Bioremediation of radioactive waste

Last updated

Bioremediation of radioactive waste or bioremediation of radionuclides is an application of bioremediation based on the use of biological agents bacteria, plants and fungi (natural or genetically modified) to catalyze chemical reactions that allow the decontamination of sites affected by radionuclides. [1] These radioactive particles are by-products generated as a result of activities related to nuclear energy and constitute a pollution and a radiotoxicity problem (with serious health and ecological consequences) due to its unstable nature of ionizing radiation emissions.

Contents

The techniques of bioremediation of environmental areas as soil, water and sediments contaminated by radionuclides are diverse and currently being set up as an ecological and economic alternative to traditional procedures. Physico-chemical conventional strategies are based on the extraction of waste by excavating and drilling, with a subsequent long-range transport for their final confinement. These works and transport have often unacceptable estimated costs of operation that could exceed a trillion dollars in the US and 50 million pounds in the UK. [2]

The species involved in these processes have the ability to influence the properties of radionuclides such as solubility, bioavailability and mobility to accelerate its stabilization. Its action is largely influenced by electron donors and acceptors, nutrient medium, complexation of radioactive particles with the material and environmental factors. These are measures that can be performed on the source of contamination ( in situ ) or in controlled and limited facilities in order to follow the biological process more accurately and combine it with other systems ( ex situ ). [3] [4]

Areas contaminated by radioactivity

Typology of radionuclides and polluting waste

The presence of radioactive waste in the environment may cause long-term effects due to the activity and half-life of the radionuclides, leading their impact to grow with time. [2] These particles exist in various oxidation states and are found as oxides, coprecipitates, or as organic or 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. The natural radioactivity does not come from human sources: it covers up to ¾ of the total radioactivity in the world and has its origins in the interaction of terrestrial elements with high energy 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 radium-226 (226Ra), radon-222 (222Rn), thorium-232 (232Th), uranium-238 (238U) and potassium-40 (40K). Potassium-40 (up to 88% of total activity), carbon-14 (14C), radium-226, uranium-238 and rubidium-87 (87Rb) are found in ocean waters. Moreover, in groundwater abound radius radioisotopes such as radium-226 and radium-228 (228Ra). [7] [8] They are also habitual in building materials radionuclides of uranium, thorium and potassium (the latter common to wood). [8]

At the same time, anthropogenic radionuclides (caused by humans) are due to thermonuclear reactions resulting from explosions and nuclear weapons tests, discharges from nuclear facilities, accidents deriving from the reprocessing of commercial fuel, waste storage from these processes and to a lesser extent, nuclear medicine. [9] Some polluted sites by these radionuclides are the US DOE facilities (like Hanford Site), the Chernobyl and Fukushima exclusion zones and the affected area of Chelyabinsk Oblast due to the Kyshtym disaster.

In ocean waters, the presence of tritium (3H), cesium-137 (137Cs), strontium-90 (90Sr), plutonium-239 (239Pu) and plutonium-240 (240Pu) has significantly increased due to anthropogenic causes. [10] [11] In soils, technetium-99 (99Tc), carbon-14, strontium-90, cobalt-60 (60Co), iodine-129 (129I), iodine-131 (131I), americium-241 (241Am), 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 waterSoils/Sediments
Bioremediation of radioactive waste
Bioremediation of radioactive waste
Source: United States Department of Energy, 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]

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 inhalation of particles or ingestion of contaminated food). [14]

In humans, single doses from 0.25 Sv produce first anomalies in the amount of leukocytes. This effect is accentuated if the absorbed dose is between 0.5 and 2 Sv, in whose first damage, nausea and hair loss are suffered. The strip ranging between 2 and 5 Sv is considered the most serious and include bleeding, ulcers and risk of death; values exceeding 5 Sv involve immediate death. [14] If radiation, likewise, is received in small doses over long periods of time, the consequences can be equally severe. It is difficult to quantify the health effects for doses below 10 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 wildlife is scarce and refers to very few species. It is very difficult to estimate from the available data the total doses that can accumulate during specific stages of the life cycle (embryonic development or reproductive age), in changes in behavior or depending on environmental factors such as seasonality. [16] The phenomena of radioactive bioaccumulation, bioconcentration and biomagnification, however, are especially known to sea level. They are caused by the recruitment and retention of radioisotopes by bivalves, crustaceans, corals and phytoplankton, which then amounted to the rest of the food chain at low concentration factors. [17]

Radiobiological literature and IAEA establish a safe limit of absorbed dose of 0.001 Gy/d for terrestrial animals and 0.01 Gy/d for plants and marine biota, although this limit should be reconsidered for long-lived species with low reproductive capacity. [18]

1909 study in which the effect of exposure to radioactive radium on lupins is shown. The radiological activity was the same for all 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. PSM V74 D230 Three plants irradiated with a fourth as the control.png
1909 study in which the effect of exposure to radioactive radium on lupins is shown. The radiological activity was the same for all 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.

