JP5837734B2 - Heavy metal absorption promoter for plant and soil purification method - Google Patents

Description

  The present invention relates to a heavy metal absorption promoter for plants and a method for purifying soil containing heavy metals by using the same to promote absorption of heavy metals in soil into plants.

  Among environmental pollution, contamination of soil by harmful substances such as heavy metals such as lead, arsenic, hexavalent chromium, cadmium and copper has become a particular problem, and various technologies have been developed to purify the contaminated soil. Has been developed. For example, there are a soil cleaning method in which contaminated soil is washed to remove harmful substances, and a heat treatment method in which polluted substances are desorbed, decomposed or dissolved by heating the contaminated soil and contained. These treatment methods have the advantage of a short construction period, but are also difficult in that they are expensive and have a large load on the soil. Therefore, as one of the methods for removing heavy metals from soil contaminated with heavy metals, there is phytoremediation, which is an environmental purification technology that utilizes the property of sowing or planting plants to absorb harmful substances. This is a soil purification method that absorbs heavy metals and nutrients at the same time as plants grow, absorbs heavy metals, lowers heavy metal concentrations in the soil, harvests plants and recovers heavy metals by post-processing. is there.

  Seeding or planting plants in contaminated soil is low cost and has little impact on the environment, so in addition to removing heavy metals from contaminated soil, preventing pollution of surrounding soil etc. in waste treatment plants Is expected to be used. For this purpose, research is being conducted to search for plant species with high heavy metal absorption efficiency and to cultivate them.

  However, many of the above plant species have restrictions on the growth environment such as temperature, moisture and soil quality, and there are problems such as limiting the area of contaminated soil that can be cultivated.

  Therefore, a method of adjusting the pH of a chelating agent such as citric acid, nitrilotriacetic acid (NTA), ethylenediaminetrichloroacetic acid (EDTA) and adding it to the soil in which the plant is planted to promote absorption of heavy metals into the plant (special feature) No. 2004-290820) has also been proposed.

  However, in the method of adding a chelating agent to the soil, the chelating agent is difficult to load on the environment during use, and the cost is also difficult, and the chelating agent is difficult to be decomposed by microorganisms and enzymes in the natural environment. In the case of persistent decomposition, the chelating agent that has not been absorbed by the plant remains in the soil and the plant is not only damaged by growth, but also the heavy metal that has been fixed in the soil continues to elute and penetrates deep into the ground. The possibility of causing secondary contamination has also been pointed out.

  From this point of view, biodegradables such as methylglycine diacetate (MGDA), ethylenediaminesuccinic acid (EDDS), L-glutamic acid diacetate (GLDA) and L-aspartate diacetate (ASDA) and their salts as chelating agents A method of preventing the above-mentioned secondary contamination using a chelating agent has also been proposed (Japanese Patent Application Laid-Open No. 2006-75777). However, it is further desired to develop a method for promoting absorption of heavy metals into plants, which has biodegradability equivalent to or higher than those of these biodegradable chelating agents and is advantageous from the viewpoint of cost.

JP 2004-290820 A JP 2006-75777 A

  The present invention has a low risk of causing environmental problems, and is an efficient promoter for absorbing heavy metals in plants at a low cost so that a large amount of heavy metals in soil can be absorbed by plants. Thus, a method for purifying soil containing heavy metals by promoting absorption of heavy metals in the soil into plants is provided.

The present invention provides the following inventions in order to solve the above problems.
(1) A cadmium absorption promoter for plants, which contains a water-soluble salt of alginic acid or a compost of brown algae and is added to cadmium-containing soil;
(2) The cadmium absorption promoter for plants according to (1) above, wherein the water-soluble salt is sodium alginate, potassium alginate, magnesium alginate or ammonium alginate ;
(3 ) The above (1) or (2 ), wherein the plant is at least one plant selected from the group consisting of Brassicaceae, Grapeaceae, Leguminosae, Rabbitaceae, Solanum, Compositae, Rubiaceae, and Gramineae ) Cadmium absorption promoter for plants described in the above;
( 4 ) A method for purifying soil containing cadmium by promoting absorption of cadmium in the soil into the plant using the cadmium absorption promoter in the plant according to any one of (1) to ( 3 ) above. ;
( 5 ) The method according to the above ( 4 ), wherein a cadmium absorption promoter is added to the soil containing cadmium, and the plant is grown in the soil;
( 6 ) The method according to ( 4 ) or ( 5 ) above, wherein the cadmium content in the soil is 0.5% or less;
( 7 ) The cadmium absorption promoter is used in any one of the above ( 4 ) to ( 6 ), wherein 1 to 2,000 g is used per 1 m ^{2 of} soil as a water-soluble salt of alginic acid or a compost of brown algae. the method of,
It is.
(8) The brown algae compost is obtained by a method in which an alginate-degrading enzyme produced by a microorganism is allowed to act, or obtained by a method using a microorganism that produces an alginate-degrading enzyme, according to any one of (1) to (3) above For producing a cadmium absorption enhancer for a plant.

