Environmental Sciences
Environmental Issues
Mineral weathering resulting in the release of acid mine drainage (AMD) is now of considerable
environmental concern. It is estimated that in Australia remediation costs will be in the order of
$900 million over the next 15 years. The dual XRF-XRD (X-ray fluorescence-X-ray difraction) mapping
facility of the Microdiffraction and Fluorescence Probe will enable the identification of
reaction and reprecipitation layering on mineral surfaces as a function of weathering. Understanding
the evolution of these layers in terms of both their elemental composition and crystalline phase
is important to the prediction and control of AMD. This combination of analyses will enable significant
contributions to be made to the understanding of the release of toxic elements, which often accompanies
AMD, and their bioavailability.
Another example is mine tailings containing arsenic. Arsenic (As) can exist structurally
bound in compounds such as FeAsO4 or adsorbed onto the surface of minerals such
as goethite (FeOOH). The manner in which the As is incorporated has a strong impact on its
'availability' to the environment and hence on the steps that must be taken in the remediation of contaminated
sites. The synergistic use of the XRF-XRD mapping facility together with X-ray absorption spectroscopy
(EXAFS) is important in understanding the nature of contaminant metals at the molecular
level, so that appropropriate action can be taken at the macro level.
Toxicology
Of all of the carcinogens, chromium (Cr) has the highest occupational exposure
to workers and is of growing environmental concern. While Cr(VI) is the carcinogenic
form of Cr, it does not interact with DNA in the absence of cellular reductants.
X-ray absorption spectroscopy is being used
to characterize for the first time the structures of a range of reactive Cr(VI),
Cr(V) and Cr(IV) complexes with biological reductants. many Cr(III) complexes,
which are the ultimate products of the reductants, have also been characterized.
Using microfocus synchrotron radiation
induced x-ray emission (Micro-SRIXE), researchers at the University of Sydney
and ANSTO have been able to follow the uptake of Cr(III) and Cr(VI) chemical
species into individual cells with sub-micron resolution.