 10, 15, 25, 40, 60, 80, 110, and 125. All water samples were filtered through a 0.45 μm water filter and stored in brown reagent bottles at 4°C until use.

[0070] The root secretions of the obtained foxtail algae and Vallisneria were subjected to ion concentration detection, UV-visible absorption spectrum scanning, three-dimensional fluorescence spectrum scanning, and size exclusion chromatography determination.

[0071] 3. Experimental results:

[0072] (1) Common anion concentrations

[0073] The Cl content in root exudates of Myriophyllum and Vallisneria during their life cycle was determined using ion chromatography. - 、NO3 - PO4 3- and SO4 2- The concentration changes of the four anions are shown in Table 1. As can be seen from Table 1, the anion content in the root secretions of Myriophyllum and Vallisneria is generally low. The anion channels contained in plant cells allow anions to flow out of the plant body. The reason why the presence of anions can be detected in the water samples of plant root secretions may be that Myriophyllum and Vallisneria release anions in their bodies in deionized water to adapt to environmental changes. In addition to organic pollutants and metal ion pollutants, anions are also another major pollutant in the water environment. Cl in water - 、NO3 - PO4 3- and SO4 2- At high concentrations, they will cause harm to the aquatic environment or plant growth, but low concentrations of anions are also required for the growth of aquatic plants, so the absorption and release of anions by aquatic plants will occur simultaneously and tend to a dynamic balance.

[0074] Table 1 Anion concentrations in root exudates of Myriophyllum and Vallisneria (mg / L)

[0075]

[0076]

[0077] (Note: “—” in the table indicates that the value does not exist)

[0078] (2) Common metal ion concentrations

[0079] The Cu content in root exudates of Myriophyllum and Vallisneria during their life cycle was determined using inductively coupled plasma optical emission spectrometry. 2+ 、Mn 2+ 、Fe 2+ / Fe 3+ 、Al 3+ Mg 2+ and Zn 2+ The concentration changes of the six metal ions are shown in Table 2. As can be seen from Table 2, in the root secretions of Myriophyllum and Vallisneria, except for Mg 2+ The presence of metal ions was detected during this experiment, which may be due to the release of metal ions from Myriophyllum and Vallisneria. At the same time, aquatic plants also have the ability to absorb metal ions, so the metal ion concentrations in the Myriophyllum and Vallisneria hydroponic systems are constantly changing.

[0080] Table 2 Metal ion concentrations in root exudates of aquatic plants (mg / L)

[0081]

[0082]

[0083] (Note: “—” in the table indicates that the value does not exist)

[0084] (3) UV-visible absorption spectrum

[0085] The root exudates of Myriophyllum and Vallisneria were scanned by UV-visible absorption spectrum. Figure 2 shown.

[0086] Depend on Figure 2 It can be seen that within the wavelength range of 200-500 nm, the absorbance of the root secretions of Myriophyllum and Vallisneria showed a decreasing trend with increasing wavelength.

[0087] Depend on Figure 2 It can also be seen that the absorbance of the root secretions of Myriophyllum as a whole shows a trend of first increasing (1-25 days), then decreasing (25-60 days), and then increasing (60-110 days) with the culture time; the absorbance of the root secretions of Vallisneria also shows a change pattern of first increasing (1-40 days), then decreasing (40-80 days), and then increasing (80-125 days).

[0088] Foxtail algae and Vallisneria species typically undergo growth, aging, and death during their life cycles. The ability of their roots to secrete substances varies during these different life stages. Generally speaking, aquatic plants have more developed root systems during periods of rapid growth and reproduction, releasing more substances. However, during aging, their root secretion capacity decreases. Although aquatic plant roots constantly secrete substances, the concentrations of these substances within the culture system do not continuously increase. This is because aquatic plants also absorb substances from the external environment during their growth. Studies by several researchers have shown that aquatic plants absorb elements such as nitrogen, phosphorus, and iron from water and convert them into nutrients necessary for their growth. However, at certain life stages, aquatic plants also absorb substances not necessary for their growth, such as organic matter and heavy metals. This is because when the concentrations of some organic matter and heavy metals in water are excessively high, they can become toxic to aquatic plants, and the plants absorb these substances to detoxify them. When aquatic plants enter the senescence stage, not only does the ability of their roots to secrete substances into the external environment decrease, but the plants' own ability to absorb substances from the environment may also increase, resulting in a decrease in the concentration of some substances in the aquatic plant's environment. Furthermore, it was observed that Myriophyllum spp. began to rot on the 80th day, and Vallisneria spp. began to rot on the 110th day. When plants begin to decompose, microorganisms in the environment increase significantly, converting plant residues into humus. This is why the absorbance of Myriophyllum spp. root secretions began to increase again from the 80th day onwards, and the absorbance of Vallisneria spp. root secretions began to increase again from the 110th day onwards.

