Heavy metal absorption inhibitor, soil and crop cultivation method

Abstract

To provide a heavy metal absorption inhibitor capable of maintaining an absorption inhibitory effect of a heavy metal to a field crop for a long period of time.SOLUTION: A heavy metal absorption inhibitor is configured to be mixed into soil so as to inhibit absorption of a heavy metal in the soil to a field crop. The heavy metal absorption inhibitor includes a plurality of granular materials. In the granular materials, an average content of zero-valent Fe elements is 80 mass% or more. A sum of average contents of CaCO3 calculated from Ca elements and SiO2 calculated from Si elements contained in the granular materials is 30 mass% or less. A sum of average contents of S elements and P elements is 1 mass% or less. At least part of the granular materials have a coating layer composed of CaCO3, SiO2 or both, at least part of a surface thereof.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a heavy metal absorption inhibitor, soil, and a method for cultivating agricultural crops. [Background technology]

[0002] The soil on which agricultural crops are grown may contain large amounts of heavy metals such as arsenic and cadmium, which have adverse effects on the crops themselves and the human body. If these heavy metals are present in the soil, the crops planted in that soil will absorb these heavy metals along with other substances necessary for growth during the growing process. For this reason, it is important to take safety measures in the cultivation of agricultural crops to prevent the crops from absorbing these heavy metals.

[0003] For example, arsenic, one of the heavy metals, is known to be insolubilized by iron, and iron-containing absorption inhibitors are known (e.g., International Publication No. 2019 / 117222). These absorption inhibitors can be mixed with soil, for example, to efficiently absorb and remove arsenic from the soil. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2019 / 117222 Summary of the Invention [Problem to be solved by the invention]

[0005] The absorption inhibitor described in Patent Document 1 uses iron powder containing phosphorus and sulfur, which improves the elution of Fe ions and allows for the immobilization of heavy metals. However, the presence of phosphorus and sulfur makes the iron powder more susceptible to rust than ordinary iron powder. Soil tends to become acidic, particularly during agricultural cultivation, due to the application of chemical fertilizers. In acidic soil, the eluted iron is more likely to be oxidized. Therefore, the absorption inhibitor may not be able to stably maintain its effect of immobilizing heavy metals for a long period of time, such as over one year.

[0006] The present invention has been made based on the above-mentioned circumstances, and aims to provide a heavy metal absorption inhibitor and soil that can maintain the effect of inhibiting the absorption of heavy metals in agricultural crops for a long period of time, as well as a method for cultivating agricultural crops using the heavy metal absorption inhibitor of the present invention. [Means for solving the problem]

[0007] A heavy metal absorption inhibitor according to one embodiment of the present invention is a heavy metal absorption inhibitor that is mixed into soil to inhibit the absorption of heavy metals by agricultural crops in the soil, and comprises a plurality of granules, wherein the average content of zero-valent Fe element in the granules is 80% by mass or more, the total average content of CaCO3 converted from the Ca element and SiO2 converted from the Si element contained in the granules is 30% by mass or less, the total average content of S element and P element is 1% by mass or less, and at least some of the granules have a coating layer composed of CaCO3, SiO2 or both on at least a portion of their surface.

[0008] The heavy metal absorption inhibitor has a zero-valent Fe content in the granules equal to or greater than the lower limit. When the granules come into contact with soil moisture, the zero-valent Fe dissolves appropriately as divalent Fe ions in the moisture. The dissolved Fe ions precipitate heavy metal elements as insolubles on the surface of the granules, allowing them to be adsorbed onto the granules. The heavy metal absorption inhibitor also has a total average content of CaCO3 (calculated from Ca) and SiO2 (calculated from Si) in the granules equal to or less than the upper limit. At least some of the granules have a coating layer composed of CaCO3, SiO2, or both on at least a portion of their surface. This appropriately delays the dissolution of Fe when the granules come into contact with soil moisture, thereby maintaining the heavy metal absorption inhibitory effect for a long period of time. Furthermore, the CaCO3 and SiO2 coating the surface dissolve in the moisture and exhibit weak alkaline properties, thereby preventing oxidation of the Fe element. Furthermore, since the elements S and P accelerate the dissolution of the element Fe, the total average content of the elements S and P in the granules is set to be equal to or less than the upper limit. This allows the duration of the effect of the heavy metal absorption inhibitor to be extended. Therefore, the heavy metal absorption inhibitor can maintain its effect of inhibiting the absorption of heavy metals in agricultural crops for a long period of time.

