Foliar resistance and control agent for reducing mercury content of crops as well as preparation method and application of foliar resistance and control agent

Abstract

The invention provides a leaf surface resistance and control agent for reducing mercury content of crops and a preparation method and application of the leaf surface resistance and control agent. The leaf surface resistance and control agent comprises Tween, a component a and a component b, wherein the component a comprises one or more of tartaric acid, tartrate, humic acid and humate, and the component b comprises one or more of selenite and metal sulfide. The content of mercury in crops can be effectively reduced by applying the foliar resistance and control agent to the crops in a foliar spraying manner.

Description

Technical Field

[0001] The present invention relates to the technical field of soil mercury pollution control, and in particular to a foliar control agent for reducing mercury content in crops, and a preparation method and application thereof. Background Art

[0002] Remediation technologies for soil mercury control pathways are currently one of the main methods for controlling mercury pollution in farmland, including both non-biological (physical and chemical) and biological (plant and microbial) technologies. The biotechnology approach is considered an environmentally friendly and cost-effective method, but it is still difficult to screen or cultivate plants that hyperaccumulate mercury, and microbial research is mainly based on ideal laboratory environments, which limits the practical application of bioremediation technologies. Non-biological technologies mainly include thermal desorption, chemical leaching, and chemical passivation. Among them, chemical passivation is currently the most commonly used method for controlling mercury pollution in farmland. However, many studies have found that passivators are more effective in inhibiting the accumulation of methylmercury in plants than inorganic mercury. For example, under field conditions, adding a low dose of activated carbon (150 kg / mu) only reduced the mercury content in rice by approximately 5%, but the reduction rate of methylmercury in rice was as high as 40%. Other studies have also shown that soil mercury passivators tend to inhibit the accumulation of methylmercury in plants (42-75%), and have a lower effect on reducing inorganic mercury (<40%). At the same time, modified clay minerals that work well in the laboratory (63-90%) do not achieve the expected remediation effect in mining farmland with higher atmospheric mercury concentrations. The above-mentioned soil passivation method is not ideal for removing inorganic mercury from plants because mercury, unlike other heavy metals, has the distinct characteristic of existing in gaseous form. In addition to the soil pathway, plants can also absorb large amounts of inorganic mercury through their leaves and transport it to other tissues. Especially in areas with high atmospheric mercury concentrations in the wild, traditional technologies that control crop mercury enrichment only through the soil pathway are difficult to achieve ideal results.

[0003] In recent years, foliar spraying of barriers to reduce heavy metal content in crops has become a new approach in the prevention and control of heavy metal pollution in farmland. Literature and patents demonstrating progress indicate that foliar spraying of inorganic barriers such as zinc (Zn), selenium (Se), and silicon (Si), as well as organic barriers such as organic acids, humic acid, and thiol-containing compounds, can effectively reduce heavy metal accumulation in the edible parts of crops. For example, spraying malic acid can reduce Cd content in rice by inhibiting its transport from vegetative organs to grains. Spraying fulvic acid can enhance the antioxidant enzyme system and reactive oxygen free radical scavenging capacity of lettuce, improving photosynthetic electron transport and nutrient absorption, thereby inhibiting Cd accumulation in lettuce. Foliar spraying of nano-selenium reduces the bioavailability of cadmium in root soil by altering soil microbial abundance, thereby reducing cadmium accumulation in wheat grains. Consequently, foliar spraying has been widely used in the remediation of heavy metal-contaminated soils, providing a promising solution for reducing heavy metal content in edible parts and ensuring agricultural product safety. However, current research on foliar spraying technology for the treatment of heavy metal-contaminated soils mainly focuses on heavy metals such as Cd and Pb, while research on foliar spraying technology and its mechanism of action for mercury-contaminated farmland is relatively lacking. Unlike other heavy metals, mercury can exist in the atmospheric environment in gaseous form at room temperature. Plants can absorb mercury from the soil and also absorb atmospheric mercury through their leaves. Especially in mining areas with severe atmospheric mercury pollution, atmospheric mercury absorption is dominant (Aslam et al. Unravelling the interactive effect of soil and atmospheric mercury influencing mercury distribution and accumulation in the soil-rice system [J]. Science of the Total Environment, 2022, 803, 149967-149967). However, the mechanisms for blocking soil mercury absorption and atmospheric mercury absorption are completely different, so it is urgent to find a foliar spraying agent that can simultaneously reduce the absorption of atmospheric mercury and soil mercury by leaves. Summary of the Invention

[0004] To address one of the aforementioned technical problems in the prior art, the present invention provides a foliar barrier agent for reducing mercury content in crops, as well as a method for reducing mercury content in crops. Furthermore, the present invention provides a preparation method and application of the foliar barrier agent. The foliar barrier agent of the present invention can simultaneously reduce mercury absorption by crops from both the soil and the atmosphere.

[0005] On the one hand, the present invention provides a foliar barrier agent for reducing the mercury content in crops, the barrier agent comprising: Tween, and at least one component selected from component a and component b; wherein the component a comprises one or more of tartaric acid, tartrate, humic acid, and humate, and the component b comprises one or more of selenite and metal sulfide.

[0006] Research has shown that spraying Tween on crop leaves can reduce mercury levels in the crops. Further research has revealed that spraying Tween on crop leaves, when combined with the aforementioned components a and b, can significantly reduce mercury levels in stems and leaves, particularly leaf mercury. Extensive experiments have also revealed that Tween exhibits a synergistic mercury-reducing effect with component a (e.g., tartaric acid or its salts) and component b (e.g., selenite).

[0007] According to some embodiments of the present invention, the Tween includes but is not limited to Tween 80, Tween 20, Tween 40, Tween 60, etc. In some embodiments, the Tween includes Tween 80.

[0008] According to some embodiments of the present invention, the barrier control agent further includes water.

[0009] According to some embodiments of the present invention, the mass concentration of Tween in the foliar control agent is 0.01-0.2%, such as 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, or any value therebetween. In some embodiments, the mass concentration of Tween in the foliar control agent is 0.02-0.1%.

[0010] According to some embodiments of the present invention, the tartrate includes an alkali metal salt of tartaric acid, such as sodium tartrate, potassium tartrate, and the like.

[0011] According to some embodiments of the present invention, the humate includes an alkali metal salt of humic acid, such as sodium humate, potassium humate, and the like.

[0012] According to some embodiments of the present invention, the concentration of component a in the foliar control agent is 1-10 mmol / L, for example, 1 mmol / L, 2 mmol / L, 3 mmol / L, 4 mmol / L, 5 mmol / L, 6 mmol / L, 7 mmol / L, 8 mmol / L, 9 mmol / L, 10 mmol / L, or any value therebetween. In some embodiments, the concentration of component a in the foliar control agent is 2-6 mmol / L.

