Regulating agent for remediation of alkaline soil polluted by heavy metal cadmium and use method of regulating agent

Abstract

The invention is applicable to the technical field of soil pollution treatment, and particularly relates to a regulating agent for remediation of heavy metal cadmium pollution of alkaline soil and a use method thereof, and the regulating agent for remediation of heavy metal cadmium pollution of alkaline soil comprises calcined silicate skarn powder, pyrite powder, zinc sulfate and manganese fertilizer. The regulating agent for repairing the heavy metal cadmium pollution of the alkaline soil, provided by the invention, has the advantages of wide sources of preparation raw materials, low price, low application amount, simple application method, ingenious and reasonable product formula design, remarkable regulating effect and the like, and can be used for efficiently regulating the heavy metal cadmium pollution of the alkalescent soil; heavy metal cadmium pollution of weakly alkaline farmland soil in northern China can be effectively controlled, and safe production of agricultural products is guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of soil pollution control, and in particular relates to a regulator for repairing heavy metal cadmium pollution in alkaline soil and a use method thereof. Background Art

[0002] At present, the most common technologies for preventing and controlling heavy metal cadmium pollution in farmland soil include: agronomic control measures, such as water and fertilizer management, foliar spraying of conditioners, tillage measures, etc.; in-situ passivation remediation, plant extraction remediation, etc. In-situ passivation remediation technology is to add passivation materials to the soil to make them physically and chemically react with the cadmium in the soil, converting the effective cadmium into a chemically inactive form, reducing the migration and bioavailability of cadmium in the soil, reducing the absorption of soil cadmium by crop roots, and reducing the accumulation of cadmium in the edible parts of crops.

[0003] At present, common passivation materials include: calcium silicate materials (sodium silicate, potassium silicate, magnesium silicate, calcium silicate, calcium oxide, calcium hydroxide, calcium carbonate, etc.), clay mineral materials (sepiolite, palygorskite, bentonite, montmorillonite, kaolin, etc.), phosphorus-containing materials (superphosphate, calcium magnesium phosphate, hydroxyapatite, etc.), biochar, metal oxides (iron oxide, ferrous sulfate, ferric sulfate, manganese oxide, potash ore, etc.), organic materials (humic acid, peat, pig manure, cow manure, chicken manure, etc.), etc. Passivation remediation technology has been widely used in the remediation of farmland soil contaminated by heavy metal cadmium because of its simple operation, good remediation effect, fast remediation rate, strong stability, low cost, and the characteristics of simultaneous remediation and production. However, studies have shown that many materials such as calcium silicon materials, clay materials, phosphorus-containing materials, biomass charcoal, metal oxides, and organic materials that have good remediation effects in acidic cadmium-contaminated rice fields in the south have no obvious passivation remediation effects in alkaline cadmium-contaminated soils in the north. There are few remediation agents that can meet the needs of remediation of alkaline cadmium-contaminated soils in the north. In addition, water and fertilizer management measures cannot be adapted to the production of dryland crops in the north, and the barrier effect of foliar spraying of conditioning agents is low, the stability is poor, and the farming measures are generally ineffective. As an auxiliary measure, super-enriched plant extraction remediation in alkaline soil cadmium pollution in the north cannot meet the needs of alkaline soil cadmium pollution remediation due to low extraction efficiency and long remediation time. Therefore, it is urgent to develop remediation agents suitable for the prevention and control of cadmium pollution in alkaline soils in northern my country to ensure the safe production of agricultural products and human health. Summary of the invention

[0004] The purpose of the present invention is to provide a regulator for the remediation of heavy metal cadmium pollution in alkaline soil, aiming to solve the urgent need to develop a regulator suitable for the prevention and treatment of cadmium pollution in alkaline soil in northern my country, and to ensure the safe production of agricultural products and human health.

[0005] The present invention is achieved by providing a regulator for the remediation of heavy metal cadmium pollution in alkaline soil, wherein the regulator for the remediation of heavy metal cadmium pollution in alkaline soil comprises: calcined silicate skarn powder, pyrite powder, zinc sulfate and manganese fertilizer.

[0006] Preferably, the regulator for remediation of heavy metal cadmium pollution in alkaline soil comprises 1 part of calcined silicate skarn powder, 1 part of pyrite powder, 0.5 to 3 parts of zinc sulfate, and 1.5 to 4 parts of manganese fertilizer.