[0009] The granular material may be steelmaking dust. Steelmaking dust is generated during the steelmaking process. The granular material can be easily obtained by using this steelmaking dust. Therefore, by using steelmaking dust as the granular material, costs and environmental loads can be reduced.

[0010] The heavy metals are preferably arsenic, and the heavy metal absorption inhibitor can effectively inhibit the absorption of arsenic, in particular, by agricultural crops.

[0011] Soil according to another embodiment of the present invention is mixed with the heavy metal absorption inhibitor of the present invention.

[0012] The soil can suppress the absorption of heavy metals into agricultural crops over a long period of time by using the heavy metal absorption inhibitor of the present invention.

[0013] The content of the heavy metal absorption inhibitor is preferably 0.1% by mass or more. By making the content of the heavy metal absorption inhibitor equal to or greater than the lower limit, absorption of heavy metals into agricultural crops can be effectively suppressed.

[0014] A method for cultivating agricultural crops according to yet another embodiment of the present invention comprises a mixing step of mixing the heavy metal absorption inhibitor of the present invention into soil, and a planting step of planting agricultural crops in the soil after the mixing step, and the planting step is repeated over multiple years.

[0015] In this method for cultivating agricultural crops, the heavy metal absorption inhibitor of the present invention is mixed into the soil, so that the effect of inhibiting the absorption of heavy metals lasts for several years, and therefore, even if crops are cultivated for several years, agricultural crops with reduced absorption of heavy metals can be harvested without the need for new mixing of the heavy metal absorption inhibitor.

[0016] Here, the "average content of zero-valent Fe element" refers to the value obtained by dividing the total content of zero-valent Fe element contained in the multiple granules constituting the heavy metal absorption inhibitor by the total mass of the multiple granules. The average contents of other substances such as CaCO3 and SiO2 are calculated in a similar manner. The "content of zero-valent Fe element" is measured by the metallic iron determination method described in JIS-M-8213:1995 "Iron ore - Method for determining soluble iron (II) oxide." The "CaCO3 converted from the Ca element contained in the granules" means that all of the Ca element contained in the granules is considered to be in the form of CaCO3. The same applies to the "SiO2 converted from the Si element." [Effects of the Invention]

[0017] As described above, the heavy metal absorption inhibitor of the present invention, the soil of the present invention, and the method for cultivating agricultural crops using the heavy metal absorption inhibitor of the present invention can maintain the effect of inhibiting the absorption of heavy metals in agricultural crops for a long period of time. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a heavy metal absorption inhibitor according to one embodiment of the present invention. [Figure 2] FIG. 2 is a flow chart showing the steps of a method for cultivating agricultural crops according to one embodiment of the present invention. [Figure 3] FIG. 3 is a graph showing the total arsenic concentration of brown rice harvested in the first year of cultivation in an example. [Figure 4] FIG. 4 is a graph showing the total arsenic concentration of brown rice harvested in the second year of cultivation in an example. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, a heavy metal absorption inhibitor, soil, and crop cultivation method according to one embodiment of the present invention will be described. In this specification, one of the upper limit values ​​and one of the lower limit values ​​described for any item can be appropriately combined. By combining them in this manner, the numerical range between the combined upper and lower limit values ​​is considered to be a preferred numerical range for the item described in this specification.

[0020] [Heavy metal absorption inhibitor] The heavy metal absorption inhibitor 1 shown in FIG. 1 is a heavy metal absorption inhibitor that is mixed with soil to inhibit absorption of heavy metals by agricultural crops in the soil.

[0021] The heavy metals include selenium, mercury, arsenic, lead, cadmium, chromium, etc., and it is preferable that the heavy metal is arsenic. The heavy metal absorption inhibitor 1 can particularly effectively inhibit the absorption of arsenic.

[0022] <Granular body> The heavy metal absorption inhibitor 1 includes a plurality of granules 10.

