Bioremediation of radioactive waste

Source: Wikipedia, the free encyclopedia.
Part of a series on
Pollution
Air pollution from a factory
Air
Biological
Digital
Electromagnetic
Natural
Noise
Radiation
Soil
Solid waste
Space
Thermal
Visual
War
Water
Topics
Misc
Lists
Categories

Bioremediation of radioactive waste or bioremediation of radionuclides is an application of

radiotoxicity problem (with serious health and ecological consequences) due to its unstable nature of ionizing radiation emissions
.

The techniques of bioremediation of environmental areas as

UK.[2]

The species involved in these processes have the ability to influence the properties of radionuclides such as

ex situ).[3][4]

Areas contaminated by radioactivity

Main article: Radioactive contamination

Typology of radionuclides and polluting waste

Main article: Radioactive waste

The presence of radioactive waste in the environment may cause long-term effects due to the

inorganic complexes, according to their origin and ways of liberation. Most commonly they are found in oxidized form, which makes them more soluble in water and thus more mobile.[4] Unlike organic contaminants, however, they cannot be destroyed and must be converted into a stable form or extracted from the environment.[5]

The sources of radioactivity are not exclusive of human activity.

cosmic rays (cosmogenic radionuclides) or in the existing materials on Earth since its formation (primordial radionuclides). In this regard, there are differences in the levels of radioactivity throughout the Earth's crust. India and mountains like the Alps are among the areas with the highest level of natural radioactivity due to their composition of rocks and sand.[6]

The most frequent radionuclides in soils are naturally

building materials radionuclides of uranium, thorium and potassium (the latter common to wood).[8]

At the same time,

Chernobyl and Fukushima exclusion zones and the affected area of Chelyabinsk Oblast due to the Kyshtym disaster
.

In ocean waters, the presence of

neptunium-237 (237Np) and various forms of radioactive plutonium and uranium are the most common radionuclides.[2][8][9]

Frequency of occurrence of selected radionuclides at US DOE facilities
Ground water Soils/Sediments
Source:
US Government (1992)[12]

The classification of radioactive waste established by the International Atomic Energy Agency (IAEA) distinguishes six levels according to equivalent dose, specific activity, heat released and half-life of the radionuclides:[13]

  • Exempt waste (EW): Waste that meets the criteria for exclusion from regulatory control for radiation protection purposes.
  • Very short lived waste (VSLW): Waste with very short half-lives (often used for research and medical purposes) that can be stored over a limited period of up to a few years and subsequently cleared from regulatory control.
  • Very low level waste (VLLW): Waste like soil and rubble (with low levels of activity concentration) that may also contain other hazardous waste.
  • Low level waste (LLW): Waste that is above clearance levels and requires robust isolation and containment for periods of up to a few hundred years and is suitable for disposal in engineered near surface facilities. LLW include short lived radionuclides at higher levels of activity concentration and also long lived radionuclides, but only at relatively low levels of activity concentration.
  • Intermediate level waste (ILW): Waste with long lived radionuclides that requires a greater degree of containment and isolation at greater depths.
  • High level waste (HLW): Waste with large amounts of long lived radionuclides that need to be stored in deep, stable
    geological formations
    usually several hundred metres or more below the surface.

Ecological and human health consequences

Radioactive contamination is a potential danger for living organisms and results in external hazards, concerning radiation sources outside the body, and internal dangers, as a result of the incorporation of radionuclides inside the body (often by

contaminated food).[14]

In humans, single doses from 0.25

mSv, but it has been shown that there is a direct relationship between prolonged exposure and cancer risk (although there is not a very clear dose-response relationship to establish clear limits of exposure).[15]

The information available on the effect of natural background radiation with respect anthropogenic pollution on

corals and phytoplankton, which then amounted to the rest of the food chain at low concentration factors.[17]

marine biota, although this limit should be reconsidered for long-lived species with low reproductive capacity.[18]

seedlings, but not the duration of exposure (descending from left to right, the fourth as control). Those exposed for longer suffered more damage and higher growth and germination deficiences.[19]