[0089] To further explore the changing patterns of some characteristics of the root secretions of Myriophyllum and Vallisneria during their life activities, the characteristic indices of the UV-visible absorption spectra of the water samples were calculated and analyzed. The calculation results are shown in Table 3.

[0090] Table 3 UV - Visible absorption spectrum characteristic index

[0091]

[0092]

[0093] As shown in Table 3, the relative contents of DOM (dissolved organic matter) and CDOM (colored dissolved organic matter) in the root secretions of Myriophyllum are generally greater than those in Vallisneria. 350 and a 355 The values showed a trend of increasing first (1-25 days) and then decreasing (25-60 days), and then increasing again after the plants decayed (60-110 days). 350and a 355 The value also increases first (1 to 40 days) and then decreases (40 to 80 days), and increases again (80 to 125 days) when the plants rot. In addition, when foxtail algae and Vallisneria begin to rot, a 350 and a 355 The values increased exponentially. It can be inferred that during the life activities of Myriophyllum and Vallisneria, the DOM and CDOM contents in their root secretions first increased and then decreased, and increased significantly after the plants decayed.

[0094] (4) Three-dimensional fluorescence spectroscopy analysis

[0095] The root secretion water samples of Myriophyllum and Vallisneria were scanned by three-dimensional fluorescence spectrum. The scanning results were as follows: Figure 3 and Figure 5 The scanning results were analyzed by PARAFC, and the analysis results were as follows: Figure 4 and Figure 6 shown.

[0096] Depend on Figure 4 PARAFAC analysis of Myriophyllum root exudates revealed three fluorescent components: component 1, which includes a fulvic acid-like fluorescence peak (Ex / Em = 230 nm / 410 nm) and a humic acid-like fluorescence peak (Ex / Em = 310 nm / 410 nm); component 2, which includes a tryptophan-like fluorescence peak (Ex / Em = 225 nm / 330 nm) and a SMP-like fluorescence peak (Ex / Em = 280 nm / 220 nm); and component 3, which includes two humic acid-like fluorescence peaks (Ex / Em = 375 nm / 460 nm and Ex / Em = 270 nm / 460 nm).

[0097] Combine Figure 5 The analysis results of Figure 4It can be seen that from day 1 to day 25 of cultivation, the fluorescence intensity of each component in the root exudates of Myriophyllum continuously increases. During this stage, Myriophyllum is in a period of rapid growth, with a well-developed root system and a strong ability to secrete substances into the external environment. Furthermore, the organic matter content in the environment during this stage is low, posing little threat to the plant. Therefore, Myriophyllum absorbs only a small amount of organic matter from the water, and the overall content of its root exudates exceeds the amount absorbed by the plant, resulting in a continuous increase in dissolved organic matter in the Myriophyllum system during this stage. After day 25, the fluorescence intensity of the protein-like peak in the root exudates significantly weakened, and the fluorescence intensity of the humic acid- and fulvic acid-like peaks no longer increased. This may be because Myriophyllum has entered a dormant or senescent phase, weakening its roots' ability to secrete substances into the environment. However, when DOM content in the water reaches a certain value, it may become harmful to the plant. During this period, Myriophyllum absorbs organic substances such as phenols, which are important precursors of humic substances. Furthermore, humic substances may be decomposed by other substances in the system, and the decomposition rate may exceed the formation rate. This is why the fluorescence peak intensity of humic substances in Myriophyllum root exudates decreased or even stopped increasing after 25 days. As Myriophyllum roots secrete protein-like substances, they also release enzymes and organic acids. Under acidic conditions, proteins are more susceptible to hydrolysis by certain enzymes, which may lead to a decrease in the intensity of the protein-like fluorescence peak. After the 80th day, the fluorescence intensity of humic and fulvic acid-like substances in Myriophyllum root exudates increased significantly again, possibly because the plant began to decay. By the 80th day, the Myriophyllum plant was already clearly decaying, leading to a significant increase in humic substances in the system.