[0023] The lower limit of the average particle size of the granules 10 is preferably 1 μm, more preferably 5 μm, even more preferably 10 μm, and particularly preferably 50 μm. On the other hand, the upper limit of the average particle size of the granules 10 is preferably 1000 μm, more preferably 500 μm, and even more preferably 100 μm. If the average particle size of the granules 10 is below the lower limit, there is a risk of reduced production yield and reduced handleability. Conversely, if the average particle size of the granules 10 exceeds the upper limit, there is a risk of the specific surface area becoming too small, resulting in a reduced rate of adsorption of heavy metals, as described below. The term "average particle size" refers to the particle size at which the cumulative mass in the particle size distribution obtained by the dry sieving test specified in JIS-Z-8801:2006 is 50%.

[0024] (Fe element) The granules 10 contain Fe (iron) element. Specifically, the granules 10 contain zero-valent Fe element. The zero-valent Fe element is present in the granules 10 in the form of so-called metallic iron. Note that the granules 10 may also contain divalent Fe element.

[0025] When soil contains moisture, heavy metals in the soil, such as arsenic, dissolve into the moisture in the form of arsenate ions or arsenite ions. On the other hand, when soil does not contain moisture, when the soil comes into contact with moisture, the arsenate ions or arsenite ions dissolve into the moisture. When the moisture containing the arsenate ions or arsenite ions is brought into contact with the granules 10, i.e., when the arsenate ions or arsenite ions are brought into contact with the granules 10 in the presence of moisture, the arsenate ions or arsenite ions are insolubilized by the Fe element. The mechanism behind this will be explained using arsenate ions as an example. Note that the same applies to arsenite ions or other heavy metals.

[0026] When the granules 10 are brought into contact with the water containing the arsenate ions, an anode reaction (oxidation reaction) occurs in which the zero-valent Fe element contained in the granules 10 is oxidized and emits electrons (Fe → Fe 2+ +2e -This oxidation reaction dissolves divalent Fe ions from zero-valent Fe into the water. At the same time, arsenate ions in the water are reduced and converted to zero-valent arsenic.

[0027] Furthermore, the divalent Fe ions eluted in the oxidation reaction react with arsenate ions to form an insoluble salt.

[0028] In this way, arsenate ions are insolubilized by the reduction reaction and salt formation described above. It is known that iron insolubilizes arsenic through the coprecipitation of arsenic by the formation of scorodite and the adsorption by goethite. Iron also has the ability to insolubilize substances contained in soil, such as cadmium, lead, chromium, selenium, mercury, fluorine, and cyanide compounds, so it can also insolubilize these harmful substances.

[0029] This insolubilization occurs on the surface of the granules 10, so the precipitated zero-valent arsenic and salts can be adsorbed onto the granules 10. Therefore, this insolubilization and adsorption can remove arsenic, a heavy metal, from the components absorbed by crops in the soil. This makes it possible to suppress the absorption of arsenic by crops grown in this soil. Note that the heavy metal absorption inhibitor 1 suppresses the absorption of arsenic by crops, but does not eliminate arsenic compounds from the soil.

[0030] The lower limit of the average content of zero-valent Fe element in the granules 10 is 80 mass%, more preferably 85 mass%. If the average content of zero-valent Fe element is less than the lower limit, the amount of divalent Fe ions eluted from the granules 10 will be too small, which may result in an insufficient effect of inhibiting absorption of heavy metals or an effect that may not last long enough. On the other hand, all elements other than CaCO3 and SiO2 may be zero-valent Fe element, or all elements other than CaCO3 and SiO2 may be zero-valent and divalent Fe element.

[0031] (CaCO3 and SiO2) The granules 10 contain, in whole or in part, calcium (Ca), silicon (Si), and oxygen (O). These elements may be contained, in whole or in part, in the form of CaCO3 and SiO2. The heavy metal absorption inhibitor 1 contains CaCO3, SiO2, or both.

[0032] As shown in Figure 1, in the heavy metal absorption inhibitor 1, at least some of the granules 10 have a coating layer 11 composed of CaCO3, SiO2, or both on at least a portion of their surfaces. Specifically, the CaCO3, SiO2, or both components coat the surfaces of the granules 10 as layered crystals or as an amorphous coating. This is also evident from the results of analyzing the surfaces of the granules 10 using an X-ray diffraction (XRD) device (Table 1). This layer has the effect of delaying the elution of Fe element from the surfaces of the granules 10.

