Nuclear test explosions and reactor wastes have deposited an estimated 16×10¹⁵ Bq of plutonium into the world's aquatic systems. However, plutonium concentration in open ocean waters is orders of magnitude less, indicating that most of the plutonium is quite insoluble in marine waters and has been incorporated into sediments. Actinide ions in waters often are not in a state of thermodynamic equilibrium and their solubility and migration behavior is related to the form in which the nuclides were introduced into the aquatic system. Actinide solubility depends on such factors as pH (hydrolysis), E_H (oxidation state), reaction with complexants (e. g. carbonate, phosphate, humic acid, etc. ), sorption to surfaces of minerals and/or colloids, etc., in the water. The most significant of these variables is the oxidation state of the metal ion. The simultaneous presence of more than one oxidation state for some actinides (e. g. plutonium) in a solution complicates actinide environmental behavior. Both Np (V) O₂⁺ and Pu (V) O₂⁺, the most significant soluble states in natural oxic waters are relatively noncomplexing and resistant to hydrolysis and subsequent precipitation but can undergo reduction to the Pu (IV) oxidation state with its different elemental behavior. The solubility of NpO₂⁺ can be as high as 10^-4 M while that of PuO₂⁺ is more limited by reduction to the insoluble tetravalent species, Pu (OH) ₄, (pK_SP∼56). The net solubility of hexavalent UO₂²⁺ in sea water is also limited by hydrolysis; however, it has a relatively high concentration due to formation of carbonate complexes. The insoluble trivalent americium hydroxocarbonate, Am (CO) ₃ (OH), is the limiting species for the solubility of Am (III) in sea water. Thorium is found exclusively as the tetravalent species and its solubility is limited by the formation of quite insoluble Th (OH) ₄. The chemistry of actinide ions in the environment is reviewed to show the spectrum of reactions that can occur in natural waters which must be considered in assessing the environmental behavior of actinides. While much is understood about sorption of actinides on surfaces, the mode of migration of actinides in such waters and the potential effects of these radioactive specials . on marine biota, much more information is needed for a satisfactory understanding of the behavior of the actinides in the environment.

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New techniques in the rapid freezing of cells, so that they are vitrified, and cryo-transmission electron microscopy (cryoTEM) of the frozen hydrated thin-sections from the vitrified cells are showing their true native structure. Unlike other forms of TEM, frozen hydrated thin-sections cannot be contrasted by heavy-metal stains (such as U, Pb, and Os) and their contrast is via the inherent density of the constituent molecules within the cells. Therefore, these frozen sections show the true mass distribution within the biomatter. Another cryoTEM technique, freeze-substitution, also produces thin sections for viewing by TEM, but these are plastic sections of heavy-metal stained cells. The heavy-metal ions of the stain complex to the available reactive sites of the biomatter. When such images are compared to those from the frozen hydrated sections, a clear interpretation of native structure and its metal reactivity can be made. These types of observations will be invaluable for the study of microbe-metal/radionuclide interactions.

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Microorganisms interact with their surroundings and in some cases they greatly modify the characteristics of their environment. Several such interactions may have a significant influence on the behaviour of radionuclides possibly escaping from underground radioactive waste repositories. Microbes can mobilise trace elements. Unattached microbes may act as large colloids, transporting radionuclides on their cell surfaces with the groundwater flow. Many microbes produce ligands that can mobilise trace elements from solid phases and that can inhibit trace element sorption to solid phases. Bacterial species from the deep subsurface have demonstrated a significant effect on the mobilization of ⁵⁹Fe (III), ¹⁴⁷Pm (III), ²³⁴Th (IV) and ²⁴¹Am (III) under varying redox conditions. The extent of bacterial immobilisation of radionuclides has been investigated under in situ conditions. Experiments have demonstrated this effect with ⁶⁰Co, ¹⁴⁷Pm, ²³⁴Th, ²³⁷Np, and ²³²U. A large group of microbes catalyse the formation of iron oxides from dissolved ferrous iron in groundwater that reaches an oxidising environment. Such biological iron oxide systems (BIOS) will have a retardation effect on many radionuclides. Microorganisms execute an important influence on the chemical situation in groundwater. Especially, they may catalyse reactions that stabilise the redox potential in groundwater at a low and, therefore, beneficial level for a radioactive waste repository.