  ADVANTAGE OF THE INVENTION According to this invention, there is little possibility of causing an environmental problem, and the efficient heavy metal absorption promoter to a plant absorbs a heavy metal in soil in large quantities at low cost, and the heavy metal absorption accelerator in a soil using it. A method for purifying soil containing heavy metals by promoting absorption into plants can be provided.

  The heavy metal absorption promoter for plants of the present invention contains alginic acid, a salt or ester thereof, or a decomposition product thereof, and is used by being added to heavy metal-containing soil on which plants are grown.

  Alginic acid is a polysaccharide unique to brown algae, and its content occupies 30% to 60% of dry algae, forming various minerals and salts in the sea, and in a gentle jelly state between cell walls and cells. Filled. Alginic acid can be obtained from brown algae by a conventional method. For example, brown algae is sufficiently dried, crushed to a size that is easy to handle, soaked with water and washed. The brown algae is not particularly limited, and examples thereof include kombu, wakame, hijiki, kajime, sujime, Ainuwakame, Honda Walla, Uganomok, and the like.

  Since most of alginic acid in the algal body forms an insoluble salt with Ca cation, it is generally extracted from the algal body as water-soluble sodium alginate by ion exchange with Na. The obtained sodium alginate is solidified and precipitated as an insoluble alginic acid by addition of an acid, and is pulverized to a desired particle size after drying. Alginic acid is a linear polymer polysaccharide having a chain structure in which β-1,4-linked D-mannuronic acid (M) and α-1,4-linked L-guluronic acid (G) are linked. The molecular weight is usually about 15,000 to 200,000 (degree of polymerization of about 80 to 1,100). The M / G ratio varies depending on the type of brown algae used as a raw material, and further depending on the season.

  Examples of the alginate include sodium alginate, potassium alginate, magnesium alginate, calcium alginate, ammonium alginate and the like. As the alginate, water-soluble sodium alginate, potassium alginate, magnesium alginate, and ammonium alginate are suitable.

  Examples of the alginic acid ester include propylene glycol ester, ethylene glycol ester, ethyl ester, methyl ester and the like, and propylene glycol ester is preferable.

  In the present invention, alginic acid or a salt or ester thereof is preferably used as a degradation product further reduced in molecular weight in order to improve the effect of promoting heavy metal absorption into plants. Although the polymerization degree of alginic acid is not particularly limited, for example, about 80 to 600 is preferable.

  As alginic acid or a salt or ester thereof, one extracted as described above, or brown algae itself can be used, but it may be commercially available as crude or purified alginic acid, alginate, etc. When brown algae itself is used, it may be waste.

  Examples of the method for decomposing alginic acid or a salt thereof include a method in which an alginic acid decomposing enzyme produced by a microorganism is allowed to act, a method using these microorganisms, a method of decomposing using an acid, and a method of irradiating with radiation.

  In the method of allowing an alginic acid-degrading enzyme produced by a microorganism to act, microorganisms belonging to the genus Alteromonas, Pseudomonas, Bacillus and the like are well known.

  Examples of the method using microorganisms include a composting process in which brown algae are allowed to stand and decompose by the power of these microorganisms. The treatment temperature is usually 20 to 80 ° C. and about 1 to 4 months. Since salt adhering to brown algae has a plant growth inhibitory action, it is preferable to remove it.

  In the method of decomposing using an acid, phosphoric acid, sulfuric acid and the like can be suitably used as the acid. For example, when phosphoric acid is used, it is preferable to hydrolyze alginic acid or a salt thereof at room temperature using phosphoric acid having a concentration of about 50 to 90% by weight.

In the method of irradiating radiation, radiation with a dose of about 50 kGy to 500 kGy is used, and as the radiation source, irradiation with γ rays from ⁶⁰ Co, irradiation using a low energy electron accelerator or the like is used.

  In the present invention, the above heavy metal absorption promoter containing alginic acid, a salt or ester thereof, or a decomposition product thereof is added to soil containing heavy metal, and the plant is grown to increase the amount of heavy metal in the soil. It promotes absorption into plants and purifies soil containing heavy metals.

