A method for repairing farmland heavy metal compound contaminated soil by using EDDS to strengthen upland cotton

Abstract

The present invention relates to the technical field of soil remediation, and in particular to a method for remediating farmland heavy metal compound contaminated soil by using EDDS to strengthen upland cotton, which comprises the following steps: planting upland cotton in the heavy metal compound contaminated soil, and during the growth of the upland cotton, adding 5mmol·kg ‑1 EDDS was applied twice. This application studies the effect of EDDS on the content of heavy metals Cd, Cu, Pb, and Zn in soil solution, and the effect on biomass and chlorophyll content of upland cotton and the absorption and enrichment of heavy metals by plants. At the same time, the effect of applying the same amount of chelating agent on the dry weight of upland cotton and the content of heavy metals in upland cotton under different levels of heavy metal complex pollution, as well as the change of heavy metal content in soil solution over time, was also studied. The research results can provide a theoretical basis for the use of chelating agents to enhance plant restoration of heavy metal complex contaminated soils.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation, and in particular to a method for remediating farmland soil contaminated with heavy metals by using EDDS-enhanced upland cotton. Background Art

[0002] At present, the remediation technology of soil heavy metal pollution has been widely studied. Compared with traditional engineering and physical and chemical remediation methods, phytoremediation has been widely favored by people because of its low cost, wide application range, environmental friendliness, and less disturbance to the remediation matrix. However, on the one hand, traditional hyperaccumulators have the disadvantages of short plants, slow growth, and susceptibility to pests and diseases, resulting in the limited overall remediation efficiency of hyperaccumulators; on the other hand, the solubility of heavy metals in the soil is low and the migration ability is poor, making it difficult for plants to effectively absorb and then be transported to the aboveground parts of plants. In recent years, people have gradually turned their attention to crops with large biomass, rapid growth, easy field management, and high tolerance to heavy metals. However, the enrichment capacity of these crops for heavy metals is very limited. Therefore, people consider taking some strengthening measures to improve the extraction capacity of these crops for heavy metals. Since chelating agents can effectively activate heavy metals in the soil and enhance the bioavailability of heavy metals, they are widely used to strengthen plant extraction of heavy metals in the soil. The high efficiency of disodium ethylenediaminetetraacetic acid (EDTA) leads to its frequent use in the study of chelating agent-induced plant extraction. However, since EDTA is difficult to degrade, it may cause groundwater pollution. Therefore, in recent years, the study of the effect of the degradable chelating agent [S,S]-ethylenediamine disuccinate trisodium (EDDS) on plant extraction of heavy metals in soil has become an international hot topic.

[0003] Patent CN 114713624 A discloses a method for promoting the economic crop castor to repair copper and cadmium compound contaminated soil, through the combined action of phosphate fertilizer and EDDS, castor's absorption of copper and cadmium is promoted. Patent CN 104550210A discloses a method for continuous repair of soil heavy metal pollution by chelating agent EDDS and ramie, comprising the following steps: implanting ramie into the soil to be repaired; after the ramie survives, applying the biodegradable chelating agent EDDS to the soil, the application amount is 75-300kg / mu; irrigating once every 30 days with EDDS solution with a concentration of 0.005-0.015mol / L, and irrigating normally at other times; regularly harvesting the stems and leaves of the aboveground part of ramie, and leaving the underground part in the soil to continue breeding and growing. However, the prior art does not disclose the research on the use of EDDS to repair farmland heavy metal compound contaminated soil in upland cotton. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a method for repairing farmland soil contaminated with heavy metals by using EDDS to strengthen upland cotton.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0006] A method for repairing farmland heavy metal compound contaminated soil by using EDDS to strengthen upland cotton is provided, which comprises the following steps:

[0007] Planting upland cotton in soil contaminated by heavy metals. During the growth of upland cotton, 5mmol·kg -1 EDDS was applied in two portions.

[0008] Furthermore, EDDS was used to induce upland cotton to repair soil contaminated by heavy metal Cu.

[0009] The beneficial effects of the present invention are:

[0010] This application studies the effect of EDDS on the content of heavy metals Cd, Cu, Pb, and Zn in soil solution, and the effect on biomass and chlorophyll content of upland cotton and the absorption and enrichment of heavy metals by plants. At the same time, the application of the same amount of chelating agent on the dry weight of upland cotton and the content of heavy metals in upland cotton under different levels of heavy metal complex pollution, as well as the change of heavy metal content in soil solution over time, is also studied. The research results can provide a theoretical basis for the use of chelating agents to enhance plant restoration of heavy metal complex contaminated soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is the difference between the dry weight of different tissues of upland cotton before EDDS application and the dry weight of each tissue of upland cotton after EDDS application; negative value indicates that the dry weight of upland cotton tissue increases after EDDS application; positive value indicates that the dry weight of upland cotton tissue decreases after EDDS application;

