JP6099124B2 - Method for treating soil or water system containing cesium contaminated soil particles - Google Patents
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- 239000002689 soil Substances 0.000 title claims description 116
- 229910052792 caesium Inorganic materials 0.000 title claims description 101
- TVFDJXOCXUVLDH-UHFFFAOYSA-N caesium atom Chemical compound [Cs] TVFDJXOCXUVLDH-UHFFFAOYSA-N 0.000 title claims description 100
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims description 74
- 239000002245 particle Substances 0.000 title claims description 39
- 238000000034 method Methods 0.000 title claims description 37
- 241000195620 Euglena Species 0.000 claims description 74
- 239000000725 suspension Substances 0.000 claims description 44
- 230000002285 radioactive effect Effects 0.000 claims description 22
- 241000223785 Paramecium Species 0.000 claims description 21
- 238000003672 processing method Methods 0.000 claims description 16
- 230000005684 electric field Effects 0.000 claims description 9
- 239000003673 groundwater Substances 0.000 claims description 6
- 238000002156 mixing Methods 0.000 claims description 6
- VMHLLURERBWHNL-UHFFFAOYSA-M Sodium acetate Chemical compound [Na+].CC([O-])=O VMHLLURERBWHNL-UHFFFAOYSA-M 0.000 claims description 5
- 229940041514 candida albicans extract Drugs 0.000 claims description 5
- 239000001632 sodium acetate Substances 0.000 claims description 5
- 235000017281 sodium acetate Nutrition 0.000 claims description 5
- 239000012138 yeast extract Substances 0.000 claims description 5
- 238000001035 drying Methods 0.000 claims description 2
- 239000007787 solid Substances 0.000 claims 1
- 210000004027 cell Anatomy 0.000 description 33
- 241000195493 Cryptophyta Species 0.000 description 18
- 241000195649 Chlorella <Chlorellales> Species 0.000 description 14
- 229910052500 inorganic mineral Inorganic materials 0.000 description 10
- 239000011707 mineral Substances 0.000 description 10
- 239000005995 Aluminium silicate Substances 0.000 description 9
- 235000012211 aluminium silicate Nutrition 0.000 description 9
- AIYUHDOJVYHVIT-UHFFFAOYSA-M caesium chloride Chemical compound [Cl-].[Cs+] AIYUHDOJVYHVIT-UHFFFAOYSA-M 0.000 description 9
- 239000004927 clay Substances 0.000 description 9
- NLYAJNPCOHFWQQ-UHFFFAOYSA-N kaolin Chemical compound O.O.O=[Al]O[Si](=O)O[Si](=O)O[Al]=O NLYAJNPCOHFWQQ-UHFFFAOYSA-N 0.000 description 9
- 239000012153 distilled water Substances 0.000 description 7
- 238000002474 experimental method Methods 0.000 description 5
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- 238000005119 centrifugation Methods 0.000 description 4
- 102100033806 Alpha-protein kinase 3 Human genes 0.000 description 3
- 101710082399 Alpha-protein kinase 3 Proteins 0.000 description 3
- 241000508318 Chlorogonium Species 0.000 description 3
- 241000196324 Embryophyta Species 0.000 description 3
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 3
- 241001279233 Paramecium bursaria Species 0.000 description 3
- TVFDJXOCXUVLDH-RNFDNDRNSA-N cesium-137 Chemical compound [137Cs] TVFDJXOCXUVLDH-RNFDNDRNSA-N 0.000 description 3
- 238000007796 conventional method Methods 0.000 description 3
- 238000012136 culture method Methods 0.000 description 3
- 238000005202 decontamination Methods 0.000 description 3
- 230000003588 decontaminative effect Effects 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
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- TVFDJXOCXUVLDH-OUBTZVSYSA-N cesium-134 Chemical compound [134Cs] TVFDJXOCXUVLDH-OUBTZVSYSA-N 0.000 description 2
- TVFDJXOCXUVLDH-NJFSPNSNSA-N cesium-135 Chemical compound [135Cs] TVFDJXOCXUVLDH-NJFSPNSNSA-N 0.000 description 2
- 239000011651 chromium Substances 0.000 description 2
- 239000012141 concentrate Substances 0.000 description 2
- 238000011109 contamination Methods 0.000 description 2
- 210000003722 extracellular fluid Anatomy 0.000 description 2
- 229910001385 heavy metal Inorganic materials 0.000 description 2
- 230000003834 intracellular effect Effects 0.000 description 2
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- 241000894007 species Species 0.000 description 2
- 241000195628 Chlorophyta Species 0.000 description 1
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- 244000067456 Chrysanthemum coronarium Species 0.000 description 1
- 235000007871 Chrysanthemum coronarium Nutrition 0.000 description 1
- 240000004808 Saccharomyces cerevisiae Species 0.000 description 1
- CIOAGBVUUVVLOB-NJFSPNSNSA-N Strontium-90 Chemical compound [90Sr] CIOAGBVUUVVLOB-NJFSPNSNSA-N 0.000 description 1
- 229910052770 Uranium Inorganic materials 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
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- 239000002244 precipitate Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 230000035755 proliferation Effects 0.000 description 1
- 239000003247 radioactive fallout Substances 0.000 description 1
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- 230000031068 symbiosis, encompassing mutualism through parasitism Effects 0.000 description 1
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Description
本発明は、ミドリゾウリムシを利用したセシウム汚染土壌粒子を含む土壌または水系からセシウムを除去する方法に関するものである。 The present invention relates to a method for removing cesium from a soil or water system containing cesium-contaminated soil particles using Euglena.
福島第一原発の事故は、放射性物質による広範囲な環境汚染を引き起こした。特に、放射性セシウムによる土壌汚染は、重大な問題である。現在まで、さまざまな汚染土壌の処理法が研究され、一部は実用化されてきている。その主たる方法は、汚染土壌を回収し、処理施設へ運搬した後に化学的処理により汚染物質の分離・濃縮を行うというものである。広範囲に汚染された土壌を運び出し改良するのは時間と費用が膨大になる。今後は、汚染土壌を現場で処理することのできる簡便な技術の開発が望まれる。 The accident at the Fukushima Daiichi nuclear power plant caused widespread environmental pollution by radioactive materials. In particular, soil contamination by radioactive cesium is a serious problem. To date, various methods for treating contaminated soil have been studied and some have been put into practical use. The main method is to collect contaminated soil, transport it to a treatment facility, and then separate and concentrate the pollutant by chemical treatment. It takes a lot of time and money to carry and improve extensively contaminated soil. In the future, it is desired to develop a simple technique that can treat contaminated soil on site.