Radiation tests in

model organisms that determine the effects of high radiation on animals and plants are:[18]

The effects of radioactivity on

genetic damage, inducing newly lysis and subsequent cell death.[20][21]

Its action on viruses, on the other hand, results in damaged

nucleic acids and viral inactivation.[22] They have a sensory threshold ranging between 1000 and 10,000 Gy (range occupying most biological organisms) which decreases with increasing genome size.[23]

Bacterial bioremediation

The biochemical transformation of radionuclides into stable isotopes by

energy transfer.[1]

Radioisotopes can be transformed directly through changes in

nutrients into the treatment area.[1][5]

Bioreduction

Main article: Biotransformation

According to the radioactive element and the specific site conditions, bacteria can enzymatically immobilize radionuclides directly or indirectly. Their

radiotoxicity. This waste treatment technique called bioreduction or enzymatic biotransformation is very attractive because it can be done in mild conditions for the environment, does not produce hazardous secondary waste and has potential as a solution for waste of various kinds.[4]

electron donors to reduce and leave radionuclides in insoluble form.[2]

Direct enzymatic reduction is the change of radionuclides of a higher oxidation state to a lower one made by

electron donors under anaerobic respiration.[4]

The

cytochromes is required. The reduction of technetium (VII) to technetium (IV) made by S. putrefaciens, G. sulfurreducens, D. desulfuricans, Geobacter metallireducens and Escherichia coli, on the other hand, requires the presence of the complex formate hydrogenlyase, also placed in this cell compartment.[2]

Other radioactive

actinides such as thorium, plutonium, neptunium and americium are enzymatically reduced by Rhodoferax ferrireducens, S. putrefaciens and several species of Geobacter, and directly form an insoluble mineral phase.[2]

The phenomenon of indirect enzymatic reduction is carried out by

hydroxide minerals. In the case of sulfate-reducing bacteria hydrogen sulfide is produced, promoting increased solubility of polluting radionuclides and their bioleaching (as liquid waste that can then be recovered).[2][4]

There are several species of reducing microorganisms that produce indirect

siderophores. These sequestering agents are crucial in the complexation of radionuclides and increasing their solubility and bioavailability. Microbacterium flavescens, for example, grows in the presence of radioisotopes such as plutonium, thorium, uranium or americium and produces organic acids and siderophores that allow the dissolution and mobilization of radionuclides through the soil. It seems that siderophores on bacterial surface could also facilitate the entry of these elements within the cell as well. Pseudomonas aeruginosa also secretes chelating agents out that meet uranium and thorium when grown in a medium with these elements. In general, it has also been found that enterobactin siderophores are extremely effective in solubilizing actinide oxides of plutonium.[2][4]

Citrate complexes

recalcitrant and persistent in the environment.[4][24] From this knowledge exists a system that combines the degradation of radionuclide-citrate complex with subsequent photodegradation of remaining reduced uranyl-citrate (previously not biodegradated but sensitive to light), which allows for stable precipitates of uranium and also of thorium, strontium or cobalt from contaminated lands.[4]

Biosorption, bioaccumulation and biomineralization

Biosorption, bioaccumulation and biomineralization strategies with a specific role for each cell compartment.[3]
Main articles: Biosorption, Bioaccumulation, and Biomineralization

The set of strategies that comprise biosorption, bioaccumulation and biomineralization are closely related to each other, because one way or another have a direct contact between the cell and radionuclide. These mechanisms are evaluated accurately using advanced analysis technologies such as

EXAFS and X-ray spectroscopies.[1][25]

Biosorption and bioaccumulation are two metabolic actions that are based on the ability to concentrate radionuclides over a thousand times the concentration of the environment. They consist of complexation of radioactive waste with

soil amendments, although most properties of these biosolids are unknown.[26]

Biosorption method is based on passive sequestration of positively charged radioisotopes by

electrostatic interaction of uranium with phosphates of their LPS.[2][3]

Quantitative analyzes determine that, in the case of uranium, biosorption may vary within a range between 45 and 615

dry weight. However, it is a technique that requires a high amount of biomass to affect bioremediation; it presents problems of saturation and other cations that compete for binding to the bacterial surface.[3]

Bioaccumulation refers to uptake of radionuclides into the cell, where they are retained by complexations with negatively charged intracellular components, precipitation or

membrane permeability).[3]

Chernikovite and meta-autunite, radioactive minerals result of possible biomineralization.