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The microbial reduction of radionuclides attracted recent interest as these transformations can play crucial roles in controlling the mobility of key redox active actinides and fission products in a range of environments and, if harnessed, may offer the basis of biotechnological processes for the remediation of radioactive waste. This review focuses on recent research on the reduction of radionuclides including U (VI), Np (V), Pu (IV), and Tc (VII). Rapid advances over the last decade have resulted in a detailed understanding of some of these transformations at a molecular level. Where known, the mechanisms of metal reduction are discussed, alongside the environmental impact of such transformations and possible biotechnological applications that could utilise these activities.

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Long-lived radioactive iodine (¹²⁹I, half-life: 1.57×10⁷ y) has been released into the environment from nuclear fuel reprocessing plants. ¹²⁹I may also be released from ground storage of nuclear waste. Given its long half-life, a better understanding of the behavior of iodine in the environment is necessary to ensure the safety of humans and the health of the environment. In this report, we summarize our recent results and new experimental data about microbial influences on the mobility and transformation of iodine. Microbial volatilization of organic iodine was observed in soil slurries and seawater samples, and various species of aerobic bacteria were considered to play a significant role through methylation of iodide (I^-) to form methyl iodide (CH₃I). The volatilization of iodine was also found in iodide-rich natural gas brine water, where iodide concentration is approximately 2, 000 times higher than that in seawater. In this case, however, a significant amount of molecular iodine (I₂) was produced together with organic iodine compounds. Iodide-oxidizing bacteria, which oxidize iodide to I₂, were isolated from seawater and natural gas brine water. Phylogenetically, they were divided into two groups within the α-subclass of the Proteobacteria (Roseovarius sp. and unidentified bacteria), and they produced not only I₂ but also diiodomethane (CH₂I₂) and chloroiodomethane (CH₂C1I). Iodide-accumulating bacteria, which accumulate iodide to concentrations 5, 500-fold over that of the medium, were also isolated from marine sediment. They were closely related to Arenibacter troitsensis, and iodide uptake was mediated by an active transport system. Our results suggest that the fate of iodine can be affected by microorganisms, particularly by bacteria, through processes such as volatilization, oxidation, and accumulation.

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The acid-base properties of humic substances (HS) (humic acid (HA) and fulvic acid (FA) ) extracted from weathered coal, peat and soils obtained from International Humic Substance Society (IHSS) and Chinese natural samples were investigated by potentiometric titration in 0.050∼1.00 M NaC1O₄ solution. For the purpose of comparison, similar titrations were carried out on the homogeneous polymeric acid, polyacrylic acid (PAA). Titrations were conducted with 0.500 g/L HA or FA solution in the range of pH 3.0∼11.2 under a nitrogen gas atmosphere at 298 K. Based on the conceptual model proposed for the cation-humic interaction considering the heterogeneous composition and polyelectrolyte property of humic substances (HS), the apparent dissociation constant expressed by pK_{i, app}=pK_i+m_ipcH-blog[Na⁺] (_i=1 for carboxylic and _i=2 for phenolic groups) for K_app=[H⁺] [R^-]/[HR] was applied to the titration results. In the expression, pK_i, m_i, and b are constant parameters depending on the HS. The result indicated that the amount of total carboxylic groups per gram HS decreased in the order of 7.2 meq/g for FA (coal) >5.1 meq/g for FA (peat) >4.4 meq/g for HA (peat) >3.4∼4.5 meq/g for HA (soil), and that the value of pK₁/ (1-m₁), which corresponds to pK_{1, app} at α (degree of dissociation) =0.5, increased in the order of 3.1∼3.3 for FA (coal) <3.5 for HA (peat) ≈3.6 for FA (peat) <3.7∼4.0 for HA (soil). As compared with the fitted values of m₁=0.45∼0.55 for PAA, the values were larger for HS (0.54∼0.70) indicating the heterogeneous distribution of the -COOH in HS. The fitted values of b were larger for PAA (0.30∼0.39) than for HS (0.15∼0.29) and higher for HA than for FA, reflecting the structure of the electrical double layer formed around the macromolecule, which in turn depends on the density of the anionic sites, molecular weight and conformation of HS.