一方で、生物を用いた処理法も盛んに研究されてきた。たとえば、セシウムを吸収・蓄積する能力の高い植物や、培養の容易な小型藻類を用いるという方法である。しかし、生物を用いたこれらの方法は、残念ながら実用的な方法とは言えないことが判明してきた。その理由は、植物や藻類には、確かにセシウムを吸収する能力が高い種が存在するが、それらの生物が吸収できるのは水中に溶解している可溶性セシウムイオンに限定されるからである。不溶化したセシウムはまったく吸収することができない。原発事故から一年以上が経過した現在では、ほとんどのセシウムは土壌中の粘土粒子に強く結合し、不溶性のものになっている。このために、植物や藻類では放射性セシウムの除去ができないのである。さらに、山林から農地に流入する潅水中にも、土壌の微粒子に結合している放射性セシウムが含まれており、土壌の除染をさらに困難にしている。 On the other hand, treatment methods using living organisms have been actively studied. For example, a method using a plant having a high ability to absorb and accumulate cesium or a small algae that can be easily cultured. However, these methods using organisms have unfortunately been found to be not practical methods. The reason is that although plants and algae have certain species that have a high ability to absorb cesium, those organisms can absorb only soluble cesium ions dissolved in water. Insolubilized cesium cannot be absorbed at all. Today, more than a year after the nuclear accident, most cesium is strongly bound to clay particles in the soil and is insoluble. For this reason, radioactive cesium cannot be removed by plants and algae. Furthermore, the irrigation water flowing from the forest into the farmland also contains radioactive cesium bound to the soil fine particles, making soil decontamination even more difficult.
ミドリゾウリムシ（学名 Paramecium bursaria）は、広く日本及び各国で、近辺で入手可能な原生動物であり、細胞内に数百の単細胞緑藻類（クロレラ（Chlorella）の近縁種：以下クロレラと称する）を共生させているゾウリムシである。他のゾウリムシに比べ比較的小型で、扁平で足形の姿をしている、長さ１００μｍ程の単細胞生物である。細胞内にクロレラを共生させているために緑色に見える。明るいところで培養すると共生しているクロレラが光合成をして、その産物をゾウリムシに供給するので、えさを与えなくても長期間飼育培養が可能である。また、暗いところで培養したり薬物処理を施すと、クロレラを欠如した白化ゾウリムシが得られる。ミドリゾウリムシよりクロレラを分離して培養することができ、それらを再感染させることも可能である。また、ミドリゾウリムシは走光性や走電性を有しており、適度な光や負電極に集まる性質を有する。 Paramecium bursaria is a protozoan widely available in Japan and around the world, and several hundred unicellular green algae (Chlorella related species: hereinafter referred to as Chlorella) coexist in the cell. It is a Paramecium. It is a single-celled organism with a length of about 100 μm that is relatively small compared to other Paramecium and is flat and foot-shaped. It looks green because of the symbiosis of chlorella in the cells. When cultivated in a bright place, symbiotic chlorella photosynthesizes and supplies the product to Paramecium, so long-term rearing culture is possible without feeding. In addition, when cultivated in a dark place or treated with drugs, bleached Paramecium lacking chlorella can be obtained. Chlorella can be isolated and cultured from Paramecium, and they can be reinfected. In addition, Euglena has phototaxis and electromotility, and has the property of gathering at moderate light and the negative electrode.
ミドリゾウリムシは、明るい場所で、室温で簡単に培養できる。例えば、管びんに再沸騰水を入れ、冷えたらドライイーストを少量（水５０ｍｌに約３０粒）加え、１日放置する。培養液にミドリゾウリムシを入れ、直射日光の当たらないところに置いて培養することができる。特定の細菌や藻類のエサを与えると増殖が速くなる。 Paramecium can be easily cultured at room temperature in a bright place. For example, reboiling water is put into a tube bottle, and after cooling, a small amount of dry yeast (about 30 grains in 50 ml of water) is added and left for one day. It can be cultured by placing Euglena in the culture and placing it in a place not exposed to direct sunlight. Feeding specific bacteria and algae will increase the growth rate.
クロレラなどの単細胞藻類は、可溶化されたセシウムなどの金属を細胞内に効率よく蓄積する能力を持っている。しかし、土壌粒子に結合したセシウムを取り込むことはできない。 Single-celled algae such as chlorella have the ability to efficiently accumulate solubilized metals such as cesium in cells. However, cesium bound to soil particles cannot be taken up.
先行特許文献１には、ミドリゾウリムシ等が、廃液中のクロム（Ｃｒ），ニッケル（Ｎｉ）等の重金属イオンを吸収できることが記載されているが、セシウム（Ｃｓ）についての記載はない。また、土壌中で不溶化した重金属についての記載もない。非特許文献１は、本願発明者による文献であり、ミドリゾウリムシの培養技術が記載されている。 Prior Patent Document 1 describes that Euglena and the like can absorb heavy metal ions such as chromium (Cr) and nickel (Ni) in the waste liquid, but there is no description about cesium (Cs). There is no description of heavy metals insolubilized in soil. Non-Patent Document 1 is a document by the present inventor and describes a culture technique of Euglena.
放射性セシウム汚染土壌粒子を含む土壌および水系から効率的にセシウムを除去するための処理方法を提供し、広い範囲に大量に存在する汚染土壌および汚染土壌を含む水系の除染を可能にする。特に土壌中で不溶化したセシウムを除去できる処理方法を提供する。 A treatment method for efficiently removing cesium from soil and water systems containing radioactive cesium-contaminated soil particles is provided, and decontamination of water systems including contaminated soil and contaminated soil existing in large amounts in a wide range is possible. In particular, a treatment method capable of removing cesium insolubilized in soil is provided.