Furthermore, biomineralization —also known as bioprecipitation— is the

cesium-137 by proton substitution of this mineral.[25] In general, biomineralization is a process in which the cells do not have limitations of saturation and can accumulate up to several times its own weight as precipitated radionuclides.[4]

Investigations of terrestrial and marine bacterial isolates belonging to the genera Aeromonas, Bacillus, Myxococcus, Pantoea, Pseudomonas, Rahnella and Vibrio have also demonstrated the removal of uranium radioisotopes as phosphate biominerals in both oxic and anoxic growth conditions.[25]

Biostimulation and bioaugmentation

Main articles: Biostimulation and Bioaugmentation
US) from 1957 (above) until 2008 (below), in which biostimulation tasks were carried out.[29]

Aside from bioreduction, biosorption, bioaccumulation and biomineralization, which are bacterial strategies for natural attenuation of radioactive contamination, there are also human methods that increase the efficiency or speed of microbial processes. This accelerated natural attenuation involves an intervention in the contaminated area to improve conversion rates of radioactive waste, which tend to be slow. There are two variants: biostimulation and bioaugmentation.[30]

Biostimulation is the addition of nutrients with

biofilms and achieve almost 90% decrease in the concentration of radioactive uranium.[2]

A number of

complex resistivity and also reactive transport modelling (RTM), which measures hydrogeological and geochemical parameters to estimate chemical reactions of the microbial community.[3]

Bioaugmentaton, on the other hand, is the deliberated addition to the environment of microorganisms with desired traits to accelerate bacterial metabolic conversion of radioactive waste. They are often added when necessary species for bioremediation do not exist in the treatment place.

subsurface environments or that can compete long term with the indigenous microbiota.[1][26]

Genetic engineering and omics

Deinococcus radiodurans has much interest in genetic engineering for bioremediation of radioactive waste.
Main articles: Genetic engineering and Omics

Omics, especially genomics and proteomics, allow identifying and evaluating

Genome sequencing of various microorganisms has uncovered, for example, that Geobacter sulfurreducens possess more than 100 coding regions for c-type cytochromes involved in bioremediation radionuclide, or that NiCoT gene is significantly overexpressed in Rhodopseudomonas palustris and Novosphingobium aromaticivorans when grown in medium with radioactive cobalt.[1][2]

From this information, different genetic engineering and

DNA damage from radiation, and reduces technetium, uranium and chromium naturally as well. Besides, through insertion of genes from other species it has been achieved that it can also precipitates uranyl phosphates and degrades mercury by using toluene as an energy source to grow and stabilize other priority radionuclides.[1][3]

uranyl ion reduction.[31]

Plant bioremediation

Main article: Phytoremediation
Phytoremediation processes. Radionuclides can not be phytodegraded but converted to more stable or less toxic forms.

