Research interests index

Above: Scanning electron micrograph of glass fibres recovered from the lung.

These fibres were manufactured by Owens Corning Fiberglas with a uniform diameter of 2 um. The fibres were used to test the in vivo lung durability of glass fibres. Durabilty in the lung is an important aspect of the potential hazard from accidental exposure, the others being dose and fibre dimensions.

Left: Histogram of the fibres length and diameter distributions

These were obtained by phase contrast optical microscopy using the Magiscan image analyser.

This work investigates the potential hazard from the inhalation of man made vitreous fibres (MMVF), such as glassfibre, Rockwool and ceramic fibres. Given the proven hazard of asbestos fibre exposure there is concern over the safety of these materials.

Right: An autoradiograph of an entire lung lobe

The lung contained inhaled radioactive asbestos fibres. Before inhalation, constituent elements within the asbestos had been neutron activated inside a nuclear reactor. This radioactivity could then be detected by photographic autoradiograph techniques to show the location of the asbestos fibre within the lung section (dark areas indicate high asbestos burdens). This is a specialised biological radiotracer technique that can measure asbestos and MMVF fibre burdens in vivo.

Once inside the body radioactive particles can irradiate cells within body tissues. Such tissue irradiation can cause cancer by damaging stem cells in the somatic tissues or can cause inheritable genetic damage to offspring by damaging the immortal germ cell line within the testes and ovaries. After some time post-exposure the radioactive material may be expelled from the body via physical lung clearance mechanisms or the urine/faeces. However it can also relocate to other locations within the body by physical transport (e.g. in motile macrohage cells) or by particle dissolution. It is therefore necessary to undertake long term studies to get a clear picture of total lifetime dose resulting from exposure.

This type of work investigates the dosimetric implications of the inhalation or ingestion of actinide materials such as plutonium and uranium dioxide. Owing to their largescale use in the nuclear and defence industries these materials are now a serious hazard to workers and the general public. Plutonium-238 is one of the most toxic substances known to man, and only certain nerve agents are more toxic per unit mass.These radioactive substances emit alpha particles, which, although having a short range, are extremely hazardous if the material is taken into the body.

Left: K5 liquid emulsion autoradiograph of plutonium dioxide particles in lung tissue

This section contains inhaled insoluble alpha-emitting plutonium-239 dioxide particles. The alpha particles leave black 'tracks' forming 'stars' within K5 photographic emulsion. Again the number of 'tracks' relates to the mass of plutonium in the lung tissue.

The number of 'tracks' counted in different tissue regions is directly related the mass, and hence radioactivety, of the actinide particles located there. The volume of tissue can be calculated from tissue section thickness and 2D surface area. This information can be used to estimate the dose to different tissue regions at any given time post exposure, i.e. from the radioactivity per unit mass of tissue.

Above: High magnification of CR-39 plastic autoradiograph used to locate uranium dioxide particles in the lung

The black 'stars' are made up of neutron-induced uranium-235 fission fragment 'tracks' from inhaled enriched uranium particles which are etched into the CR-39 plastic along with a shadow image of the lung tissue. The highly insoluble uranium dioxide particles are mainly within motile alveolar macrophage cells that scavange within the alveolar (AL) lung tissue, in this case congregating to form a large cluster at the lung periphery (pleura: PL).

Below: CR-39 plastic autoradiograph used to locate uranium dioxide particles deposited within lung tissue

The uranium dioxide particles are denoted as a series of uranium-235 neutron-induced fission fragment 'tracks' (black stars) eminating from the particle. The number of 'tracks' is proportional to the mass of the particle. Below the CR-39 autoradiograph is a standard serial H&E stained section of the same location showing the detailed tissue structure.

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The detection and identification of airborne particles of biological origin that have implications for health and air pollution.

Chapter title: Modern microscopic methods of bioaerosol analysis