本発明者等は、課題を解決するために鋭意研究した結果、捕食性原生動物であるミドリゾウリムシを用いて、土壌懸濁液中のセシウムを効率よく除去する新たな方法を見出して本発明を完成した。さらに本発明者等は、ミドリゾウリムシを土壌懸濁液と混合した後に、ミドリゾウリムシのみを効率よく回収する方法も見出した。 As a result of diligent research to solve the problem, the present inventors have found a new method for efficiently removing cesium in a soil suspension by using a predatory protozoan, Euglena, and completed. Furthermore, the present inventors have also found a method for efficiently recovering only Euglena after mixing Euglena with soil suspension.
即ち、本発明は以下からなる。
１．セシウムによって汚染された土壌と水の懸濁液中で、ミドリゾウリムシを培養する工程を含む、セシウムが吸着した土壌粒子を含む土壌、または、該土壌粒子が懸濁されている水系の処理方法。
２．前記ミドリゾウリムシに、セシウムが吸着した土壌粒子を取り込ませて、前記土壌または前記水系からセシウムを除去する、前項１に記載の処理方法。
３．前記ミドリゾウリムシに、前記懸濁液に溶解しているセシウムを取り込ませて、前記土壌または前記水系からセシウムを除去する、前項１または２に記載の処理方法。
４．前記懸濁液が、放射性セシウムによって汚染された土壌を分取し、分取された土壌と水を混合して調製された懸濁液である、前項１〜３のいずれか一に記載の処理方法。
５．前記懸濁液が、放射性セシウムによって汚染された土壌に水を導入し、表面土壌を掘返して懸濁化して調製された懸濁液である、前項１〜３のいずれか一に記載の処理方法。
６．前記懸濁液が、放射性セシウムが吸着した土壌粒子が懸濁されている水系である、前項１〜３のいずれか一に記載の処理方法。
７．前記水系が、河川、池、湖、沼、地下水、水田、または、水たまりである、前項１〜６のいずれか一に記載の処理方法。
８．前記土壌１ｋｇに対して、ミドリゾウリムシを１×１０４〜１×１０１１個体を添加して培養する、前項１〜７のいずれか一に記載の処理方法。
９．イーストエキストラクト、酢酸ナトリウムおよび水からなる培養液で前培養したミドリゾウリムシを前記懸濁液に添加する、前項１〜８のいずれか一に記載の処理方法。
１０．前記懸濁液中でミドリゾウリムシを３〜５日間培養する、前項１〜９のいずれか一に記載の処理方法。
１１．前記培養後に、ミドリゾウリムシを含む懸濁液に直流電場処理を行い、ミドリゾウリムシを集積させて回収する工程を含む、前項１〜１０のいずれか一に記載の処理方法。
１２．０．１〜０．５Ｖ／ｃｍの直流電場を印加する、前項１１に記載の処理方法。
１３．ミドリゾウリムシを回収し、乾燥および固形化する工程を含む、前項１〜１２のいずれか一に記載の処理方法。
That is, this invention consists of the following.
1. A method for treating soil containing soil particles adsorbed with cesium or a water system in which the soil particles are suspended, comprising a step of cultivating Euglena in a suspension of water contaminated with cesium and water.
2. The treatment method according to item 1 above, wherein soil particles adsorbed with cesium are incorporated into the Euglena, and cesium is removed from the soil or the water system.
3. 3. The treatment method according to item 1 or 2, wherein cesium dissolved in the suspension is taken into the euglena and cesium is removed from the soil or the water system.
4). The treatment according to any one of the preceding items 1 to 3, wherein the suspension is a suspension prepared by separating soil contaminated with radioactive cesium and mixing the separated soil and water. Method.
5. The treatment according to any one of the preceding items 1 to 3, wherein the suspension is a suspension prepared by introducing water into soil contaminated with radioactive cesium and digging and suspending the surface soil. Method.
6). The processing method according to any one of the preceding items 1 to 3, wherein the suspension is an aqueous system in which soil particles adsorbed with radioactive cesium are suspended.
7). The processing method according to any one of the preceding items 1 to 6, wherein the water system is a river, pond, lake, swamp, groundwater, paddy field, or puddle.
8). The treatment method according to any one of 1 to 7 above, wherein 1 × 10 4 to 1 × 10 11 individuals are added to 1 kg of the soil and cultured.
9. The processing method according to any one of the preceding items 1 to 8, wherein euglena pre-cultured with a culture solution comprising yeast extract, sodium acetate and water is added to the suspension.
10. 10. The treatment method according to any one of 1 to 9 above, wherein the Euglena is cultured in the suspension for 3 to 5 days.
11. 11. The treatment method according to any one of the preceding items 1 to 10, comprising a step of subjecting a suspension containing euglena to direct current electric field treatment to accumulate and recover euglena.
12. The processing method according to 11 above, wherein a DC electric field of 0.1 to 0.5 V / cm is applied.
13. 13. The processing method according to any one of the preceding items 1 to 12, comprising a step of recovering green paramecium, drying and solidifying.
本発明の処理方法により、水中に溶解しているセシウムは、ミドリゾウリムシに取り込まれ、ミドリゾウリムシ細胞内で５〜６倍の濃度に濃縮される。さらに、土壌粒子に強く結合した不溶性のセシウムも土壌粒子と共にミドリゾウリムシに取り込まれ、ミドリゾウリムシ細胞内にセシウムが大量に蓄積される。よって本発明により、効率的に土壌中または土壌粒子が懸濁されている水系中のセシウムを除去することが可能になる。そして、本発明の処理方法は、セシウム汚染土壌およびそれを含む水系の現場における処理が比較的簡単に実現でき、処理に要する費用や時間を従来法と比較して大幅に軽減・短縮することが可能である。 By the treatment method of the present invention, cesium dissolved in water is taken up by Euglena and is concentrated to a concentration of 5 to 6 times in Euglena cells. Furthermore, insoluble cesium that is strongly bound to the soil particles is also taken up by Euglena along with the soil particles, and a large amount of cesium accumulates in Euglena cells. Therefore, according to the present invention, it is possible to efficiently remove cesium in the soil or in an aqueous system in which soil particles are suspended. In addition, the treatment method of the present invention can relatively easily realize on-site treatment of cesium-contaminated soil and a water system including the soil, and can greatly reduce and shorten the cost and time required for the treatment as compared with the conventional method. Is possible.