[0013] According to some embodiments of the present invention, the component a comprises one or both of tartaric acid and sodium humate. In some embodiments, the component a comprises tartaric acid. In some embodiments, the component a comprises sodium humate.

[0014] According to some embodiments of the present invention, the selenite comprises an alkali metal selenite, such as sodium selenite.

[0015] According to some embodiments of the present invention, the metal sulfide comprises an alkali metal sulfide, such as sodium sulfide.

[0016] In some embodiments, the component b comprises sodium selenite. In some embodiments, the component b comprises sodium sulfide. In some embodiments, the component b comprises sodium selenite and sodium sulfide.

[0017] In some embodiments, the concentration of component b in the foliar barrier agent is 1 mg / L-2 g / L, for example, 1 mg / L, 2 mg / L, 4 mg / L, 6 mg / L, 8 mg / L, 10 mg / L, 50 mg / L, 0.1 g / L, 0.2 g / L, 0.5 g / L, 0.8 g / L, 1.0 g / L, 1.2 g / L, 1.5 g / L, 1.8 g / L, 2 g / L, preferably 2 mg / L-1 g / L.

[0018] According to some embodiments of the present invention, the concentration of selenite in the foliar dampening agent is 1-10 mg / L, for example, 1 mg / L, 2 mg / L, 3 mg / L, 4 mg / L, 5 mg / L, 6 mg / L, 7 mg / L, 8 mg / L, 9 mg / L, 10 mg / L, or any value therebetween. In some embodiments, the concentration of selenite in the foliar dampening agent is 2-6 mg / L.

[0019] According to some embodiments of the present invention, the concentration of the metal sulfide in the foliar dampening agent is 0.1-2 g / L, for example, 0.1 g / L, 0.2 g / L, 0.5 g / L, 0.8 g / L, 1.0 g / L, 1.2 g / L, 1.5 g / L, 1.8 g / L, 2 g / L, or any value therebetween. In some embodiments, the concentration of the metal sulfide in the foliar dampening agent is 0.2-1.0 g / L.

[0020] According to some preferred embodiments of the present invention, the foliar barrier agent includes: tartaric acid, sodium selenite and Tween 80.

[0021] According to some embodiments of the present invention, the foliar control agent includes: tartaric acid, sodium sulfide and Tween 80.

[0022] According to some embodiments of the present invention, the foliar barrier agent includes: tartaric acid, sodium selenite, sodium sulfide and Tween 80.

[0023] According to some embodiments of the present invention, the foliar control agent includes sodium humate, sodium sulfide and Tween 80.

[0024] According to some embodiments of the present invention, the foliar control agent includes sodium humate, sodium selenite and Tween 80.

[0025] According to some embodiments of the present invention, the foliar control agent includes: sodium humate, sodium selenite, sodium sulfide and Tween 80.

[0026] On the other hand, the present invention provides a method for preparing a foliar barrier agent for reducing the mercury content in crops, comprising: mixing Tween, component a and component b with water to obtain a foliar barrier agent; wherein the component a comprises one or more of tartaric acid, tartrate, humic acid, and humate, and the component b comprises one or more of selenite and metal sulfide.

[0027] In the preparation method of the foliar barrier control agent of the present invention, the raw material components are dissolved in water so that the foliar barrier control agent meets the use concentration requirements, and no special requirements are made on the order of adding the raw material components.

[0028] According to some embodiments of the present invention, the Tween includes but is not limited to Tween 80, Tween 20, Tween 40, Tween 60, etc. In some embodiments, the Tween includes Tween 80.

[0029] According to some embodiments of the present invention, the tartrate includes an alkali metal salt of tartaric acid, such as sodium tartrate, potassium tartrate, and the like.

[0030] According to some embodiments of the present invention, the humate includes an alkali metal salt of humic acid, such as sodium humate, potassium humate, and the like.

[0031] According to some embodiments of the present invention, the component a comprises one or both of tartaric acid and sodium humate. In some embodiments, the component a comprises tartaric acid. In some embodiments, the component a comprises sodium humate.

[0032] According to some embodiments of the present invention, the selenite comprises an alkali metal selenite, such as sodium selenite.

[0033] According to some embodiments of the present invention, the metal sulfide comprises an alkali metal sulfide, such as sodium sulfide.

[0034] In some embodiments, the component b comprises sodium selenite. In some embodiments, the component b comprises sodium sulfide. In some embodiments, the component b comprises sodium selenite and sodium sulfide.

[0035] According to some embodiments of the invention, component a comprises tartaric acid, and component b comprises sodium selenite.

[0036] According to some embodiments of the invention, component a comprises tartaric acid, and component b comprises sodium sulfide.

[0037] According to some embodiments of the invention, component a comprises tartaric acid, and component b comprises sodium selenite and sodium sulfide.

[0038] According to some embodiments of the invention, component a comprises sodium humate, and component b comprises sodium sulfide.

[0039] According to some embodiments of the present invention, component a includes sodium humate, and component b includes sodium selenite.

[0040] According to some embodiments of the present invention, component a includes sodium humate, and component b includes sodium selenite and sodium sulfide.

[0041] According to some embodiments of the present invention, the amount of Tween used satisfies: the mass concentration of Tween in the prepared foliar control agent is 0.01-0.2%, for example, 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, or any value therebetween. In some embodiments, the amount of Tween used satisfies: the mass concentration of Tween in the prepared foliar control agent is 0.02-0.1%.

[0042] According to some embodiments of the present invention, the amount of component a is such that the concentration of component a in the prepared foliar control agent is 1-10 mmol / L, for example, 1 mmol / L, 2 mmol / L, 3 mmol / L, 4 mmol / L, 5 mmol / L, 6 mmol / L, 7 mmol / L, 8 mmol / L, 9 mmol / L, 10 mmol / L, or any value therebetween. In some embodiments, the amount of component a is such that the concentration of component a in the prepared foliar control agent is 2-6 mmol / L.

[0043] According to some embodiments of the present invention, component b is used in an amount such that the concentration of selenite in the prepared foliar control agent is 1-10 mg / L, for example, 1 mg / L, 2 mg / L, 3 mg / L, 4 mg / L, 5 mg / L, 6 mg / L, 7 mg / L, 8 mg / L, 9 mg / L, 10 mg / L, or any value therebetween. In some embodiments, component b is used in an amount such that the concentration of selenite in the prepared foliar control agent is 2-6 mg / L.

[0044] According to some embodiments of the present invention, the amount of component b is such that the concentration of the metal sulfide in the prepared foliar control agent is 0.1-2 g / L, for example, 0.1 g / L, 0.2 g / L, 0.5 g / L, 0.8 g / L, 1.0 g / L, 1.2 g / L, 1.5 g / L, 1.8 g / L, 2 g / L, or any value therebetween. In some embodiments, the amount of component b is such that the concentration of the metal sulfide in the prepared foliar control agent is 0.2-1.0 g / L.