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

The effects of radioactivity on bacteria are given, as in eukaryotes, by ionization of water and production of reactive oxygen species. These compounds mutate DNA strands and produce 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 bacterial species significantly differs from the metabolism of organic compounds coming from carbon sources. They are highly energetic radioactive forms which can be converted indirectly by the process of microbial energy transfer. [1]

Radioisotopes can be transformed directly through changes in valence state by acting as acceptors or by acting as cofactors to enzymes. They can also be transformed indirectly by reducing and oxidizing agents produced by microorganisms that cause changes in pH or redox potential. Other processes include precipitation and complexation of surfactants, or chelating agents that bind to radioactive elements. Human intervention, on the other hand, can improve these processes through genetic engineering and omics, or by injection of microorganisms or nutrients into the treatment area. [1] [5]

Bioreduction

According to the radioactive element and the specific site conditions, bacteria can enzymatically immobilize radionuclides directly or indirectly. Their redox potential is exploited by some microbial species to carry out reductions that alter the solubility and hence, mobility, bioavailability and 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]

Depiction of direct enzymatic reduction. Microorganisms use organic compounds as lactate, acetate or formate as electron donors to reduce and leave radionuclides in insoluble form. Enzymatic reduction of radionuclides (en).png
Depiction of direct enzymatic reduction. Microorganisms use organic compounds as lactate, acetate or formate as electron donors to reduce and leave radionuclides in insoluble form.

Direct enzymatic reduction is the change of radionuclides of a higher oxidation state to a lower one made by facultative and obligate anaerobes. The radioisotope interact with binding sites of metabolically active cells and is used as terminal electron acceptor in the electron transport chain where compounds such as ethyl lactate act as electron donors under anaerobic respiration. [4]

The periplasm plays a very important role in these bioreductions. In the reduction of uranium (VI) to insoluble uranium (IV), made by Shewanella putrefaciens , Desulfovibrio vulgaris , Desulfovibrio desulfuricans and Geobacter sulfurreducens , the activity of periplasmic 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 sulfate-reducing and dissimilatory metal-reducing bacteria on excretion reactions of metabolites and breakdown products. There is a coupling of the oxidation of organic acids —produced by the excretion of these heterotrophic bacteria— with the reduction of iron or other metals and radionuclides, which forms insoluble compounds that can precipitate as oxide and 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 sequestering agents and specific chelators, such as 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

Citrate is a chelator which binds to certain transition metals and radioactive actinides. Stable complexes such as bidentate, tridentate (ligands with more than one atom bound) and polynuclear complexes (with several radioactive atoms) can be formed with citrate and radionuclides, which receive a microbial action. Anaerobically, Desulfovibrio desulfuricans and species of the genera Shewanella and Clostridium are able to reduce bidentate complexes of uranyl-citrate (VI) to uranyl-citrate (IV) and make them precipitate, despite not being able to degrade metabolically complexed citrate at the end of the process. [2] In denitrifying and aerobic conditions, however, it has been determined that it is not possible to reduce or degrade these uranium complexes. Bioreduction do not get a head when they are citrate complex mixed metal complexes or when they are tridentate, monomeric or polynuclear complexes, since they become 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. Biosorption, biomineralization and bioaccumulation of radionuclides (en).png
Biosorption, bioaccumulation and biomineralization strategies with a specific role for each cell compartment.

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 electron microscopy, X-ray diffraction and XANES, 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 phosphates, organic compounds and sulfites so that they become insoluble and less exposed to radiotoxicity. They are particularly useful in biosolids for agricultural purposes and soil amendments, although most properties of these biosolids are unknown. [26]