[0007] Preferably, the median particle size of silicate skarn powder and pyrite powder is 5-10 μm, and the content of particles with a particle size greater than 30 μm does not exceed 0.1%.

[0008] Preferably, the manganese salt is one or more of manganese sulfate, manganese acetate, manganese chloride and manganese nitrate.

[0009] Preferably, the preparation step of calcined silicate skarn powder is to calcine silicate skarn ore, wherein the calcination temperature of the silicate skarn is 800-1000° C. and the calcination time is 2-3 hours to obtain calcined silicate skarn powder.

[0010] Another object of the present invention is to provide a method for using a regulator for remediation of heavy metal cadmium pollution in alkaline soil, the method comprising directly spreading the regulator for remediation of heavy metal cadmium pollution in alkaline soil and heavy metal cadmium contaminated soil in a mass ratio of 1:200-1:500 in a weakly alkaline soil contaminated by heavy metal cadmium, and tilling the soil evenly.

[0011] Preferably, the pH value of the weakly alkaline soil is between 7 and 10.

[0012] The present invention provides a regulator for the restoration of heavy metal cadmium pollution in alkaline soil. The raw materials for its preparation are widely available, inexpensive, low in application amount, simple in application method, ingenious and reasonable in product formula design, and have the advantages of significant regulation effect, etc. The regulator can be used for efficient regulation of heavy metal cadmium pollution in weakly alkaline soil, and can effectively control heavy metal cadmium pollution in weakly alkaline farmland soil in northern my country, thereby ensuring the safe production of agricultural products. DETAILED DESCRIPTION

[0013] A regulator for remediation of heavy metal cadmium pollution in alkaline soil, comprising: calcined silicate skarn powder, pyrite powder, zinc sulfate and manganese fertilizer.

[0014] In this embodiment, the mass ratio of the silicate skarn powder, pyrite powder, zinc sulfate and manganese salt is 1:1:0.5:1.5 to 1:1:3:4.

[0015] The median particle size of silicate skarn powder and pyrite powder is 5 to 10 μm, and the maximum content of particles with a particle size greater than 30 μm is not more than 0.1%;

[0016] The manganese salt is one or more of manganese sulfate, manganese acetate, manganese chloride and manganese nitrate.

[0017] The purity of zinc sulfate and manganese salt is industrial grade and there is no secondary pollution.

[0018] The preparation steps of calcined silicate skarn powder are as follows:

[0019] Silicate skarn ore is calcined at a temperature of 800-1000°C for 2-3 hours, and calcined silicate skarn powder is obtained after grinding.

[0020] The preparation process is to evenly mix calcined silicate skarn powder, pyrite powder, zinc sulfate and manganese fertilizer to obtain a regulator suitable for the prevention and control of heavy metal cadmium pollution in weakly alkaline soil.

[0021] A method for using a regulator for remediating heavy metal cadmium pollution in alkaline soil, comprising directly spreading the regulator for remediating heavy metal cadmium pollution in alkaline soil and heavy metal cadmium contaminated soil at a mass ratio of 1:200-1:500 in weakly alkaline soil contaminated by heavy metal cadmium, and tilling the soil evenly.

[0022] The regulator for remediation of heavy metal cadmium pollution in alkaline soil (referred to as the regulator for short) and heavy metal cadmium contaminated soil are directly spread on the weakly alkaline soil contaminated by heavy metal cadmium at a mass ratio of 1:200-1:500, and the soil is evenly plowed before sowing.

[0023] The soil is weakly alkaline farmland soil contaminated by cadmium, with a pH value of about 7-10, and the soil is dry land.

[0024] The edible crops are wheat, corn, vegetables or soybeans.

[0025] The mass ratio of the added amount of the regulator to the heavy metal cadmium contaminated soil is 1:200 to 1:500.

[0026] 1. The raw materials for preparing the conditioning material of the present invention are widely available, low in price, low in application amount, simple in application method, ingenious and reasonable in product formula design, and have the advantages of significant regulation effect, etc., and can be used for efficient regulation of heavy metal cadmium pollution in weakly alkaline soil, and can effectively control heavy metal cadmium pollution in weakly alkaline farmland soil in northern my country, and ensure the safe production of agricultural products. The conditioning material and heavy metal cadmium contaminated soil are directly spread in the weakly alkaline soil contaminated by heavy metal cadmium at a mass ratio of 1:200 to 1:500, and the soil is evenly ploughed before sowing.