[0045] In another aspect, the present invention provides a method for reducing mercury content in crops, comprising:

[0046] Select consecutive cloudy days to spray the foliage barrier agent of the present invention or the foliage barrier agent prepared by the above method on the leaf surfaces of crops planted on mercury-contaminated soil.

[0047] The foliar barrier agent of the present invention can be used in different growth stages of crops, for example, it can be sprayed on the leaf surface (including the front and back) during the seedling stage, growth stage, flowering stage, and fruiting stage of crops.

[0048] According to some embodiments of the present invention, the spraying amount of the foliar barrier agent is such that the surface of the crop leaves is moistened without dripping.

[0049] According to some embodiments of the present invention, the crops include but are not limited to dryland crops such as lettuce, corn, cabbage, and pepper.

[0050] According to some embodiments of the present invention, the foliar barrier agent is sprayed 1-3 times. According to some embodiments of the present invention, the spraying interval for leafy vegetables is 7-8 days when spraying multiple times, and the fruit crops are sprayed during different growth cycles.

[0051] For different types of crops, the foliar barrier control agent of the present invention can be sprayed at different growth stages. For example, lettuce and cabbage can be sprayed at the seedling stage, growth stage, and maturity stage; pepper can be sprayed at the seedling stage, flowering stage, and fruiting stage; corn can be sprayed at the seedling stage, horn stage, flowering stage, and fruiting stage.

[0052] The foliar control agent of the present invention is preferably sprayed in the middle or late growth period of crops if it is sprayed once; and is preferably sprayed in the middle and late growth period of crops if it is sprayed twice.

[0053] According to some embodiments of the present invention, the total mercury content in the mercury-contaminated soil is 0.1-13 mg / kg.

[0054] In another aspect, the present invention provides the use of the above-mentioned foliar barrier agent or the foliar barrier agent prepared by the above-mentioned method in reducing the mercury content in crops, including but not limited to dryland crops such as lettuce, cabbage, corn, and pepper.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] 1. The foliar control agent for reducing mercury content in crops provided by the present invention has a simple preparation method and low use cost. In addition, each component is non-toxic to the environment and does not affect plant growth after spraying, and may even promote plant growth.

[0057] 2. The foliar barrier agent provided by the present invention can not only reduce the absorption of soil mercury by the edible parts of crops, but also reduce the absorption of atmospheric mercury by plant leaves. This is particularly advantageous in mining areas with serious atmospheric mercury pollution, and is of great significance for improving the utilization rate of mercury-contaminated farmland and ensuring the food safety of regional crops. Its mechanism for simultaneously reducing the absorption of atmospheric mercury and soil mercury includes the following aspects: (1) After spraying, the macromolecular substances generated between the components of the foliar barrier agent significantly reduce the stomatal conductance of plants without reducing biomass, closing the channel for atmospheric mercury to enter the plant body, thereby reducing the absorption of atmospheric mercury by leaves. (2) The foliar barrier agent induces the synthesis of a large amount of non-protein thiol NPT in plant roots, chelates and fixes the mercury entering the plant in the roots, reducing the migration of soil mercury to the edible parts of the plant; or reduces the absorption of soil mercury by plants by reducing the activity of soil mercury. (3) It significantly improves the interception function of plant cell walls and the compartmentalization function of cell sap, ensuring the normal growth of plants while also reducing the migration of mercury in plants.

[0058] 3. The components of the foliar barrier agent provided by the present invention have a synergistic effect in reducing the mercury content in crops. That is, the foliar barrier agent has a greater effect on reducing leaf mercury than the sum of the effects of each component sprayed separately, and its effect on reducing stem mercury is also greater than the effect of each component sprayed separately.

[0059] 4. The foliar barrier agent provided by the present invention has a stable effect and can effectively reduce the total mercury content in dryland crops, different mercury-contaminated soils and sites. The combination of tartaric acid + sodium selenite + Tween has an effect of reducing the mercury content in the stems, leaves and fruits of various crops by 32-68%.

[0060] 5. The foliar barrier agent provided by the present invention can not only significantly reduce the total mercury in crops, but also significantly reduce the methylmercury in crops, with the reduction rate ranging from 77-86%. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 The color changes of the foliar spraying control agent in Example 2 before and after mixing different components are shown.

[0062] Figure 2 The malondialdehyde (MDA) and peroxidase (POD) contents in the roots, stems and leaves of lettuce in different spraying groups in Example 2 are shown, wherein CK represents the control group, FXT represents the sodium humate + sodium selenite + Tween group; JXT represents the tartaric acid + sodium selenite + Tween group; JST represents the tartaric acid + sodium sulfide + Tween group; T represents the Tween group; F represents the sodium humate group; and X represents the sodium selenite group.

[0063] Figure 3 The figures show the non-protein thiol (NPT) content in the roots, stems and leaves of lettuce in different spraying groups in Example 2, wherein CK represents the control group, FXT represents the sodium humate + sodium selenite + Tween group; JXT represents the tartaric acid + sodium selenite + Tween group; JST represents the tartaric acid + sodium sulfide + Tween group; T represents the Tween group; F represents the sodium humate group; and X represents the sodium selenite group.

[0064] Figure 4 The mercury percentages in the subcellular structures of lettuce roots, stems, and leaves in different spraying groups in Example 2 are shown.

[0065] Figure 5 The pictures of the field experiment of Example 4 are shown. DETAILED DESCRIPTION

[0066] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and drawings. The specific embodiments described herein are only used to illustrate the present invention and are not intended to constitute any limitation to the present invention.

[0067] Unless otherwise specified, the reagents used in the following experiments were commercially available or prepared according to conventional methods. The methods used in the experiments were conventional experimental methods unless otherwise specified. The instruments used in the experiments were commercially available unless otherwise specified.

[0068] In the following embodiments of the present invention, the preparation method of the barrier control agent solution is: dissolving the raw materials of each component in water to make the components in the barrier control agent solution reach corresponding concentrations, and the order of adding the raw materials is not particularly limited.

[0069] Example 1 (mercury reduction effect experiment):

[0070] ⑴Experimental materials:

[0071] Soil was collected from Tianzhu County, Qiandongnan Prefecture, Guizhou Province (THg = 0.2 mg / kg). The topsoil (0-20 cm) of the paddy field was collected, air-dried, cleaned, and crushed through a 6 mm mesh sieve for later use.

[0072] Lettuce seedlings were purchased from Chengdu, Sichuan Province.

[0073] The tartaric acid, sodium sulfide and sodium selenite used are all analytical grade with a purity of more than 98%; the sodium humate is reagent grade; and the Tween used is Tween 80, pharmaceutical grade.

