(Tingming Shi, Hai Zhang, and Ming Zhao) - Editorial, Thorax, July 2025 (Thorax is the BMJ’s journal for Respiratory Physicians)

Summary

In an editorial in the July 2025 edition of Thorax, the question is raised as to whether international permissible exposure limits, PELs (in UK the Workplace Exposure Limit - WEL) for respirable crystalline silica (RCS) sufficiently protect workers from silicosis. It is RCS, the fine silica dust produced by force (cutting/ drilling/ grinding etc of silica containing materials), which can enter the respiratory system and so lead to silicosis.

The editorial refers to a study (also within July’s Thorax) comprising a large historical cohort of Chinese silicon miners and pottery workers followed between 1960 and 2003 to test risks of exposure levels at or below these internationally used limits.

The analysis reports a clear dose response at ‘low’ levels of silica: after 40 years of exposure, cumulative risks of silicosis were 7.25% at 0.05 mg/m³, 8.34% at 0.10 mg/m³ and 13.04% at 0.35 mg/m³. Set against an increase in case numbers worldwide, the paper questions whether current PELs are adequate across all industries and recommends reducing limits, alongside strengthened controls and, of course, protective equipment.

Detail

The paper notes that despite decades of prevention efforts, incidence remains substantial, with growth concentrated in developing and rapidly industrialising regions where dust control is inconsistent and surveillance systems are often weak.

A key contribution is the analysis of over 30,000 workers with long-term follow-up (retrospectively and prospectively). The authors define ‘low-level’ exposure by reference to established PELs from the USA (0.05 mg/m³), the UK and France (0.10 mg/m³) and China (up to 0.35 mg/m³). Interestingly, the Chinese PEL appears to vary (from 0.07 mg/m³ up to 0.35 mg/m³), depending on the percentage of RCS in dust produced.

The findings are that there is a graded increase in silicosis risk even where lifetime mean exposure remained at or below these PELs. This strongly suggests that, even when complying with current limits, this does not guarantee safety over a working lifetime.

The paper also shows differences across industries. It queries whether even 0.05 mg/m³ (while more protective) is sufficient in all settings, especially with high-dust processes and sectors with poor engineering controls. The authors highlight increasing risks in ‘non-traditional’ or re-emergent sectors such as artificial stone processing, denim finishing, container welding, and jewellery polishing - areas where outbreaks have been documented and where small operators, dry-cutting practices, and inadequate respiratory protection are seemingly common.

A recent UK case series on artificial stone (see my earlier articles) confirms faster-onset, more aggressive silicosis among young workers in small enterprises, often with minimal controls and surveillance, highlighting the concern that current limits and traditional surveillance intervals may miss early disease in these situations.

Finally, the authors discuss behavioural and other risks. They observe higher risks among smokers across all subgroups, emphasising the need for further health information/ training. 

Conclusion:

Even ‘low-level’ lifetime exposures, defined at or below current PELs, carry a material risk of silicosis. The estimated 40-year risks at 0.05, 0.10 and 0.35 mg/m³ were 7.25%, 8.34% and 13.04%, respectively. Accordingly, compliance does not result in protection across a working lifetime.

The authors recommend lowering PELs - specifically from 0.10 mg/m³ (the UK WEL) to 0.05 mg/m³ as well as strengthening controls.