[0012] Figure 2 The effects of EDDS application and non-EDDS application on the migration coefficient (TF) of Cd, Cu, Pb and Zn in upland cotton under different heavy metal concentrations;

[0013] Figure 3 The effects of EDDS application and non-EDDS application on the enrichment factor (BCF) of upland cotton under different heavy metal concentrations;

[0014] Figure 4 The changes of heavy metal contents in soil solution over time after EDDS application (mg L -1 ); Note: 3db: 3 days ago; 1da: 1 day later; 4da: 4 days later; 7da: 7 days later; 10da: 10 days later; 13da: 13 days later; 16da: 16 days later; 31da: 31 days later. DETAILED DESCRIPTION

[0015] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0016] Test example

[0017] 1 Research content

[0018] This test case uses a potted plant experiment to study the effects of two applications of the chelating agent EDDS on the biomass of upland cotton and the heavy metal accumulation capacity of upland cotton plants under different heavy metal complex pollution backgrounds (6 concentration gradients, four heavy metals). At the same time, the study studies the changes in the content of four heavy metals in the soil solution over time after two applications of the chelating agent EDDS (from 3 days before application to 31 days after application, a total of 8 soil solution extractions).

[0019] A single application is more likely to increase the content of target heavy metals in the soil solution than multiple applications, but it is easy to increase the toxic effect on plants and the risk of heavy metals leaching into the ground. Therefore, the choice of dosing mode should comprehensively consider many factors such as soil properties, target heavy metals, chelating agent types and plants. On the one hand, due to the degradability of EDDS, divided application can make full use of EDDS; on the other hand, multiple applications can reduce the toxic effects on plants and enhance the tolerance of plants to chelating agents. Therefore, in this study, 5mmol kg -1 EDDS was applied twice, and 9 days after the first application, it was applied again. In this way, not only the chelating agent EDDS was effectively utilized, but also the toxicity of EDDS application to upland cotton plants was reduced.

[0020] 2 Materials and methods

[0021] 2.1.1 Research Materials

[0022] The soil used in the experiment was collected from farmland in Tongzhou District, Beijing. The soil samples were collected at a depth of 0 to 20 cm, and after natural air drying, they were passed through a 2.0 mm nylon sieve for later use. As upland cotton has the characteristics of large biomass, this plant was selected as a potted test plant. The seeds were purchased from the Chinese Academy of Agricultural Sciences, and the variety was Huanong Cotton No. 1. The test pot was a plastic pot with a diameter of 22 cm and a height of 20 cm, purchased from the Chinese Academy of Agricultural Sciences.

[0023] 2.1.2 Potted experiment design

[0024] Each pot was filled with 5 kg of air-dried soil that had been sieved through a 2 mm sieve. Cd, Cu, Pb, and Zn were respectively expressed as cadmium nitrate (Cd(NO 3 )2 ·4H 2 O), copper nitrate (Cu(NO 3 ) 2 ·3H 2 O), lead nitrate (Pb(NO 3 ) 2 ) and zinc chloride (ZnCl 2 ) solution was added to the soil to make the heavy metal concentration in the soil reach the designed concentration, see Table 1. The soil was kept dry and wet alternately for 2 weeks to make the heavy metal ions in the soil reach a balance (a tray was set at the bottom of the pot to prevent the loss of heavy metals from the seepage at the bottom of the pot). 0.43g kg -1 Nitrogen fertilizer (NH 4 NO 3 form) and 0.33 g·kg -1 Phosphate fertilizer (KH 2 PO 4 In addition, an in-situ soil solution sampler was buried horizontally 10 cm above the soil surface in each pot.

[0025] In early May, 12 upland cotton seeds were sown in each pot. After germination, 4-5 upland cotton seedlings with uniform growth were ensured in each pot. During the growth of upland cotton, deionized water was added by weighing method to ensure that the soil moisture content was about 60% of the field water holding capacity. After the upland cotton grew for 60 days, chelating agent was added. This experiment set up a control treatment (only heavy metals were added) and an EDDS treatment (applied twice). The specific experimental treatments are shown in Table 1, and each treatment was repeated 3 times.

[0026] The chelating agent was prepared into a solution according to the designed concentration and applied to the pot with irrigation water. Soil solution samples were taken one day before the chelating agent treatment as a control, and soil solution samples were taken on the first day, fourth day, and seventh day after the first EDDS treatment and on the first day, fourth day, seventh day, and 22 day after the second EDDS treatment. The extracted soil solution samples were placed in polyethylene bottles and stored in a refrigerator at 4°C for testing. The contents of the target heavy metals Cd, Cu, Pb, Zn and the major elements Ca, Mg, Mn, and Fe were determined by ICP-AES.