[0074] ⑵Pot experiment:

[0075] Example 1 The potted experiment was carried out at the end of May 2023. The experiment selected 3L flower pots as experimental pots, all with air holes and trays to retain water at the bottom, added 1.5kg of treated spare mercury-contaminated soil, added a certain amount of mercury-free tap water and stirred it to make it fully mixed, and aged for 3 to 4 days for use. The above-mentioned spraying group and control group were set up, and 3 parallels were set up for each treatment. After the soil was aged, 2 lettuce seedlings were planted. 20 days after the seedlings were transplanted, continuous cloudy days were selected, and the barrier control agent solution was sprayed on the front and back of the plant leaves (the leaf surface was moist but not dripping). The control group was sprayed with an equal amount of water, and then sprayed twice in succession. The interval between each spraying was 7-8 days, and the plants were harvested one week after the third foliar spraying treatment.

[0076] The types and concentrations of the components in the barrier control agent solution are as follows:

[0077] Spraying group 1: tartaric acid, 4mmol / L;

[0078] Spraying group 2: sodium humate, 4mmol / L;

[0079] Spraying group 3: sodium selenite, 4 mg / L;

[0080] Spraying group 4: sodium sulfide, 0.5 g / L;

[0081] Group 5 was sprayed with: tartaric acid 4 mmol / L + sodium selenite 4 mg / L + Tween 0.05 wt%;

[0082] Group 6 was sprayed with: tartaric acid 4mmol / L + sodium sulfide 0.5g / L + Tween 0.05wt%;

[0083] Group 7 was sprayed with: tartaric acid 4mmol / L + sodium selenite 4mg / L + sodium sulfide 0.5g / L + Tween 0.05wt%;

[0084] Group 8 was sprayed with: sodium humate 4mmol / L + sodium sulfide 0.5g / L + Tween 0.05wt%;

[0085] Group 9 was sprayed with: sodium humate 4mmol / L + sodium selenite 4mg / L + Tween 0.05wt%;

[0086] Spray 10 groups: sodium humate 4mmol / L + sodium selenite 4mg / L + sodium sulfide 0.5g / L + Tween 0.05wt%.

[0087] ⑶Sample collection and measurement:

[0088] After collecting the stems and leaves, they were washed with tap water three times, then rinsed with deionized water and the surface moisture of the plants was dried, and then the fresh weight was weighed using an electronic balance.

[0089] Plant samples were freeze-dried, pulverized, and ground for the determination of total plant mercury. Total plant mercury was measured using a DMA-80 solid-sample mercury analyzer (DMA-80, Milestone Inc., Shelton, CT). 0.02–0.05 g of plant sample (accurate to 0.0001 g) was weighed directly onto the sampler for the determination of plant THg.

[0090] (4) Experimental results:

[0091] The biomass of lettuce stems and leaves is shown in Table 1. The results showed that, except for the tartaric acid + sodium sulfide + Tween treatment group which significantly reduced the biomass of lettuce, most of the inhibitors had no significant effect on the lettuce stems, but significantly promoted the growth of leaves.

[0092] Table 1 Biomass of lettuce stems and leaves (g)

[0093] stem leaf comparison 4.9±0.1 21.8±1.5 Spray 1 group: tartaric acid 5.6±0.1 26.1±1.3 Spraying Group 2: Sodium Humate 8.6±0.4 30.8±1.0 Spraying group 3: sodium selenite 5.5±0.2 24.7±1.5 Spraying group 4: sodium sulfide 5.7±1.0 26.1±4.2 Spray 5 groups: tartaric acid + sodium selenite + Tween 5.5±0.1 27.9±1.4 Spray 6 groups: tartaric acid + sodium sulfide + Tween 3.6±0.2 20.6±1.6 Spray 7 groups: tartaric acid + sodium selenite + sodium sulfide + Tween 4.2±0.3 26.2±3.8 Spray 8 groups: sodium humate + sodium sulfide + Tween 5.1±0.3 28.0±1.0 Spraying group 9: sodium humate + sodium selenite + Tween 4.3±0.2 24.4±1.0 Spray 10 groups: sodium humate + sodium selenite + sodium sulfide + Tween 4.8±0.04 29.4±1.0

[0094] Table 2 shows the total mercury content in lettuce stems and leaves. The results showed that single-component inhibitors were not effective in reducing leaf mercury, while sodium humate, sodium sulfide, or sodium selenite alone significantly reduced lettuce stem mercury. Among the mixed spraying treatments, all significantly reduced lettuce stem and leaf mercury content. The sodium humate + sodium selenite + Tween group achieved the highest reduction rates, with leaf mercury reductions of 63% and stem mercury reductions of 57%. Tartaric acid + sodium selenite + Tween reduced leaf mercury by 42% and stem mercury by 42%. Tartaric acid + sodium sulfide + Tween reduced leaf mercury by 47% and stem mercury by 28%.

[0095] Table 2 Total mercury content in lettuce stems and leaves (ug / kg)

[0096]

[0097]

[0098] Example 2 (reduction effect verification and mechanism):

[0099] Because the potted soil in Example 1 was too little and the weather was too hot to grow lettuce, and the mercury concentration in the test soil did not meet the pollution standard, a second potted verification experiment was conducted. In this experiment, these factors were not only improved, but also plant and soil parameters were analyzed simultaneously with mercury content to explore the reduction mechanism.

[0100] (1) Experimental materials:

[0101] Soil was collected from Danzhai County, Qiandongnan Prefecture, Guizhou Province (THg = 5.67 mg / kg). The topsoil (0-20 cm) of mercury-contaminated rice fields was collected, air-dried, cleaned, and crushed through a 6 mm mesh sieve for later use.

[0102] Lettuce seedlings were purchased from Chengdu, Sichuan Province.

[0103] The tartaric acid, sodium sulfide and sodium selenite used are all analytical grade with a purity of more than 98%; the sodium humate is reagent grade; and the Tween used is Tween 80, pharmaceutical grade.

[0104] (2) Potted experiment and time:

[0105] Example 2 The potted experiment was carried out in September 2023. The experiment selected 5L flower pots as experimental pots, all with air holes and trays to retain water at the bottom, added 3.0kg of treated spare mercury-contaminated soil, added a certain amount of mercury-free tap water and stirred it to make it fully mixed, and aged for 3 to 4 days for use. The above-mentioned spraying group and control group were set up, and 3 parallels were set up for each treatment. After the soil was aged, 4 lettuce seedlings were planted in each pot. 20 days after the seedlings were transplanted, continuous cloudy days were selected, and the barrier control agent solution was sprayed on the front and back of the plant leaves (the leaf surface was moist but not dripping), and the control group was sprayed with an equal amount of water, followed by two consecutive sprayings, with an interval of 7-8 days between each spraying. Destructive sampling was set up for the tartaric acid + sodium selenite + Tween, tartaric acid + sodium sulfide + Tween, sodium humate + sodium selenite + Tween and Tween groups, that is, whole plant samples were collected one week after each spraying, while the sodium selenite and sodium humate treatment groups were only harvested one week after the third foliar spraying.

