Biological toxicity relates to the shape of asbestos fibres. The mesothelial cell appears to be a predominant target of the asbestos fibre – consequently leading to the disease ‘mesothelioma’. Understanding how the shape, chemical composition, and surface structure interact to result in a harmful biological agent is paramount to the study of prospective harmful fibrous materials in the future.

Amphibole needle-like fibres

The long thin shape of an asbestos fibre may enhance its entry deep into the lung. Following inhalation, fibres of several micrometres in length can enter the respiratory airways, whereas other particles larger than 5 micrometres could not penetrate. Once in the lung – the long fibres may not be cleared by the bodies natural defence mechanism such as ‘macrophage clearance’ macrophages generally mop up foreign bodies, but scientists have discovered that certain stubborn asbestos fibres (such as needle-like shape) cannot be cleared by macrophages. These fibres may more easily migrate along tissue planes, lymphatic channels and make their way into the pleural space.

 Animal studies show certain asbestos shapes induce mesothelioma

Asbestos shape has been considered to be a primary characteristic determining asbestos toxicity, i.e. ‘Stanton et al’ 1977, recognised size and shape as a major factor in inducing mesothelioma in animal studies. For instance – other materials with the same shape but different chemical composition share the ability to produce mesothelioma. Also – studies of asbestos fibres with a long thin shape were shown to be able to induce chromosomal abnormalities.

 Studies of human epidemiological trials and lung mineral toxicity conclude that ‘amphibole’ asbestos fibres (crocidolite and amosite) are more predominantly associated with mesothelioma than chrysotile fibres. Amphibole fibres contain more iron; possess a higher aspect ratio, and their needle-like shape is more brittle.

 Conclusion

Asbestos shapes have chemical differences. Physical properties are important in determining the toxicity of the fibre, predominantly – the fibres shape, surface reactivity and chemical composition.

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What is asbestos?

Asbestos is a natural rock mineral, mined or quarried and used commercially since the 18th century. It was discovered for its excellent fire retardant and insulation properties. It consists of strong pliable fibres that can be separated into thread like strands and spun or woven to produce several types of bonded material for many uses, predominantly in the building and construction industries between 1900’s – mid 1970’s.

 How  mesothelioma develops

As a rule most fibres and irritants that are inhaled are cleared through the natural body’s defence mechanism of coughing which forces them back up to the throat in a layer of mucus, the mucus is then either spat out, or swallowed, and makes it way out of the body naturally.

The theory is though – is that some inhaled asbestos fibres (particularly smaller strands) are not cleared from the lungs and have the ability to translocate to the lungs into other tissues such the alveolar sacs the tiny pockets where the fibres may remain indefinitely. Asbestos fibres that enter the alveoli can undergo a series of fates. I.e. some of the fibres may penetrate the alveolar wall and enter into the interstitial fluid thus posing of risk of them being cleared by the natural process of the lymphatic system and deposited in the perihilar lymph nodes. Other fibres particularly amphiboles (blue and brown asbestos fibres) may penetrate the lung parenchyma and enter the pleural or peritoneal space.

Amphibole fibres are considered to be more of a health hazard as they are less degradable than other asbestos fibres such as chrysotile fibres (white asbestos) and can stay in the lungs for much longer. Studies have concluded that smaller quantities of chrysotile fibres have been found in lung tissue than amphibole fibres and amphibole fibres cannot easily be degraded by macrophages (white blood cells that engulf and destroy foreign material). However – fibre size is believed to play a crucial role in determining the risk of a particular asbestos-related disease, and the health safety issues surrounding white asbestos still poses as a threat as medical evidence proves its significance in the development of mesothelioma.

Biopsy below shows a strand of asbestos fibre in a human lung.

Asbestos particles are capable of stimulating chronic inflammatory responses in the pleura, inducing an array of cellular responses, i.e. interfering with mesothelial cells, damaging DNA that controls cell division, thus promoting malignant cell division – resulting in asbestos-induced tumours – mesothelioma.

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