[0027] 14 days after the first application of the chelating agent, the cotton plant samples were harvested and the plants were divided into three parts: roots, stems, and leaves using aluminum scissors (the plant stems were taken from the above-ground part of the cotton plant that was more than 1 cm above the soil surface). The debris on the surface of the plants was washed away, and then washed with distilled water for 3 times, sterilized at 105°C for 15 minutes, and then placed in an oven at 80°C to a constant weight, and the dry weight of different tissues of the plants was weighed. After being crushed with a grinder, the samples were tested.

[0028] Table 1 Design of pot experiment of upland cotton

[0029]

[0030] 2.1.3 Design of soil solution sample extraction

[0031] Before use, wet the PE tube of the soil solution sampler (with a glass fiber booster and a 2.5mm diameter hole that is water-permeable), and then insert it horizontally into the hole 10cm from the soil surface and 8cm from the bottom of the pot. When using, use a medical syringe to draw a vacuum, then extract 2-4mL of soil solution and place it in a polyethylene bottle for testing.

[0032] 2.1.4 Sample pretreatment and analysis

[0033] 2.1.4.1 Determination of basic physical and chemical properties of soil

[0034] Pretreatment of soil samples: Spread the soil after removing gravel and broken roots on a large piece of filter paper, air dry naturally, mix it by quartering, grind about 200g of soil sample in a quartz mortar (or agate mortar), pass through a 20-mesh nylon sieve, and then take about 50g of it and further grind it in an agate ball mill, and pass through a 100-mesh nylon sieve. Put the prepared 20-mesh and 100-mesh soil samples into envelopes and store them in a dry place for later use.

[0035] Determination of basic soil properties: Mainly refer to Lu Rukun's "Soil Agricultural Chemical Analysis Methods". Soil pH determination - using a pH meter (PB-10sartorius pH), where the soil: liquid ratio is 1:2.5.

[0036] ②Soil CaCO 3 Content determination - gas volume method.

[0037] ③ Determination of soil organic matter content - using element analyzer (CHNS Vario ELIII, Germany).

[0038] OM (g kg -1 )=1.724×(C 总 -C 无机 )

[0039] Where: C 总 : Total carbon content in soil; C 无机 : The content of inorganic carbon (carbon in calcium carbonate) in the soil; 1.724: The coefficient of converting organic carbon into organic matter.

[0040] ④ Determination of soil particle size distribution: The particle size distribution was determined using a laser particle size analyzer (Micro Trac S3000, Germany). The results were divided into particle size distributions according to the American soil particle size classification scheme, and then the soil texture was determined according to the soil texture triangle map made by the United States Department of Agriculture.

[0041] ⑤ Determination of soil total nitrogen—element analyzer (CHNS Vario ELIII, Germany).

[0042] 2.1.4.2 Determination of heavy metal and nutrient content in soil samples

[0043] Accurately weigh 0.1000 g of soil sample that has passed through a 100-mesh sieve and place it in a digestion tank. Add 3 ml of HNO 3 1 ml HClO 4 After adding 1 ml HF, tighten the cap and digest in a microwave oven at 160 °C for 3 hours. After cooling, slowly heat and evaporate to 1 drop, add 1 ml HNO 3 Afterwards, the solution was diluted to 10 ml with high-purity water for testing. Afterwards, the concentration of each solution was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES, ULTIMA, France).

[0044] 2.1.4.3 Distribution of heavy metal forms in soil

[0045] According to the five-step continuous extraction method proposed by Tessier, the forms of heavy metals in soil are divided into five forms: ion exchange state, carbonate binding state, iron and manganese oxide binding state, organic state and residual state. The specific extraction procedure is:

[0046] ① Ion exchange state: Weigh 2.000g of soil sample that has passed through a 100-mesh sieve and place it in a 50ml centrifuge tube. Add 20ml of 1mol / l MgCl 2 Solution, pH = 7.0, shake at 25 ± 5 ° C for 2h, centrifuge at 4000r for 20min, filter the supernatant for analysis, and add 20ml of ultrapure ion-free water to the residue for centrifugation and washing;

[0047] ② Carbonate binding state: add 20 ml of 1 mol / l NaOAC solution to the residue, pH = 5.0 (HOAC adjustment), shake at 25±5℃ for 5 hours, centrifuge at 4000r for 20 minutes, filter the supernatant for analysis, and add 20 ml of ultrapure ionized water to the residue for centrifugation and washing;

[0048] ③ Iron and manganese oxidation state: add 20ml of 0.1mol / l NH 2 25% HOAC solution of OH·HCl (hydroxylamine hydrochloride), pH = 2.0 (HNO 3 Adjust), shake at 25±5℃ for 5h, centrifuge at 4000r for 20min, filter out the supernatant for analysis, and add 20ml of ultrapure ion-free water to the residue for centrifugation and washing;