The use of plants to remove contaminants from the environment or to render them less harmful is called phytoremediation. In the case of radionuclides, it is a viable technology when decontamination times are long and waste are scattered at low concentrations.[32][33]

Some plant species are able to transform the state of radioisotopes (without suffering toxicity) concentrating them in different parts of their structure, making them rush through the roots, making them volatile or stabilizing them on the ground. As in bacteria, plant

Agrobacterium rhizogenes, for example, is quite widespread and significantly increases radionuclide uptake by the roots.[citation needed
]

Phytoextraction

Main article:
Phytoextraction

In phytoextraction (also phytoaccumulation, phytosequesteration or phytoabsorption)

neptunium-237 and various radioisotopes of thorium and radium.[33] By contrast, it requires large biomass production in short periods of time.[citation needed
]

Species like

mustard greens could remove up to 22% of average levels of cesium activity in a single growing season. In the same way, bok choy and mustard greens can concentrate 100 times more uranium than other species.[33]

Rhizofiltration

Connected pond system at River Dearne (England).
Main article: Rhizofiltration

Rhizofiltration is the adsorption and precipitation of radionuclides in plant roots or absorption thereof if soluble in effluents. It has great efficiency in the treatment of

wetlands,[34] but must have a continuous and rigorous control of pH to make it an optimal process.[35]

From this process, some strategies have been designed based on sequences of

ponds with a slow flow of water to clean polluted water with radionuclides. The results of these facilities, for flows of 1000 liters of effluent are about 95% retention of radiation in the first pond (by plants and sludge), and over 99% in three-base systems.[33]

The most promising plants for rhizofiltration are

dry weight all the cesium and strontium radioactivity from an area of 75 m2 (stabilized material suitable for transfer to a nuclear waste repository).[33]

Phytovolatilization

Main article:
Phytovolatilization

Phytovolatilization involves the capture and subsequent transpiration of radionuclides into the atmosphere. It does not remove contaminants but releases them in volatile form (less harmful). Despite not having too many applications for radioactive waste, it is very useful for the treatment of tritium, because it exploits plants' ability to transpire enormous amounts of water.[33][34]

The treatment applied to tritium (shielded by air produces almost no external radiation exposure, but its incorporation in water presents a health hazard when absorbed into the body) uses polluted effluents to irrigate phreatophytes. It becomes a system with a low operation cost and low maintenance, with savings of about 30% in comparison to conventional methods of pumping and covering with asphalt.[33]

Phytostabilization

Main article:
Phytostabilization

Phytostabilization is an specially valid strategy for radioactive contamination based on the immobilization of radionuclides in the soil by the action of the roots. This can occur by adsorption, absorption and precipitation within root zone, and ensures that radioactive waste can not be dispersed because soil erosion or leaching. It is useful in controlling tailings from strip and open pit uranium mines, and guarantees to retrieve the ecosystem.[33][34] However, it has significant drawbacks such as large doses of fertilizer needed to reforest the area, apart from radioactive source (which implies long-term maintenance) remaining at the same place.[citation needed]

Fungal bioremediation

Chernobyl Nuclear Power Station
.
Main article: Mycoremediation

Several fungi species have radioactive resistance values equal to or greater than more radioresistant bacteria; they perform mycoremediation processes. It was reported that some fungi had the ability of growing into, feeding, generating

radiotrophic fungi.[36]

Since then, it has been shown that some species of

oyster mushrooms can bioremediate plutonium-239 and americium-241.[39]

Ways of research

Current research on bioremediation techniques is fairly advanced and molecular mechanisms that govern them are well known. However, there are many doubts about the effectiveness and possible adversities of these processes in combination with the addition of

mycorrhizae on radioactive waste is poorly described and sequestration patterns of radionuclides are not known with certainty.[40]

Longevity effects of some bacterial processes, such as maintenance of uranium in insoluble form because of bioreductions or biomineralizations, are unknown. There are not clear details about the

electronic transfer from some radionuclides with these bacterial species either.[3]

Another important aspect is the change of

ex situ or laboratory scale processes to their real application in situ, in which soil heterogeneity and environmental conditions generate reproduction deficiencies of optimal biochemical status of the used species, a fact that decreases the efficiency. This implies finding what are the best conditions in which to carry out an efficient bioremediation with anions, metals, organic compounds or other chelating radionuclides that can compete with the uptake of interest radioactive waste.[2] Nevertheless, in many cases research is focused on the extraction of soil and water and its ex situ biological treatment to avoid these problems.[4]

