Crystalline silica exposure, radiological silicosis, and lung cancer mortality in diatomaceous earth industry workers.

Abstract

BACKGROUND:

The role of silicosis as either a necessary or incidental condition in silica associated lung cancer remains unresolved. To address this issue a cohort analysis of dose-response relations for crystalline silica and lung cancer mortality was conducted among diatomaceous earth workers classified according to the presence or absence of radiological silicosis.

METHODS:

Radiological silicosis was determined by median 1980 International Labour Organisation system readings of a panel of three "B" readers for 1809 of 2342 white male workers in a diatomaceous earth facility in California. Standardised mortality ratios (SMR) for lung cancer, based on United States rates for 1942-94, were calculated separately for workers with and without radiological silicosis according to cumulative exposures to respirable crystalline silica (milligrams per cubic meter x years; mg/m3-years) lagged 15 years.

RESULTS:

Eighty one cases of silicosis were identified, including 77 with small opacities of > or = 1/0 and four with large opacities. A slightly larger excess of lung cancer was found among the subjects with silicosis (SMR 1.57, 95% confidence interval (CI) 0.43 to 4.03) than in workers without silicosis (SMR 1.19, 95% CI 0.87 to 1.57). An association between silica exposure and lung cancer risk was detected among those without silicosis; a statistically significant (p = 0.02) increasing trend of lung cancer risk was seen with cumulative exposure, with SMR reaching 2.40 (95% CI 1.24 to 4.20) at the highest exposure level (> or = 5.0 mg/m3-years). A similar statistically significant (p = 0.02) dose-response gradient was observed among non-silicotic subjects when follow up was truncated at 15 years after the final negative radiograph (SMR 2.96, 95% CI 1.19 to 6.08 at > or = 5.0 mg/m3-years), indicating that the association among non-silicotic subjects was unlikely to be accounted for by undetected radiological silicosis.

CONCLUSIONS:

The dose-response relation observed between cumulative exposure to respirable crystalline silica and lung cancer mortality among workers without radiological silicosis suggests that silicosis is not a necessary co-condition for silica related lung carcinogenesis. However, the relatively small number of silicosis cases in the cohort and the absence of radiographic data after employment limit interpretations.

• Authors: H Checkoway, J M Hughes, H Weill, N S Seixas, P A Demers
• Journal: Thorax (Thorax) Vol. 54 Issue 1 Pg. 56-9 (Jan 1999) ISSN: 0040-6376 [Print] England
• PMID: 10343633 (Publication Type: Journal Article, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Dust
• Silicon

Topics

• Adult
• Aged
• California (epidemiology)
• Cohort Studies
• Dust (adverse effects)
• Humans
• Lung Neoplasms (mortality)
• Male
• Middle Aged
• Occupational Exposure (adverse effects)
• Silicon (adverse effects)
• Silicosis (mortality)