[0033] [Table 1]

[0034] Table 1 shows the results of semi-quantitative analysis using the WPF method using a SmartLab X-ray diffractometer manufactured by Rigaku Corporation. The results are shown in the RIR column as simplified quantitative values ​​based on the reference intensity ratio, with larger values ​​indicating higher mass fractions. The target was Cu, the target output was 45 kV-200 mA, the monochromator receiving slit was 0.8 mm, the detector was a scintillation counter, the scanning speed was 2° / min, the sampling width was 0.02°, and the measurement range (2θ) was 5–90°.

[0035] 1, the heavy metal absorption inhibitor 1 may include granules 10 that are completely covered with a coating layer 11 (lower right), or granules 10 that do not have a coating layer 11 (upper left). The coating layer 11 may cover the majority of the granules (lower left), only a small portion (center), or multiple portions intermittently (upper right).

[0036] The lower limit of the ratio of the total coverage area of ​​the coating layer 11 to the total surface area of ​​the plurality of granules 10 is preferably 0.1%, more preferably 1%, and even more preferably 5%. On the other hand, the upper limit of the ratio of the total coverage area of ​​the coating layer 11 is not particularly limited, but it is preferable that there is at least an exposed uncoated portion, and it can be, for example, 99%.

[0037] The proportion of granules 10 having coating layers 11 among the granules 10 (the proportion of the total mass of granules 10 having coating layers 11 to the total mass of granules 10) is greater than 0% by mass, but the lower limit of this proportion is preferably 1% by mass, more preferably 5% by mass, even more preferably 10% by mass, and particularly preferably 30% by mass. If the proportion is less than the lower limit, the effect of inhibiting the absorption of heavy metals may not be sufficiently sustained. On the other hand, the upper limit of the proportion is not particularly limited and may be 100% by mass. Whether or not a granule 10 has a coating layer 11 can be determined by, for example, visually observing a plurality of granules 10 with an electron microscope. The mass of each granule 10 can be calculated, for example, by converting the area of ​​each granule 10 observed with the above-mentioned electron microscope.

[0038] When the granules 10 come into contact with moisture in the soil, CaCO3 and SiO2 dissolve into the moisture. Because CaCO3 and SiO2 are alkaline components, they form a coating of iron hydroxide on the surface of the Fe element, preventing excessive dissolution of the Fe element. They also prevent the Fe element from being oxidized. Therefore, the heavy metal absorption inhibitor 1's effect of inhibiting the absorption of heavy metals in agricultural crops can be maintained for a long period of time.

[0039] To explain in more detail how excessive dissolution of Fe element is suppressed, the alkaline component forms a layered coating of Goethite (FeOOH) and Lepidocrocite (FeOOH) on the surface of the granules 10. This layered coating prevents excessive dissolution of divalent Fe ions from the granules 10, allowing the granules 10 to maintain the dissolution of divalent Fe ions for a longer period of time. This long-term dissolution of divalent Fe ions allows the heavy metal absorption inhibitor 1 to exert its heavy metal absorption suppression effect for a longer period of time.

[0040] The upper limit of the total average content of CaCO3 calculated from Ca element and SiO2 calculated from Si element contained in the granules is 30% by mass, more preferably 10% by mass, and even more preferably 5% by mass. On the other hand, the lower limit of the total average content is preferably 0.1% by mass, more preferably 1% by mass. If the total average content exceeds the upper limit, the elution of Fe element may be too slow, and the effect of inhibiting the absorption of heavy metals may not be sufficiently obtained. Conversely, if the total average content is less than the lower limit, the elution or oxidation of Fe element may be accelerated, and the effect of inhibiting the absorption of heavy metals may not be sufficiently sustained.

[0041] (S and P elements) The upper limit of the total average content of S and P elements in the granules 10 is 1% by mass, and 0.5% by mass is more preferable. S and P elements accelerate the dissolution of Fe and enhance the insolubilization performance of heavy metals by supplying Fe ions, but conversely, premature ionization shortens the duration of the effect. In this case, there is a concern that the frequency of application to the field will increase, resulting in increased fertilizer costs. To prevent this, so-called sustained release, which slows the dissolution rate of iron, is important. The structure that effectively exerts the sustained release effect is CaCO3 and SiO2 present on the surface of the granules 10, and the content of S and P elements contained in the granules 10. The lower limit of the total average content of S and P elements is not particularly limited and may be 0% by mass, excluding unavoidable contamination.