  Examples of heavy metals absorbed by the heavy metal absorption promoter include cadmium, zinc, lead, chromium, copper, mercury, arsenic, tin and selenium and their metal compounds such as oxides, salts, sulfides, organometallic compounds, and the like. One or more. The content of these heavy metals in the soil is not particularly limited as long as the plant grows. Specifically, it is a case where the target heavy metal exceeds the value that seems to have an impact on human health, such as when it exceeds the legal environmental standard value, and is usually 0.5% or less, preferably the content Is 0.1 to 1000 ppm. When it is contained at a concentration exceeding 0.5%, it is desirable to grow the plant after reducing the concentration in advance by an appropriate method such as a chemical treatment method.

  The soil containing these heavy metals is not particularly limited, and examples thereof include agricultural land such as paddy fields and farmland, industrial land, and residential land.

  According to the heavy metal absorption promoter of the present invention, it is presumed that the heavy metal in the soil is chelated to a form that is easy to be taken up by the plant, and therefore the plant species is not limited, but the plant used in the present invention absorbs the heavy metal. What is said to be effective is suitable. For example, Brassica such as mustard, rapeseed, Nozawana, Komatsuna, Hakusan Hatazao, suzushiro, etc .; Aoiaceae such as kenaf and okra; Leguminosae such as Crotalaria and Sesbania; Asteraceae such as sunflower and safflower; Taceae such as buckwheat, buckwheat, itadori, and starfish; Amaranth such as amaranthus; Cranidae such as clover, ciraceae such as seri and ashitaba; lily family such as haran; iris family such as iris; scorpion family such as abalone; cynosida family such as saxifrage and astilbe; , Convolvulaceae such as sweet potato; Rubiaceae, such as piste; Dokudami family, such as Dokudami, Hangesho; Amamiaceae, such as flax; Lepidopteraceae, such as Apiaceae, Daffodil, etc .; , Salnaci, Kiwi, etc .; Parasitaceae; Cloveraceae, Euphorbiaceae, such as Euphorbiaceae, Benihimonoki, etc .; Honeysuckle Family, such as Elderberry, Cyprinus elegans; As well as plants such as Oleaceae, such as geranium, that are capable of absorbing heavy metals. These can be selected appropriately according to the climate, topography, soil quality, heavy metal type, etc., for example, cruciferous, mallow, leguminous, rhododendron, eggplant, chrysanthemum, teraceae, gramineous, etc. Plants are particularly preferably used.

  Of these, those that grow faster, those that have a large dry weight of leaves, stems, and roots, and those that can absorb heavy metals at higher concentrations are more efficient because they absorb and accumulate heavy metals, such as sunflower, kenaf, and buckwheat. , Mustard, Japanese pampas grass, fern, okra, chard, Komatsuna, rice, sorghum, sagebrush, hakusanhatazao, suzushiro, etc. are particularly suitable.

  Furthermore, a recombinant plant in which a gene for promoting heavy metal absorption and accumulation is introduced into a selected plant species including these can also be used as a plant.

In order to grow plants on soil containing heavy metals, methods such as direct sowing or methods of transplanting and growing plants grown elsewhere, such as seedlings from seed beds, cell seedlings, pot seedlings, etc. However, direct sowing is preferable from the viewpoint of cost. The density of sowing can be appropriately selected depending on the type of plant and the like. For example, in the case of buckwheat, about 1 to 10 g of seed per 1 m ^{2 of} soil is usually used.

  The pH of the soil on which the plant is grown is suitably 3-10. For example, in the case of buckwheat, the pH is 4-8, preferably about 6. Since the pH value is greatly related to the absorbability of heavy metals depending on the soil conditions, it is preferable to adjust the pH according to the cultivation conditions. A soil acidifying agent, a fertilizer, etc. can also be applied as needed.

  The heavy metal absorption promoter for plants of the present invention can contain a pH adjuster, a fertilizer component and the like as appropriate in addition to the main component, alginic acid or a salt thereof, or a decomposition product thereof.

  If there is no continuous cropping failure, the plant having the best heavy metal absorption ability can be cultivated every year as necessary. If not, a plurality of plants may be combined in order and cultivated. Plant species can be appropriately selected according to the type and concentration of heavy metals contained in the soil. It is also preferable to consider soil conditions, climatic conditions, and the like.

