Speaker
Mr
Jefferson Vianna Bandeira
(National Nuclear Energy Commission (CNEN-CDTN), Brazil)
Description
Technetium $^{99m}$Tc is, nowadays, the most
applied radioisotope in nuclear medicine, whose use began in the
mid-1960s. Features such as emission of $\gamma$-radiation of low energy
($140$ keV) with very good imaging properties, half-life
$\tau_{1/2}=6.02$ h, and production via relatively long-lived
generators, facilitating their supply and use in locations far
from manufacturing sites, were instrumental for the widespread use of
the radionuclide.
However, in the aquatic environment, heavy metals and many organic
compounds are usually associated with the fine sediment phase (silt,
clay, or mud). The fate of these contaminants will be associated with
the dynamic behaviour of suspended or bottom sediments in polluted
streams. The study of suspended sediment behaviour is central to many
environmental studies. Of special interest is the study of individual
discharges of contaminants associated with suspended sediments, the
short-term dispersion of contaminated material dredged from harbours
and reservoirs when dumped into water bodies and the behaviour of
natural sediment in suspension in bays, estuaries or reservoirs.
Tracking for few hours of the contaminated suspended sediments
introduced into streams or in the coastal area by individual
discharges could allow the quantitative in situ determination of the
advection, dispersion, dilution and sedimentation rates, parameters
important for the calibration and validation of hydrodynamic models
that comprise both the solid and liquid phases.
Radioactive tracers, in appropriate chemical form, are used to
label fine sediment by chemical sorption, and some (such as
$^{198}$Au and $^{51}$Cr) have been employed to study the
dynamics of fine sediment in suspension. But these tracers have to be
produced in nuclear reactor each time they are used and require heavy
shielding due to the dense flux of high-energy $\gamma$-radiation they
emit, which hampers their use in remote areas.
Given the favourable characteristics of $^{99m}$Tc, the
feasibility of its use for labelling mud, through the chemical
reduction of the TcO$_4^-$ eluted from Mo/Tc generators, was studied
in laboratory with regard to the following aspects: 1) labelling yield
as function of different factors (type and amount of reductant; effect
of pH; sediment concentration; contact time; labelling stability); and
2) hydrodynamic behaviour of labelled and non-labelled sediment,
through sedimentation tests. The laboratory tests were successful and
this new use of the $^{99m}$Tc allowed already interesting
results obtained in various applications: Montevideo Bay (Uruguay),
Pampulha Hydrographic Basin (Brazil), Orinoco River (Venezuela),
environmental impact due to the fine sediment originated from bottom
discharge of small hydroelectric power plant (Brazil), etc.
The work performed in some field applications used second week generators obtained, at no cost, from Nuclear Medicine laboratories. The reason is that the $^{99m}$Tc detector for environmental applications is placed into the water, in $4\pi$ geometry and for medical applications it is situated externally to the patient. So, the necessary activity concentrations for environmental use (Bq/m$\ell$ in water) are much lower ($10^{-7}$) than in nuclear medicine utilization (Bq/m$\ell$ in blood).
| Country/Organization invited to participate | Brazil |
|---|
Primary author
Mr
Jefferson Vianna Bandeira
(National Nuclear Energy Commission (CNEN-CDTN), Brazil)
Co-author
Mr
Lecio Hannas Salim
(National Nuclear Energy Commission (CNEN-CDTN), Brazil)