[0027] 2. The raw materials of the control material of the present invention are widely available and low in cost. The silicate skarn material and pyrite material in the raw material components have abundant reserves in nature, and the calcination process of the silicate skarn material is simple, eliminating the purification process of magnesium oxide and calcium oxide. At the same time, both zinc sulfate and manganese salt can be industrial-grade products, which greatly reduces the production cost.

[0028] 3. The regulating material of the present invention has no secondary pollution, is green and environmentally friendly, has simple production and preparation, reduces energy consumption, and has no emission of wastewater, waste and greenhouse gases.

[0029] 4. The regulating material of the present invention can effectively passivate / stabilize heavy metal cadmium pollution in weakly alkaline soil, and while achieving the regulation of cadmium pollution in weakly alkaline soil, it can promote the increase of the content of trace elements necessary for plant growth such as magnesium, silicon, calcium, zinc, manganese, iron, phosphorus, and sulfur in the soil after safe utilization, and effectively improve soil fertility.

[0030] 5. The preparation method of the present invention is simple to operate and can be carried out in large-scale and industrialized production.

[0031] 6. Silicate skarn is a metamorphic rock mainly composed of silicate minerals rich in silicon, calcium and magnesium. This makes the raw materials of this control material extremely easy to obtain. After high-temperature calcination, the decomposition products of silicate skarn contain components such as MgO, Fe3(BO3)O2, and Ca3Si3O9. Pyrite is a complex sulfide mineral with FeS2 as its main component. It is a common metal mineral in nature and the most widely distributed sulfide in the earth's crust. Therefore, the above-mentioned control material is a mixture containing magnesium oxide, lime, phosphate, silicon, zinc, manganese and sulfur. The hydration of active magnesium oxide produces brucite (Mg(OH)2), and the layered crystal structure of the hydrate can restrict heavy metal cadmium ions to the interlayer, thereby achieving the purpose of fixing and passivating heavy metal cadmium in the soil. In addition, calcium and magnesium are macronutrients required for plant growth. They can compete with cadmium ions for ion absorption sites and transport channels on plant roots, inhibit crop roots from absorbing and transporting cadmium in the soil, and reduce the accumulation of cadmium in the aboveground and edible parts of crops. Phosphate ions in phosphates can combine with cadmium ions in the soil to form precipitation, reducing the bioavailability of cadmium in the soil. Zinc is a trace element necessary for plant growth. Applying zinc fertilizer on cadmium-contaminated soil can alleviate cadmium toxicity through zinc / cadmium antagonism. At the same time, zinc and cadmium can compete for absorption sites on the surface of crop root cell membranes and transport proteins in cells, inhibiting crop roots from absorbing and transporting cadmium in the soil, and reducing the accumulation of cadmium in the aboveground and edible parts of crops.

[0032] Shi et al. (2005) showed that silicon can reduce the porosity of root cell walls and inhibit the transport of cadmium by the root xylem, thereby effectively reducing the transport of cadmium to the stem. In addition, Ma et al. (2015) believed that silicon in the root cell wall can bind to hemicellulose, thereby hindering the transport of cadmium. The manganese element contained in manganese salts plays an important role in plant photosynthesis, lipid biosynthesis, and oxidative stress. Cadmium is a non-essential element for plant growth, and there are no dedicated transport proteins and ion channels in plants. A large number of studies have shown that proteins of the Nramp protein family in plants are not only involved in the transport of manganese ions, but also accompany the absorption of cadmium ions. Increasing the plant effectiveness of manganese in soil and plants can also inhibit the absorption of cadmium by plants through the antagonistic effect of manganese and cadmium. The increase in the effective sulfur content in the soil can promote the synthesis of sulfur-containing compounds in plants. The combination of sulfur proteins and cadmium in plants can further inhibit the transport process of cadmium from plants to seeds and reduce the cumulative amount of cadmium absorbed in edible parts.