本願発明では、ミドリゾウリムシが、セシウムが吸着している土壌粒子を取り込み（捕食して）、取り込まれた土壌粒子は高酸性の食胞中に送り込まれることが見出された。食胞は直径約５μｍであり、取り込まれた土壌粒子の直径は、０．５〜１μｍであった。土壌に吸着しているセシウムなどの金属は、高酸性の食胞中で、その一部が可溶化されると考えられる。 In the present invention, it has been found that Euglena grab the soil particles adsorbed with cesium (feeding in), and the incorporated soil particles are fed into highly acidic vesicles. The phagosome was about 5 μm in diameter, and the diameter of the incorporated soil particles was 0.5-1 μm. A part of the metal such as cesium adsorbed on the soil is considered to be solubilized in the highly acidic phagosome.
一方、クロレラなどの単細胞藻類は、可溶化されたセシウムなどの金属を細胞内に効率よく蓄積する能力を持っている。ミドリゾウリムシの細胞内にはもともとクロレラが多数共生しているので、この二種類の生物の持つ特性がうまく働き、ミドリゾウリムシが環境中の不溶性セシウムを吸収・蓄積できたと考えられる。ミドリゾウリムシは、１０ｍＭ以上の塩化セシウム溶液中で死滅するが、不溶性のセシウムを細胞内に、可溶化した場合には３０．４ｍＭの濃度に匹敵するセシウム量を蓄積できた。これは、細胞外液中の可溶性セシウム溶液の耐性限界を超える高濃度であり、このような高濃度のセシウムを無害な状態で細胞内に蓄積できることは、予想外の結果であった。 On the other hand, unicellular algae such as chlorella have the ability to efficiently accumulate solubilized metals such as cesium in cells. Since a large number of chlorella originally coexisted in the cells of Paramecium, it seems that the characteristics of these two types of organisms worked well, and the Paramecium could absorb and accumulate insoluble cesium in the environment. Midori Paramecium dies in a 10 mM or more cesium chloride solution, but when solubilized insoluble cesium in cells, it was able to accumulate a cesium amount comparable to a concentration of 30.4 mM. This is a high concentration exceeding the tolerance limit of the soluble cesium solution in the extracellular fluid, and it was an unexpected result that such a high concentration of cesium can be accumulated in a cell in a harmless state.
本発明は、セシウムによって汚染された土壌と水の懸濁液中で、ミドリゾウリムシを培養する工程を含む、セシウムが吸着した土壌粒子を含む土壌、または、該土壌粒子が懸濁されている水系の処理方法である。 The present invention relates to a soil containing soil particles adsorbed with cesium, or a water system in which the soil particles are suspended, including a step of cultivating Euglena in a suspension of water contaminated with cesium and water. It is a processing method.
本発明において、セシウムとは、セシウムの同位体すべてを含み、放射能のないセシウム１３３および放射性セシウム（セシウム１３７、セシウム１３５、セシウム１３４等）を含む。ウランの代表的な核分裂生成物として、ストロンチウム９０と共にセシウム１３５、セシウム１３７が、また原子炉内の反応によってセシウム１３４が生成される。この中でセシウム１３７は比較的多量に発生しベータ線を出し半減期も約３０年と長く、放射性降下物として特に環境中の存在や残留が問題となっている。 In the present invention, cesium includes all isotopes of cesium and includes non-radioactive cesium 133 and radioactive cesium (cesium 137, cesium 135, cesium 134, etc.). As typical fission products of uranium, cesium 135 and cesium 137 are produced together with strontium 90, and cesium 134 is produced by reaction in the reactor. Among them, cesium 137 is generated in a relatively large amount, emits beta rays, has a long half-life of about 30 years, and is particularly problematic as a radioactive fallout in the environment.
セシウムによって汚染された土壌とは、原子力発電所の事故や核兵器の使用（実験）により環境中に放出された放射性セシウムによって汚染された土壌である。本発明の処理対象とする土壌のセシウムの汚染量は限定されず、セシウム量が多い土壌でも処理可能である。 Soil contaminated with cesium is soil contaminated with radioactive cesium released into the environment due to accidents at nuclear power plants or the use (experiment) of nuclear weapons. The amount of cesium contamination in the soil to be treated according to the present invention is not limited, and treatment is possible even in soil with a large amount of cesium.
セシウムによって汚染された土壌中のセシウムのほとんどは、土壌粒子に強く結合し不溶性になっている。本発明において、セシウムが吸着した土壌粒子とは、セシウムによって汚染された土壌中に存在する、セシウムが不溶性になって結合している土壌粒子である。 Most of the cesium in soil contaminated with cesium is strongly bound to soil particles and is insoluble. In the present invention, the cesium-adsorbed soil particles are soil particles that are present in soil contaminated with cesium and in which cesium is insoluble and bound.
セシウムが吸着した土壌粒子が懸濁されている水系とは、放射性セシウムが吸着した土壌粒子が、自然に浮遊または懸濁されている河川や水たまり等であり、農業用に貯留された水を含む。例えば、河川、池、湖、沼、地下水、水田、水たまり等が挙げられる。 Aqueous system in which soil particles adsorbed by cesium are suspended are rivers and puddles in which soil particles adsorbed by radioactive cesium are naturally suspended or suspended, including water stored for agriculture . Examples include rivers, ponds, lakes, swamps, groundwater, paddy fields, and puddles.
土壌と水の懸濁液は、放射性セシウムによって汚染された土壌を分取し、分取された土壌と水を混合して調製される。土壌の分取は、例えば、土壌の表面を機械等で剥ぎ取ることにより行われる。分取された土壌は、例えばタンクやプールで水と十分混合して調製される。懸濁液が循環状態であることが好ましい。水は、川の水、池の水、地下水等が使用可能である。 The suspension of soil and water is prepared by separating soil contaminated with radioactive cesium and mixing the separated soil and water. For example, the soil is separated by peeling off the surface of the soil with a machine or the like. The separated soil is prepared by sufficiently mixing with water in a tank or a pool, for example. It is preferred that the suspension is in circulation. The water can be river water, pond water, ground water, or the like.