[0098] Depend on Figure 6 PARAFAC analysis of Vallisneria root exudates revealed three fluorescent components: component 1, which included a fulvic acid-like fluorescence peak (Ex / Em = 230 nm / 410 nm) and a humic acid-like fluorescence peak (Ex / Em = 310 nm / 410 nm); component 2, which included a tryptophan-like fluorescence peak (Ex / Em = 225 nm / 330 nm) and a SMP-like fluorescence peak (Ex / Em = 280 nm / 220 nm); and component 3, which included two humic acid-like fluorescence peaks (Ex / Em = 375 nm / 460 nm and Ex / Em = 270 nm / 460 nm).

[0099] Combine Figure 6 The analysis results of Figure 5It can be seen that: from the 1st to the 15th day of cultivation of Vallisneria ovata, the fluorescence intensity of each component in its root exudates continued to increase, especially on the 15th day, the protein-like peak was significantly enhanced. This may be because Vallisneria ovata at this stage is in a rapid growth and reproduction period, with a well-developed root system and a strong ability to secrete substances to the outside world. The secretion amount is greater than the absorption or hydrolysis amount, so the fluorescence intensity of each component shows an increasing trend; from the 15th to the 80th day, the fluorescence intensity of the humus-like peak in the root exudates of Vallisneria ovata still increases, while the fluorescence intensity of the protein-like peak begins to gradually weaken. This may be because the protein-like substances in the water undergo hydrolysis reactions, and Vallisneria ovata gradually enters a dormant or declining period, the root system's ability to secrete substances to the outside world is weakened, and the overall protein secretion amount is less than the hydrolysis amount. Until the 110th day, the fluorescence intensity of each component in the root secretions of Vallisneria salsa increased significantly again. This is because the Vallisneria salsa has begun to show obvious signs of decay at this time, and the plant residues have increased significantly. After the aquatic plants begin to decompose, they will first enter the leaching stage. During this stage, the substances in the aquatic plants will dissolve rapidly, and the microorganisms will also increase significantly. Under the action of microorganisms, the aquatic plant extracts are used by microorganisms to convert into humus, resulting in a significant increase in the fluorescence intensity of the humus-like substances in the root secretions of Vallisneria salsa.

[0100] (5) Size exclusion chromatography analysis

[0101] Size exclusion chromatography was used to determine the changes in the average molecular size and molecular weight of root exudates during the growth of Myriophyllum and Vallisneria.

[0102] The results showed that the average molecular size of the root secretions of Myriophyllum and Vallisneria were mainly distributed around 10kDa; in the later stage of cultivation of Myriophyllum and Vallisneria, especially after the plants decayed, the average molecular size of the root secretions was higher than that in the early stage; the average molecular weight of the root secretions of the two plants showed a trend of first increasing and then decreasing, and then increasing again when the plants decayed.

[0103] In summary, the main conclusions are as follows:

[0104] ① Foxtail Algae and Vallisneria ovata secrete relatively more Mg during their growth 2+ The contents of other metal ions and anions are relatively small.

[0105] ② During the growth of Myriophyllum and Vallisneria, the DOM and CDOM contents in their root secretions showed a trend of first increasing and then decreasing, and then increasing again when the plants decayed.

[0106] ③ The root secretions of Myriophyllum and Vallisneria during their growth mainly contained fluorescent components such as humic acid-like, fulvic acid-like, tryptophan-like and SMP-like substances. Before the decay of Myriophyllum and Vallisneria, the humic acid-like and protein-like substances showed a trend of first increasing and then decreasing. After the plants decayed, the humic acid-like substances increased significantly.

[0107] ④The average molecular size of the root secretions of Myriophyllum and Vallisneria were mainly distributed around 10kDa; in the later stages of cultivation of Myriophyllum and Vallisneria, especially after the plants decayed, the average molecular size of the root secretions was higher than that in the early stages; the average molecular weight of the root secretions of both plants showed a trend of first increasing and then decreasing, and then increasing again when the plants decayed.