Biosorption method is based on passive sequestration of positively charged radioisotopes by lipopolysaccharides (LPS) on the cell membrane (negatively charged), either live or dead bacteria. Its efficiency is directly related to the increase in temperature and can last for hours, being a much faster method than direct bioreduction. It occurs through the formation of slimes and capsules, and with a preference for binding to the phosphate and phosphoryl groups (although it also occurs with carboxyl, amine or sulfhydryl groups). Bacillota and other bacteria like Citrobacter freudii have significant biosorption capabilities; Citrobacter does it through 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 milligrams per gram of cell 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 granules formations. Unlike biosorption, this is an active process: it depends on an energy-dependent transport system.[ citation needed ] Some metals or radionuclides can be absorbed by bacteria accidentally because of its resemblance to dietary elements for metabolic pathways. Several radioisotopes of strontium, for example, are recognized as analogs of calcium and incorporated within Micrococcus luteus . [4] Uranium, however, has no known function and is believed that its entry into the cell interior may be due to its toxicity (it is able to increase membrane permeability). [3]

Chernikovite and meta-autunite, radioactive minerals result of possible biomineralization. Chernikovite 1.jpg
Chernikovite and meta-autunite, radioactive minerals result of possible biomineralization.

Furthermore, biomineralization —also known as bioprecipitation— is the precipitation of radionuclides through the generation of microbial ligands, resulting in the formation of stable biogenic minerals. These minerals have a very important role in the retention of radioactive contaminants. A very localized and produced enzymatically ligand concentration is involved and provides a nucleation site for the onset of biomineral precipitation. [27] This is particularly relevant in precipitations of phosphatase activity-derivate biominerals, which cleavage molecules such as glycerol phosphate on periplasm. In Citrobacter and Serratia genera, this cleavage liberates inorganic phosphates (HPO42−) that precipitates with uranyl ion (UO22+) and cause deposition of polycrystalline minerals around the cell wall. [2] [28] Serratia also form biofilms that promote precipitation of chernikovite (rich in uranium) and additionally, remove up to 85% of cobalt-60 and 97% of 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

Evolution of the Old Rifle UMTRA Site (Colorado, US) from 1957 (above) until 2008 (below), in which biostimulation tasks were carried out. Evolution of the Old Rifle Processing Site.jpeg
Evolution of the Old Rifle UMTRA Site (Colorado, US) from 1957 (above) until 2008 (below), in which biostimulation tasks were carried out.

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 trace elements, electron donors or electron acceptors to stimulate activity and growth of natural indigenous microbial communities. [4] [30] It can range from simple fertilization or infiltration (called passive biostimulation) to more aggressive injections to the ground, and is widely used at US DOE sites. [26] Nitrate is used as nutrient to biostimulate the reduction of uranium, because it serves as very energetically favorable electron acceptor for metal-reducing bacteria. However, many of these microorganisms ( Geobacter , Shewanella or Desulfovibrio ) exhibit resistance genes to heavy metals that limit their ability to bioremediate radionuclides. In these particular cases, a carbon source such as ethanol is added to the medium to promote the reduction of nitrate at first, and then of uranium. Ethanol is also used in soil injection systems with hydraulic recirculations: it raises the pH and promotes the growth of denitrifying and radionuclide-reducing bacteria, that produce biofilms and achieve almost 90% decrease in the concentration of radioactive uranium. [2]

A number of geophysical techniques have been used to monitor the effects of in situ biostimulation trials including measurement of: spectral ionization potential, self potentials, current density, 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. [4] [30] This technique has shown in field trials over the years that it does not offer better results than biostimulation; neither it is clear that introduced species can be distributed effectively through the complex geological structures of most 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. Deinococcus radiodurans.jpg
Deinococcus radiodurans has much interest in genetic engineering for bioremediation of radioactive waste.

Omics, especially genomics and proteomics, allow identifying and evaluating genes, proteins and enzymes involved in radionuclide bioremediation, apart from the structural and functional interactions that exist between them and other metabolites. 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 recombinant DNA techniques are being developed to generate specific bacteria for bioremediation. Some constructs expressed in microbial species are phytochelatins, polyhistidines and other polypeptides by fusion-binding domains to outer-membrane-anchored proteins. [2] Some of these genetically modified strains are derived from Deinococcus radiodurans , one of the most radiation-resistant organisms. D. radiodurans is capable to resist oxidative stress 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]

Directed evolution of bacterial proteins related to bioremediation of radionuclides is also a field research. YieF enzyme, for example, naturally catalyzes the reduction of chromium with a very wide range of substrates. Following protein engineering, however, it has also been able to participate in uranyl ion reduction. [31]

Plant bioremediation

Phytoremediation processes. Radionuclides can not be phytodegraded but converted to more stable or less toxic forms. Phytoremediation Process.svg
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 genetic engineering procedures and biostimulation —called phytostimulation— have improved and accelerate these processes, particularly with regard to fast-growing plants. [33] The use of Agrobacterium rhizogenes , for example, is quite widespread and significantly increases radionuclide uptake by the roots.[ citation needed ]