あるいは、土壌と水の懸濁液は、放射性セシウムによって汚染された土壌に水を導入し、表面土壌を掘返して懸濁化して調製される。田畑等の耕作地や、水を貯めることのできる山林等の土地に、本調製方法は適している。水は、川の水、池の水、地下水等が使用可能である。土壌に水を導入した後、耕運機等により表面を耕して水と十分に混合して懸濁液を調製できる。 Alternatively, the suspension of soil and water is prepared by introducing water into soil contaminated with radioactive cesium and digging up and suspending the surface soil. This preparation method is suitable for cultivated land such as fields and mountainous land where water can be stored. The water can be river water, pond water, ground water, or the like. After introducing water into the soil, the surface can be cultivated with a cultivator or the like and thoroughly mixed with water to prepare a suspension.
あるいは、土壌と水の懸濁液は、放射性セシウムが吸着した土壌粒子が懸濁されている水系である。放射性セシウムが吸着した土壌粒子が自然に浮遊または懸濁されている河川や水たまり等であり、農業用に貯留された水を含む。例えば、河川、池、湖、沼、地下水、水田、水たまり等が挙げられる。 Or the suspension of soil and water is a water system in which soil particles adsorbed with radioactive cesium are suspended. Rivers and puddles where soil particles adsorbed with radioactive cesium are naturally suspended or suspended, including water stored for agriculture. Examples include rivers, ponds, lakes, swamps, groundwater, paddy fields, and puddles.
土壌は、水と混合前に粉砕処理をして、土壌粒子を小さくしてもよい。好ましい土壌粒子の大きさは、０．１〜２μｍ、さらに好ましくは０．５〜１μｍである。また、懸濁液を調製する際に、ミドリゾウリムシのエサとなるバクテリアや藻類等を添加してもよい。 The soil may be pulverized before mixing with water to reduce the soil particles. The size of a preferable soil particle is 0.1 to 2 μm, more preferably 0.5 to 1 μm. In addition, when preparing the suspension, bacteria, algae, or the like serving as food for Euglena may be added.
懸濁液中の土壌の量は特に限定されないが、ミドリゾウリムシが動き回り、土壌粒子を取り込むことができる水の量が必要である。例えば、土壌１ｋｇあたり１０〜２０００Ｌ、好ましくは２０〜１０００Ｌ、さらに好ましくは５０〜５００Ｌの水量が挙げられる。 The amount of soil in the suspension is not particularly limited, but an amount of water that can move the green paramecium and take up soil particles is necessary. For example, the amount of water is 10 to 2000 L, preferably 20 to 1000 L, more preferably 50 to 500 L per 1 kg of soil.
本発明に用いられるミドリゾウリムシは特に限定されるものではない。ミドリゾウリムシは、世界どこでも入手可能であり、例えば、株式会社科学クラブ（滋賀県高島市マキノ町知内１８８４−７）、岩国市立ミクロ生物館（山口県岩国市由宇町潮風公園みなとオアシスゆう交流館内）から購入可能である。また、非特許文献１に培養法が記載されている。 The euglena used in the present invention is not particularly limited. Midori Paramecium can be obtained anywhere in the world, for example, Science Club Co., Ltd. (1884-7, Makinocho, Takashima City, Shiga Prefecture), Iwakuni City Micro Biological Museum (Minato Oasis Yu Exchange Museum, Yuucho Shiokaze Park, Iwakuni City, Yamaguchi Prefecture) Can be purchased from Non-Patent Document 1 describes a culture method.
本発明に用いられるミドリゾウリムシは、土壌懸濁液に添加する前に前培養される。前培養は、非特許文献１に記載の培養方法、または公知の培養方法により行うことができる。前培養に好適に使用できる培養液として、イーストエキストラクトと酢酸ナトリウムと水からなる培養液が挙げられる。イーストエキストラクトの濃度は０．０５〜０．５％、好ましくは０．１〜０．３％である。酢酸ナトリウムの濃度は、０．０１〜０．０７％、好ましくは、０．０３〜０．０５％である。水はミネラル水が好ましい。組成が極めて単純であり、簡易で安価に調製可能であるが、ミドリゾウリムシの増殖に好適であり、この培養液を用いて３〜５日で約１５００個体／ｍｌのミドリゾウリムシを得ることができる。 Euglena used in the present invention is pre-cultured before being added to the soil suspension. The pre-culture can be performed by the culture method described in Non-Patent Document 1 or a known culture method. As a culture solution that can be suitably used for pre-culture, a culture solution comprising yeast extract, sodium acetate, and water can be mentioned. The concentration of yeast extract is 0.05 to 0.5%, preferably 0.1 to 0.3%. The concentration of sodium acetate is 0.01 to 0.07%, preferably 0.03 to 0.05%. The water is preferably mineral water. Although the composition is very simple and can be easily prepared at low cost, it is suitable for the growth of Euglena, and about 1500 individuals / ml of Euglena can be obtained in 3 to 5 days using this culture solution. .
前培養したミドリゾウリムシを、土壌懸濁液と混合して、一定期間培養する。例えば、前培養したミドリゾウリムシを、前培養液から回収し水に懸濁してから、土壌懸濁液に添加して混合する。または、前培養液をそのまま土壌懸濁液に添加して混合する。土壌の量に対するミドリゾウリムシの添加量は、特に限定されるものではない。好適には、土壌１ｋｇに対して１×１０４〜１×１０１１個体、さらに好適には、１×１０５〜１×１０１０個体、より好適には１×１０６〜１×１０９個体のミドリゾウリムシを添加する。 Pre-cultured Euglena is mixed with soil suspension and cultured for a certain period. For example, pre-cultured Euglena is collected from the pre-culture solution and suspended in water, and then added to the soil suspension and mixed. Alternatively, the preculture is directly added to the soil suspension and mixed. The addition amount of Euglena relative to the amount of soil is not particularly limited. Preferably, 1 × 10 4 to 1 × 10 11 individuals per 1 kg of soil, more preferably 1 × 10 5 to 1 × 10 10 individuals, more preferably 1 × 10 6 to 1 × 10 9 individuals. Of euglena.