[0108] 2. Generation of photoactive substances in root secretions during the growth of aquatic plants

[0109] The root secretions of aquatic plants are an important component of DOM in natural water environments. Under the irradiation of light, the chromophores in the root secretions of aquatic plants absorb photon energy to form 1 DOM * , and further transformed into DOM excited triplet state ( 3 DOM * ), singlet oxygen ( 1 Root secretions are produced by aquatic plants to adapt to their growth and development and environmental changes. The composition of root secretions varies at different stages of aquatic plant life. Therefore, as the physical and chemical properties of root secretions change during aquatic plant growth, their photochemical activity also changes accordingly.

[0110] 1. Experimental plants:

[0111] Two aquatic plants: foxtail algae and Vallisneria.

[0112] 2. Experimental methods:

[0113] With 365nm UV-LED (light source irradiance of about 30mW.cm -2 .nm -1 , light intensity ) was used as the experimental light source to measure the production of photoactive substances in the root secretions of two aquatic plants, Myriophyllum and Vallisneria. The EPR spectroscopy was used to qualitatively analyze the photoactive substances in Myriophyllum and root secretions. 1 The generation of O2 and OH; 2,4,6-trimethylphenol (TMP), furfurylalcohol (FFA) and disodium terephthalate (TPA) were used as 3 DOM * 、 1Chemical probes for O2 and OH were used to determine the generation rate, steady-state concentration and quantum yield of three photoactive substances, and correlation analysis was performed to explore the generation mechanism of photoactive substances in root secretions during the growth of aquatic plants.

[0114] 3. Experimental results:

[0115] (1) Under 365nm UV-LED irradiation, the root secretions of Myriophyllum and Vallisneria were 1 The EPR spectrum of O2 is as follows Figure 7 As shown, the EPR spectrum of OH is as follows Figure 8 shown.

[0116] (2) Under 365nm UV-LED irradiation, the degradation of TMP in the root secretions of Myriophyllum and Vallisneria is as follows Figure 9 The degradation rate constant is shown as Figure 10 As shown;

[0117] The degradation of FFA in the root exudates of Myriophyllum and Vallisneria under 365nm UV-LED irradiation is shown in Figure 2. Figure 11 The degradation rate constant is shown as Figure 12 As shown;

[0118] The production of hTPA in the root exudates of Myriophyllum and Vallisneria under 365nm UV-LED irradiation is shown in Figure 2. Figure 13 The degradation rate constant is shown as Figure 14 As shown;

[0119] (3) Yes 3 DOM * The generated quantum yield coefficient (f TMP ) and the quantum yield of ROS generation ( and Φ ·OH ) were subjected to correlation analysis respectively, and the results of the correlation analysis were as follows Figure 15 shown.

[0120] In summary, the main conclusions are as follows:

[0121] ① The root secretions of Myriophyllum and Vallisneria will produce 1 O2 and OH, and as the illumination time increases, 1 The concentrations of O2 and OH will also increase.

[0122] ② The photochemical activity of the root secretions of Myriophyllum and Vallisneria will change during their growth. Under 365nm UV-LED irradiation, the root secretions of Myriophyllum and Vallisneria produce photoactive substances ( 3 DOM * 、 1The rate and steady-state concentration of O2 and OH showed a trend of increasing first, then decreasing, and then increasing again with the cultivation time. The quantum yield of photoactive substances produced by the root secretions of Myriophyllum showed an overall increasing trend, while there was no obvious change pattern in Vallisneria.

[0123] ③ 3 DOM * Quantum yield coefficient (f TMP )and 1 O2 quantum yield showed good correlation (R 2 =0.81), indicating that in this study 3 DOM * yes 1 The main precursor of O2; f TMP and OH quantum yield (Φ ·OH ) were positively correlated, but the correlation was not significant, indicating that in this study 3 DOM * Not the main precursor of OH.

[0124] 3. Photochemical activity of root secretions during the growth of aquatic plants

[0125] 1. Experimental plants:

[0126] Two aquatic plants: foxtail algae and Vallisneria.