[0106] The types and concentrations of the components in the barrier control agent solution are as follows:

[0107] Spraying group 1: tartaric acid 4mmol / L + sodium sulfide 0.5g / L + Tween 0.05wt%;

[0108] Group 2 was sprayed with: tartaric acid 4 mmol / L + sodium selenite 4 mg / L + Tween 0.05 wt%;

[0109] Group 3 sprayed: sodium humate 4mmol / L + sodium selenite 4mg / L + Tween 0.05wt%;

[0110] Spraying group 4: Tween: 0.05wt%;

[0111] Spraying group 5: sodium humate, 4mmol / L;

[0112] Group 6 was sprayed with sodium selenite, 4 mg / L.

[0113] (3) Sample collection and measurement:

[0114] Roots, stems, and leaves were collected and washed three times with tap water, then rinsed with deionized water. The surface moisture was then blotted dry and the fresh weight was measured. Some samples were stored at -80°C for the determination of physiological and biochemical parameters, while the remaining samples were freeze-dried, pulverized, and ground for the determination of other parameters. Root soil was collected, freeze-dried, ground, and sieved for later use.

[0115] Total mercury in plants was determined using a DMA-80 solid injection mercury analyzer (DMA-80, Milestone Inc., Shelton, CT): 0.02–0.05 g (accurate to 0.0001 g) of plant sample was weighed and placed directly on the injector for plant THg determination.

[0116] At the same time, in order to analyze the source and mechanism of mercury reduction by foliar barrier agents, the photosynthetic parameters, physiological and biochemical indices of plants, methylmercury in plant samples and methylmercury in root soil were also analyzed after the third spraying.

[0117] Plant photosynthetic parameters were analyzed using a JC-FS-3080DPro photosynthesis meter before sample collection.

[0118] Methylmercury in plants was digested with KOH, extracted with CH2Cl2, and back-extracted by heating in a water bath, then ethylated and determined by GC-CVAFS. Methylmercury in soil was digested with HNO3-CuSO4, extracted with CH2Cl2, and back-extracted by heating in a water bath, then ethylated and determined by GC-CVAFS.

[0119] Physiological and biochemical parameters were analyzed in the supernatant after homogenate centrifugation. Malondialdehyde was measured using the thiobarbituric acid method, peroxidase was measured using the guaiacol method, and non-protein sulfhydryl groups were measured using a kit (Suzhou Grace Biotechnology Co., Ltd., China). Subcellular fractions were extracted using differential centrifugation. Cell walls and organelles were freeze-dried and then measured for mercury using DM80. Cell sap was oxidized with BrCl and reduced with SnCl2 using a gold tube trap coupled to a CVAFS mercury analyzer.

[0120] (4) Experimental results:

[0121] Table 3 shows the stem and leaf biomass of lettuce after each spraying. After the first spraying, there were no significant differences in stem and leaf biomass among the treatments. After the second spraying, there was little difference in lettuce leaf biomass among the treatments, but spraying with Tween and tartaric acid + sodium selenite + Tween was beneficial to lettuce stem growth. After the third spraying, the stem and leaf biomass of the mixed spraying group was slightly lower than that of the control, but the difference was not significant. These results indicate that spraying the control agent did not significantly affect plant growth.

[0122] Table 3 Lettuce stem and leaf biomass (g)

[0123]

[0124]

[0125] The total mercury in the roots, stems and leaves of lettuce after each spraying is shown in Table 4.

[0126] Table 4 Total mercury content in lettuce roots, stems and leaves (ug / kg)

[0127]

[0128] As can be seen from Table 4, after the first spraying, the total mercury in the stems and leaves of all experimental groups was reduced to varying degrees, among which the reduction rates of leaf mercury were as follows:

[0129] Tartaric acid + sodium sulfide + Tween, 50%; tartaric acid + sodium selenite + Tween, 65%; sodium humate + sodium selenite + Tween, 56%; Tween, 54%.

[0130] The stem mercury reduction rates were as follows:

[0131] Tartaric acid + sodium sulfide + Tween, 55%; tartaric acid + sodium selenite + Tween, 68%; sodium humate + sodium selenite + Tween, 37%; Tween, 35%.

[0132] The tartaric acid + sodium selenite + Tween group significantly reduced total mercury in stems and leaves compared to Tween alone. Changes in mercury content in the inedible roots showed that after the first spraying, root mercury levels in the tartaric acid + sodium selenite + Tween, sodium humate + sodium selenite + Tween, and Tween spray groups were significantly higher than the control, with increases of 26%, 219%, and 125%, respectively.

[0133] After the second spraying, the total mercury in stems and leaves of all experimental groups was reduced to varying degrees, with the leaf mercury reduction rates as follows:

[0134] Tartaric acid + sodium sulfide + Tween, 52%; tartaric acid + sodium selenite + Tween, 42%; sodium humate + sodium selenite + Tween, 41%; Tween, 38%.

[0135] The stem mercury reduction rates were as follows:

[0136] Tartaric acid + sodium sulfide + Tween, 48%; tartaric acid + sodium selenite + Tween, 57%; sodium humate + sodium selenite + Tween, 30%; Tween, 64%.

[0137] Among them, the effects of tartaric acid + sodium selenite + Tween and tartaric acid + sodium sulfide + Tween on reducing leaf mercury were better than spraying Tween alone.

[0138] After the third spraying, the single spraying of sodium humate and sodium selenite did not significantly reduce the mercury in lettuce leaves, while the reduction rates for stem mercury were 40% and 26%, respectively. The leaf mercury reduction rates of the remaining treatment groups were as follows:

[0139] Tartaric acid + sodium sulfide + Tween, 3%; tartaric acid + sodium selenite + Tween, 43%; sodium humate + sodium selenite + Tween, 24%; Tween, 19%.

[0140] The stem mercury reduction rates were as follows:

[0141] Tartaric acid + sodium sulfide + Tween, 33%; tartaric acid + sodium selenite + Tween, 53%; sodium humate + sodium selenite + Tween, 21%; Tween, 47%.

[0142] As can be seen, after the third spraying, all mixed sprays showed a greater reduction in leaf mercury than either spray alone, but only the tartaric acid + sodium selenite + Tween combination showed a greater reduction in stem mercury than either spray alone. Regarding root mercury, the tartaric acid + sodium selenite + Tween spray group significantly increased mercury by 49% compared to the control, while the other spray groups showed no significant differences from the control.

