Assessment of spirometric decline from silica dust: threshold values and calculation methods for cumulative exposure

This study investigates the association between crystalline silica dust exposure and lung function decline. Understanding whether exposure-response relationships include threshold values is critical for contributing to workplace health protection. We compared four mechanistically different models to determine which best characterizes this association.

Data from 1,418 workers from the Wismut German Uranium Mining Cohort Study from 1970 to 1991 with 7,116 spirometry measurements were analysed. Cumulative exposure was calculated using a job exposure matrix. Four models based on different pathophysiological mechanisms were compared: (1) constant annual threshold without overload, (2) constant annual threshold with overload, (3) delayed onset (cumulative threshold only), and (4) dynamic threshold decreasing over time.

Models 1, 3 and 4 showed a critical annual exposure value of approximately 0.09-0.10 mg/m³ (the concentration below which no harmful accumulation occurs). Model 2 had convergence problems due to mathematical discontinuity. Model 1 demonstrated the biologically most plausible relationship between threshold exceedance and spirometric decline, with a cumulative threshold of 2 mg/m³. This model predicts clinically significant functional decline within realistic occupational timeframes (e.g., 10 years at 0.3 mg/m³ exposure).

The results confirm that high silica dust exposure leads to an accelerated decline in lung function. Model 1 appears to be the most appropriate, despite limitations such as limited age range and sole focus on spirometry. The results demonstrate an association between cumulative silica dust exposure above approximately 0.09 mg/m³ and accelerated spirometric decline. Model 1 (constant annual threshold) provides the most consistent and biologically plausible results. These threshold estimates have high relevance in occupational health settings aimed at preventing workers exposed to silica dust from lung function decline. Study limitations include the limited follow up and lack of data on individuals reaching the cumulative threshold. The majority of included persons were smokers (84%), which also affected lung function.