[0042] (Heavy metal elements) The granules 10 themselves may inevitably contain heavy metal elements. Examples of such heavy metal elements include Hg (mercury), Pb (lead), As (arsenic), and Cr (arsenic). 6+Examples of heavy metals include hexavalent chromium (HxA). If the heavy metal content in the granules 10 is high, there is a risk of heavy metal element ions that should be excluded from the granules 10 leaching out. For this reason, the lower the heavy metal element content, the more preferable. In particular, it is preferable that the total average content of Hg, Pb, As, and Cr in the granules 10 is less than 0.1% by mass. The total average content of these heavy metals can be calculated based on the "Testing Methods for Fertilizers, etc. (2020)" established by the Agriculture, Forestry, and Fisheries Materials Inspection Center (FAMIC). Specifically, for example, Hg can be calculated according to 5.1.a, Pb 5.6.d, As 5.2.a, and Cr 5.5.f of the Testing Methods for Fertilizers, etc. (2020).

[0043] (Other elements) Other elements that may be contained in the granules 10 include, for example, Al (aluminum), Mg (magnesium), K (potassium), Na (sodium), and C (carbon). Of these, Al, Mg, K, and Na may be contained in the granules 10 in the form of oxides or compounds, and C may be contained in the form of a solid solution in metallic iron or in the form of a compound. The lower the content of these elements, the better. Specifically, the upper limit of the average content of other elements in the granules 10, excluding Fe, CaCO3, SiO2, and heavy metals, is preferably 5% by mass, more preferably 2% by mass, and even more preferably 1% by mass.

[0044] The granular material 10 is preferably steelmaking dust. Steelmaking dust is generated during the steelmaking process. The granular material 10 can be easily obtained by using this steelmaking dust. Therefore, by using steelmaking dust as the granular material 10, costs and environmental impact can be reduced. The steelmaking dust is selected to have an average content of zero-valent Fe element of 80 mass% or more, a total average content of CaCO3 converted from Ca element and SiO2 converted from Si element contained in the steelmaking dust of 30 mass% or less, a total average content of S element and P element of 1 mass% or less, and at least a portion of the steelmaking dust having a coating layer composed of CaCO3, SiO2, or both on at least a part of its surface.

[0045] <Advantages> In the heavy metal absorption inhibitor 1, the zero-valent Fe element content of the granules 10 is 80% by mass or more. When the granules 10 come into contact with water in the soil, the zero-valent Fe element moderately dissolves into the water as divalent Fe ions. The dissolved Fe ions cause the heavy metal elements to precipitate as insoluble matter on the surface of the granules 10 and be adsorbed onto the granules 10. Furthermore, the heavy metal absorption inhibitor 1 has a total average content of CaCO3 (calculated from Ca element) and SiO2 (calculated from Si element) contained in the granules 10 of 10% by mass or less, and at least some of the granules 10 have a coating layer 11 composed of CaCO3, SiO2, or both on at least a portion of their surface. Therefore, when the granules 10 come into contact with water in the soil, the dissolution of the Fe element is moderately delayed, and the effect of inhibiting the absorption of heavy metals is maintained for a long period of time. Furthermore, the CaCO3 and SiO2 covering the surface dissolve in the water and exhibit a weak alkalinity, thereby preventing oxidation of the Fe element. Furthermore, since the S element and P element accelerate the dissolution of the Fe element, the heavy metal absorption inhibitor 1 has an average total content of the S element and P element in the granules 10 of 1 mass% or less. This allows the duration of the effect of the heavy metal absorption inhibitor 1 to be extended. Therefore, the heavy metal absorption inhibitor 1 can maintain its effect of inhibiting the absorption of heavy metals in agricultural crops for a long period of time.

[0046] 〔soil〕 Soil according to another embodiment of the present invention is mixed with the heavy metal absorption inhibitor 1 of the present invention. The soil is suitably used for planting and cultivating agricultural crops such as rice.

[0047] As described above, the heavy metal absorption inhibitor 1 dissolves Fe ions from the granules 10 into the water in the soil. The ease of this dissolution is affected by the pH of the water in the soil. The pH of the water in the soil is determined by the pH of the soil. The lower limit of the soil pH is preferably 3, and more preferably 4. On the other hand, the upper limit of the soil pH is preferably 9.5, and more preferably 9. Note that the above pH may temporarily increase due to the addition of fertilizer, or may temporarily decrease due to a reaction with CO2 in the air, but the pH referred to here refers to the steady pH excluding such temporary states.