Phytoextraction

In phytoextraction (also phytoaccumulation, phytosequesteration or phytoabsorption) [34] plants carry radioactive waste from the root system to the vascular tissue and become concentrated in the biomass of shoots. It is a technique that removes radionuclides without destroying the soil structure, with minimal impact on soil fertility and valid for large areas with a low level of radioactivity. Its efficiency is evaluated through bioaccumulation coefficient (BC) or total removal of radionuclides per m2, and is proven to attract cesium-137, strontium-90, technetium-99, cerium-144, plutonium-240, americium-241, 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 common heather or amaranths are able to concentrate cesium-137, the most abundant radionuclide in the Chernobyl Exclusion Zone. In this region of Ukraine, 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). Reedbeds - geograph.org.uk - 380204.jpg
Connected pond system at River Dearne (England).

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 cesium-137 and strontium-90, particularly by algae and aquatic plants, such as Cladophora and Elodea genera, respectively. It is the most efficient strategy for bioremediation technologies in 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 sunflowers. They are able to remove up to 95% of uranium of contaminated water in 24 hours, and experiments in Chernobyl have demonstrated that they can concentrate on 55 kg of plant 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

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

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

Radiotrophic fungi growth has been described in reactor 4 at the Chernobyl Nuclear Power Station. Chernobyl nuclear plant2.jpg
Radiotrophic fungi growth has been described in reactor 4 at the Chernobyl Nuclear Power Station.

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 spores and decomposing pieces of graphite from destroyed reactor No. 4 at the Chernobyl Nuclear Power Station, which is contaminated with high concentrations of cesium, plutonium and cobalt radionuclides. They were called radiotrophic fungi. [36]

Since then, it has been shown that some species of Penicillium , Cladosporium , Paecilomyces and Xerocomus are able to use ionizing radiation as energy through the electronic properties of melanins. [36] [37] In their feeding they bioaccumulate radioisotopes, creating problems on concrete walls of deep geological repositories. [38] Other fungi like 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 agrochemicals. In soils, the role 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 GMOs is limited by regulatory agencies in terms of responsibility and bioethical issues. Their release require support on the action zone and comparability with indigenous species. Multidisciplinary research is focused on defining more precisely necessary genes and proteins to establish new cell-free systems, which may avoid possible side effects on the environment by the intrusion of transgenic or invasive species. [2]

See also

Related Research Articles

A radionuclide is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferred to one of its electrons to release it as a conversion electron; or used to create and emit a new particle from the nucleus. During those processes, the radionuclide is said to undergo radioactive decay. These emissions are considered ionizing radiation because they are powerful enough to liberate an electron from another atom. The radioactive decay can produce a stable nuclide or will sometimes produce a new unstable radionuclide which may undergo further decay. Radioactive decay is a random process at the level of single atoms: it is impossible to predict when one particular atom will decay. However, for a collection of atoms of a single nuclide the decay rate, and thus the half-life (t1/2) for that collection, can be calculated from their measured decay constants. The range of the half-lives of radioactive atoms has no known limits and spans a time range of over 55 orders of magnitude.

Radioactive waste Unwanted or unusable radioactive materials

Radioactive waste is a type of hazardous waste that contains radioactive material. Radioactive waste is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, rare-earth mining, and nuclear weapons reprocessing. The storage and disposal of radioactive waste is regulated by government agencies in order to protect human health and the environment.

Geomicrobiology Intersection of microbiology and geology

Geomicrobiology is the scientific field at the intersection of geology and microbiology and is a major subfield of geobiology. It concerns the role of microbes on geological and geochemical processes and effects of minerals and metals to microbial growth, activity and survival. Such interactions occur in the geosphere, the atmosphere and the hydrosphere. Geomicrobiology studies microorganisms that are driving the Earth's biogeochemical cycles, mediating mineral precipitation and dissolution, and sorbing and concentrating metals. The applications include for example bioremediation, mining, climate change mitigation and public drinking water supplies.

Nuclear chemistry Branch of chemistry concerned with radioactivity, transmutation and other nuclear processes

Nuclear chemistry is the sub-field of chemistry dealing with radioactivity, nuclear processes, and transformations in the nuclei of atoms, such as nuclear transmutation and nuclear properties.

