47
Technetium [Tc, 43]
47.1 INTRODUCTION
Technetium (Tc) is a silvery-gray radioactive transition metal of group 7 in the
periodic table of elements (PTEs), without any stable isotopes. Only minute traces of
99 Tc, the most common radioisotope, occurs naturally in the Earth’s crust. It is associated mainly with U ores and some Mo ores. Oxidation states of Tc are +4, +6, and
+7, of which the last one is the most often. Its common species are insoluble cation
TcO 2 and soluble anion TcO 4 .
Nearly all Tc is produced synthetically, and only minute amounts are found in the
nature. Its chemical properties are similar to those of Re and Mn, which are of the
same PTE group.
Technetium is the only artificial metal that is used in metal processing, mainly in
alloys with Mo and Nb, to obtain electrical superconductivity. It is very resistant to
the oxidation and may be added to some Fe alloys to inhibit the corrosion. Its isotope
is widely used in the medicine, for X-ray diagnostics, in particular thyroid disorders.
47.2 ENVIRONMENT
The source of Tc is mainly global fallout and is released from various nuclear processes. Paddy soils of Japan contain 99 Tc from 6.1 to 110 mBq/kg, and its uptake by
rice plants is much lower from flooded soils than from nonflooded soils (Zhang et al.
2002). Apparently, it is controlled by ratio of both cationic and anionic Tc species.
Plant uptake of Tc from soils is relatively low, being lowest by tomato and the
highest by spinach. Oxidized Tc species are easily available to plants than species of
a lower oxidation. Due to the microbial oxidation, it becomes more phytoavailable.
Because Tc is slightly mobile in plants, it is concentrated in older plant tissues.
Technetium in the form of TcO
4 follows the behavior of NO
3 in soils. Organic and
N fertilizers inhibit Tc phytoavailability, because they stimulate changes of mobile
TcO
4 to slightly mobile TcO 2 and TcS 2 . In reduced groundwaters, Tc is likely to
occur as almost immobile TcO 2 ·nH 2 O.
The disposal of Tc-enriched wastes is an environmental hazard, because it is
easily included in the biocycle.
47.3 HUMANS
Technetium has no biological role. It does not occur naturally in the biosphere,
and thus normally never presents a risk. All Tc compounds should be regarded as
highly toxic, largely because of its radiological toxicity. It is studied in a few nuclear
research laboratories, where its high radioactivity requires special handling techniques and precautions.
317
Technetium [Tc, 43]
47.1 INTRODUCTION
Technetium (Tc) is a silvery-gray radioactive transition metal of group 7 in the
periodic table of elements (PTEs), without any stable isotopes. Only minute traces of
99 Tc, the most common radioisotope, occurs naturally in the Earth’s crust. It is associated mainly with U ores and some Mo ores. Oxidation states of Tc are +4, +6, and
+7, of which the last one is the most often. Its common species are insoluble cation
TcO 2 and soluble anion TcO 4 .
Nearly all Tc is produced synthetically, and only minute amounts are found in the
nature. Its chemical properties are similar to those of Re and Mn, which are of the
same PTE group.
Technetium is the only artificial metal that is used in metal processing, mainly in
alloys with Mo and Nb, to obtain electrical superconductivity. It is very resistant to
the oxidation and may be added to some Fe alloys to inhibit the corrosion. Its isotope
is widely used in the medicine, for X-ray diagnostics, in particular thyroid disorders.
47.2 ENVIRONMENT
The source of Tc is mainly global fallout and is released from various nuclear processes. Paddy soils of Japan contain 99 Tc from 6.1 to 110 mBq/kg, and its uptake by
rice plants is much lower from flooded soils than from nonflooded soils (Zhang et al.
2002). Apparently, it is controlled by ratio of both cationic and anionic Tc species.
Plant uptake of Tc from soils is relatively low, being lowest by tomato and the
highest by spinach. Oxidized Tc species are easily available to plants than species of
a lower oxidation. Due to the microbial oxidation, it becomes more phytoavailable.
Because Tc is slightly mobile in plants, it is concentrated in older plant tissues.
Technetium in the form of TcO
4 follows the behavior of NO
3 in soils. Organic and
N fertilizers inhibit Tc phytoavailability, because they stimulate changes of mobile
TcO
4 to slightly mobile TcO 2 and TcS 2 . In reduced groundwaters, Tc is likely to
occur as almost immobile TcO 2 ·nH 2 O.
The disposal of Tc-enriched wastes is an environmental hazard, because it is
easily included in the biocycle.
47.3 HUMANS
Technetium has no biological role. It does not occur naturally in the biosphere,
and thus normally never presents a risk. All Tc compounds should be regarded as
highly toxic, largely because of its radiological toxicity. It is studied in a few nuclear
research laboratories, where its high radioactivity requires special handling techniques and precautions.
317