[0048] The lower limit of the content of the heavy metal absorption inhibitor 1 in the soil is preferably 0.1% by mass, more preferably 0.3% by mass, and even more preferably 0.5% by mass. On the other hand, the upper limit of the content of the heavy metal absorption inhibitor 1 is preferably 10% by mass, more preferably 5% by mass, and even more preferably 1% by mass. If the content of the heavy metal absorption inhibitor 1 is below the lower limit, the amount of eluted divalent Fe ions may be too small, and the effect of inhibiting the absorption of heavy metals may be insufficient. Conversely, if the content of the heavy metal absorption inhibitor 1 exceeds the upper limit, the cost of cultivating agricultural crops may increase unnecessarily compared to the effect obtained.

[0049] <Advantages> The soil can suppress the absorption of heavy metals into agricultural crops over a long period of time by the heavy metal absorption inhibitor 1 of the present invention.

[0050] [Crop cultivation methods] The method for cultivating agricultural crops shown in FIG. 2 includes a mixing step S1 and a planting step S2.

[0051] <Mixing process> In the mixing step S1, the heavy metal absorption inhibitor 1 of the present invention is mixed with soil.

[0052] The soil into which the heavy metal absorption inhibitor 1 is mixed is not particularly limited as long as it is capable of growing agricultural crops, and for example, soil from a paddy field can be used.

[0053] A known agitator may be used to mix the heavy metal absorption inhibitor 1. The mixing method is not particularly limited, and the heavy metal absorption inhibitor 1 may be sprayed on the laid soil and then mixed using the agitator, or the soil before laying and the heavy metal absorption inhibitor 1 may be mixed in advance using the agitator, and the soil may be laid. Furthermore, fertilizers and the like may be mixed together with the heavy metal absorption inhibitor 1.

[0054] The amount of the heavy metal absorption inhibitor 1 to be mixed is preferably 0.1% by mass or more and 10% by mass or less with respect to the soil after mixing, as described above.

[0055] <Cropping process> In the planting step S2, crops are planted on the soil after the mixing step S1. Specifically, crops are planted on the soil in which the heavy metal absorption inhibitor 1 has been mixed and laid.

[0056] The planting of agricultural crops may be carried out using known agricultural machinery such as a rice transplanter, or may be carried out manually.

[0057] In the method for cultivating agricultural crops, the planting step S2 is repeated for several years. The heavy metal absorption inhibitor 1 maintains its effect of inhibiting the absorption of heavy metals at least until the second year of planting, so the soil can be used for several years without newly performing the mixing step S1.

[0058] <Advantages> In this agricultural crop cultivation method, the heavy metal absorption inhibitor 1 of the present invention is mixed into the soil, so the effect of inhibiting the absorption of heavy metals lasts for several years. Therefore, even if crops are cultivated for several years, crops with reduced absorption of heavy metals can be harvested without newly mixing the heavy metal absorption inhibitor 1.

[0059] [Other embodiments] The present invention is not limited to the above-described embodiment. [Example]

[0060] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0061] [1st year] <No.1> Steelmaking dust (steelmaking dust generated at the Kakogawa Works of Kobe Steel, Ltd.) corresponding to the heavy metal absorption inhibitor of the present invention was prepared as a heavy metal absorption inhibitor. 20 g of the heavy metal absorption inhibitor was mixed with 2 kg of soil equivalent to dry soil in a pot. The average content of zero-valent Fe in this steelmaking dust was 86.28 mass%, the average combined content of CaCO3 (calculated from Ca element) and SiO2 (calculated from Si element) was 2.20 mass%, and the average combined content of S and P elements was 0.037 mass%.

[0062] Next, a liquid fertilizer containing 0.2g each of nitrogen (N), phosphorus (P2O5 equivalent), and potassium (K2O equivalent) was applied to the soil as base fertilizer, and then stirred with a hand drill. After the suspended soil had settled to the bottom, three Hitomebore seedlings were transplanted.

[0063] Approximately two and three months after transplanting, ammonium sulfate solution containing 0.08 g of nitrogen was applied as top dressing to the pots. Approximately four months later, the mature rice was harvested, threshed, and hulled to obtain brown rice. The brown rice was then thermally decomposed using concentrated nitric acid and hydrogen peroxide, and the arsenic concentration in the decomposition solution was measured using inductively coupled plasma mass spectrometry (ICP-MS) to determine the total arsenic concentration in the brown rice. The results are shown in Figure 3.