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The complexation of uranium (VI), thorium (IV), and neodymium (III) with acetate was studied from 10 to 70°C. The formation constants and the enthalpies of complexation were determined by titration potentiometry and calorimetry. The complexes become stronger at higher temperatures, despite that the enthalpy of complexation becomes more positive and unfavorable to the complexation as the temperature is increased. Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) and optical absorption spectroscopy provide additional information to support the thermodynamic results. The effect of temperature on the thermodynamic parameters is discussed in terms of the electrostatic model.

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Acid-mine drainage is an important environmental problem associated with base-metal mining and numerous studies have looked at the chemical and microbial processes involved in the oxidation of metal sulfides under oxic conditions. However, little is known about the activity of bacteria living in the same sulfide-rich tailings, but under sub-oxic to anoxic conditions. Recent work on Cu-Zn mine tailings have shown that sulfate-reducing bacteria (SRB) are present and active in these tailings (under a wide range of pH conditions) and that their activity is season dependent. In fact, acidic conditions and low organic carbon availability in the spring tend to greatly limit the activity of SRB in the tailings. On the other hand, IRB populations tend to increase in number in the spring, maybe as a result of the lack of activity of SRB. These findings are in agreement with studies on acidic coal mining lakes in Germany, which showed that IRB were mainly active in acidic and oxic sediments whereas SRB dominated in the more anoxic and pH neutral sediments. The presence and activity of SRB and IRB also represents a potential bioremediation tool, because both microbial pathways generate alkalinity. Recent work on acidic mining lakes indicates that IRB and SRB activity could be enhanced in a control manner and be used as an acidity neutralizing process to treat environments impacted by AMD.

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Microorganisms are ubiquitous in subsurface environments and play a major role in the biogeochemical recycling of various elements. In this paper, we have developed a general approach for a systematic evaluation of microbial impact on the long-term performance of the repository. We have demonstrated that data on microbial population alone are not sufficient for the evaluation of microbial impact on repository performance and a sensible approach for such evaluation must be based on the consideration of environmental constraints on microbial reaction pathways. We have applied our approach to both the Yucca Mountain (YM) repository and the Waste Isolation Pilot Plant (WIPP). We have demonstrated that the effect of microbial activity on the near-field chemistry in the Yucca Mountain repository is negligible because of limited nutrient supply and harsh environmental conditions created by waste emplacement. Whereas for the WIPP, we have shown that, due to the presence of a large quantity of organic materials and nutrients in the wastes, a significant microbial activity can potentially be stimulated and its impact on repository performance can be evaluated with carefully designed incubation experiments coupled with performance assessment calculations. The impact of microbial gas generation on disposal room chemistry in the WIPP can be mitigated by introducing MgO as a backfill material.

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Stability constants for trivalent f-elements of Eu, Am, and Cm with dicarboxylates containing neutral donors such as secondary amine and ether oxygen were determined by the solvent extraction method in 0.1 M NaClO₄ at 25°C. Six carboxylic acids of suberic acid, 3, 6-dioxaoctanedioic acid, ethylenediamine-N, N'-diacetic acid, glutaric acid, diglycolic acid, and iminodiacetic acid were examined for a systematic comparison. The hydration number of Eu³⁺ in the 1:2 complex was also determined by time resolved laser-induced fluorescence spectroscopy. The role of the softdonor atoms in the complex formation of f-elements and the impact of multiple softdonor atoms on An/Ln selectivity are discussed.

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The ion transport from one aqueous phase (W1) to another (W2) across a bilayer lipid membrane (BLM) in a cell system in the presence of a hydrophobic ion or an ionophore was investigated by voltammetry. The ion transport current was observed by addition of a small amount of hydrophobic ion such as tetraphenylborate, dipicrylaminate, etc. into W1 or/and W2 containing a hydrophilic salt serving as a supporting electrolyte. The hydrophobic ion was distributed into the BLM with the counter ion to hold the electroneutrality within the BLM. It was pointed out that the counter ion could transfer between W1 and W2 across the BLM since concentrations of the counter ion in W1, BLM, and W2 were so high as to cause the ion transfer current while concentrations of the hydrophobic ion were very low. The facilitated transports of alkali ions across a BLM containing valinomycin (Val) used as an ionophore were also investigated by considering the hydrophobicity of both the objective cation and the counter anion and the formation of the alkali metal ion-Val complex.