[0033] After calcination, silicate skarn materials produce components such as Mg, Fe, B, Si, and Ca. Different calcination temperatures will result in different ratios of Mg, Fe, B, and Si in the calcined products. In addition, the calcination temperature has a certain effect on the activity of MgO. The MgO produced by a lower calcination temperature is more active, but a lower calcination temperature will also lead to a lower CaO content. The soil pH value after hydration is low, which is not conducive to the stimulation of blue iron ore materials.

[0034] In order to ensure the activity of MgO in the calcined product, the calcination temperature of the silicate skarn material is preferably 800-1000°C and the calcination time is 2-3h.

[0035] Example 1: Preparation of control materials:

[0036] Weigh an appropriate amount of the above-mentioned silicate skarn powder material, place it in a crucible, put it in a muffle furnace, and start heating at a heating rate of 10°C / min. When the muffle furnace is heated to 900°C, maintain this temperature for 2 hours. After cooling, the calcined silicate skarn powder material is obtained, and the sample with a median particle size of 5 to 10 μm and a maximum content of particles greater than 30 μm of no more than 0.1% is obtained for standby use. The calcined silicate skarn powder material is mixed with zinc sulfate and manganese salt in a certain mass ratio, and stirred with a stirrer for more than 5 minutes to ensure uniform mixing to prepare a regulating agent 1#.

[0037] Example 2: Preparation of regulating agent:

[0038] The pyrite material was crushed by a high-speed crusher and sieved to obtain a sample with a median particle size of 5 to 10 μm and a maximum content of particles larger than 30 μm of no more than 0.1%. The pyrite powder material was mixed with zinc sulfate and manganese salt in a certain mass ratio, and stirred with a mixer for more than 5 minutes to ensure uniform mixing, to prepare a regulating agent 3#.

[0039] Example 3: Preparation of regulating agent:

[0040] Similar to Example 1, the calcined silicate skarn powder material was mixed with a 200-mesh sieve-passed pyrite powder material, zinc sulfate and manganese salt in a certain mass ratio, and stirred with a stirrer for more than 5 minutes to ensure uniform mixing, to prepare a regulating agent 3#.

[0041] Example 4: Potted experiment:

[0042] In order to better verify the regulating effect of the regulating material of the present invention on cadmium pollution in alkaline soil, the cadmium-contaminated soil in alkaline wheat fields with moderate cadmium pollution and clay soil type was selected for experimental verification. This example selected cadmium-contaminated farmland soil in a certain place in the north, and the soil type was clay. The wheat variety planted was Shijiazhuang No. 8. The basic physical and chemical properties of the test soil are shown in Table 1.

[0043] Table 1 Basic physical and chemical properties of soil in potted plant experiment of Example 4

[0044]

[0045] Example 4

[0046] 1. Experimental design:

[0047] Regulators 1#, 2# and 3# were applied to 5kg potted soil at a dose of 3.0g / kg (soil), mixed thoroughly and added with 1L of distilled water for soil culture, which were marked as H1, H2 and H3. Three replicates were set for each treatment, and a blank control CK was set with three replicates. The wheat variety planted was Shijiazhuang No. 8. After 14 days of soil culture, wheat grains were sown in each pot, and after 240 days of growth, wheat was harvested. Soil samples and wheat grain samples were collected after wheat maturity for analysis.

[0048] 2. Sample analysis:

[0049] The available cadmium content in soil was determined by 0.1M CaCl2 extraction method, the available manganese and zinc content in soil was determined by DTPA extraction method, the total amount of cadmium, manganese and zinc in soil was determined by nitric acid and hydrofluoric acid digestion method, the available sulfur in soil was determined by barium sulfate turbidimetry, and the cadmium, manganese and zinc content in wheat grains was determined by nitric acid digestion method. The extract and digestion solution obtained after sample treatment were determined by ICP-MS, and the quality control of the test data was carried out by setting blank and standard samples. The regulatory effect of the soil regulation material on cadmium in wheat grains was determined by potted test design.

[0050] 3. Application effect:

[0051] The changes in soil pH, soil available cadmium, available manganese, available zinc and available sulfur content after wheat harvest are shown in Table 2. The average soil pH of the control treatment was 8.36, which was alkaline. After the application of the regulator, the soil pH increased to varying degrees. Compared with the blank control, the soil available cadmium content gradually decreased under the H1, H2 and H3 treatments, among which the soil available cadmium content decreased most significantly under the H3 treatment; the soil available manganese content and available zinc content increased significantly, but the changes between the H1, H2 and H3 treatments were not obvious; the soil available sulfur content increased significantly, but there was no obvious pattern in the changes between the H1, H2 and H3 treatments.

