Comparison of transfer and distribution of technetium and rhenium in radish plants from nutrient solution
Introduction
Technetium has no stable isotopes. Among its isotopes, 99Tc is of potential long-term importance in the environment because it has a long half-life of 2.11×105 yr and it is produced in the fissions of 235U and 239Pu at relatively high ratios (ca. 6%). The radionuclide has been widely distributed in the environment as a result of fallout from nuclear weapons testing (Attrep et al., 1971; Holm et al., 1988; Garcı́a-León et al., 1990; Tagami and Uchida, 2002) and discharges from nuclear facilities (Dahlgaard, 1994; Aarkrog et al., 1997; Smith et al., 2001).
The most stable chemical form of Tc in the surface environment is TcO4− (Brookins, 1988), which is considered to be highly mobile in biogeochemical cycles; indeed, a transfer factor (TF) of 5 (on a wet weight basis) for Tc in the edible parts of common plants was recommended as allowable by the IAEA (1982). The fact that Tc has the highest TF in plants among non-nutrient elements (Wildung et al., 1977; Hoffman et al., 1982; IAEA, 1994) makes Tc unique. Thus, knowledge of Tc behavior in the soil to plant systems is of special interest because of potential long-term radiological consequences.
The chemical forms of Tc in the environment presumably play an important role in determining the fate of Tc in the soil to plant systems. The TFs of Tc obtained from recent field observations (Green and Wilkins, 1995; Uchida et al., 2000) are lower than those obtained from laboratory studies (Wildung et al., 1977; Hoffman et al., 1982; Yanagisawa and Muramatsu, 1993). Determination of the physico-chemical forms of 99Tc in soil and plant samples would advance our understanding of its behavior in the environment, but the amount of 99Tc in the natural environment is at ultra-trace levels even in soil (Tagami and Uchida, 2002), therefore, the chemical species formed by 99Tc in the environment are unclear.
Rhenium, which lies just above Tc in the periodic table, may be considered as a potential chemical analogue for Tc. These two elements behave similarly in the environment (Brookins, 1988). Although the amount of Re in the environment is greater than that of 99Tc, no data are available for terrestrial plant samples. This lack is primarily due to Re being one of the rarest elements in the earth's crust (Wedepohl, 1995). Also, Re is not considered an essential element for animals or plants, so there is little practical interest in it. Radiochemical neutron activation analysis has been used to measure Re and some data on the concentrations of the element in seaweeds were obtained (Fukai and Meinke, 1962; Scadden, 1969). Other more sensitive methods such as flameless atomic absorption spectrophotometry (Yang, 1991) and inductively coupled plasma mass spectrometry, ICP-MS (Mas et al., 2004) have recently been applied for Re determination in seaweeds. The concentration ratios (CFs) of Re (Re [g] per gram of dried seaweed divided by Re [g] per gram of seawater) were calculated to range from 380 to 8900 in brown seaweeds (Fukai and Meinke, 1962; Scadden, 1969; Yang, 1991); the average Re content in seawater is 8.24 pg g−1 (Colodner et al., 1993). High CFs for Tc were also found in brown seaweeds (Hurtgen et al., 1988). The dominant chemical forms of Re and Tc in open seawater are thought to be ReO4− and TcO4−, respectively, and these highly soluble chemical forms would be readily absorbable by seaweeds.
We believe that a terrestrial plant might absorb Re at as high rate as that reported for Tc. In which case, Re could be used as a chemical analogue for Tc in soil solution to plant systems if their uptake behavior was the same, although no study from that viewpoint has been carried out yet. Therefore, we carried out experiments using a multi-tracer technique (Ambe, 2000; Ambe et al., 2002) and a stable multi-element technique with the addition of 99Tc. The multi-element technique, which employs 10–30 stable elements, has recently become available without using radioisotopes even at the low concentrations through the application of ICP-MS. The uptake of Tc and Re by plants, and their distribution in different plant parts, were studied using nutrient solutions. It was assumed that if uptake ratios and distribution ratios of Tc and Re were the same in the plants, then their TFs from nutrient solutions to the plants would also be very close.
Section snippets
Plant cultivation
Radish seedlings, 3 days after germination, were grown in a nutrient solution prepared from a commercially available nutrient powder, HYPONeX®, by dissolving it in deionized water (1 : 1000 in weight). The mjor anion concentrations in the nutrient solution were 2 mm for Cl−, 1.8 mm for SO42−, 0.4 mm for H2PO4− and 3.4 mm for NO3−. The plants were placed in a greenhouse at 21°C and exposed to normal daylight conditions for about 1 month. The average fresh weight of the plants was 5.5 g.
