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Safeguard OSH Solutions - Thomson Reuters

Safeguard OSH Solutions - Thomson Reuters



Safeguard Magazine

Health matters—The new asbestos?

IAN SHAW fears for the health of Christchurch demolition workers exposed to silica-bearing concrete dust, which he says could be the new asbestos.

Asbestos has long been known to be a significant workplace hazard. Its small sharp fibres – often less that 10 μm – can penetrate deep into the lungs, and by a process that is not fully understood can pierce the lung cells and work their way through to the outer lining of the lungs (pleura).

The pleura are designed to help lubricate the surface of the lungs to prevent damage when the lungs inflate and deflate during the breathing process. Without the pleura the repeated rubbing of the lungs against the inner surface of the chest cavity (thorax) would damage the outer surface of the lungs. The cells of the pleura (mesothelial cells) produce a lubricant and divide frequently to replace the huge numbers that slough off during breathing.

Sharp asbestos fibres can interact with mesothelial cells and alter the way that specific genes are expressed. For example, the gene that helps to control cell division (P53) can be affected in such a way that cells divide uncontrollably. This uncontrolled growth is cancer, and since it affects mesothelial cells it is called mesothelioma.

Mesothelioma is the cancer associated with asbestos. The time between exposure to asbestos and development of mesothelioma can be as short as 12 years. The disease is inevitably fatal. Not everyone who gets exposed to asbestos contracts mesothelioma. The risk of mesothelioma is dependent on the number of asbestos fibres breathed in.

Asbestos also causes other lung diseases that, while not fatal, are seriously debilitating. Asbestosis is the most common non-malignant manifestation of asbestos exposure. In this disease the sharp asbestos fibres irritate lung cells, causing inflammation and the production of fluids which fill some of the air spaces and reduce lung capacity.

It is clear from this explanation of the science behind asbestosis and mesothelioma that it is the small size and sharpness of the asbestos fibres that make them a significant hazard. And that the risk of contracting asbestosis or mesothelioma is dependent on the level of exposure to the hazard. The obvious message is: don’t get exposed to asbestos!

It is becoming increasingly clear that other small, sharp particles can have similar effects to asbestos – the body does not distinguish between the chemical make-up of fibres, it simply responds to the sharp physical insult if the fibre is small enough to get deep into the lungs.

Miners’ lung was a very common affliction suffered by coal miners. Many older (retired) miners in the UK still wheeze and splutter their way through their days due to years of breathing fine silica particles generated from the rocks adjacent to the coal seams they were bashing apart to release the coal. Silica particles can be small and sharp just like asbestos, and so can have the same deleterious effects on the lungs.

Concrete is made from aggregate held together by cement. Aggregate varies in composition according to the intended use of the concrete. In years gone by, asbestos was used as an aggregate which, of course, makes dust from this type of concrete incredibly hazardous to demolition workers.

Aggregates can also be based on siliceous rocks which have sharp crystals of silica in their make-up. It is becoming clearer that exposure to fine dusts from siliceous rocks can result in lung damage similar to that caused by asbestos. Whether they cause mesothelioma is unknown, but based on their physical make-up it is likely they will. Concrete dust might be the new asbestos – you should treat it with respect unless you would like to be a statistic that proves the link to mesothelioma.

As discussed above, the level of exposure to a hazard determines the risk. So, if you work with siliceous concrete, wearing appropriate respiratory protection will minimise exposure and minimise the health risk. The question is what is acceptable exposure? From epidemiological information, it appears that people repeatedly exposed to high levels of concrete dust are (obviously) at greatest risk – this includes workers drilling, carving or smashing up siliceous concrete (eg demolition workers); the drilling, carving and smashing are necessary to break the silica up into sharp and small particles that can penetrate deep into the lungs.

This need for high exposure levels to cause significant harm makes silicosis (and perhaps cancer) an occupational disease. It is unlikely that people walking by a demolition site or having a cup of coffee in a café next to a demolition site will suffer harm. Not even people who do this many times over a few months would be expected to suffer unless they have underlying respiratory disease. However, people who work in the demolition industry, for example, are exposed repeatedly, daily for years and years. This is when problems arise.

Christchurch has presented us with a new exposure scenario to both asbestos and silica dust. The earthquakes of 4 September 2010 and 22 February 2011 caused buildings to collapse and led to massive demolition projects, leading to worker exposure to asbestos and siliceous concrete dust on an unprecedented scale.

I walk around my workplace and the streets of Christchurch and repeatedly see workers drilling and smashing concrete with no respiratory protection. Sadly, these men will likely be the data points for future studies on the respiratory effects of small sharp particles. The evidence we already have should be quite enough to persuade us take concrete dust far more seriously than we do currently.

Ian Shaw is Professor of Toxicology at the University of Canterbury.

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