[0049] ④Organic binding state: add 10ml of 30% H 2 O 2(HNO 3 Adjust pH = 2), 5 ml of 0.1 mol / l HNO 3 Heat the solution at 85°C for 2-6 hours, shaking and heating intermittently until there are no bubbles (ensure that H 2 O 2 is sufficient). After cooling to room temperature, add 10 ml of 3.2 mol / l CH 3 COONH 4 20% HNO 3 The solution was shaken continuously for 30 min, centrifuged at 4000 r for 20 min, the supernatant was filtered out for analysis, and the residue was washed by centrifugation with 20 ml of ultrapure ion-free water;

[0050] ⑤ Residue state: Take 0.1g of the residue and place it in a digestion tank, add 3ml of HNO 3 1 ml HClO 4 After adding 1 ml of HF, tighten the cap and digest in a microwave oven at 160 °C for 3 hours. After cooling, slowly heat and evaporate until 1 drop is reached. Add 1 ml of HNO 3 Then, dilute to 10 ml with high-purity water for testing.

[0051] 2.1.4.4 Determination of metal content in soil solution

[0052] The contents of target elements Cd, Cu, Pb, Zn and major elements Ca, Mg, Fe, Mn in each solution were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES, ULTIMA, France).

[0053] 2.1.4.5 Determination of heavy metal and nutrient element contents in plant tissues

[0054] Sample pretreatment: Separate soybean tissue into above-ground and underground parts, separate upland cotton tissue into roots, stems, and leaves, and use Teflon scissors to cut roots, stems, and other tissues short to 1-2 cm. First, rinse the soil and dust adhering to the surface with tap water, then use ultrasonic cleaning, then wash three times with deionized water, and dry in the shade. After killing in an oven at 105°C for 15 minutes, place in an oven at 60°C and dry to constant weight, then weigh the dry weight of the plant on an analytical balance and record. Use a grinder to crush the dried plant tissue, then pass through a 40-mesh nylon sieve, put it in an envelope, and store it in a desiccator for later use.

[0055] Determination of heavy metal and trace element content in samples: Accurately weigh 0.2000g of plant sample and place it in a digestion tank, add 2ml HNO 3 (66%) and 1 ml H 2 O 2(33%) was allowed to stand for more than 3 hours, then digested in an oven at 160°C for 3 hours, and diluted to 10 mL with high-purity water for testing.

[0056] 2.1.4.6 Determination of chlorophyll content in plant leaves

[0057] Select mature fresh plant leaves, wipe off the dirt on the surface of the tissue, weigh 0.1g, cut into pieces (remove the midrib), put into a test tube with a stopper scale, add 10ml of mixed solution (80% acetone and 95% ethanol mixed in equal volumes of 1:1), immerse the leaves completely in the liquid, cover and extract for 24 hours in a dark place. To improve the extraction efficiency, the test tube can be gently shaken several times during the extraction. After the leaves turn completely white, take the supernatant and use a spectrophotometer to measure the absorbance at wavelengths of 663nm and 645nm respectively. The mixed solution is used as a control. Calculate the chlorophyll content according to the following formula:

[0058] C a =(12.71A 663 -2.59A 645 )V / 1000W

[0059] C b =(22.88A 645 -4.67A 663 )V / 1000W

[0060] C T =C a +C b

[0061] Where: 1) A 663 , A 645 It is the spectral brightness value at wavelengths of 663nm and 645nm;

[0062] 2) C a , C b , C T are the concentrations of chlorophyll a, chlorophyll b and total chlorophyll, respectively.

[0063] 2.1.4.7 Determination of malondialdehyde (MDA) content in plant leaves

[0064] Reagent preparation: 1) 5% trichloroacetic acid (TCA); 2) 0.6% thiobarbituric acid (TBA) solution.

[0065] Weigh 0.1g of plant leaves, cut them into pieces, put them in a pre-cooled mortar, add 2ml of 5% TCA, add a small amount of quartz sand, grind until homogenous and pour into a centrifuge tube, then add 8ml of TCA to wash the mortar and pour into the previous centrifuge tube. Place the centrifuge tube in a centrifuge at 4000r / min and centrifuge for 10 minutes. Take 2ml of supernatant, add 2ml of distilled water to the control test tube, then add 2ml of 0.6% TBA to each, add a stopper and mix evenly, put it in a boiling water bath and boil for 10 minutes, after cooling, quickly (to reduce errors) put it in a centrifuge and centrifuge it again for 15 minutes, and take the supernatant. Use spectrophotometry to measure the absorbance at 450nm, 532nm and 600nm, and calculate the MDA content using the following formula:

[0066] MDA concentration (μmol / L) = 6.45 (A 532 -A 600 )-0.56A 450

[0067] MDA content (μmol / g) = MDA concentration (μmol / L) × 2 (mL) / sample weight (g) × 1000 Where: A 450 , A 532 , A 600 They are the absorbance values ​​at wavelengths of 450nm, 532nm, and 600nm respectively.