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The complex formation of Ca²⁺ with a phosphatidylcholine adsorbed at the interface between water and 1, 2-dichloroethane, W|DCE, was evaluated to elucidate the adsorption of ions on biomembrane surfaces. An electrochemical method combined with interfacial tension measurement was adopted for evaluation of the complex formation of the phospholipid and the ion. The association constant for the complex formation of Ca²⁺ with the lipid was three orders of magnitude higher than those of monovalent cations with the lipid. The present result suggests that the strong complex formation of highly hydrophilic metal cations with a lipid membrane results in a higher affinity to biomembrane surfaces.

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To develop a microsystem for determining the oxidation state of actinides, we tested the performance of a mm-scale continuous-flow system in measuring the change in oxidation state of Ce (III) to Ce (IV) with time using X-ray absorption near-edge structure (XANES) analysis. A 1 mM Ce (III) solution mixed with a 1 mM desferrioximine B solution (DFO) was pumped into the system, and then the solution was carried through it at a constant flow rate to the point at which the XANES spectra were captured. The system revealed the distinct peaks of Ce (III) and Ce (IV) in L_III edge Ce XANES spectra. The peak intensity of Ce (IV) increased when the reaction time after mixing the two solutions was extended, reflecting the continued oxidation state change of Ce (III) by DFO. Five XANES spectra repeated taken during the test showed no changes in the spectra, indicating the constancy of the oxidation states of Ce throughout the duration of the measurements. Measurements of XANES spectrum over longer periods in the system revealed only low fluctuations in the spectrum around the Ce (III) and Ce (IV) peaks. These results indicate that the mm-scale continuous flow system with XANES analysis is suitable for measuring changes in the oxidation state of actinides with time.

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A novel external scanning proton microprobe system has been developed at JAERI Takasaki. The system enables multi-elemental mapping of samples in-air environment with spatial resolution of 1 μm. The elemental analysis is based on Particle Induced X-ray Emission (PIXE) and Particle Induced Gamma-ray Emission (PIGE) techniques. Sodium and heavier elements can be analyzed by the former method while light elements such as fluorine and boron can be detected by the latter. This system has already been targeted for a wide variety of applications in fields such as biomedical research, dental study, environmental science, and geology.

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We studied the association of Eu (III) with Gram-negative bacteria, Alcaligenes faecalis, Shewanella putrefaciens, and Paracoccus denitrificans by a batch method and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The kinetics study showed that the Eu (III) adsorption on the bacteria rapidly proceeded. The Eu (III) adsorption on A. faecalis and P. denitrificans at pHs 3, 4, and 5, and that on S. putrefaciens at pHs 4 and 5 reached a maximum within 5 minutes after contact. For P. denitrificans, the percent adsorption of Eu (III) decreased after the maximum percent adsorption was attained, which suggests the existence of exudates with an affinity with Eu (III). TRLFS showed that the coordination of Eu (III) on these bacteria is multidentate through an inner-spherical process. The ligand field of Eu (III) on P. denitrificans was as strong as the ones observed for halophilic microorganisms, while that of A. faecalis and S. putrefaciens was the typical one observed for non-halophilic microorganisms. The coordination environment of Eu (III) on the bacteria differed from each other, though they are categorized as Gram-negative bacteria with the similar cell wall components.

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Adsorption of Th (IV) and Pu (IV) on a Gram-negative bacterium Pseudomonas fluorescens and a Gram-positive bacterium Bacillus subtilis in the presence of siderophore desferrioxamine B (DFO) was studied. Thorium (IV) and Pu (IV) were dissociated from DFO during adsorption on the cells. Thorium (IV) adsorption on bacterial cells in the presence of DFO was larger than that of Pu (IV) because of the smaller stability of the Th (IV) -DFO complex than that of the Pu (IV) -DFO complex. On the other hand, adsorption of Pu (IV) was larger than that of Fe (III), wherein the stability of the Pu (IV) - and Fe (III) -DFO complex is comparable. P. fluorescens showed a higher affinity for Th (IV) and Pu (IV) than B, subtilis, though potentiometric titration of bacterial cells indicated that surfaces of P. fluorescens and B. subtilis cells showed similar proton binding properties.