土壌懸濁液中でのミドリゾウリムシの培養は、ミドリゾウリムシの増殖に適した条件がよい。例えば、温度は１５〜３０℃が好適であり、より好ましくは、１８〜２６℃、さらに好ましくは２０〜２４℃である。土壌懸濁液のｐＨは特に限定はなく、ｐＨ６〜７．５において、好適にミドリゾウリムシは増殖する。共生しているクロレラが光合成をして、その産物をゾウリムシに供給するので、光があれば、増殖が促進される。例えばミネラルウォーター中で好適に培養可能である。エサを与えた方が増殖が速くなり好適である。好ましいエサは、単細胞藻類クロロゴニウム等である。 Culture of Euglena in a soil suspension should be under conditions suitable for the growth of Euglena. For example, the temperature is preferably 15 to 30 ° C, more preferably 18 to 26 ° C, still more preferably 20 to 24 ° C. The pH of the soil suspension is not particularly limited, and the euglena preferably grows at pH 6 to 7.5. The symbiotic chlorella photosynthesizes and supplies the product to Paramecium, so if there is light, growth is promoted. For example, it can be suitably cultured in mineral water. Feeding food is preferable because it allows faster growth. Preferred foods are unicellular alga chlorogonium and the like.
培養時間は、１〜７日、好適には２〜６日、さらに好適には３〜５日である。約５日で、ミドリゾウリムシは、飽和状態まで、セシウムを細胞内に取り込むことができる。好適には、ミドリゾウリムシの個体数が、１×１０３〜１×１０６個体／ｍｌになるまで、さらに好ましくは、１×１０４〜１×１０５個体／ｍｌになるまで培養する。 The culture time is 1 to 7 days, preferably 2 to 6 days, and more preferably 3 to 5 days. In about 5 days, Euglena can take up cesium into cells until saturation. Preferably, the culture is performed until the number of Euglena is 1 × 10 3 to 1 × 10 6 individuals / ml, and more preferably 1 × 10 4 to 1 × 10 5 individuals / ml.
土壌懸濁液中でミドリゾウリムシを培養し、ミドリゾウリムシにセシウムを吸収させた後、ミドリゾウリムシを単離・回収することが好適である。例えば、遠心分離等の比重差による分離は好適である。また、直流電場処理も好適である。直流電場処理は、直流の電場を与えると、負電極にミドリゾウリムシが集積する性質を利用するものである。土壌懸濁液に直流電場を印加すると効率的にミドリゾウリムシが負電極に集積され、セシウムを取り込んだミドリゾウリムシを土壌懸濁液から単離・回収できる。直流電場の電圧は、好適には、０．１〜０．５Ｖ／ｃｍ、より好ましくは、０．２〜０．４Ｖ／ｃｍ、最適には、０．３Ｖ／ｃｍである。 It is preferable to isolate and recover Euglena after cultivating Euglena in a suspension in the soil and allowing cesium to absorb cesium. For example, separation by specific gravity difference such as centrifugation is suitable. A direct current electric field treatment is also suitable. The direct current electric field treatment utilizes the property that green paramecium accumulates on the negative electrode when a direct electric field is applied. When a DC electric field is applied to the soil suspension, the Euglena is efficiently accumulated on the negative electrode, and the Euglena that incorporates cesium can be isolated and recovered from the soil suspension. The voltage of the DC electric field is preferably 0.1 to 0.5 V / cm, more preferably 0.2 to 0.4 V / cm, and most preferably 0.3 V / cm.
直流電圧処理の具体例として次のような方法が挙げられる。タンク、プールまたは田畑や山林等に貯留された土壌懸濁液に直接直流電圧を印加して、ミドリゾウリムシを単離・回収することができる。また、田畑や山林等に貯留された土壌懸濁液は、吸引ポンプ等でタンク、プール等に保管してからミドリゾウリムシを単離・回収することもできる。また、土壌懸濁液を、直流電圧を印加した水路に流してミドリゾウリムシを単離・回収してもよい。 The following method is mentioned as a specific example of DC voltage processing. It is possible to isolate and recover Euglena by applying a direct voltage to a tank, a pool, or a soil suspension stored in a field or a forest. In addition, the soil suspension stored in a field or a forest can be stored in a tank, a pool or the like with a suction pump or the like, and then Euglena can be isolated and recovered. Alternatively, the euglena may be isolated and recovered by flowing a soil suspension through a water channel to which a DC voltage is applied.
回収されたセシウムを取り込んだミドリゾウリムシは、乾燥し、固形化されて廃棄される。処理量が減量されているため、取扱いが容易で、処理に要する費用や時間を従来法と比較して大幅に軽減・短縮することが可能である。また、ミドリゾウリムシをいったん分解処理し、セシウムの可溶化処理を行った後、セシウム沈殿剤で固化し、乾燥、固形化して廃棄することもできる。 The euglena that has collected the collected cesium is dried, solidified and discarded. Since the amount of processing is reduced, handling is easy, and the cost and time required for processing can be greatly reduced and shortened as compared with the conventional method. It is also possible to disintegrate euglena once and perform solubilization treatment of cesium, then solidify with a cesium precipitant, dry, solidify and discard.
本発明の一連の工程の具体例として、次のような工程が挙げられる。汚染土壌を含む農地に水を張り、表面土壌を耕運機で懸濁した後、あらかじめ培養しておいたミドリゾウリムシを必要量投入する。一定時間後に、土壌懸濁液を回収し、直流電圧が印加された水路に流し、負電極に集まるミドリゾウリムシを回収する。回収したミドリゾウリムシは、そのまま乾燥・固形化して廃棄する。 Specific examples of the series of steps of the present invention include the following steps. Water is applied to the farmland including the contaminated soil, the surface soil is suspended by a cultivator, and then a necessary amount of Euglena cultivated in advance is added. After a certain period of time, the soil suspension is collected, and the suspension is passed through a water channel to which a DC voltage is applied, and green paramecium that collects on the negative electrode is collected. The collected Euglena is dried and solidified as it is and discarded.