Each plant was
Uptake of TcO4− and ReO4− by radish plants
The physicochemical forms of Re in plants are not known, but there are several reports on those of Tc (Krijger et al., 1999; Bennet and Willey, 2003). Technetium is known to be absorbed by plants through their roots as TcO4−, which is the most stable chemical form in water under aerobic conditions. The TcO4−, is passed through the xylem, and finally Tc is translocated to the leaves. No evaporation of Tc from the leaves has been reported. We assume that Re would also be taken up as ReO4−, which
Acknowledgements
We are grateful to Dr. S. Enomoto, Dr. R. Hirunuma and Dr. H. Haba, The Institute of Physical and Chemical Research (RIKEN), Japan, for kindly providing us with the multitracer solution. We would lie to express our deep gratitude to Dr. T. Sekine, Tohoku University, Japan, for his cooperation with making 95mTc. We thank Ms. N. Ogiu and Mr. K. Tabei for their assistance with the experiments. This work has been partially supported by the Agency for Natural Resources and Energy, the Ministry of
References (35)
- et al.
Evidence of 99Tc in ural river sediments
J. Environ. Radioact
(1997) - et al.
Uptake of trace elements by rice plants inoculated with pyricularia oryzae
Appl. Radiat. Isot
(2002) Sources of 137Cs, 90Sr and 99Tc in the east Greenland current
J. Environ. Radioact
(1994)- et al.
Transfer of radionuclides to vegetable and other crops grown on land reclaimed from the sea
Sci. Total. Environ
(1995) - et al.
The determination of technetium-99 in the brown marine alga fucus spiralis collected along the Belgian coast
Sci. Total Environ
(1988) - et al.
Chemical forms of technetium in tomato plants; TcO4− Tc-cysteine, Tc-glutathione and Tc-proteins
Environ. Exp. Bot
(1999) - et al.
A method for the detection of Tc in environmental samples by ICP-MS using Re as chemical tracer
Anal. Chim. Acta
(2004) Rheniumits concentration in pacific ocean surface waters
Geochim. Cosmochim. Acta
(1969)- et al.
Technetium-99 in the Irish marine environment
J. Environ. Radioact
(2001) - et al.
Separation of Tc-99 in soil and plant samples collected around the chernobyl reactor using a Tc-selective chromatographic resin and determination of the nuclide by ICP-MS
Appl. Radiat. Isot
(2000)
Multitracers in chemistry and biochemistry
J. Radioanal. Nucl. Chem
Atmospheric technetium-99
Environ. Sci. Technol
Soil availability, plant uptake and soil to plant transfer of 99Tc—a review
J. Environ. Radioact
Eh-pH Diagrams for Geochemistry
Root absorption and transport behavior of technetium in soybean
Plant. Physiol
Determination of rhenium and platinum in natural waters and sediments, and iridium in sediments by flow injection isotope dilution inductively coupled plasma mass spectrometry
Anal. Chem
Cited by (19)
Extractability of global fallout Pu from agricultural soils and its potential indication of bioavailability
2022, CatenaCitation Excerpt :These results suggested that Pu present in the water soluble form in the rice paddy soils was bioavailable for rice plants. This finding is similar to the conclusion of Tagami and Uchida (2004) that the radionuclide Tc could be readily taken up in a water soluble form (TcO4-) although it is also non-essential for plant growth. These results was also comparable to those of other studies on heavy metals which observed the total concentration of a heavy metal element (e.g. Cu, Cd, Pb) in the soil was less reliable for representing metal bioavailability for plants compared with the mobile fractions (Menzies et al., 2007; Zhang et al., 2010).
Imaging of I, Re and Tc plant uptake on the single-cell scale using SIMS and rL-SNMS
2022, Journal of Hazardous MaterialsOn the uptake of rhenium by plants: Accumulation and recovery from plant tissue
2021, Journal of Cleaner ProductionCitation Excerpt :Further bench-scale studies have also demonstrated the ability of certain plants to accumulate extraordinary amounts of Re in their aboveground parts (Bozhkov et al., 2012; Novo et al., 2015). The mechanism of Re uptake has not been yet elucidated; still, it is preferably accumulated in the aboveground plant parts (Tagami and Uchida, 2004). Alike other metals, greater soil Re levels can have a detrimental effect on the plant, leading to reduced growth, impaired photosynthetic activity, and increased oxidative stress (Novo et al., 2018).
Charge transfer rhenium complexes analogue to pertechnetate removal
2020, Journal of Environmental Chemical EngineeringCitation Excerpt :Although 99Tc is not found to exhibit significant chemical toxicity, like Re, it shows radiotoxicity due to its beta emissions and accumulates in different plants [16]. Re is also widely used as a 99Tc analogue for 99Tc immobilization and transport studies [17] as the chemical properties of Re resemble those of 99Tc [18]. Re as analogue of Tc is justified by many authors due to similar crystal chemistry, electronic configuration, stereochemistry, and thermodynamic data [19].
Immobilization of perrhenate using synthetic pyrite particles: Effectiveness and remobilization potential
2020, Science of the Total EnvironmentTerrestrial Radioecology in Tropical Systems
2012, Radioactivity in the Environment