Silicosis – why it’s back and how to find it

Dr Stephen Melsom, Radiologist

Silicosis was a disease of the distant past. Some of us remember stories about underground miners in the mid-20th century, working in terrible conditions in tunnels filled with the dust created from their old-fashioned pneumatic drills with only a cloth to filter the air. These mine workers would end up terribly disabled, slowly dying as their lungs were destroyed by chronic silicosis.

We felt reassured that our technology had fixed this terrible problem. Modern mining drills used water to prevent dust escaping into the air, and modern mine ventilation and protective equipment kept their air clean. Silicosis disappeared.

Some clinicians kept yellowed x-rays of silicosis patients to show us what they used to see. Occasionally we would see a survivor; a long-retired miner bearing scars and nodules in his upper lungs telling the story of how terrible it used to be to work as a miner.

Then silicosis came back. 

Initially in the eastern states, the first of these new cases were diagnosed in 2015. This time many were not miners; they were stonemasons involved in cutting, grinding, and polishing engineered stone to make kitchen benchtops. Many had been previously monitored with chest x-rays, which had been normal. Now they had silicosis, some terminal. Australia’s first death attributed to engineered stone was a 36-year-old Gold Coast stonemason in 2019. 

Normal CT chest compared to silicosis CT in WA stonemason, aged 34

How did this happen?

The blame is often pointed at artificial stone benchtops, but this is not the only cause.

Various forms of artificial stone have been produced and cut and grinded by stone masons since the 1700s. The white lion at Westminster Bridge in London was sculpted from the first commercially available artificial stone almost 200 years ago (although originally fabricated as a gate emblem for the Lion Brewery down the road, rather than as a symbol of British power).

The more modern ‘engineered stone’ now used in benchtops and bathrooms is generally made from quartz and marble-based materials in resin mixtures. These became commercially available in the 1980s and were first manufactured in Israel. Initially, in Australia, benchtops made from these materials were relatively expensive and exclusive, with the materials often being privately imported from the overseas manufacturers at a greater cost than some natural stone at the time.

In the early 21st century, international manufacturers recognised growing demand for their products in Australia and set up local subsidiaries, increasing availability and reducing cost. Quickly, the beautiful artificial stone benchtops became almost the default standard in Australian homes, with Laminex relegated to business lunchrooms.

Today’s silicosis cannot be solely attributed to more stonemasons making more benchtops. Much of the modern artificial stone material contains a lot more silica (up to 95%) than is found in natural stone (5-50%). Many of these businesses were providing inadequate controls to reduce the fine dust released when the stone is cut or machined. Consequently, some benchtop workers were inhaling large amounts of silica into their lungs. 

Why did it take so long to recognise the problem? 

 Damage from silicosis can be slow and progressive, taking years for symptoms to occur. Additionally, many workers were being checked with chest -x-rays, which failed to identify abnormalities. Some, investigated for symptoms, had been misdiagnosed with other lung diseases which can appear similar to silicosis (e.g., sarcoidosis, respiratory bronchiolitis, old tuberculosis changes). In some cases, the patient’s exposure to silica dust was not considered, or even mentioned.

The doctors at WorkSafe Western Australia saw what was happening in the east and realised our local workers were also at risk. The WorkSafe team organised funding for a clinical trial resulting in 90 workers (mean age = 40, dust exposure over five years with previous normal screening x-rays) who agreed to have a low-dose chest CT. Eight were diagnosed with silicosis. Early changes of lung damage, potentially due to silica inhalation, was found in 44.

In 2021, WA became the first state (and possibly worldwide) to introduce mandatory screening with very low-dose chest CT for workers exposed to silica. Employers of engineered-stone workers with significant dust exposure are now required to provide two-yearly very low-dose CT scan surveillance, and a further scan within two years of leaving the industry. 

It is important to remember that not just benchtop workers are at risk of occupational silica exposure. Natural stone workers, demolition workers, construction, abrasive blasting, quarrying and other industries can also be exposed to silica dust, and if at risk require surveillance CT scans every five years.

As this surveillance program involves scans on potentially young and asymptomatic workers, WorkSafe WA has specified that these must be performed at very low doses of radiation. A conventional chest CT scan can potentially require up to 8 millisieverts (mSv) of radiation. These very low dose scans use less than 1 mSv of radiation (for reference, the background radiation we receive from living in Perth each year is 2-5 mSv). 

Such a low radiation dose was considered acceptable for screening asymptomatic workers. These very low dose CT scans require specialised CT equipment and specific imaging protocols and must be reported by experienced specialist chest radiologists.

In June 2021, the final report from the National Dust Disease Taskforce (NDDT) found that up to 600,000 Australians are potentially being exposed to silica dust across a broad range of industries each year with evidence of nearly one in four stonemasons being diagnosed with silica-related lung disease. The report includes recommendations for “better support [for] medical, health and other related professionals to improve the diagnosis and management of workers affected by silicosis.” 

It is important to remember that many workers previously exposed to dust have already left their industries and will not be covered by the new legislation. It then becomes important to identify those at risk and have a low threshold for CT investigation, particularly if their dust exposure was significant, or if they have respiratory symptoms.

Key messages
  • Previously dust exposed workers may have left their industries and may not be covered by new mandatory employee screening programs.
  • Consider occupational dust exposure in patients presenting with respiratory symptoms and indicate the history on clinical and imaging referrals.
  • Chest x-ray is inadequate for assessment. High resolution CT imaging is required as a very low radiation dose study for screening workers.

Author competing interests – nil