（実験材料・前培養）
実験に用いた日本産ミドリゾウリムシ Paramecium bursaria（Kb-1株）は、岩国市立ミクロ生物館から入手したものを、非特許文献１の方法に準じて無菌的に培養した。培養液としては、０．２％イーストエキストラクトと０．０４％酢酸ナトリウムを市販のミネラル水に加えたものを用いた。培養開始５日後に、約１，５００個体／ｍｌとなったものを集め、ミネラル水で洗った後、実験に用いた。ミドリゾウリムシには約１０００個体の共生藻類（クロレラ類）が共生しているが、これを人為的に取り除いた株を、非特許文献１に記載されている方法で作製した。共生藻類を有する株を「共生藻あり」の株、共生藻類を持たない株を「共生藻なし」の株と呼ぶ。実験に用いた溶液は、すべてミネラル水に溶解あるいは懸濁したものを使用した。
(Experimental materials and pre-culture)
The Japanese green Paramecium bursaria (Kb-1 strain) used in the experiment was aseptically cultured according to the method of Non-Patent Document 1 obtained from Iwakuni City Microbiological Museum. As the culture solution, 0.2% yeast extract and 0.04% sodium acetate added to commercially available mineral water were used. Five days after the start of the culture, those with about 1,500 individuals / ml were collected, washed with mineral water, and used for the experiment. About 1000 symbiotic algae (Chlorellas) coexist with Midori Paramecium, but a strain from which this was artificially removed was prepared by the method described in Non-Patent Document 1. Strains having symbiotic algae are called “symbiotic algae” strains, and strains having no symbiotic algae are called “symbiotic algae-free” strains. The solutions used in the experiment were all dissolved or suspended in mineral water.
（ミドリゾウリムシによる可溶性セシウムの取り込み）
方法：「共生藻あり」と「共生藻なし」の株を、直径９ｃｍのプラスチックシャーレ中で２０ｍｌの１ｍＭ ＣｓＣｌ溶液に懸濁した。２日おきに１日で食べ尽くす量のエサ（クロロゴニウム）を与え、４日間培養した。その後遠心操作（ｘ５０ｇ，１０ｍｉｎ）で細胞を集め、セシウムを含まないミネラル水で３回洗浄した後、全体の半量を１ｍｌのミネラル水に再懸濁したものを測定試料としてセシウムの含有量を原子吸光法により測定した。細胞の個体密度は、１ｍｌのミネラル水に懸濁したものを一部採取し、その中に含まれる細胞の個体数を顕微鏡で数えて推定した。ミドリゾウリムシの細胞体積は約２．２×１０５μｍ３と見積もられるので、細胞の個体数と細胞体積から細胞内のセシウム濃度を推定した。１ｍＭ ＣｓＣｌ処理直後の「共生藻あり」のミドリゾウリムシの細胞中に取り込まれたセシウムの量を１００％とした。
(Incorporation of soluble cesium by Euglena)
Method: Strains “with symbiotic algae” and “without symbiotic algae” were suspended in 20 ml of 1 mM CsCl solution in a plastic petri dish with a diameter of 9 cm. Every two days, an amount of food (chlorogonium) that can be consumed in one day was given, and cultured for 4 days. Thereafter, the cells were collected by centrifugation (x50 g, 10 min), washed three times with mineral water not containing cesium, and half of the whole was resuspended in 1 ml of mineral water. It was measured by absorption method. The individual density of the cells was estimated by counting a part of the cells suspended in 1 ml of mineral water and counting the number of individual cells contained therein. Since the cell volume of Paramecium is estimated to be about 2.2 × 10 5 μm 3 , the intracellular cesium concentration was estimated from the number of cells and the cell volume. The amount of cesium incorporated into the cells of Euglena euglena “with symbiotic algae” immediately after treatment with 1 mM CsCl was taken as 100%.
結果：本実験の結果を表１および図１に示す。これにより、１）ミドリゾウリムシには外液のセシウムを吸収し、それを５倍以上の濃度に濃縮して細胞内に蓄積する能力があることがわかった。さらに、２）セシウムの蓄積には、ミドリゾウリムシの細胞内に共生している共生藻（クロレラ）が必要であることも判明した。 Results: The results of this experiment are shown in Table 1 and FIG. As a result, it was found that 1) Euglena has the ability to absorb cesium in the external solution, concentrate it to a concentration of 5 times or more, and accumulate it in the cell. Furthermore, 2) it was also found that the accumulation of cesium requires a symbiotic alga (Chlorella) symbiotic in the cells of Euglena.
