Why silica dust could become the 'new asbestos'

New limits to a person's daily exposure to silica dust in the construction, mining, dentistry and other industries could save about 13,000 lives worldwide.

That's what researchers in the UK recommend, having found that a worker's lifetime exposure to current, "acceptable" limits can result in serious risk of developing silicosis, a potentially fatal lung disease.

They warn that silicosis could become as big a health problem as exposure to asbestos.

"Our research supports the reduction of exposure to silica dust from 0.1 mg/m3 to 0.05 mg/m3 over a working day," said study author Patrick Howlett from London's Imperial College.

The study was published in the British Medical Journal title Thorax on August 8, 2024. It highlights a need for more data on silicosis risks because the total burden of the disease is unclear, especially in developing countries where data about silicosis is scarce.

What exactly is silicosis?

Silicosis is a respiratory disease which causes a hardening of the lungs. It is caused by silica dust or silica crystals, which are found in soil, sand, concrete, mortar, granite and artificial stone.

It is common in construction, mining, oil and gas extraction, kitchen engineering, dentistry, pottery and sculpting.

People working in these industries are often exposed to silica every day, and are at higher risk of developing silicosis as a result. The illness has, for instance, wreaked havoc in small mining communities in India.

Silicosis is a progressive disease and has no cure.

Why are workers inhaling silica?

When the materials are cut or drilled, crystalline silica is released into the air as a very fine dust. Workers breathe it in as they work, especially where industrial health and saftey standards are poor.

It can take a long time for silicosis to develop — typically 10 to 20 years of occupational exposure to silica dust.

"It's estimated that millions [of people] worldwide have silicosis, but data is very scarce. In the UK and Europe, we see hundreds of cases per year," Howlett told DW in an interview.

Silicosis can lead to other serious diseases, including lung cancer, but scientists aren't sure exactly how this happens. Some speculate that the silica dust forms deposits in the lungs and that those deposits cause persistent inflammation.

Call for silica dust exposure levels to be reduced

This new study, or meta-analysis, assessed eight existing studies that looked at the cumulative risk of silicosis.

The studies involved 8,792 cases of silicosis among 65,977 participants, and included evidence from x-ray analysis of lungs, postmortem examination results, and death certificates.

"We calculated the accumulated risk of silicosis over 40 years of work with exposure to silica dust. Most studies involved miners, and only two studies had non-miners," said Howlet.

The researchers found that if average exposure over a 40-year working lifetime in mining was halved, from 0.1 mg/m3 to 0.05 mg/m3, there would be a reduction of silicosis cases by 77%.

"It would also lower risk among non-miners, but the caveat was that [there were] only two studies included non-miners, so the data was less clear," said Howlett.

Reducing silica dust exposure 'is achievable'

The UK's occupational limit for silica dust exposure is 0.1 mg/m3. That is in line with most European countries , including France, Austria, and Switzerland. Other countries, such as China, have much higher limits of around 1 mg/m3.

Lowering silica dust exposure limits to 0.05 mg/m3 would be in-line with US standards.

Howlett said it was an achievable goal to reduce silica dust exposure in the workplace. He cited experience from the US and Australia, where such health and safey meaures had proved effective.

Australia has banned the use of engineered stone due to its propensity to release high levels of silica dust when cut or drilled.

"There are established methods to follow, including using water suppression methods of foams and mists to precipitate dust out of air effectively, better ventilation, and personal protective equipment," said Howlett.

But he said the issue of silicosis was likely to be much worse in developing countries, where there are few or no safety measures for silica dust.

"Miners in developing countries are exposed to a lifetime's worth of dust in a year's work," he said.

Edited by: Zulfikar Abbany

Sources:

Relationship between cumulative silica exposure and silicosis: a systematic review and dose response meta-analysis. Published by Howlett et al. in the journal BMJ Thorax (August 2024) https://thorax.bmj.com/content/early/2024/07/04/thorax-2024-221447

Global and national burden and trends of mortality and disability-adjusted life years for silicosis, from 1990 to 2019: results from the Global Burden of Disease study 2019. Published by Chen S, Liu M, Xie F. in BMC Pulmonary Medicine (June 2022) https://bmcpulmmed.biomedcentral.com/articles/10.1186/s12890-022-02040-9