[0127] 2. Experimental methods:

[0128] DIP and CIM were selected as target pollutants to test the indirect photodegradation rate of two typical PPCPs in the root exudates of Myriophyllum and Vallisneria, and to evaluate the changes in the photochemical activity of the root exudates during the growth of Myriophyllum and Vallisneria. The photosensitized degradation mechanism of DIP and CIM in the root exudates of aquatic plants was explored through quenching experiments, and the quantum yield coefficient and the relationship between the indirect photodegradation of DIP and CIM were analyzed. 3 DOM * and 1 Based on the results of high-resolution liquid chromatography-mass spectrometry, the photosensitized degradation products and pathways of DIP and CIM were speculated and analyzed.

[0129] 2. Experimental results:

[0130] (1) Diphenhydramine DIP photosensitization degradation

[0131] ① Under 365nm UV-LED light source, the degradation of DIP in root exudates samples during the life cycle of Myriophyllum and Vallisneria was determined. Figure 16 As shown, the photosensitized degradation rate constant of DIP is as follows Figure 17 As shown. Figure 16 、 17 It can be seen that DIP undergoes significant photodegradation in plant root secretions. Since DIP has almost no absorbance at a wavelength of 365nm and does not undergo direct photodegradation, the photodegradation of DIP under 365nm UV-LED irradiation is mainly indirect photodegradation caused by plant root secretions. During the growth of Myriophyllum, the rate of photosensitized degradation of DIP by root secretions generally shows a trend of first increasing (1 to 25 days), then decreasing (25 to 60 days), and then increasing again when the plant decays (60 to 110 days), reaching a maximum on the 25th day before decay (k obs =2.51×10 -5 s -1 ), and reaches its maximum value on the 110th day during the entire life cycle (k obs =5.01×10 -5 s -1 During the growth of Vallisneria, the rate of photosensitized degradation of DIP by root secretions also showed a trend of first increasing (1-40 days), then decreasing (40-80 days), and then increasing (80-125 days), reaching a maximum on the 40th day before decay (k obs =2.87×10 -5 s -1 ), and reaches its maximum value on the 125th day during the entire life cycle (k obs =4.66×10 -5 s -1 The variation of the rate of photosensitized degradation of DIP by root secretions of Myriophyllum and Vallisneria during their growth is similar to that of 3 DOM * The variation patterns of the generation rate are basically consistent and highly similar to those of UV-Vis, 3DEEM and SEC.

[0132] The quantum yield coefficients of photosensitized degradation of DIP by root exudates of Myriophyllum and Vallisneria were further calculated ( M -1 ), and finally the following results can be obtained: During the growth of Myriophyllum, the quantum yield coefficient of photosensitized degradation of DIP by root secretions showed a trend of first decreasing and then increasing with the culture time, which was consistent with the 3 DOM * The change trend of quantum yield coefficient is basically the same. It reached its maximum value (0.2806M on the first day -1 ), throughout the life cycle of foxtail algae It reached its maximum value (0.3374M on the 110th day -1 The quantum yield coefficient of photosensitized degradation of DIP by root exudates of Vallisneria ovata during its growth period showed no significant change with the culture time, but 3DOM * The change trend of quantum yield coefficient is basically the same. It reaches its maximum value (0.6410M on the 80th day -1 ).

[0133] ② The root exudates of Myriophyllum truncatum cultured for 110 days and Vallisneria truncatum cultured for 125 days were selected to explore the photodegradation mechanism of DIP in the root exudates of aquatic plants. Sorbic acid, L-histidine and isopropanol were selected as the indirect photodegradation agents of DIP. 3 DOM * 、 1 The quenchers of O2 and OH were used to explore the role of three photoactive substances in the photosensitized degradation of DIP by plant root exudates.

[0134] The results showed that adding 1 After the addition of L-histidine, an O2 quencher, the photodegradation rate of DIP in the root exudates of Myriophyllum and Vallisneria was reduced by 42.5% and 40.8%, respectively. After the addition of isopropyl alcohol, an OH quencher, to the root exudates, the photodegradation rate of DIP in the root exudates of Myriophyllum and Vallisneria was reduced by 35.4% and 35.5%, respectively. This indicates that 1 O2 and OH do not play a major role in the degradation of DIP. 3 DOM * After the addition of quencher sorbic acid, the photodegradation rate of DIP in the root exudates of Myriophyllum and Vallisneria was reduced by 95.1% and 93.2%, respectively. 3 DOM * It is the main active substance for photosensitized degradation of DIP in the root secretions of Myriophyllum and Vallisneria.