[0064] <No.2> Brown rice was harvested in the same manner as in No. 1, except that iron powder containing 1% by mass of sulfur (S) was used as a heavy metal absorption inhibitor, and the total arsenic concentration in the brown rice was measured. The results are shown in Figure 3.

[0065] <No.3> Brown rice was harvested in the same manner as in No. 1, except that no heavy metal absorption inhibitor was used, i.e., only soil was used, and the total arsenic concentration in the brown rice was measured. The results are shown in Figure 3.

[0066] [2nd year] In the second year, three Hitomebore seedlings were transplanted into the soil from which brown rice was harvested in the first year in the above No. 1 to No. 3 plants, without any heavy metal absorption inhibitors being added. The brown rice was harvested using the same procedure as in the first year, and the total arsenic concentration in the brown rice was measured. The results are shown in Figure 4.

[0067] [result] Figure 3, which shows the results from the first year, shows that the total arsenic concentration in the brown rice was high in soil No. 3, where no heavy metal absorption inhibitor was used, whereas the arsenic concentration in the brown rice decreased in soils No. 1 and No. 2, where heavy metal absorption inhibitors were added.

[0068] Furthermore, from the results of the second year in Figure 4, it can be seen that the total arsenic amount in brown rice of No. 1, which used the heavy metal absorption inhibitor of the present invention, was lower than that of No. 3, which did not use the heavy metal absorption inhibitor, and the effect of reducing the total arsenic concentration is continuing.On the other hand, in No. 2, which used iron powder containing 1 mass% S (sulfur), the reduction in total arsenic concentration was small, and the arsenic absorption inhibitory effect was small.

[0069] Looking more closely, in the results for the first year shown in Figure 3, No. 2 had a greater arsenic absorption inhibitory effect than No. 1, but the relationship reversed in the second year. No. 1, which used the heavy metal absorption inhibitor of the present invention, moderately delayed the elution of Fe element, so the effect was suppressed in the first year and was therefore maintained over a long period of time. In contrast, No. 2 did not delay the elution of Fe element, so while it showed a high absorption inhibitory effect in the first year, the effect was significantly reduced in the second year, and it was found that the effect could not be maintained over a long period of time.

[0070] From the above, it can be said that the heavy metal absorption inhibitor of the present invention can maintain the effect of inhibiting the absorption of heavy metals in agricultural crops for a long period of time. [Industrial Applicability]

[0071] The heavy metal absorption inhibitor of the present invention, the soil of the present invention, and the method for cultivating agricultural crops using the heavy metal absorption inhibitor of the present invention can maintain the effect of inhibiting the absorption of heavy metals in agricultural crops for a long period of time. [Explanation of symbols]

[0072] 1. Heavy metal absorption inhibitor 10 Granules 11 Covering layer

Claims

1. A heavy metal absorption inhibitor that is mixed with soil to suppress absorption of heavy metals by agricultural crops in the soil, A plurality of granular bodies are included, The average content of zero-valent Fe element is 80% by mass or more, CaCO calculated from the Ca element contained in the granules ３ and SiO converted from Si element ２ The total average content is 30% by mass or less, The total average content of the S element and the P element is 1% by mass or less, At least some of the granules have CaCO ３ , SiO ２ or a coating layer composed of both, The heavy metal absorption inhibitor, wherein the granular material is steelmaking dust.

2. A heavy metal absorption inhibitor as described in claim 1, wherein the ratio of the total coating area of ​​the coating layer to the total surface area of ​​the plurality of granular bodies is 99% or less.

3. 3. The heavy metal absorption inhibitor according to claim 1, wherein the heavy metal is arsenic.

4. 4. Soil containing the heavy metal absorption inhibitor according to claim 1, 2 or 3.

5. 5. The soil according to claim 4, wherein the content of the heavy metal absorption inhibitor is 0.1 mass % or more.

6. a mixing step of mixing the heavy metal absorption inhibitor according to claim 1, claim 2 or claim 3 with soil; a planting step of planting crops in the soil after the mixing step; Equipped with A method of cultivating crops in which the above-mentioned cultivation process is repeated over several years.

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