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The selective accumulation of rare earth elements in Gram-positive bacteria and actinomycetes was examined. The resting cells of 18 strains having high capacities to accumulate rare earth elements were screened for selectivity using a solution containing 5 elements: Y, La, Sm, Er, and Lu. Among the strains tested, Bacillus megaterium accumulated Sm, Streptomyces albus accumulated Lu, and Arthrobacter nicotianae accumulated both Sm and Lu in higher quantities than the other metals. Similar results were also obtained from a solution containing Y and 14 rare earth elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu). The amount of Sm accumulated in B. megaterium and that of Lu accumulated in S. albus increased as the initial metal concentration increased. S. albus and B. megaterium cells show the highest capacity to accumulate Lu and Sm, respectively, from a solution containing 5 elements, Y, La, Sm, Er, and Lu when each metal concentration ranged from 20 to 100 μM. These results suggest that the separation of these two rare earth elements using microorganisms should be possible.

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We investigated the capacity of the sulfate-reducing bacterium Desulfovibrio desulfuricans to facilitate the removal of Np (V) from aqueous solution. For comparison, we also examined the removal of Np (V) by bentonite under aerobic and anaerobic conditions with sodium sulfide. Np (V) removal (probably afteer reduction to Np (IV) ) was most rapid in the presence of cells, whereas there was little or no removal by bentonite under aerobic conditions. In the presence of cells, Np in suspension declined by 95% or more within 10h, suggesting that D. desulfuricans enzymatically reduces mobile Np (V) to immobile Np (IV) and eventually to stable Np, though chemical reduction by cell metabolite H₂S may contribute. This finding highlights the importance of understanding microbial effects when considering the migration of radioactive elements from waste repositories.

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The formation of insoluble Tc (>0.2μm in size) in ponding water of paddy soil was investigated. The ponding water prepared by flooding with deionized water was collected at a one-week intervals during the 120 days of the experimental period. The collected sample was incubated with 3 kBq mL^-1 TcO₄^- at 25°C for 14 days. The mean value of relative amounts of insolubilized Tc was less than 0.6% of total Tc. This result suggested that flooding with deionized water was not effective for the formation of insoluble Tc. When the ponding water sample was incubated with TcO₄^- under anaerobic conditions, Tc was scarcely insolubilized. On the other hand, a significant fraction of the Tc was insolubilized in the ponding water sample supplemented with nutrients that promote bacterial activity. Also, the amount of insoluble Tc increased with time. From these results, it was concluded that the formation of insoluble Tc in the ponding water depends on enhanced bacterial activity rather than just anaerobic conditions.

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We studied the sorption of Eu (III) on Pseudomonas fluorescens in the absence and presence of citric acid by a batch method. The cells were placed in a solution containing 2μM of Eu (III) and 0, 100, or 1000μM of citric acid at pH 3-9 for 5 hours. In the absence of citric acid, almost 100% of Eu (III) was sorbed on P. fluorescens at pHs below 7; above 7, sorption decreased with an increase in pH. The time course of Eu (III) sorption on P. fluorescens showed that a fraction of it was desorbed into the solution at alkaline pHs, suggesting that the bacterium may release some exudates. With citric acid present, we found that at higher concentrations there was lower sorption of Eu (III), reflecting the formation of Eu (III) -citrate complexes competes with the Eu (III) -cell-surface complexes. This decrease in Eu (III) sorption was significant in alkaline pHs. These findings suggest that citric acid which is ubiquitously found in the environment enhances migration of trivalent actinides in the alkaline environment.

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We studied the effect of Europium, Eu (III), on the degradation of malic acid by the bacterium Pseudomonas fluorescens. Its breakdown depended upon the ratio of Eu (III) - to malic acid-concentrations; the higher the ratio, the less malic acid was degraded. The resulting chemical species of Eu (III), determined by calculations using thermodynamic data, indicated that predominant ones were Eu (Mal) ₂^- and EuMal⁺; free Eu (III) constituted less than 1% of the total Eu (III). The degradation of malic acid was independent of Eu (Mal) ₂^- concentrations. Even though more than 80% of malic acid was present as free malic acid, its degradation was retarded with an increase in the ratio of Eu (III) to malic acid. According to the speciation calculation, the degradation of malic acid was hindered by the presence of EuMal⁺, as well as by free Eu (III). We also assessed the amount of pyruvic acid generated, which is the major degradation product of malic acid complexed with Eu (III).