Finally, the potential of

transgenic or invasive species.[2]

See also

References

  1. ^ a b c d e f g Faison, B; McCullough, J; Hazen, TC; Benson, SM; Palmisano, A (2003). A NABIR Primer (ed.). Bioremediation of metals and radionuclides: What it is and how it works (PDF) (2nd edition. Revision by the Lawrence Berkeley National Laboratory ed.). Washington: United States Department of Energy. Archived from the original (PDF) on 2021-01-25. Retrieved 2016-05-20.
  2. ^
    PMID 23617701
    .
  3. ^
    doi:10.1016/j.chemgeo.2013.10.034
    .
  4. ^
    ISBN 978-1-78242-231-0
    .
  5. ^ a b Francis, A.J (2006). Microbial Transformations of Radionuclides and Environmental Restoration Through Bioremediation (PDF). Symposium on "Emerging Trends in Separation Science and Technology". Mumbai: Brookhaven National Laboratory.
  6. ^ Consejo de Seguridad Nuclear. Ministerio de Industria, Turismo y Comercio de España (ed.). "Radiación natural y artificial" (Web) (in Spanish). Retrieved 24 February 2016.
  7. ISBN 978-82-92538-01-2
    .
  8. ^ a b c Idaho State University (ed.). "Radioactivity in Nature". Archived from the original (Web) on 5 February 2015. Retrieved 25 February 2016.
  9. ^
    PMID 18819734
    .
  10. ISBN 9781483219837
    .
  11. ISSN 1569-4860. {{cite book}}: |journal= ignored (help
    )
  12. doi:10.2172/10147081
    .
  13. ISSN 1020-525X. {{cite book}}: |journal= ignored (help
    )
  14. ^
    ISBN 9788182830127
    .
  15. PMID 14610281
    .
  16. ^ Linsley, G (1997). "Radiation & the environment: Assessing effects on animals and plants" (PDF). IAEA Bulletin.
  17. ISSN 1569-4860
    .
  18. ^ a b Barnthouse, L.W (1995). Environmental Sciences Division (ed.). "Effects of ionizing radiation on terrestrial plants and animals: a workshop report" (PDF) (4496). Tennessee: United States Department of Energy. Archived from the original (PDF) on 2016-12-21. Retrieved 2016-05-21. {{cite journal}}: Cite journal requires |journal= (help)
  19. The Popular Science Monthly
    . 74. New York: 222–232.
  20. doi:10.1088/1742-6596/261/1/012005
    .
  21. PMID 14363075
    .
  22. ISBN 9780080543581
    .
  23. ISSN 1566-7693
    .
  24. ISBN 9780857097194
    .
  25. ^
    doi:10.1155/2014/786929
    .
  26. ^
    S2CID 129843161
    .
  27. ISBN 9783319221717
    .
  28. ISBN 9781843390015
    .
  29. ^ Chang, Y (2005). "In Situ Biostimulation of Uranium Reducing Microorganisms at the Old Rifle UMTRA Site" (Web). Doctoral Dissertations. Knoxville.
  30. ^ a b c Natural and Accelerated Bioremediation Research. United States Department of Energy (ed.). "II. Program Goals and Management Strategy" (Web). Retrieved 14 May 2015.
  31. S2CID 138099083. {{cite journal}}: Cite journal requires |journal= (help
    )
  32. ISBN 9780080474892
    .
  33. ^
    ISBN 9783319076652
    .
  34. ^ "Rhizofiltration". www.hawaii.edu. Retrieved 2022-06-18.
  35. ^
    PMID 18848901
    .
  36. doi:10.1016/S0308-8146(01)00171-6
    .
  37. ISBN 9780521845793
    .
  38. S2CID 96123551
    .
  39. PMID 10819188
    .

External links
Library resources about
Bioremediation of radioactive waste
Retrieved from "https://en.wikipedia.org/w/index.php?title=Bioremediation_of_radioactive_waste&oldid=1184094349"