[0135] ③ Known 3 DOM * It is the main active substance for photosensitized degradation of DIP in the root secretions of Myriophyllum and Vallisneria, and the quantum yield coefficient of photosensitized degradation of diphenhydramine is The triplet quantum yield coefficient (f TMP ) for correlation analysis.

[0136] The results show that: With f TMP There is a good positive correlation (R 2 =0.75), indicating 3 DOM * It plays an important role in the photosensitized degradation of DIP by the root exudates of Myriophyllum and Vallisneria, which is consistent with the results of the quenching experiment. With f TMPThe correlation is not very significant, which may be because the chemical probe TMP used in this experiment can only capture most (~70%) of the high energy 3 DOM * , and plant root secretions may produce low energy under light conditions 3 DOM * , and then electron or energy transfer occurs, which cannot be captured by TMP, which leads to f TMP Cannot accurately express 3 DOM * Therefore, the correlation analysis results are not accurate.

[0137] (2) Photosensitized degradation of cimetidine CIM

[0138] ① Under 365nm UV-LED irradiation, the degradation of CIM in the root exudates of Myriophyllum and Vallisneria during their life cycle was determined. Figure 18 The degradation rate constant is shown as Figure 19 As shown. Figure 18 、 19 It can be seen that CIM undergoes a relatively obvious photodegradation in plant root secretions. Since CIM has almost no absorbance at a wavelength of 365nm and does not undergo direct photodegradation, the photodegradation of CIM under 365nm UV-LED irradiation is mainly indirect photodegradation caused by plant root secretions. During the growth of Myriophyllum, the rate of photosensitized degradation of CIM by root secretions basically shows a trend of first increasing (1 to 25 days), then decreasing (25 to 60 days), and then increasing again after the plant decays (60 to 110 days). The k obs The maximum value (2.51×10 -5 s -1 ), k obs The maximum value (5.01×10 -5 s -1 ); The rate of photosensitized degradation of DIP by root secretions during the growth of Vallisneria also showed a trend of first increasing (1-40 days), then decreasing (40-80 days), and then increasing again after the plant decayed (80-125 days). obs The maximum value (2.87×10 -5 s -1 ), k obs The maximum value (k obs =4.66×10 -5 s -1 The variation of the rate of photosensitized degradation of DIP by root secretions of Myriophyllum and Vallisneria during their growth is similar to that of3 DOM * The variation patterns of the generation rate are basically consistent and highly similar to those of UV-Vis, 3DEEM and SEC.

[0139] Calculate the quantum yield coefficient of photosensitized degradation of CIM by root exudates of Myriophyllum and Vallisneria during their growth ( M -1 ), the results showed that the quantum yield coefficient of photosensitized degradation of CIM by root exudates during the growth of Myriophyllum was 1 The trend of the O2 quantum yield coefficient is basically the same. It reached its maximum value (10.94M on the 60th day -1 ), throughout the life cycle of foxtail algae It reached its maximum value (12.10M on the 110th day -1 The quantum yield coefficient of photosensitized degradation of CIM by root exudates during the growth of Vallisneria is also similar to 1 The changing trends of the O2 quantum yield coefficient are basically the same. It reached its maximum value (14.58M on the 80th day -1 ), throughout the life cycle of foxtail algae It reached its maximum value (17.01M on the 110th day -1 ).

[0140] ② The root exudate water samples from Myriophyllum truncatum on the 110th day of cultivation and Vallisneria truncatum on the 125th day of cultivation were selected to explore the photosensitized degradation mechanism of CIM in plant root exudates. TMP, NaN3 and isopropanol were selected as the indirect photodegradation agents of CIM in the experiment. 3 DOM * 、 1 The quenchers of O2 and OH were used to explore the role of three photoactive substances in the photosensitized degradation of CIM by plant root exudates.

[0141] The results showed that adding 3 DOM * After the addition of quencher TMP, the photodegradation rate of CIM in the root exudates of Myriophyllum and Vallisneria decreased by 16.6% and 29.5%, respectively; after adding OH quencher isopropyl alcohol to the plant root exudates, the photodegradation rate of CIM in the root exudates of Myriophyllum and Vallisneria decreased by 0.01% and 0.06%, respectively. This indicates that 3 DOM * and OH have little effect on the degradation of CIM. 1 After the addition of O2 quencher NaN3, the photodegradation rate of CIM in the root exudates of Myriophyllum and Vallisneria was reduced by 94.3% and 98.7%, respectively.3 DOM * It is the main active substance in the photosensitized degradation of CIM by the root secretions of Myriophyllum and Vallisneria.