In the method of the present invention, the heavy metal absorption promoter is applied to the soil surface as an aqueous solution, powder or bulk, or is mixed with the soil and added. It can be added to the soil before sowing of the plant and further added for a predetermined period after sowing, but it is usually added to the soil after the plant has grown to some extent or after transplanting. The addition can also be sprayed (sprayed) uniformly on the soil or on the soil near the root of the plant. Usage, heavy metal content in the soil, plant species may vary depending on the type of soil (water retention etc.), etc., alginic acid, as the amount of a salt or ester or a degradation product thereof, usually per soil 1 m ^2,. 1 to About 2,000 g, preferably about 2 to 1,000 g is used. Preferably, the heavy metal absorption promoter of the present invention is used as an aqueous solution diluted 10 to 100 times.

  The harvesting of plants can be directed to the above-ground part of the plant body including stems, leaves, or the underground part of the plant body including roots, or both, and the harvesting time can be appropriately selected depending on the plant species. Harvested plants are reduced in weight by herbicide treatment, drying treatment, composting treatment, squeezing treatment, crushing / grinding treatment, etc. to concentrate heavy metals, and then recover heavy metals from plants or use concrete etc. It can be solidified and detoxified.

  As a method for recovering heavy metals, in addition to a general incineration method, for example, a known coagulation precipitation method, ion exchange method, solvent extraction method, etc. can be selected according to the type of heavy metal, but the heavy metal is cadmium, arsenic. In the case of lead, it is preferable to use a solvent extraction method or an ion exchange method.

  In the case of the solvent extraction method, it is preferable to use water to which an acid has been added. That is, the harvested plant is crushed and pulverized, and poured into water of about 2 to 50 times the weight of the plant. Water may be heated at normal temperature, but it is preferable to add an acid. Examples of the acid include inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, and organic acids such as acetic acid, formic acid, oxalic acid, and tartaric acid. It is preferable to select the type of acid according to the type of heavy metal in the soil. For example, in the case of cadmium and mercury, it is easily dissolved in concentrated sulfuric acid, and lead is easily dissolved in acetic acid or nitric acid. The concentration of the acid is usually selected from about 0.01 to 3 mol / L. In addition, by adding a chelating agent capable of forming a complex with heavy metal such as ethylenediaminetetraacetic acid (EDTA) in water, the heavy metal dissolved in water becomes a complex compound, so that the solubility of heavy metal is increased. And can be filtered off. In this case, the concentration of the chelating agent is preferably about 0.05 to 2% by weight in water. Next, this extract is applied to a filter such as a filter press together with the plant to perform solid-liquid separation. The heavy metal in the complex is precipitated as an insoluble substance by using a known method, for example, a method in which the pH of the separation liquid is adjusted to alkaline, and then a heavy metal insolubilizing agent such as sodium sulfide or ammonium sulfide is added thereto. Can be recovered.

  Furthermore, from the residual plant, carbohydrates of alcohol raw materials, lignin or the like can be recovered as by-products by a conventional method. For example, polysaccharides such as cellulose can be extracted by hydrolysis using sulfuric acid.

  When the heavy metal absorption promoter of the present invention is used, soil containing heavy metals up to about 5,000 mg / kg can be efficiently purified. For example, the content of heavy metals in soil up to a depth of about 50 cm is an environmental standard value. It is effective to reduce to the following.

  The heavy metal absorption promoter of the present invention is easily biodegraded by microorganisms, enzymes, etc. of the heavy metal absorption promoter and hardly remains in the soil, so there is almost no risk of secondary contamination. In addition, the heavy metal absorption accelerator of the present invention is advantageous in terms of cost because it can basically secure the raw material by simple extraction without using chemical synthesis.

  200 g of cadmium-contaminated field soil (5 mg Cd / kg) added with lime so as to have a pH of 6.0 in a cultivation pot (upper diameter 8.5 cm × lower diameter 6.5 cm × height 7.5 cm) (control), Ammonium alginate (made by Kimika Co., Ltd.) solution was added to 5 mg, 10 mg, 25 mg and 50 mg per 100 g of soil, and green mustard (manufactured by Sakata Seed Co., Ltd.) and chard (Sakata Seed) were used as plants. (Manufactured by Kogyo Co., Ltd.) was conducted at quadruplicate each concentration. These seeds were sown and cultivated for 40 days under a light condition (natural light + fluorescent lamp for breeding) at 25 ° C. for 15 hours. Water was supplied every day such that the water content was 60% of the maximum water volume, and 20 ml of liquid manure (trademark “Hyponex”) diluted 2000 times every two weeks was given. After completion of the cultivation, the dry weight (70 ° C., dried for 24 hours) of the above-ground part was measured for each pot, and this was pulverized in an agate mortar and subjected to nitric acid decomposition (110 ° C., 5 hours). The Cd concentration of this sample solution was measured with a high-frequency plasma emission spectrometer (“Shimadzu ICP-7510”) to determine the amount of cadmium absorbed in the plant. The results are shown below.