Bioremediation Process used to treat contaminated media such as water and soil

Bioremediation broadly refers to any process wherein a biological system, living or dead, is employed for removing environmental pollutants from air, water, soil, flue gasses, industrial effluents etc, in natural or artificial settings. The natural ability of organisms to adsorb, accumulate, and degrade common and emerging pollutants has attracted the use of biological resources in treatment of contaminated environment. In comparison to conventional physiochemical treatment methods which suffer serious drawbacks, bioremediation is sustainable, eco-friendly, cheap, and scalable. Most bioremediation is inadvertent, involving native organisms. Research on bioremediation is heavily focused on stimulating the process by inoculation of a polluted site with organisms or supplying nutrients to promote the growth. In principle, bioremediation could be used to reduce the impact of byproducts created from anthropogenic activities, such as industrialization and agricultural processes. Bioremediation could prove less expensive and more sustainable than other remediation alternatives.

Radioactive contamination Undesirable radioactive elements on surfaces or in gases, liquids, or solids

Radioactive contamination, also called radiological pollution, is the deposition of, or presence of radioactive substances on surfaces or within solids, liquids, or gases, where their presence is unintended or undesirable.

Nuclear fission product Atoms or particles produced by nuclear fission

Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons, the release of heat energy, and gamma rays. The two smaller nuclei are the fission products..

The Mayak Production Association is one of the biggest nuclear facilities in the Russian Federation, housing a reprocessing plant. The closest settlements are Ozyorsk to the northwest and Novogornyi to the south.

Biological augmentation is the addition of archaea or bacterial cultures required to speed up the rate of degradation of a contaminant. Organisms that originate from contaminated areas may already be able to break down waste, but perhaps inefficiently and slowly.

Radiochemistry

Radiochemistry is the chemistry of radioactive materials, where radioactive isotopes of elements are used to study the properties and chemical reactions of non-radioactive isotopes. Much of radiochemistry deals with the use of radioactivity to study ordinary chemical reactions. This is very different from radiation chemistry where the radiation levels are kept too low to influence the chemistry.

Mycoremediation Process of using fungi to degrade or sequester contaminants in the environment

Mycoremediation is a form of bioremediation in which fungi-based remediation methods are used to decontaminate the environment. Fungi have been proven to be a cheap, effective and environmentally sound way for removing a wide array of contaminants from damaged environments or wastewater. These contaminants include heavy metals, organic pollutants, textile dyes, leather tanning chemicals and wastewater, petroleum fuels, polycyclic aromatic hydrocarbons, pharmaceuticals and personal care products, pesticides and herbicides in land, fresh water, and marine environments.

Caesium-137 Radioactive isotope of caesium

Caesium-137, cesium-137 (US), or radiocaesium, is a radioactive isotope of caesium that is formed as one of the more common fission products by the nuclear fission of uranium-235 and other fissionable isotopes in nuclear reactors and nuclear weapons. Trace quantities also originate from spontaneous fission of uranium-238. It is among the most problematic of the short-to-medium-lifetime fission products. Caesium-137 has a relatively low boiling point of 671 °C (1,240 °F) and is volatilized easily when released suddenly at high temperature, as in the case of the Chernobyl nuclear accident and with atomic explosions, and can travel very long distances in the air. After being deposited onto the soil as radioactive fallout, it moves and spreads easily in the environment because of the high water solubility of caesium's most common chemical compounds, which are salts. Caesium-137 was discovered by Glenn T. Seaborg and Margaret Melhase.

Spent nuclear fuel Nuclear fuel thats been irradiated in a nuclear reactor

Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor. It is no longer useful in sustaining a nuclear reaction in an ordinary thermal reactor and depending on its point along the nuclear fuel cycle, it may have considerably different isotopic constituents.. The term "fuel" is slightly confusing, as it implies a combustion of some type, which does not occur in a nuclear power plant. Nevertheless, this term is generally accepted.

Actinides in the environment

Environmental radioactivity is not limited to actinides; non-actinides such as radon and radium are of note. While all actinides are radioactive, there are a lot of actinides or actinide-relating minerals in the Earth's crust such as uranium and thorium. These minerals are helpful in many ways, such as carbon-dating, most detectors, X-rays, and more.

Environmental radioactivity Radioactivity naturally present within the Earth

Environmental radioactivity is produced by radioactive materials in the human environment. While some radioisotopes, such as strontium-90 (90Sr) and technetium-99 (99Tc), are only found on Earth as a result of human activity, and some, like potassium-40 (40K), are only present due to natural processes, a few isotopes, e.g. tritium (3H), result from both natural processes and human activities. The concentration and location of some natural isotopes, particularly uranium-238 (238U), can be affected by human activity.