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We have carried out the growth experiments of 3 strains of yeast in a medium containing uranium (VI) to elucidate the effect of U (VI) on the growth of microorganisms. Hansenula fabianii J640 grew in the liquid medium containing 0.1 mM U (VI) at lower rate than the control, but Saccharomyces cerevisiae did not grow under this condition. The H. fabianii J640 pre-cultured for 21 h in the liquid medium without U (VI) grew even after the exposure to 1 mM U (VI), but did not grow without pre-cultivation. For the pre-cultured H. fabianii J640, radioactivity of U in the medium was the same as the initial one for 110 h, and then gradually decreased. TEMEDS analysis of H. fabianii J640 exposed to 1 mM U (VI) for 165 h showed accumulation of U (VI) on the cells. When H. fabianii J640 was not pre-cultured, radioactivity of U in the medium was lower than the initial one. These results indicated that U (VI) inhibits the growth of yeast, and that the adsorption of U (VI) by the cells depends on the metabolism of yeast.

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The effect of soil microorganisms on the redistribution of Zn and Pb compounds between solution and goethite precipitated as a coating on a sand matrix was studied. Mixed colonies of microorganisms extracted from the soil of an urban park were used to prepare cell and microbial debris suspensions. Chemical states of metal ions retained on the goethite were determined as either exchangeable (extractable by 1.0 M KNO₃) and nonexchangeable (extractable by 0.3 M NH₂OH-HCl in 1 M HNO₃). Pure goethite without microorganisms sorbed about 99% of the added Pb and 99.4% of the Zn although 96% of the sorbed Pb and 78% of the sorbed Zn were in the nonexchangeable state. Pb concentrations decreased on the surface of the iron mineral due to living microorganisms. Sorption of Pb was inversely correlated with the concentration of organic carbon (C_org) in the solution. Microorganisms clearly influenced the Zn sorption by goethite at concentrations of C_org > 450 mg L^-1. The amount of retained Zn was decreased primarily due to the decrease in its exchangeable fraction. Microbial debris prepared by autoclaving reduced the Pb sorption in accordance with the results for living cells. Living microorganisms accumulate more Zn than did microbial debris.

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Cs accumulation by Pseudomonas fluorescens was examined under conditions of growth and resting to elucidate the interaction between Cs and bacteria. In the growth condition, P. fluorescens was cultured in citric acid media containing 50 μM CsCl and 0, 0.1, 1.0, and 10 mM K for 64 h at 30°C. Adsorption and Aeorption behaviors of Cs were examined by the contact of the cells with 50 μM CsCl solution under the resting condition. Cs-accumulated P. fluorescens was exposed to a 1 CH₃COONH₄ solution to examine the reversibility of Cs accumulation. In the growth condition, P. fluorescens did not accumulate Cs irrespective of the presence of K. In the resting condition, the cells quickly adsorbed approximately 5 μmol Cs/g_{cell dry-weight} and subsequently released approximately 90% of the adsorbed Cs with 1 M CH₃COONH₄. The amount of Cs adsorption by cells of P. fluorescens varied with changing pH and ionic strength of the solution. These results indicate that Cs accumulation by P. fluorescens occurs mainly by reversible adsorption on the cell walls, but not by intracellular accumulation under nutrient conditions.

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Uptake of Cs and its effects on mushroom growth were studied using a simulated medium in which K⁺ and NH₄⁺ concentrations were lowered as much as possible. The hyphae of H. vinosophyllum did not grow in the simulated medium with 2 mmol CsCl. The growth increased with the addition of K, indicating that K lowers the toxicity of Cs to mushrooms in the simulated medium. The inhibition of mushroom growth by Cs was greater than that by Rb. The uptake of Cs was reduced by the addition of the monovalent cations of K⁺, Rb⁺, and NH₄⁺

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We studied the association of a Cu tolerant mycobiont, Tremolecia atrata (rusty-rock lichen) with Cu. T. atrata mycobiont cell aggregates, which grew into a sperical shape, rapidly absorbed Cu into their inner and outer parts. The EDS/SEM study showed that Cu was more highly accumulated in the inner part than the outer part of theaggregates. The XANES study revealed that the Cu absorbed by the T. atrata mycobiont was both monovalentand divalent. These results suggested that the T. atrata mycobiont's high tolerance to Cu is attributable to its ability to store Cu (I) inside the cytoplasm and to adsorb Cu (II) on the cell wall.

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