[0068] 2.1.4.8 Calculation of plant enrichment capacity

[0069] Plant enrichment characteristics are usually expressed by bioconcentration factor (BCF). for:

[0070]

[0071] In the formula is the heavy metal content in the aboveground parts of plants, The heavy metal content in the soil.

[0072] The migration of heavy metals in plants is usually expressed by the migration factor (TF). for:

[0073]

[0074] In the formula is the heavy metal content in the aboveground parts of plants, It refers to the heavy metal content in the underground part of plants.

[0075] 2.1.4.9 Quality Control and Data Analysis

[0076] To ensure the accuracy of the data during the analysis, soil standard materials (GBW 07401 (GSS-1)) and plant standard materials (GBW08503) were digested in the same way as soil and plant samples to monitor the stability of the instrument. The standard materials were all from the National Center for Standard Materials. At the same time, reagent blanks were added to each batch of analytical samples, and 10% of the samples were repeated to ensure the precision and accuracy of the analysis. The analysis results were processed using Excel; and the relevant charts were made using origin 8.0.

[0077] 3 Results Analysis

[0078] 3.1.1 Effects of EDDS on biomass of various tissues of upland cotton

[0079] from Figure 1 It can be seen that in potted plants without heavy metals or with low concentrations of heavy metals, the application of the chelating agent EDDS increased the dry weight of various tissues of upland cotton, and the dry weight of upland cotton tissues without heavy metals was the largest. Many studies have shown that low concentrations of heavy metals can promote plant growth. In addition, this may be because the application of EDDS increases the activity of nutrients in the soil while increasing the target heavy metals, thereby promoting plant growth. After adding higher concentrations of heavy metals to the soil, the application of EDDS reduced the dry weight of various tissues of upland cotton, mainly because the application of EDDS increased the activity of heavy metals in the soil, thereby exerting a certain stress on upland cotton plants. Among them, the decrease in the dry weight of various tissues of upland cotton first increased and then decreased with the increase in the concentration of heavy metals in the soil. The concentrations of heavy metals Cd, Cu, Pb, and Zn in the soil were 5, 400, 200, and 400 mg kg, respectively. -1 The dry weight of various tissues of upland cotton decreased the most when EDDS was applied. This may be because the higher concentration of heavy metals has already exerted certain stress on various tissues of upland cotton. After the application of EDDS, the extent to which the dry weight of various tissues of upland cotton can be reduced has become smaller. In addition, in terms of the extent of change in various tissues of upland cotton, leaves>stems>roots, which is consistent with the law of dry weight of upland cotton itself, leaves>stems>roots.

[0080] 3.1.2 Effect of EDDS on the ability of upland cotton to absorb and accumulate heavy metals

[0081] Table 2 Effects of EDDS application on Cd content in upland cotton tissues at different heavy metal concentrations (mg·kg -1 )

[0082]

[0083]

[0084] Note: T1 in this table corresponds to T1-1 and T2-1 in Table 1, T2 corresponds to T1-2 and T2-2 in Table 1, and so on. These are the Cd contents in upland cotton tissues without and with EDDS under different soil heavy metal concentration gradients, as well as the multiple increase of Cd content in upland cotton tissues after EDDS application.

[0085] As can be seen from Table 2, with the increase of Cd content in the soil, the Cd content in plant roots, stems and leaves increased with the increase of Cd content in the soil, regardless of whether EDDS was applied or not. -1 When the Cd content in the roots, stems and leaves of the control plants reached the maximum, which were 18.7, 11.6 and 17.4 mg·kg -1 After adding EDDS, the Cd content in the roots reached 115.5 mg kg -1 , which was 6.2 times of the control, and the Cd content in the stems reached 26.4 mg kg -1 , which was 2.3 times that of the control, and the Cd concentration in the leaves was lower than that of the control. Under other soil Cd concentrations, the application of EDDS did not increase the Cd content in the roots and stems of upland cotton, but only slightly increased the Cd content in the leaves of upland cotton.

[0086] Table 3 Effects of EDDS on Cu content in upland cotton tissues at different heavy metal concentrations (mg·kg -1 )

[0087]

[0088] Note: T1 in this table corresponds to T1-1 and T2-1 in Table 1, T2 corresponds to T1-2 and T2-2 in Table 1, and so on. These are the Cu contents in upland cotton tissues without and with EDDS under different soil heavy metal concentration gradients, as well as the multiple increase of Cu content in upland cotton tissues after EDDS application.