Strontium-90 Radioactive isotope of strontium

Strontium-90 is a radioactive isotope of strontium produced by nuclear fission, with a half-life of 28.8 years. It undergoes β− decay into yttrium-90, with a decay energy of 0.546 MeV. Strontium-90 has applications in medicine and industry and is an isotope of concern in fallout from nuclear weapons, nuclear weapons testing, and nuclear accidents.

Plutonium in the environment Plutonium present within the environment

Since the mid-20th century, plutonium in the environment has been primarily produced by human activity. The first plants to produce plutonium for use in cold war atomic bombs were at the Hanford nuclear site, in Washington, and Mayak nuclear plant, in Chelyabinsk Oblast, Russia. Over a period of four decades, "both released more than 200 million curies of radioactive isotopes into the surrounding environment – twice the amount expelled in the Chernobyl disaster in each instance".

Biomining Technique of extracting metals from ores using prokaryotes or fungi

Biomining is the technique of extracting metals from ores and other solid materials typically using prokaryotes, fungi or plants. These organisms secrete different organic compounds that chelate metals from the environment and bring it back to the cell where they are typically used to coordinate electrons. It was discovered in the mid 1900s that microorganisms use metals in the cell. Some microbes can use stable metals such as iron, copper, zinc, and gold as well as unstable atoms such as uranium and thorium. Companies can now grow large chemostats of microbes that are leaching metals from their media, these vats of culture can then be transformed into many marketable metal compounds. Biomining is an environmentally friendly technique compared to typical mining. Mining releases many pollutants while the only chemicals released from biomining is any metabolites or gasses that the bacteria secrete. The same concept can be used for bioremediation models. Bacteria can be inoculated into environments contaminated with metals, oils, or other toxic compounds. The bacteria can clean the environment by absorbing these toxic compounds to create energy in the cell. Microbes can achieve things at a chemical level that could never be done by humans. Bacteria can mine for metals, clean oil spills, purify gold, and use radioactive elements for energy.

<i>Nuclear Power and the Environment</i>

Nuclear Power and the Environment, sometimes simply called the Flowers Report, was released in September 1976 and is the sixth report of the UK Royal Commission on Environmental Pollution, chaired by Sir Brian Flowers. The report was dedicated to "the Queen's most excellent Majesty." "He was appointed "to advise on matters, both national and international, concerning the pollution of the environment; on the adequacy of research in this field; and the future possibilities of danger to the environment." One of the recommendations of the report was that:

"There should be no commitment to a large programme of nuclear fission power until it has been demonstrated beyond reasonable doubt that a method exists to ensure the safe containment of longlived, highly radioactive waste for the indefinite future."

<i>Deinococcus radiodurans</i> Species of bacterium

Deinococcus radiodurans is an extremophilic bacterium and one of the most radiation-resistant organisms known. It can survive cold, dehydration, vacuum, and acid, and therefore is known as a polyextremophile. It has been listed as the world's toughest known bacterium in The Guinness Book Of World Records.

