Lowering dust limits in the workplace could significantly reduce cases of silicosis

Scientists have found that a worker’s lifetime exposure to ‘tolerable’ levels of silica dust carries a significant risk of developing silicosis.

New research led by Imperial College London has found that exposure to silica dust in the workplace is linked to an increased risk of the acute lung disease silicosis and recommends that current occupational exposure limits should be halved.

Silicosis is a progressive, incurable lung disease caused by inhaling silica dust. Millions of people around the world work in jobs where they are exposed to silica dust, including miners, potters and those involved in the production and installation of quartz and granite kitchen countertops. The legal occupational limit in Great Britain is 0.1 mg/m2³ but in some other countries a lower limit applies.

An all-party parliamentary group in the UK government has called for evidence on whether current occupational exposure levels are safe.

The researchers from Imperial’s National Heart and Lung Institute looked at all available evidence related to silicosis research, including studies based on X-rays, post-mortem examination results and death certificates. They wanted to determine the cumulative risk of silicosis and identify the exposure level at which the risk would be reduced.

In the study, published in the journal Thorax today titled “Association between cumulative silica exposure and silicosis: a systematic review and dose-response meta-analysis”, the team reviewed eight studies with 8792 cases of silicosis among 65,977 participants.

The majority (six) of the studies involved miners. For this group, researchers found that if the average exposure over a 40-year working life were halved, from 0.1 mg/m³ up to the current US allowable limit of 0.05 mg/m2³there would likely be a significant reduction of 298-344 fewer cases per 1000 miners, which equates to a 77% reduction.

Although only two studies involved non-miner workers, the researchers believe the same reduction would result in 9 to 33 fewer cases per 1,000 of these workers.

Study author Dr. Patrick Howlett, MRC Clinical Research Fellow at Imperial College London, said: “This research supports halving the legal limits over an 8-hour work shift. Although lowering exposure limits is challenging in different environments, this has been shown to be achievable. We believe it is important to reduce the number of cases of silicosis, given the severity of the disease.”

The authors caution that more research is needed among non-miners to understand the differences between occupations. In particular, there are no studies linking dust exposure to the risk of silicosis in artificial stone workers, who suffer from a particularly severe form of silicosis.