[0089] As shown in Table 3, as the Cu content in the soil increases, the Cu content in the leaves and roots of upland cotton also increases. After applying EDDS, the Cu content in the leaves of upland cotton increased significantly compared with the control, ranging from 1.3 to 205.4 times that of the control. Among them, the Cu content in the soil is 400 mg kg -1 When the Cu content in the leaves of upland cotton reached 2676.2 mg kg -1 , which is 205.4 times the Cu content in the leaves of the control upland cotton. It can be seen that the application of EDDS can significantly increase the Cu content in the leaves of upland cotton. For the stems of upland cotton, the Cu content in the soil is 421.4 mg kg -1When EDDS was applied, the Cu content in the stem of upland cotton reached 856.0 mg kg -1 , which is 117.7 times that of the control. At the same time, at this concentration, the Cu concentration in the roots reached 416.2 mg kg -1 , which is 4.4 times that of the control. It can be seen that at low concentrations, the application of EDDS mainly increased the Cu content in the leaves of upland cotton, and at high concentrations (421.4 and 521.4 mg kg -1 ), the application of EDDS can simultaneously increase the Cu content in the roots, stems and leaves of upland cotton.

[0090] Table 4 Effects of EDDS on Pb content in upland cotton tissues at different heavy metal concentrations (mg·kg -1 )

[0091]

[0092] Note: T1 in this table corresponds to T1-1 and T2-1 in Table 1, T2 corresponds to T1-2 and T2-2 in Table 1, and so on. These are the Pb contents in upland cotton tissues without and with EDDS under different soil heavy metal concentration gradients, as well as the multiple increase of Pb content in upland cotton tissues after EDDS application.

[0093] As can be seen from Table 4, with the increase of Pb content in the soil, the Pb content in the roots, stems and leaves of upland cotton increased, and after the application of EDDS, the Pb content in each tissue of upland cotton increased, but the increase multiples varied with different tissues and different Pb concentrations in the soil. The increase multiples of Pb content in leaves ranged from 1.2 to 6.7, and the Pb concentration in the soil was 515.2 mg kg -1 When -1 The increase times reached a maximum of 6.7; the increase times of Pb concentration in stems were 1.8 to 9.6, among which the Pb concentration in soil was 615.2 mg kg -1 , reaching a maximum value of 138.2 mg kg -1 , which was 9.6 times of the control; the increase in roots was between 1.3 and 5.1, similar to that in stems. The Pb content in soil was 615.2 mg kg -1 When -1 , which is 5.1 times of the control. It can be seen that the application of EDDS can significantly increase the Pb content in the roots, stems and leaves of upland cotton.

[0094] Similar to other heavy metals, the Zn content in various tissues of upland cotton increased with the increase of Zn content in the soil. The application of EDDS had different effects on the Zn content in different tissues of upland cotton. For upland cotton leaves, except for the Zn concentration in the soil of 654.4 mg kg -1 When the Zn content in the leaves of upland cotton was 1.4 and 2.0, the application of EDDS reduced the Zn content in the leaves of upland cotton. At other soil Zn concentrations, the application of EDDS increased the Zn content in the leaves, with the increase multiple ranging from 1.4 to 2.0. For the stems and roots of upland cotton, the Zn content in the leaves of upland cotton increased significantly at high soil Zn concentrations (554.4 and 654.4 mg kg -1 ), the application of EDDS increased the Zn concentration in the stem and root, the increase was 1.2-3.3 times, 1.1-1.4 times. However, at low concentrations, the application of EDDS reduced the Zn concentration in the stem and root, which may be because the application of EDDS promoted the transfer of Zn to the leaves of upland cotton at low concentrations.

[0095] Table 5 Effects of EDDS on Zn content in upland cotton tissues at different heavy metal concentrations (mg·kg -1 )

[0096]

[0097] Note: T1 in this table corresponds to T1-1 and T2-1 in Table 1, T2 corresponds to T1-2 and T2-2 in Table 1, and so on. These are the Zn contents in upland cotton tissues without and with EDDS under different soil heavy metal concentration gradients, as well as the multiple increase of Zn content in upland cotton tissues after EDDS application.

[0098] In summary, with the increase of heavy metal content in soil, whether EDDS was applied or not, the heavy metal content in plant roots, stems and leaves increased with the increase of heavy metal concentration in soil. The application of EDDS generally increased the content of Cu and Pb in plants, but only the content of Cd and Zn in some upland cotton tissues was increased.

[0099] 3.1.3 Effect of EDDS on heavy metal transfer coefficient

[0100] The transfer coefficient (TF) refers to the ratio of the heavy metal content in the aboveground part of the plant to the heavy metal content in the underground part. It can reflect the difficulty of heavy metal transfer from the underground part to the aboveground part. The larger the TF value, the easier it is for the heavy metal to transfer from the underground part to the aboveground part, and the more conducive it is to phytoremediation.