[0143] The results in Table 4 show that after three sprayings, Tween reduced leaf mercury by 19%, while sodium selenite reduced leaf mercury by only 5%. The results of Example 1 also indicate that spraying tartaric acid alone is ineffective in reducing leaf mercury in lettuce. However, the experimental results of Example 2 show that spraying a combination of tartaric acid, sodium selenite, and Tween reduced leaf mercury by up to 43%. In Example 1, the tartaric acid, sodium selenite, and Tween spraying group also achieved a 42% reduction in leaf mercury. Therefore, the leaf mercury reduction rate of tartaric acid, sodium selenite, and Tween was significantly higher than the sum of the reduction rates of each component sprayed individually, demonstrating a synergistic effect. Compared to stem mercury, leaf mercury likely originates more from atmospheric mercury. Therefore, spraying tartaric acid, sodium selenite, and Tween may, through some mechanism (see the Mechanism Analysis section for details), effectively block atmospheric mercury from entering the plant foliage, thereby achieving the goal of reducing leaf mercury. In addition, after further research, the present invention found that the effect of spraying tartaric acid + Tween is equivalent to the effect of spraying Tween alone in reducing mercury, indicating that when only tartaric acid is added to Tween without adding sodium selenite, the effect of reducing leaf mercury and stem mercury is not significantly improved.

[0144] ⑸Mechanism analysis

[0145] Unlike other heavy metals, mercury can exist in the atmospheric environment in gaseous form at room temperature. Plants can absorb mercury both from the soil and through their leaves. This is particularly predominant in mining areas with severe atmospheric mercury pollution (Aslam et al. 2022. Unravelling the interactive effect of soil and atmospheric mercury influencing mercury distribution and accumulation in the soil-rice system [J]. Science of the Total Environment, 803, 149967-149967). Table 5 shows the change rates of root, stem, and leaf mercury. Single spraying of sodium humate and sodium selenite reduced mercury concentrations only in the stem, while the combined spraying reduced both leaf and stem mercury concentrations. The tartaric acid + sodium selenite + Tween group showed the greatest effect in reducing both stem and leaf mercury. Based on the stem and leaf mercury reduction rates, we can preliminarily infer that the treatment with a high leaf mercury reduction rate may have blocked more atmospheric mercury sources, while the treatment with a high stem mercury reduction rate may have reduced more soil mercury sources. To further clarify the source and mechanism of mercury blocking by these inhibitors, we further analyzed the changes in plant photosynthetic parameters and soil methylmercury.

[0146] Table 5 Change rate of total mercury in lettuce roots, stems and leaves after the third spraying of Example 2

[0147] leaf stem root Spray 1 group: tartaric acid + sodium sulfide + Tween -30％ -33％ +9％ Spray 2 groups: tartaric acid + sodium selenite + Tween -43％ -53％ +49％ Spraying group 3: sodium humate + sodium selenite + Tween -24％ -21％ -5％ Spray 4 groups: Tween -19％ -47％ +10％ Spraying group 5: sodium humate +4％ -26％ +15％ Spray Group 6: Sodium Selenite -5％ -40％ +9％

[0148] Note: In Table 5, “+” represents an increase; “-” represents a decrease.

[0149] ① Verification and mechanism of atmospheric mercury barrier:

[0150] Table 6 shows the photosynthetic parameters of lettuce leaves after three sprayings. The results showed that after three sprayings, the stomatal conductance of the group treated with tartaric acid + sodium selenite + Tween was the lowest, with a maximum reduction of 36% compared to the control group, while the group sprayed with sodium selenite alone actually increased stomatal conductance. Stomatal conductance indicates the degree of opening of the stomata, which are the main channels for gas exchange between plant leaves and the outside world. Since mercury, unlike other heavy metals, has the distinct characteristic of existing in gaseous form, reducing stomatal conductance can prevent atmospheric mercury from entering plant leaves, thereby achieving the purpose of reducing plant leaf mercury. This largely explains why the tartaric acid + sodium selenite + Tween group has the best effect in reducing leaf mercury. Although the stomatal conductance of the tartaric acid + sodium selenite + Tween group was significantly reduced, the biomass of this treatment group was not affected, and in Example 1, it was significantly promoted. Factors affecting plant photosynthesis primarily include stomatal and non-stomatal factors. Stomatal limitation is caused by partial stomata closure, while non-stomatal limitation includes photochemical activity limitation, ribulose diphosphate carboxylation limitation, and inorganic phosphorus limitation. Intercellular CO2 concentration is the basis for evaluating these two factors. Stomata are considered the primary factor affecting photosynthesis only if both intercellular CO2 concentration and photosynthetic rate decrease simultaneously; otherwise, non-stomatal factors are considered. The results in Table 5 show that although the photosynthetic rate in the tartaric acid + sodium selenite + Tween spraying group was lower than that in the control and Tween spraying groups, the difference in intercellular CO2 concentration was not significant, indicating that stomatal conductance was not the dominant factor limiting photosynthesis. Therefore, the reduction in stomatal conductance did not restrict plant growth, but it did significantly block the entry of atmospheric mercury into the leaves, thereby reducing leaf mercury.

[0151] Tartaric acid is a dihydroxysuccinic acid, and its structural formula contains two hydroxyl groups. After the selenium in sodium selenite enters the tartaric acid, the introduction of selenium may react with the hydroxyl groups in the tartaric acid (Zhou Shufang, Hao Yong. Preparation and characterization of selenium-doped hydroxyapatite / silk fibroin composites [J]. Chemical Research and Application, 2017, 29(03): 429-434), and may generate selenol substances. In addition, the solution of sodium selenite, a strong base and weak acid salt, is alkaline after hydrolysis. Selenol makes selenium become selenium anion under alkaline conditions. Selenium anion has strong nucleophilicity. According to the mechanism of charge-induced ring opening, strong nucleophilic substances can easily attack the positively charged carbon ion of ethylene oxide. Tween-80 is polyoxyethylene stearyl ether ester generated by the polymerization of sorbitol monooleate and ethylene oxide. Selenium anion causes ethylene oxide to open the ring. The polyoxyethylene stearyl ether ester after ring opening and sodium alcohol form macromolecular substances on the surface of lettuce leaves. Figure 1The color changes of tartaric acid, sodium selenite, and Tween, when mixed individually, in pairs, and when mixed together, are shown. The color of the liquid becomes significantly lighter when sodium tartaric acid, sodium selenite, and Tween are mixed. This is likely due to the reaction of some Tween with tartaric acid and sodium selenite. The formation of macromolecules blocks the stomata of the lettuce leaves, reducing stomatal conductance and narrowing the pathways through which atmospheric mercury enters the plant, ultimately preventing atmospheric mercury from entering the leaves.