(Green mustard)
The dry mass of the group with no ammonium alginate added was about 0.03 g, while the group with 10 mg added showed the highest value of about 0.05 g. On the other hand, the cadmium content was about 0.9 μg / pot in the group without addition of ammonium alginate, whereas the 10 mg addition group showed the maximum value of about 1.5 μg / pot.

(Culture)
The dry mass was about 0.06 g in the group with no ammonium alginate added, while the maximum value in the group with 5 mg added was about 0.12 g. On the other hand, the cadmium content was about 3.2 μg / pot in the group with no ammonium alginate added, while the maximum value in the group with 5 mg added was about 6.9 μg / pot.

  After the brown algae waste was pulverized and the raw garbage compost was mixed at a mass ratio of 12 kg: 4 kg, this mixture was put into a compost production machine. The temperature of the mixture was measured twice a day, and water was added at a rate of once a week so that the water content did not become 30% or less, and composted for 4 months (composting in the seed bag root elongation test). Confirmed the completion of conversion.)

A resin pot (inner diameter 11.3 cm, height 6.5 cm) was used, and black goku soil (plastic greenhouse cultivation site, total Cd concentration 1.22 ± 0.0221 mg / kg) was used as the soil, and 500 g / pot was filled. . Komatsuna with the treatment temperature of 1.88 g / pot and 7.52 g / pot added to the above compost and the non-added treatment group with a repetition rate of 4 at a set temperature of 30 ° C. and a sunshine duration of 24 h / day. Cultivated. That is, 25 seeds of Komatsuna were sown per pot, and ion-exchanged water was appropriately added so that the water content was 50% of the maximum volume, and nitrogen (N), phosphoric acid (P ₂ O ₅ ), potassium (K ₂ O) were added. ) Was applied to 500 g of soil so that the chemical fertilizer would be 25 mg (corresponding to 5 kg / 10a) of ammonium sulfate, lime superphosphate and potassium chloride.

  Water supply was carried out every day so that the maximum water volume was 50%. On the 21st day, the ground part of each pot was cut with scissors from the ground, dried for 24 hours with a heat dryer at 80 ° C., measured for dry mass, decomposed with nitric acid-perchloric acid, and Cd in the plant body. The content was measured. The results are shown below.

(Dry mass)
No addition group about 1.7 g / pot; 1.88 g addition group about 2.1 g / pot; 7.52 g addition group about 2.3 g / pot (Cd absorption)
No addition group about 0.19 μg / pot; 1.88 g addition group about 3.2 μg / pot; 7.52 g addition group about 3.5 μg / pot

  ADVANTAGE OF THE INVENTION According to this invention, there is little possibility of causing an environmental problem, and the efficient heavy metal absorption promoter to a plant absorbs a heavy metal in soil in large quantities at low cost, and the heavy metal absorption accelerator in a soil using it. A method for purifying soil containing heavy metals by promoting absorption into plants can be provided.

Claims (8)

  A cadmium absorption promoter for plants, which contains a water-soluble salt of alginic acid or a compost of brown algae and is added to cadmium-containing soil. The cadmium absorption promoter for plants according to claim 1, wherein the water-soluble salt is sodium alginate, potassium alginate, magnesium alginate or ammonium alginate . The plant according to claim 1 or 2 , wherein the plant is at least one plant selected from the group consisting of Brassicaceae, Muranoaceae, Legumeaceae, Rubiaceae, Solanum, Compositae, Rubiaceae, and Gramineae. Cadmium absorption enhancer. A method for purifying soil containing cadmium by promoting absorption of cadmium in the soil into the plant by using the cadmium absorption promoter for the plant according to any one of claims 1 to 3 . The method of Claim 4 which adds a cadmium absorption promoter to the soil containing cadmium and grows a plant in the soil. The method according to claim 4 or 5 , wherein the cadmium content in the soil is 0.5% or less. The method according to any one of claims 4 to 6 , wherein the cadmium absorption promoter is used in an amount of 1 to 2,000 g per 1 m ^{2 of} soil as a water-soluble salt of alginic acid or a compost of brown algae. The compost of brown algae is obtained by a method in which an alginate-degrading enzyme produced by a microorganism is allowed to act, or obtained by a method using a microorganism that produces an alginate-degrading enzyme. A method for producing a cadmium absorption promoter.