（ミドリゾウリムシによる土壌粒子に吸着したセシウムの取り込み）
方法：土壌の代用として、カオリン粘土（Ｎａｃａｌａｉ社製）を用いた。カオリン粘土１００ｍｇを蒸留水（ＤＤＷ）１ｍｌと混合後、遠心操作（７，７４０×ｇ，５ｍｉｎ）により沈殿させ、上清を捨てた後、ＤＤＷを加えて再懸濁した。その後、遠心操作で同様にＤＤＷで再度洗浄した後、沈殿に０．２Ｎ ＨＣｌを加えて再懸濁し、ローテーターで１０分間撹拌した。その後ＤＤＷで２回洗浄した後、１００ｍＭ ＣｓＣｌ ｉｎ ＤＤＷを１ｍｌ加えて１０分撹拌した。その後、ＤＤＷで２回洗浄後、２０ｍｌのミドリゾウリムシ細胞懸濁液（１，５００ｃｅｌｌｓ／ｍｌ）中に加えた。カオリン粘土粒子に結合したセシウムを定量したところ、１．２９ｍｇ Ｃｓ／ｇ ｋａｏｌｉｎの量のセシウムが結合していることがわかった。セシウム結合カオリン粘土粒子と混合したミドリゾウリムシは、２日おきに１日で食べ尽くす量のエサ（クロロゴニウム）を与え、４日間培養した。その後、シャーレの両端に３Ｖの電圧の直流電流を通電し、負電極に集まる細胞をピペットで吸い集めた。集めたミドリゾウリムシは、セシウムを含まないミネラル水の入った新しいシャーレに入れ、ふたたびシャーレの両端に３Ｖの電圧の直流電流を通電し、集めた。この操作を３回繰り返し、カオリン粘土粒子を除去した。集めた細胞は、１ｍｌのミネラル水に再懸濁し、測定試料としてセシウム含量を定量した。
(Uptake of cesium adsorbed on soil particles by Euglena)
Method: Kaolin clay (manufactured by Nacalai) was used as a substitute for soil. 100 mg of kaolin clay was mixed with 1 ml of distilled water (DDW), precipitated by centrifugation (7,740 × g, 5 min), the supernatant was discarded, and DDW was added to resuspend. Thereafter, after washing again with DDW in the same manner by centrifugation, 0.2N HCl was added to the precipitate for resuspension, and the mixture was stirred for 10 minutes with a rotator. Then, after washing twice with DDW, 1 ml of 100 mM CsCl in DDW was added and stirred for 10 minutes. Then, after washing twice with DDW, it was added to 20 ml of Euglena cell suspension (1,500 cells / ml). When cesium bound to the kaolin clay particles was quantified, it was found that cesium in an amount of 1.29 mg Cs / g kaolin was bound. Euglena mixed with cesium-bonded kaolin clay particles were fed every second day for the amount of food (chlorogonium) eaten every day, and cultured for 4 days. Thereafter, a direct current of 3 V was applied to both ends of the petri dish, and the cells collected on the negative electrode were collected by a pipette. The collected Euglena was placed in a new petri dish containing mineral water not containing cesium, and again a DC current of 3 V was applied to both ends of the petri dish and collected. This operation was repeated three times to remove kaolin clay particles. The collected cells were resuspended in 1 ml of mineral water, and the cesium content was quantified as a measurement sample.
結果：ミドリゾウリムシは、直径０．５〜１μｍのカオリン粘土粒子を取り込むことがわかった（図２）。４日間のセシウム吸着土壌処理により、ミドリゾウリムシの細胞内には、それが可溶化した場合には３０．４ｍＭの濃度に匹敵するセシウムが蓄積していた。この濃度は、下記参考例によりわかった細胞外液中の可溶性セシウム溶液の耐性限界を超える高濃度である。従って、ミドリゾウリムシは高濃度のセシウムを無害な状態で細胞内に蓄積する能力があることが示唆された。 Results: It was found that Euglena grab kaolin clay particles having a diameter of 0.5 to 1 μm (FIG. 2). By treatment with cesium-adsorbed soil for 4 days, cesium equivalent to a concentration of 30.4 mM was accumulated in the cells of green paramecium when solubilized. This concentration is a high concentration exceeding the tolerance limit of the soluble cesium solution in the extracellular fluid found by the following reference example. Therefore, it was suggested that Euglena has the ability to accumulate high concentrations of cesium in cells in a harmless state.
（参考例：ミドリゾウリムシの可溶性セシウム耐性）
方法：「共生藻あり」の株をさまざまな濃度の塩化セシウム（ＣｓＣｌ）溶液に懸濁し、２４時間後の様子を観察した。用いたセシウム濃度は、０．１ｍＭ〜５０ｍＭである。
結果：図３に示すように、１ｍＭ以下の濃度ではミドリゾウリムシはセシウムなしの状態（ｃｏｎｔｒｏｌ）と変わらず、細胞の形状・運動性・増殖の度合いは正常であった。一方、１０ｍＭ以上の濃度では、細胞は死に、細胞内部にある共生藻が外液中に拡散していた。これより、ミドリゾウリムシの塩化セシウムに対する耐性は１ｍＭであることがわかった。
(Reference example: Soluble cesium tolerance of Euglena)
Method: The strain “with symbiotic algae” was suspended in various concentrations of cesium chloride (CsCl) solution, and the appearance after 24 hours was observed. The cesium concentration used is 0.1 mM to 50 mM.
Results: As shown in FIG. 3, at a concentration of 1 mM or less, Euglena was not different from the state without cesium (control), and the shape, motility, and proliferation of cells were normal. On the other hand, at a concentration of 10 mM or more, the cells died and the symbiotic algae inside the cells were diffused in the external liquid. From this, it was found that the resistance of euglena to cesium chloride is 1 mM.
放射性セシウムも、非放射性セシウムと同様にミドリゾウリムシに取り込まれるので、放射性セシウムで汚染された土壌、あるいは放射性セシウムで汚染された土壌粒子を含む河川水等の水系からのセシウム除去に本発明は有効に利用できる。本発明により、水中に溶解しているセシウム、および粘度等の土壌に強く結合した不溶性のセシウムが、ミドリゾウリムシに取り込まれ、ミドリゾウリムシ細胞内にセシウムが大量に蓄積されるので、効率的に土壌中のセシウムを除去することが可能になる。そして、本発明の処理方法は、セシウム汚染土壌またはその土壌を含む水系の現場における処理が比較的簡単に実現でき、処理に要する費用や時間を従来法と比較して大幅に軽減・短縮することが可能である。したがって、本発明は、広い範囲に大量に存在する汚染土壌の除染を可能にする。 Since radioactive cesium is also taken up by Euglena as well as non-radioactive cesium, the present invention is effective in removing cesium from water systems such as soil contaminated with radioactive cesium or river water containing soil particles contaminated with radioactive cesium. Available to: According to the present invention, cesium dissolved in water and insoluble cesium strongly bound to soil such as viscosity are taken up by Euglena, and a large amount of cesium is accumulated in Euglena cells, so that the soil is efficiently It becomes possible to remove cesium inside. In addition, the treatment method of the present invention can relatively easily realize the treatment of cesium-contaminated soil or a water system including the soil, and greatly reduce and shorten the cost and time required for the treatment as compared with the conventional method. Is possible. Therefore, the present invention enables decontamination of contaminated soil existing in large amounts in a wide range.
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