[0101] from Figure 2It can be seen that the application of EDDS generally promoted the transfer of heavy metals from the underground part to the aboveground part of upland cotton, and only some transfer coefficients were not improved. In the case of heavy metals Cu, Pb, and Zn without the addition of EDDS, TF showed a certain downward trend with the increase of heavy metal concentration in the soil, only when the concentrations of Cd, Cu, Pb, and Zn in the soil were 1, 100, 300, and 300 mg kg, respectively. -1 TF increased slightly under the condition of EDDS. The TF values ​​of Cd in upland cotton tissues were greater than 1 in both the control and after EDDS application, and the TF reached a maximum value of 12.8 after EDDS application. In addition, at high concentrations, the application of EDDS reduced the TF value. In the control soil, the TF of Cu was between 0.5 and 11.5. After EDDS application, the TF increased to between 8.1 and 22.4. It can be seen that the application of EDDS significantly increased the transfer coefficient of Cu in upland cotton, which was about 2 to 26 times that of the control. After EDDS application, the TF values ​​of Pb at all concentrations increased, reaching a maximum of 15.1. In the control, only T6 had a TF value less than 1, but after EDDS application, it also increased to 2.0. Under the control conditions, the TF value of heavy metal Zn was between 5.7 and 12.2. After EDDS application, the TF value increased to between 5.8 and 26.2, and the maximum increase was 15, which was 2.6 times that of the control.

[0102] 3.1.4 Effect of EDDS on the enrichment coefficient of upland cotton

[0103] The bioaccumulation factor (BCF) refers to the ratio of the heavy metal content in the aboveground part of the plant to the heavy metal content in the soil. It is generally used to indicate the ability of plants to enrich certain heavy metals. After the application of the chelating agent EDDS, the bioavailability of heavy metals in the soil is improved, which promotes the absorption and enrichment of heavy metals by plants, thereby increasing the enrichment factor of plants for heavy metals.

[0104] from Figure 3 It can be seen that with the increase of the degree of heavy metal complex pollution in the soil, the plant enrichment coefficient has a certain downward trend. The application of EDDS increased the enrichment coefficient of Cu and Pb in upland cotton, and at the same time, it also increased the enrichment coefficient of Cd and Zn in upland cotton under some heavy metal complex pollution concentrations. Among them, the amount of Cd, Cu, Pb, and Zn added to the control and soil was 0.5, 50, 200, and 200 mg kg, respectively. -1 Under the condition of , the enrichment factor of Cd in upland cotton increased after applying EDDS, but under the condition of other heavy metal complex pollution concentration, the application of EDDS reduced the enrichment factor of Cd. After applying chelating agent EDDS, the enrichment factor of Cu and Pb in upland cotton increased, which were 2.2-73.5 times and 1.6-5 times of the control, respectively.

[0105] 3.1.5 Effect of EDDS on heavy metal content in soil solution

[0106] Before applying EDDS, the Cd content in the soil solution was between 0 and 0.05 mg L -1 Between the ranges, 2.5 mmol kg - 1 After 1 day of EDDS, the maximum Cd content in the soil solution reached 4.36 mg L -1 , which was 89 times of the control. After 7 days, it dropped to 0.82 mg / L -1 , which was 17 times of the control. After the second application of EDDS, the Cd content in the soil solution increased again. After 31 days, the Cd content in the soil solution decreased to 0.2-8.4 times of the control.

[0107] Before applying EDDS, the Cu content in the soil solution was between 0.01 and 0.16 mg L -1 The Cu content in soil solution increased with the increase of Cu content in soil. -1 After EDDS, the copper content in the soil solution increased to 12.2-434 mg L -1 After 3 days, the copper content in the soil solution continued to increase, ranging from 15 to 490 mg L -1 After the second application of EDDS, the Cu content in the soil solution continued to rise, reaching 1410 to 4329 times that of the control. 31 days after the first application, the Cu content in the soil solution became 0.1 to 2.0 mg / L -1 , which is 8 to 28 times that of the control.

[0108] Due to the immobility of Pb, Pb could not be detected or its content was extremely low in the soil solution before the application of EDDS. After the application of EDDS, the Pb content in the soil solution increased, with the maximum value reaching 75.1 mg L -1 After 31 days, the Pb content in the soil solution decreased significantly, with the maximum value dropping to 1.2 mg L -1 , and other values ​​were slightly higher than the original soil levels.

[0109] Before applying EDDS, the Zn content in the soil solution was 0.1-0.4 mg L -1 One day after EDDS application, the Zn content in the soil solution increased by 4 to 2474 times, reaching a maximum of 569 mg L -1. As time went by, the zinc content in the soil solution gradually decreased. Seven days after the application of EDDS, the zinc content in the soil solution became 4 to 267 times that before the application. After the second application of EDDS, the Zn content in the soil solution became 7 to 1613 times the initial content. After three weeks, the Zn content in the soil solution, with a few exceptions, basically dropped to 1 to 2 times the initial concentration.