[0142] ③ Known from quenching experiments 1 O2 is the main active substance in the photosensitized degradation of CIM in plant root secretions. The quantum yield coefficient of CIM photosensitized degradation is and 1 O2 quantum yield Conduct correlation analysis.

[0143] The results are as follows Figure 20 As shown, it shows that: and There is a good positive correlation (R 2 =0.73), which again shows 1 O2 plays an important role in the photosensitized degradation of CIM by plant root exudates.

[0144] In summary, the main conclusions are as follows:

[0145] ① The root secretions of Myriophyllum and Vallisneria had a good photosensitized degradation effect on DIP and CIM, and the rates of photosensitized degradation of DIP and CIM were respectively 3 DOM * and 1 The changing trend of O2 generation rate is consistent, that is, it increases first and then decreases, and then increases again when the plants decay.

[0146] ② In the process of photosensitization degradation of target pollutants by root secretions of Myriophyllum and Vallisneria, 3 DOM * and 1 O2 is the main photoactive species for the degradation of DIP and CIM, respectively, and With f TMP 、、 and Both have good correlation (0.75, 0.73).

[0147] ③During the process of DIP being photosensitized and degraded by the root secretions of aquatic plants, 3 DOM * The degradation is mainly achieved by electron transfer with nitrogen atoms in DIP. 1 O2 mainly degrades CIM molecules by attacking oxidation reactions and attacking the CS bonds in the CIM molecules.

[0148] 4. Summary and Analysis

[0149] This experiment, by hydroponically cultivating two aquatic plants, Myriophyllum and Vallisneria, obtained root secretion water samples during their growth process and explored the changes in the physical and chemical properties of the root secretions of Myriophyllum and Vallisneria during their growth. Using a 365nm UV-LED as the experimental light source, the generation of photoactive substances in the root secretions of Myriophyllum and Vallisneria during their growth was explored. Using two typical PPCPs, diphenhydramine and cimetidine, as target pollutants, the photochemical activity of the root secretions of Myriophyllum and Vallisneria during their growth was evaluated, and the correlation between PPCPs and the quantum yield of photoactive substances was analyzed. The main conclusions are as follows:

[0150] (1) During the growth of Foxtail Algae and Vallisneria, the concentrations of common anions and cations in the root secretions were generally low; the average molecular size remained almost unchanged, all maintained at around 10 kDa; the root secretions mainly contained four fluorescent components: protein-like, humic acid-like, fulvic acid-like, and SMP-like; the average molecular weight, protein-like, humic acid-like, and DOM and CDOM contents of the root secretions showed a trend of first increasing and then decreasing, and then increasing again when the plants decayed.

[0151] (2) The root secretion water samples of "Myriophyllum" and "Vallis" can be effectively excited under 365nm UV-LED irradiation 1 The generation of O2 and OH. Under 365nm UV-LED irradiation, the root secretions of Myriophyllum produce photoactive substances ( 3 DOM * 、 1 The rates of O2 and OH) first increased with the incubation time (1-25 days) and then decreased (25-60 days), and then increased again when the plants rotted (60-110 days); the rate of photoactive substances produced by the root secretions of Vallisneria lappa also first increased with the incubation time (1-40 days) and then decreased (40-80 days), and then increased again when the plants rotted (80-125 days). and the triplet quantum yield coefficient f TMP showed good correlation (R 2 =0.81), hydroxyl quantum yield Φ ·OH With f TMP The correlation shown was not significant (R 2 =0.49), it is inferred that 3 DOM * Not the main precursor of OH.