[0052] Table 2 Soil pH value and available contents of cadmium, zinc, manganese and sulfur after applying regulating materials

[0053]

[0054] The changes in cadmium content in wheat grains in the potted test are shown in Table 3. In the potted soil without adding regulating materials, the cadmium content of wheat grains was 0.42 mg / kg; under the H1, H2 and H3 treatments, the cadmium content in wheat grains was 0.26 mg / kg, 0.30 mg / kg and 0.17 mg / kg, respectively, and the cadmium content reduction rates were 38.10%, 28.57% and 59.52%, respectively. Among them, under the H3 treatment, the cadmium content in wheat grains decreased significantly compared with the H2 and H3 treatments. Under the H1, H2 and H3 treatments, the zinc content in wheat grains increased significantly compared with the control, but the manganese content was not significantly different from the blank control. The experimental results verified that the application of regulating agents to alkaline cadmium-contaminated soil can effectively reduce the cadmium content in wheat grains, while increasing the zinc content in wheat grains and improving wheat quality. The experimental results of this embodiment verify the reliability of the results of Example 3.

[0055] Table 3 Changes in cadmium, zinc and manganese contents in wheat grains after application of regulatory materials

[0056]

[0057] Example 5

[0058] 1. Potted plant experiment:

[0059] In order to better verify the blocking effect of the weakly alkaline soil cadmium pollution control material of the present invention on the absorption and accumulation of cadmium in wheat grains, the weakly alkaline soil contaminated by cadmium in a sewage irrigation area in the north was further selected, and the effect of the control material on the change of cadmium content in the soil and wheat grains was studied through potted experiments. The weakly alkaline farmland soil contaminated by cadmium in a sewage irrigation area in the north was selected for verification test in this example, and the soil type was tidal soil. The wheat variety planted was Bainong 207. The physical and chemical properties of the test soil are shown in Table 4.

[0060] Table 4 Basic physical and chemical properties of farmland soil in a sewage irrigation area in the north of China in potted plant experiment

[0061]

[0062] 2. Experimental design

[0063] The regulating materials 1#, 2# and 3# were applied to 5kg potting soil at a dose of 3.0g / kg (soil), mixed thoroughly and added with 1L of distilled water for soil culture, which were marked as T1, T2 and T3. Three replicates were set for each treatment, and a blank control CK was set with three replicates. The wheat variety planted was Shijiazhuang No. 8. After 14 days of soil culture, wheat grains were sown in each pot, and after 240 days of growth, wheat was harvested. Soil samples and wheat grain samples were collected after wheat maturity for analysis.

[0064] 3. Sample analysis:

[0065] The available cadmium content in soil was determined by 0.1M CaCl2 extraction method, the available manganese and zinc content in soil was determined by DTPA extraction method, the total amount of cadmium, manganese and zinc in soil was determined by nitric acid and hydrofluoric acid digestion method, the available sulfur in soil was determined by barium sulfate turbidimetry, and the cadmium, manganese and zinc content in wheat grains was determined by nitric acid digestion method. The extract and digestion solution obtained after sample treatment were determined by ICP-MS, and the quality control of the test data was carried out by setting blank and standard samples. The regulatory effect of the soil regulation material on cadmium in wheat grains was determined by potted test design.

[0066] 4. Application effect:

[0067] The changes in soil pH, soil available cadmium, available manganese, available zinc and available sulfur content after wheat harvest are shown in Table 5. The average soil pH value of the control treatment was 8.26, which was weakly alkaline. The pH value of the soil increased to varying degrees after the application of the regulating materials. Compared with the blank control, the content of available cadmium in the soil gradually decreased under the T1, T2 and T3 treatments, with a reduction rate of 24.42%, 17.44% and 41.46%, respectively. Among them, the content of available cadmium in the soil decreased most significantly under the T3 treatment; the content of available manganese and available zinc in the soil increased significantly, but the changes between the T1, T2 and T3 treatments were not obvious; the content of available sulfur in the soil also increased significantly, but there was no obvious pattern between the T1, T2 and T3 treatments.