References

  1. 1 2 3 4 5 6 7 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.
  2. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Prakash, D; Gabani, P; Chandel, A.K; Ronen, Z; Singh, O.V (2013). "Bioremediation: a genuine technology to remediate radionuclides from the environment". Microbial Biotechnology. New York. 6 (4): 349–360. doi:10.1111/1751-7915.12059. PMC   3917470 . PMID   23617701.
  3. 1 2 3 4 5 6 7 8 Newsome, L; Morris, K; Lloyd, J.R (2014). "The biogeochemistry and bioremediation of uranium and other priority radionuclides". Chemical Geology. 363: 164–184. Bibcode:2014ChGeo.363..164N. doi: 10.1016/j.chemgeo.2013.10.034 .
  4. 1 2 3 4 5 6 7 8 9 10 11 12 13 Francis, A.J; Nancharaiah, Y.V (2015). "9. In situ and ex situ bioremediation of radionuclide-contaminated soils at nuclear and NORM sites". In van Velzen, L (ed.). Environmental Remediation and Restoration of Contaminated Nuclear and Norm Sites (PDF). Woodhead Publishing Series in Energy. Elsevier. pp. 185–236. doi:10.1016/B978-1-78242-231-0.00009-0. ISBN   978-1-78242-231-0.
  5. 1 2 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. ↑ Varskog, P; Stralberg, E; Varskog, A.T.S; Raaum, A (2003). Naturally occurring radionuclides in the marine environment: an overview of current knowledge with emphasis on the North Sea area (PDF). Kjeller: Norse Decom AS. p. 7. ISBN   978-82-92538-01-2.
  8. 1 2 3 Idaho State University (ed.). "Radioactivity in Nature". Archived from the original (Web) on 5 February 2015. Retrieved 25 February 2016.
  9. 1 2 Hu, Q; Weng, J; Wang, J (2010). "Sources of anthropogenic radionuclides in the environment: a review". Journal of Environmental Radioactivity. Arlington. 101 (6): 426–437. doi:10.1016/j.jenvrad.2008.08.004. PMID   18819734.
  10. ↑ Campbell, J.A (1983). "44.4.1. Tritium" (Web). In Riley, J.P; Chester, R (eds.). Chemical Oceanography. Vol. 8. New York: Academic Press. pp. 111–117. ISBN   9781483219837.
  11. ↑ Aoyama, M; Hirose, K (2008). Radiometric determination of anthropogenic radionuclides in seawater. Radioactivity in the Environment. Vol. 11. pp. 137–162. doi:10.1016/S1569-4860(07)11004-4. ISBN   9780080449883. ISSN   1569-4860.
  12. ↑ Riley, R.G; Zachara, J.M; Wobber, F.J (1992). "Chemical Contaminants on DOE Lands and Selection of Contaminant Mixtures for Subsurface Science Research" (PDF). Office of Energy Research: 22. doi:10.2172/10147081.
  13. ↑ Vienna International Centre (2009). Classification of radioactive waste: general safety guide (PDF). IAEA Safety Standards Series. Viena: International Atomic Energy Agency. pp. 5–6. ISBN   9789201092090. ISSN   1020-525X.
  14. 1 2 Sharma, B.K; Sharma, A; Sharma, M (2007). "Effects of radioactive pollution" (Web). In Sharma, B.K (ed.). Environmental Chemistry. Meerut: Krishna Prakashan Media. ISBN   9788182830127.
  15. ↑ Brenner, D.J; Doll, R; Goodhead, D.T; Hall, E.J; Land, C.E (2003). "Cancer risks attributable to low doses of ionizing radiation: Assessing what we really know". PNAS. 100 (24): 13761–13766. Bibcode:2003PNAS..10013761B. doi: 10.1073/pnas.2235592100 . ISSN   1091-6490. PMC   283495 . PMID   14610281.
  16. ↑ Linsley, G (1997). "Radiation & the environment: Assessing effects on animals and plants" (PDF). IAEA Bulletin.
  17. ↑ Stewart, G.M; Fowler, S.W; Fisher, N.S (2011). "8. The bioaccumulation of U- and Th- series radionuclides in marine organisms". In Krishnaswami, S; Cochran, J.K (eds.). U-Th Series Nuclides in Aquatic Systems. Radioactivity in the Environment. Vol. 13. Amsterdam: Elsevier. pp. 269–305. doi:10.1016/S1569-4860(07)00008-3. ISBN   9780080564883. ISSN   1569-4860.
  18. 1 2 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. ↑ Gager, C.S (1909). "The Influence of Radium Rays on a Few Life Processes of Plants" (Djvu). The Popular Science Monthly . New York. 74: 222–232.
  20. ↑ Confalonieri, F; Sommer, S (2011). "Bacterial and archaeal resistance to ionizing radiation". Journal of Physics: Conference Series. Orsay. 261 (1): 012005. Bibcode:2011JPhCS.261a2005C. doi: 10.1088/1742-6596/261/1/012005 .
  21. ↑ Kelner, A; Dexter Bellamy, W; Stapleton, G.E; Zelle, M.R (1955). "Symposium on radiation effects on cells and bacteria". Bacteriological Reviews. 19 (1): 22–24. doi:10.1128/MMBR.19.1.22-44.1955. PMC   180808 . PMID   14363075.
