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Supervising Scientist Division

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Atmospheric transport of dust

Background

Airborne dust (also called 'aeolian dust') can be created by a variety of processes including the effect of wind on the soil surface, and mining and milling practices such as explosions and earthmoving. Such dust particles are mostly greater than about 0.2 µm (micrometres) in diameter. Once airborne, these particles can be dispersed in the atmosphere and potentially inhaled by people. Dust from uranium mining operations has elevated levels of uranium-series radionuclides and so its inhalation and deposition in the lungs can lead to a radiation dose to the person.

The differences between stable lead (²⁰⁴Pb, ²⁰⁶Pb, ²⁰⁷Pb and ²⁰⁸Pb) isotopic composition of uranium rich minerals compared to natural dust are large. ²⁰⁶Pb and ²⁰⁷Pb are end-members of the uranium decay chain and are thus more abundant than ²⁰⁸Pb in uranium rich minerals. Consequently, the measurement of lead isotope ratios allows discriminating natural dust from dust originating from the mining and milling of uranium ores.

Once airborne, dust can be removed from the atmosphere either by wet deposition (e.g. by rain) or dry deposition (arising from settling due to the weight of the particle or else deposition onto surfaces by impaction). These deposition processes are dependent on the size of the particles in a complex fashion; in general, for particles greater than 0.2 µm diameter, larger particles will deposit at a faster rate than smaller particles.

Current research projects

The use of lead isotope ratios to determine the dose received from the inhalation of mine-origin dust particles

A new method is being investigated to determine the mine-origin contribution to the radiation dose received by the public via the inhalation of radioactivity trapped in or on dust. The aim of this project is to develop an innovative approach for mine-site dust monitoring, that allows unambiguous discrimination between mine origin and natural dust using lead isotope ratios. Combined with the measurement of airborne alpha activity this will enable the mine origin doses via the dust inhalation pathway to be estimated. Project leader: Dr Andreas Bollhöfer.

Some relevant publications

Bollhöfer A, Honeybun R, Rosman KJR & Martin P 2006. The lead isotopic composition of dust in the vicinity of a uranium mine in northern Australia and its use for radiation dose assessment. Science of the Total Environment 366, 579-589.

Martin P 2003.  Uranium and thorium series radionuclides in rainwater over several tropical rainstorms. Journal of Environmental Radioactivity 65, 1–18.

Vanderzalm JL, Hooper MA, Hooper BM, Martin P, Ryan B & Nurhayati MS 2000. Particulate air quality in regional northwest Australia and southeast Asia. Clean Air 34, 29-34.

Pettersson HBL & Koperski J 1991. Investigation of aerial dispersion of radioactive dust from an open-pit uranium mine by passive vinyl collectors. Health Physics 60, 681-690.