By Dr. Timothy E Payne
Chair,
WCI Committee on Environmental Applications
Australian Nuclear Science and Technology Organization
Radionuclides and environmental research
The relationship between radionuclides and environmental research has several divergent aspects, in which radioactivity can be cast in the role of either an ally or an opponent to those interested in the preservation or improvement of the world’s environment.
On the one hand, radionuclides can be perceived as representing an
environmental problem which requires a solution, when they are present in the
environment as a result of weapons testing or as a consequence of nuclear
accidents. Such perceptions can become prominent in community discussions
following events such as the Fukushima or Chernobyl accidents, and several
decades ago there was animated debate about the consequences of, and the
justification for, nuclear weapons tests.
Such public discussions can have considerable ramifications, such as the effective campaign against atmospheric testing of nuclear weapons in the 1960s and 1970s, or more recently, the winding-back of nuclear power in some countries.
However, an aspect of nuclear science which is perhaps
much less well-known relates to the many useful applications of radionuclides,
and nuclear techniques, in the environmental sciences. Here, nuclear science is
instrumental in providing solutions (rather than perceived as creating
problems) and nuclear science contributes to a large range of beneficial
environmental research outcomes, addressing problems as diverse as climate
change, ocean circulation, contaminant tracing and groundwater research.
An intriguing aspect of radionuclide science is that in some cases, radionuclides can be part of both a problem and also contribute to finding a solution. This is often the case when, for example, isotopic techniques are applied to solve a problem related to the nuclear industry. An example of this type of problem is the use of isotope techniques to assist in characterising potential sites for nuclear waste repositories.
Fields of environmental research involving radioisotopes
As implied above, natural and anthropogenic (man-made)
radioisotopes have been applied in a wide range of environmental studies. These
include:
·
Atmospheric composition and circulation – the measured
distribution of tracer isotopes (such as naturally-occurring Radon-222) can
provide information on the movement of air masses, help to characterise
near-surface mixing for urban and regional pollution studies, and refine
baseline estimates of global greenhouse gas concentrations.
· Erosion – the rate of soil erosion can be studied, for example by measuring the re-distribution of a fallout isotope (such as cesium-137) released in weapons tests. Some natural isotopes can be applied in similar studies.
·
Sedimentation – a peak corresponding to a deposition
from natural radionuclides or atmospheric fallout becomes gradually more deeply
buried in the sediment layers, allowing an estimation of sedimentation rates.
·
Hydrology (water-cycle) – there are numerous isotope
applications in the hydrological sciences. For example, the age of groundwater
can be determined, or the movement of water in catchments can be studied. Such
data can be very useful in assessing the sustainable patterns of water usage –
for example the rates at which groundwater can be removed from an aquifer
without depleting the resource. A wide range of isotopes, both natural and
artificial can be used in such studies.
·
Oceanography – many isotopic techniques are used in
oceanography to study circulation of water masses in the world’s oceans,
sedimentation rates, elemental cycling, and numerous related topics.
·
Pollution – nuclear techniques can be used to analyse
particles deposited from the atmosphere, which may be derived from natural
processes (e.g. dust storms, salt-spray from the oceans) or from anthropogenic
sources (e.g. combustion from power stations, or automobiles). Radionuclides
can also be used in laboratory tests designed to simulate the behaviour of
contaminants in the environment.
The analysis of environmental samples containing artificial or naturally-occurring isotopes may be based on radiation emissions or non-nuclear techniques. The table below shows some selected examples where artificial radioisotopes have been used in environmental science. The studies include both laboratory based and field studies. The list of case-studies includes examples of both deliberate and incidental release of radionuclides, as well as laboratory studies.
In summary, there is a considerable variety of roles for isotopes in environmental research. The isotopes involved may be artificial or natural, the scale can range from sub-microscopic to global, and, the problems addressed may be nuclear or non-nuclear. The work with radioisotopes can be undertaken in the laboratory or in the field. Where artificial isotopes are used in tracing environmental processes, they may be present in the environment either as the result of controlled or inadvertent releases. Studies of environmental processes continue to provide numerous opportunities for the application of isotopic techniques and these techniques are a key component of the environmental scientist’s “tool-kit” for addressing environmental problems.
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