  22. ↑ Specter, S; Jeffries, D (1996). "18. Disinfection" (Web). In W.J Mahy, B; O Krango, H (eds.). Virology Methods Manual. San Diego: Academic Press. pp. 353–356. ISBN   9780080543581.
  23. ↑ Lowy, R.J (2005). "Ionizing Radiation Inactivation of Medically Relevant Viruses" (Web). In Gazsó, L.G; Ponta, C.C (eds.). Radiation Inactivation of Bioterrorism Agents. NATO Science Series. Series I, Life and behavioural sciences. Vol. 365. Budapest: IOS Press. pp. 175–186. ISBN   9781586034887. ISSN   1566-7693.
  24. ↑ Francis, A.J (2012). "6. Impacts of microorganisms on radionuclides in contaminated environments and waste materials". In Poinssot, C; Geckeis, H (eds.). Radionuclide Behaviour in the Natural Environment: Science, Implications and Lessons for the Nuclear industry . Woodhead Publishing Series in Energy. Woodhead Publishing. pp.  161–226. ISBN   9780857097194.
  25. 1 2 3 Martinez, R.J; Beazley, M.J; Sobecky, P.A (2014). "Phosphate-Mediated Remediation of Metals and Radionuclides". Advances in Ecology. 2014: 1–14. doi: 10.1155/2014/786929 .
  26. 1 2 3 Hazen, T.C; Tabak H.H (2005). "Developments in bioremediation of soils and sediments polluted with metals and radionuclides: 2. Field research on bioremediation of metals and radionuclides". Reviews in Environmental Science and Bio/Technology. 4 (3): 157–183. doi:10.1007/s11157-005-2170-y. ISSN   1572-9826. S2CID   129843161.
  27. ↑ Walther, C; Guptha, D.K (2015). "2.3 Biomineralization/Bioprecipitation" (Web). Radionuclides in the Environment: Influence of chemical speciation and plant uptake on radionuclide migration. Switzerland: Springer. p. 178. ISBN   9783319221717.
  28. ↑ Mackasie, L.E; Young, P; Patterson-Beedle, M (2004). "24. Bacterial precipitation of metal phosphates" (Web). In Valsami-Jones, E (ed.). Phosphorus in Environmental Technologies: Principles and Applications. Integrated environmental technology series. London: International Water Publishing. pp. 553–557. ISBN   9781843390015.
  29. ↑ Chang, Y (2005). "In Situ Biostimulation of Uranium Reducing Microorganisms at the Old Rifle UMTRA Site" (Web). Doctoral Dissertations. Knoxville.
  30. 1 2 3 Natural and Accelerated Bioremediation Research. United States Department of Energy (ed.). "II. Program Goals and Management Strategy" (Web). Retrieved 14 May 2015.
  31. ↑ Matin, A.C (2006). Stanford University (ed.). "Development of combinatorial bacteria for metal and radionuclide bioremediation" (PDF). Stanford: DOE's Office of Scientific and Technical Information. doi:10.2172/883649. S2CID   138099083.{{cite journal}}: Cite journal requires |journal= (help)
  32. ↑ Willey, N; Collins, C (2007). "Phytoremediation of soils contaminated with radionuclides". In Shaw, G (ed.). Radioactivity in the Terrestrial Environment. Vol. 10. Elsevier. pp. 43–69. doi:10.1016/S1569-4860(06)10003-0. ISBN   9780080474892.
  33. 1 2 3 4 Kumar, D; Walther, C, eds. (2014). "4. Phytoremediation techniques". Radionuclide Contamination and Remediation Through Plants. Hannover: Springer. pp. 9–14. ISBN   9783319076652.
  34. ↑ "Rhizofiltration". www.hawaii.edu. Retrieved 2022-06-18.
  35. 1 2 Dadachova, E; Casadevall, A (2008). "Ionizing Radiation: how fungi cope, adapt, and exploit with the help of melanin". Current Opinion in Microbiology. 11 (6): 525–531. doi:10.1016/j.mib.2008.09.013. PMC   2677413 . PMID   18848901.
  36. ↑ Kalac, P (2001). "A review of edible mushroom radioactivity". Food Chemistry. 75 (1): 29–35. doi:10.1016/S0308-8146(01)00171-6.
  37. ↑ Fomina, M; Burford, E.P; M. Gadd, G (2006). "Fungal dissolution and transformation of minerals: significance for nutrient and metal mobility" (Web). In Gadd, G.M (ed.). Fungi in Biogeochemical Cycles. Cambridge University Press. pp. 236–266. doi:10.1017/CBO9780511550522.011. ISBN   9780521845793.
  38. ↑ Galanda, D; Mátel, L; Strišovská, J; Dulanská, S (2014). "Mycoremediation: the study of transfer factor for plutonium and americium uptake from the ground". Journal of Radioanalytical and Nuclear Chemistry. Budapest. 299 (3): 1411–1416. doi:10.1007/s10967-013-2909-9. ISSN   1588-2780. S2CID   96123551.
  39. ↑ Zhu, Y.G; Shaw, G (2000). "Soil contamination with radionuclides and potential remediation". Chemosphere. 41 (1–2): 121–128. Bibcode:2000Chmsp..41..121Z. doi:10.1016/S0045-6535(99)00398-7. PMID   10819188.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.