[0152] Table 6 Photosynthetic parameters of lettuce leaves

[0153]

[0154]

[0155] ②Verification and mechanism of soil mercury barrier pathways

[0156] Inhibitors can reduce the active absorption of heavy metals by plants by changing the physiological and biochemical indicators of plants, or fix the absorbed heavy metals in the roots, reducing the transfer to edible parts. In addition, inhibitors can also change the soil environment and the bioavailability of heavy metals in the soil by changing the secretions of plant roots. The degree of methylation of mercury in the soil is an important indicator of the bioavailability of soil mercury. Generally, the higher the soil methylmercury, the higher the bioavailability activity. Table 7 shows the changes in methylmercury in roots and soil of each treatment group in this study. The results showed that the tartaric acid + sodium selenite + Tween spraying group did not significantly reduce soil methylmercury, while other spraying groups (except sodium selenite) significantly reduced soil methylmercury, indicating that foliar spraying of tartaric acid + sodium selenite + Tween cannot reduce the accumulation of methylmercury in plants by reducing soil methylmercury. However, from the reduction rate of total mercury in roots, stems and leaves in Table 5, it can be found that the increase rate of root mercury in the group sprayed with tartaric acid + sodium selenite + Tween on the leaves was significantly higher than that in the other spraying groups, indicating that this treatment group reduced the enrichment of soil mercury in the lettuce stems mainly through the interception effect of the roots.

[0157] Table 7 Example 2 Lettuce rhizomes and soil methylmercury content (ng / g)

[0158]

[0159] Note: In Table 7, “+” represents an increase; “-” represents a decrease

[0160] ③Other blocking mechanisms

[0161] In order to explore other mechanisms of reducing mercury by foliar barrier agents, the peroxidase (POD, Figure 2 ), non-protein thiol (NPT, Figure 3 ) and subcellular mercury ( Figure 4) were analyzed. The results showed that foliar spraying of tartaric acid + sodium selenite + Tween can reduce the membrane lipid peroxidation of plants by increasing the POD content. The NPT results showed that foliar spraying of tartaric acid + sodium selenite + Tween induced the roots to generate a large number of non-protein thiols, which were fixed on the roots through chelation with mercury entering the plant body, reducing the ability of mercury to migrate in the plant body, which just explains why the root mercury content increased significantly after the third spraying of tartaric acid + sodium selenite + Tween. The results of subcellular structure mercury showed that foliar spraying of tartaric acid + sodium selenite + Tween significantly improved the cell wall interception and cell sap compartmentalization of lettuce roots, protected the plant's organelles, maintained the normal growth of the plant, and improved the plant's tolerance to mercury stress.

[0162] In summary, spraying tartaric acid, sodium selenite, and Tween not only reduced mercury absorption from the soil but also from the atmosphere. Stomatal barrier plays a dominant role in reducing atmospheric mercury absorption; root interception limits mercury transfer to aboveground parts of the soil. Furthermore, antioxidant and compartmental effects also influence plant mercury distribution and absorption.

[0163] Example 3 (Other crop effect verification experiments):

[0164] (1) Experimental materials:

[0165] Soil was collected from Danzhai County, Qiandongnan Prefecture, Guizhou Province (THg = 12.64 mg / kg). The topsoil (0-20 cm) of mercury-contaminated rice fields was collected, air-dried, cleaned, and crushed through a 6 mm mesh sieve for later use.

[0166] Corn and pepper seedlings were purchased from Chengdu, Sichuan Province.

[0167] The tartaric acid and sodium selenite used are both analytically pure with a purity of more than 98%; the Tween used is Tween 80, pharmaceutical grade.

[0168] (2) Potted plant experiment:

[0169] Example 3 The potted experiment was carried out in early April 2024. The experiment selected 5L (pepper planting group) and 7L (corn planting group) flower pots as experimental pots, each with air holes and trays for water retention at the bottom. 3.0kg (pepper planting group) and 5.0kg (corn planting group) of treated spare mercury-contaminated soil were added, and a certain amount of mercury-free tap water was added and stirred to mix it thoroughly and evenly. It was aged for 3 to 4 days for use. The above-mentioned spraying group and control group were set up, and 3 parallels were set up for each treatment. After soil aging, pepper and corn seedlings were transplanted, and 2 plants were planted in each pot. Select consecutive cloudy days, spray the inhibitor solution on the leaves of the plants on the front and back of the plant growth cycle (the leaves are moist but not dripping), and the control group was sprayed with an equal amount of water. The pepper spraying time is: growth period, flowering period, and fruiting period. The corn spraying time is: growth period, large trumpet, flowering period, and fruiting period.

[0170] The types and concentrations of the components in the barrier control agent solution are as follows:

[0171] Tartaric acid 4mmol / L+sodium selenite 4mg / L+Tween 0.05wt%.

[0172] (3) Sample collection and measurement:

[0173] Pepper and corn fruits were collected and washed three times with tap water, then rinsed with deionized water and dried, and the fresh weight was measured. The fruits were freeze-dried, crushed, and ground for the determination of total plant mercury. Plant total mercury was measured using a DMA-80 solid-sample mercury analyzer (DMA-80, Milestone Inc., Shelton, CT): 0.02–0.05 g (accurate to 0.0001 g) of plant sample was weighed and placed directly on the sampler for the determination of plant THg.

[0174] (4) Experimental results:

[0175] The biomass of pepper and corn are shown in Table 8. The results show that spraying the inhibitor has a promoting effect on increasing pepper yield, but has no significant effect on corn yield.

[0176] Table 8 Biomass of pepper and corn (g)

[0177]

[0178] The total mercury content of pepper and corn fruits is shown in Table 9. The results showed that spraying foliar control agents of tartaric acid + sodium selenite + Tween during the growth period of pepper and corn respectively reduced the mercury content of fruits.

[0179] Table 9 Total mercury content in pepper and corn fruits (ug / kg)

[0180]

[0181] Example 4 (field trial and optimization of spraying times and time):

[0182] (1) Experimental soil:

[0183] Example 4: A field experiment was conducted in Danzhai County, Qiandongnan Prefecture, Guizhou Province (THg = 12.64 mg / kg) from November to December 2024. Figure 5 ) to verify the applicability of the inhibitor in actual production and optimize the spraying period and frequency. The experimental crop was lettuce, and the planting method was seedling transplanting.

[0184] The tartaric acid and sodium selenite used are both analytically pure with a purity of more than 98%; the Tween used is Tween 80, pharmaceutical grade.