[0110] 3.1.6 Changes of heavy metal content in soil solution over time

[0111] from Figure 4 It can be seen that the situation of Cd and Pb is similar. Both applications of EDDS significantly increased the content of heavy metals in the soil solution, but the second increase was slightly smaller than the first. Four days after the application of EDDS, the heavy metals in the soil solution decreased significantly. After 31 days, it basically dropped to the level before application. For the heavy metal Cu, the Cu content in the soil solution increased significantly one day after the application of EDDS. As time went on, it continued to increase and then decreased significantly. After the second application of EDDS, the situation was similar, and it also increased first and then decreased. After 31 days, it dropped to the level before application. For the heavy metal Zn, after the application of EDDS, the Zn content in the soil solution increased significantly, then first slowly decreased, and then sharply decreased. After 7 days, the concentration decreased significantly. After the second application of EDDS, the Zn concentration in the soil solution increased significantly again, but the increase was smaller than the increase after the first application. After 31 days, the Zn content in the soil solution also dropped to the level before application.

[0112] In this study, the biodegradable chelating agent EDDS was applied to improve the enrichment effect of heavy metals Cd, Cu, Pb, and Zn in upland cotton. The results showed that the application of EDDS generally increased the content of heavy metals Cu and Pb in upland cotton tissues, however, only under some soil heavy metal pollution concentrations, the content of Cd and Zn in upland cotton tissues was increased; at the same time, the results showed that the application of the chelating agent EDDS increased the transfer coefficients of heavy metals Cu and Pb under all soil pollution concentrations, and the transfer coefficients of heavy metals Cd and Zn under most soil heavy metal pollution concentrations.

[0113] The experiment found that under the control conditions and when Cd, Cu, Pb, and Zn were added to the soil at the amounts of 0.5, 50, 200, and 200 mg kg -1 Under the condition of , the application of EDDS can increase the biomass of various tissues of upland cotton, which may be because the application of EDDS increases the activity of nutrients in the soil while increasing the target heavy metals, thereby promoting plant growth; under the condition of simulating other concentrations of heavy metal complex pollution, the application of EDDS reduces the dry weight of various tissues of upland cotton, mainly because the application of EDDS increases the activity of heavy metals in the soil, thereby producing a certain stress effect on upland cotton plants.

[0114] The Cu content in the soil is 421.4 mg kg -1 When the Cu content in the leaves of upland cotton reached 2676.2 mg kg -1 , which is 205.4 times the Cu content in the leaves of the control upland cotton. At this time, the Cu enrichment coefficient of upland cotton is 1.5 and the transfer coefficient is 13.2. According to the absolute enrichment content of hyperaccumulators greater than 1000 mg kg -1 , the enrichment coefficient is greater than 1, and the transfer coefficient is greater than 1. Upland cotton has reached the requirements of hyperaccumulators and has the potential to repair Cu pollution in the soil. At different growth stages of upland cotton, the proportion of leaves varies greatly, so when applying the chelating agent EDDS, it should be selected when the upland cotton grows vigorously and has a large amount of leaves, which is more conducive to the completion of plant restoration.

[0115] By studying the changes in the content of heavy metals Cd, Cu, Pb, and Zn in the soil solution over time after two applications of the chelating agent EDDS, it was found that the content of heavy metals in the soil solution increased significantly one day after the application of the chelating agent EDDS, and decreased significantly after 7 days. After the second application of EDDS, the content of heavy metals in the soil solution increased significantly again, but the increase was slightly less than the first increase. After 31 days, the content of heavy metals in the soil solution basically dropped to the level before application. It can be seen that due to the degradability of EDDS, the risk of groundwater pollution by applying EDDS chelation to induce upland cotton to repair soil contaminated by heavy metal Cu is relatively small.

[0116] In summary, this application uses a potted plant simulation experiment method to study the effects of EDDS on the content of heavy metals Cd, Cu, Pb, and Zn in soil solution, and the effects on the biomass and chlorophyll content of upland cotton and the absorption and enrichment of heavy metals by plants. At the same time, the application of the same amount of chelating agent on the dry weight of upland cotton and the content of heavy metals in upland cotton under different levels of heavy metal complex pollution, as well as the changes in the content of heavy metals in soil solution over time, is also studied. The research results can provide a theoretical basis for the use of chelating agents to enhance plant restoration of heavy metal complex contaminated soils.

[0117] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0118] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for repairing farmland heavy metal compound contaminated soil by using EDDS to strengthen upland cotton, characterized in that: The following steps are involved: Planting upland cotton in soil contaminated by heavy metals. During the growth of upland cotton, 5mmol·kg -1 EDDS was applied in two portions.

2. The method for repairing farmland heavy metal compound contaminated soil by using EDDS to strengthen upland cotton according to claim 1, characterized in that: Using EDDS to induce upland cotton to repair soil contaminated by heavy metal Cu.

Images