[0152] (3) Under 365nm UV-LED irradiation, the degradation rate of DIP and CIM by the root secretions of Myriophyllum first increased (1-25 days) and then decreased (25-60 days), and then increased again when the plants rotted (60-110 days); the degradation rate of DIP and CIM by the root secretions of Vallisneria also first increased (1-40 days) and then decreased (40-80 days), and then increased again when the plants rotted (80-125 days). The degradation rates of DIP and CIM by the two aquatic plants reached their maximum values when the plants were completely rotten (110 days and 125 days). Quenching experiments proved 3 DOM * It is the main active substance for indirect photodegradation of DIP. 1 O2 is the main active substance for indirect photodegradation of CIM. The quantum yield coefficients of DIP and CIM ( and ) and f TMP and Both showed good correlation (R 2 =0.75, 0.73). 3 DOM * It is mainly degraded by electron transfer with the nitrogen atom of DIP. 1 O2 mainly degrades CIM through oxidation reactions and attacks on the CS bonds.

[0153] Based on this, in order to obtain the aquatic plant root secretions with the highest degradation efficiency, Myriophyllum / Vallis can be selected as the target aquatic plants, and the corresponding water samples in the hydroponic system are taken as the target aquatic plant root secretions. When their seedlings are hydroponically cultivated for 25 / 40 days and rot, they may cause secondary pollution to the water body. Before the rot occurs, Myriophyllum produces the highest rate of photoactive substances at 25 days and Vallisneria at 40 days, and the degradation rate of DIP and CIM is also the highest. In specific applications, the root secretions are put into the polluted water body to achieve the degradation of the target pollutant PPCPs under 365nm UV-LED irradiation environment.

[0154] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for degrading PPCPs in water using root secretions of aquatic plants, characterized in that: The steps include: (1) Select Myriophyllum or Vallisneria as target aquatic plants and place their seedlings in a plexiglass tank filled with ultrapure water for hydroponics; (2) After culturing for 25 to 40 days, water samples are taken from the hydroponic system and filtered using a water filter membrane to obtain the desired aquatic plant root secretions; (3) adding the aquatic plant root secretions obtained in step (2) into the polluted water body and adding 365nm UV-LED light; the root secretions degrade the target pollutants PPCPs in the water body under the 365nm UV-LED irradiation environment; Among them, under the 365nm UV-LED irradiation environment, the root secretions of Myriophyllum and Vallisneria lappa photosensitized and degraded diphenhydramine DIP and cimetidine CIM in the polluted water. During the DIP photosensitized degradation process, 3 DOM * The CIM is degraded by electron transfer with the nitrogen atoms in DIP; in the process of CIM photosensitization degradation, 1 O2 degrades CIM molecules by attacking oxidation reactions and attacking the CS bonds in the CIM molecules.

2. The method for degrading PPCPs in water using aquatic plant root secretions according to claim 1, characterized in that: In the step (1), a foxtail algae or Vallisneria seedling with an intact root system and in good condition is selected, the seedling is first rinsed with tap water until the surface of the seedling is free of impurities, and then rinsed with ultrapure water; then, the rinsed seedling is placed in a plexiglass tank filled with ultrapure water for hydroponics, and the roots of the plant are fixed with clean quartz sand; during the hydroponics, the plant is placed in a ventilated room and supplemented with light every day.

3. The method for degrading PPCPs in water using aquatic plant root secretions according to claim 2, characterized in that: When the target aquatic plant is specifically foxtail algae, the hydroponic temperature is 20-30°C, and 100W simulated sunlight is supplemented for 8-10 hours every day.

4. The method for degrading PPCPs in water using aquatic plant root secretions according to claim 2, characterized in that: When the target aquatic plant is specifically Vallisneria, the hydroponic temperature is 28-32°C, and 100W simulated sunlight is supplemented for 5-8 hours every day.

5. The method for degrading PPCPs in water using aquatic plant root secretions according to claim 1, characterized in that: In the step (2), when the Myriophyllum is hydroponically cultivated, a water sample is taken out from the hydroponic system after culturing for 25 days and filtered to obtain the desired Myriophyllum root secretions.

6. The method for degrading PPCPs in water using aquatic plant root secretions according to claim 1, characterized in that: In the step (2), when hydroponically cultivating Vallisneria, after culturing for 40 days, a water sample is taken out from the hydroponic system and filtered to obtain the desired Vallisneria root secretions.

7. The method for degrading PPCPs in water using aquatic plant root secretions according to claim 1, characterized in that: In the step (2), when filtering the water sample, a 0.45 μm water filter membrane is used; thereafter, the water sample is stored in a brown reagent bottle and placed in a 4° C. refrigerator for later use.

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