[0185] (2) Implementation process:

[0186] In order to avoid affecting the two adjacent rows of plants when spraying on the leaves, foliar spraying was carried out every other row, and the blocks were separated by trenches with a width and depth of 20 cm. The first spraying was carried out about 20 days after the lettuce was transplanted, and the second spraying was carried out after an interval of 10 days, for a total of 1-3 sprayings. Based on the verification of the foliar barrier agent, the field experiment also conducted an optimization experiment on the spraying period and number of spraying, which was set up as follows: early stage (only spray once); mid-term (only spray once); late stage (only spray once); early + mid-term (spray twice); early + mid-term + late stage (spray three times). Spraying was carried out on consecutive cloudy days, and the barrier agent solution was sprayed on the front and back sides of the plant growth cycle (the leaf surface was moist but not dripping), and the control group was sprayed with an equal amount of water. All spraying groups were sampled after the crops matured.

[0187] The types and concentrations of the components in the barrier control agent solution are as follows:

[0188] Tartaric acid 4mmol / L+sodium selenite 4mg / L+Tween 0.05wt%.

[0189] (3) Sample collection and measurement:

[0190] Edible plant samples were collected and washed three times with tap water, then rinsed with deionized water. The leaf surface was blotted dry and the fresh weight was weighed. Plant samples were freeze-dried, ground, and then used for total mercury determination. Total mercury in plants was measured using a DMA-80 solid sampler (Milestone Inc., Shelton, CT). 0.02–0.05 g (accurate to 0.0001 g) of plant sample was weighed and placed directly onto the sampler for THg determination.

[0191] (4) Experimental results:

[0192] Table 10 shows the biomass and THg of lettuce. Biomass results showed that spraying the inhibitor had no significant effect on crop biomass (no statistical difference). Total mercury results showed that spraying only in the early stages had little effect, but a single foliar application of the inhibitor in the middle or late stages significantly reduced total mercury in lettuce. This is likely because the macromolecular substances in the inhibitor block the channels until the leafy vegetables reach maturity, making it easier to meet the actual needs of agronomic regulation from an economic and operational perspective.

[0193] Table 10 Lettuce biomass and total mercury content

[0194] Treatment group Spraying period and frequency Biomass (g) Total mercury (ug / kg) comparison 0 times 78.3±8.1 86.91±20.04 Tartaric acid + sodium selenite + Tween (Q) Spray once before planting 66.8±7.4 71.24±2.88 Tartaric acid + sodium selenite + Tween (Z) Spray once during the middle of planting 72.3±7.2 49.67±3.47 Tartaric acid + sodium selenite + Tween (H) Spray once in the late planting period 74.4±10.0 44.98±3.05 Tartaric acid + sodium selenite + Tween (Q + Z) Spray twice before and during planting 69.4±6.0 44.98±5.31 Tartaric acid + sodium selenite + Tween (Q + Z + H) Spray 3 times before, during and after planting 71.8±8.6 49.95±4.71

[0195] The technical solution of the present invention is not limited to the above-mentioned specific embodiments. Any technical variations made according to the technical solution of the present invention fall within the protection scope of the present invention.

Claims

1. A foliar control agent for reducing mercury content in crops, comprising: Tween, component a and component b; The component a comprises one or more of tartaric acid, tartrate, humic acid, and humate, and the component b comprises one or more of selenite and metal sulfide.

2. The foliage control agent according to claim 1, characterized in that The Tween comprises one or more of Tween 80, Tween 20, Tween 40 and Tween 60; and / or The tartrate includes alkali metal salts of tartaric acid, preferably sodium tartrate and potassium tartrate; and / or The humate salt includes an alkali metal salt of humic acid, preferably sodium humate and potassium humate; and / or Selenites include alkali metal selenites, preferably sodium selenite; and / or The metal sulfide comprises an alkali metal sulfide, preferably sodium sulfide; and / or The foliage control agent also includes water.

3. The foliage control agent according to claim 1 or 2, characterized in that: In the foliar control agent, the mass concentration of Tween is 0.01-0.2%, preferably 0.02-0.1%; and / or In the foliar control agent, the concentration of component a is 1-10 mmol / L, preferably 2-6 mmol / L; and / or In the foliar control agent, the concentration of component b is 1 mg / L-2 g / L, preferably 2 mg / L-1 g / L; and / or In the foliar control agent, the concentration of selenite is 1-10 mg / L, preferably 2-6 mg / L; and / or In the foliar control agent, the concentration of metal sulfide is 0.1-2 g / L, preferably 0.2-1.0 g / L.

4. The foliage control agent according to any one of claims 1 to 3, characterized in that: The component a comprises one or both of tartaric acid and sodium humate, preferably tartaric acid; and / or The component b comprises one or both of sodium selenite and sodium sulfide, preferably sodium selenite.

5. The foliage control agent according to any one of claims 1 to 4, characterized in that: The foliar control agent includes: Tartaric acid, sodium selenite, and Tween 80, or Tartaric acid, sodium sulfide, and Tween 80, or Tartaric acid, sodium selenite, sodium sulfide, and Tween 80, or Sodium humate, sodium sulfide, and Tween 80, or Sodium humate, sodium selenite, and Tween 80, or Sodium humate, sodium selenite, sodium sulfide, and Tween 80; Preferably, the foliar barrier agent comprises tartaric acid, sodium selenite and Tween 80.

6. A method for preparing the foliar control agent according to any one of claims 1 to 5, comprising: Mixing Tween, the component a and the component b with water to obtain the foliar barrier agent; Preferably, the amount of Tween is such that: in the prepared foliar control agent, the mass concentration of Tween is 0.01-0.2%, preferably 0.02-0.1%; Preferably, the amount of component a satisfies the following conditions: in the prepared foliar control agent, the concentration of component a is 1-10 mmol / L, preferably 2-6 mmol / L; Preferably, the amount of component b satisfies the following conditions: in the prepared foliar barrier agent, the concentration of selenite is 1-10 mg / L, preferably 2-6 mg / L, and / or the concentration of metal sulfide is 0.1-2 g / L, preferably 0.2-1.0 g / L.

7. A method for reducing mercury content in crops, comprising: Select consecutive cloudy days to spray the foliage barrier agent according to any one of claims 1 to 5 or the foliage barrier agent prepared by the method according to claim 6 on the leaf surfaces of crops planted on mercury-contaminated soil.

8. The method according to claim 7, characterized in that The spraying amount of the foliar control agent is: to make the surface of the crop leaves wet without dripping; and / or, the spraying frequency is 1-3 times; Preferably, the spraying interval for leafy vegetables is 7-8 days when spraying multiple times, and the spraying for fruit crops is carried out during their different growth cycles.

9. The method according to claim 7 or 8, characterized in that The total mercury content in the mercury-contaminated soil is 0.1-13 mg / kg; and / or the crops include one or more of lettuce, corn, cabbage, and pepper.

10. Use of the foliar barrier agent according to any one of claims 1 to 5 or the foliar barrier agent prepared by the method according to claim 6 in reducing the mercury content in crops.

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