[0068] Table 5 Soil pH value and available contents of cadmium, zinc, manganese and sulfur after applying regulating materials

[0069]

[0070] The changes in cadmium content in wheat grains in the potted test are shown in Table 6. In the potted soil without the addition of the regulator, the cadmium content of the wheat grains was 0.35 mg / kg; under the T1, T2 and T3 treatments, the cadmium content in the wheat grains was 0.22 mg / kg, 0.26 mg / kg and 0.15 mg / kg, respectively, and the cadmium content reduction rates were 37.14%, 25.71% and 57.14%, respectively. Among them, under the T3 treatment, the cadmium content in the wheat grains was also significantly reduced compared with the T2 and T3 treatments. Under the T1, T2 and T3 treatments, the zinc content in the wheat grains increased significantly compared with the control, but the manganese content was also no significant difference compared with the blank control. The experimental results further verified that the application of regulatory materials to alkaline cadmium-contaminated soil can effectively reduce the cadmium content in wheat grains, while increasing the zinc content in wheat grains and improving wheat quality. The experimental results of this embodiment further verify the reliability of the results of Example 3.

[0071] Table 6 Changes in cadmium, zinc and manganese contents in wheat grains after application of regulatory materials

[0072]

[0073]

[0074] The main mechanism by which the soil regulation material of the present invention can effectively reduce the cadmium content in wheat grains is:

[0075] (1) Applying regulatory materials increased the content of magnesium ions, silicon ions, manganese ions, zinc ions, iron ions and phosphate ions in the soil, effectively reducing the effective cadmium content in the soil that can be absorbed by wheat roots;

[0076] (2) The competition between magnesium, manganese and zinc ions in the soil and cadmium ions in the wheat roots further reduces the wheat roots' ability to absorb the available cadmium in the soil.

[0077] (3) The increase in available sulfur content in the soil promoted the synthesis of sulfur-containing compounds in wheat. The combination of sulfur proteins in wheat and cadmium further inhibited the transport of cadmium from the wheat body to the grains, thereby reducing the accumulation of cadmium in wheat grains.

[0078] 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 protection scope of the present invention.

Claims

1. A regulator for remediation of heavy metal cadmium pollution in alkaline soil, characterized in that: The regulating agent for remediation of heavy metal cadmium pollution in alkaline soil comprises: calcined silicate skarn powder, pyrite powder, zinc sulfate and manganese fertilizer.

2. The regulating agent for remediation of heavy metal cadmium pollution in alkaline soil according to claim 1, characterized in that: The regulator used for remediation of heavy metal cadmium pollution in alkaline soil contains 1 part of calcined silicate skarn powder, 1 part of pyrite powder, 0.5 to 3 parts of zinc sulfate, and 1.5 to 4 parts of manganese fertilizer.

3. The regulating agent for remediation of heavy metal cadmium pollution in alkaline soil according to claim 1, characterized in that: The median particle size of silicate skarn powder and pyrite powder is 5 to 10 μm, and the content of particles with a particle size greater than 30 μm does not exceed 0.1%.

4. The regulating agent for remediation of heavy metal cadmium pollution in alkaline soil according to claim 1, characterized in that: The manganese salt is one or more of manganese sulfate, manganese acetate, manganese chloride and manganese nitrate.

5. The regulating agent for remediation of heavy metal cadmium pollution in alkaline soil according to claim 1, characterized in that: The preparation steps of calcined silicate skarn powder are as follows: calcining silicate skarn ore, wherein the calcination temperature of the silicate skarn is 800-1000° C. and the calcination time is 2-3 hours to obtain calcined silicate skarn powder.

6. A method for using a regulator for remediation of heavy metal cadmium pollution in alkaline soil, characterized in that: The method comprises directly spreading a regulator for repairing heavy metal cadmium pollution in alkaline soil and heavy metal cadmium polluted soil at a mass ratio of 1:200-1:500 on weakly alkaline soil polluted by heavy metal cadmium, and tilling the soil evenly.

7. The method for using the regulating agent for remediation of heavy metal cadmium pollution in alkaline soil according to claim 6, characterized in that: The pH value of slightly alkaline soil is between 7-10.

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