Correlating exposure to Respirable Crystalline Silica (RCS) with loss of lung function : treatment of data and statistical analysis

In a study looking at potential impact to respiratory health of quarry workers exposed to airborne respirable crystalline silica (RCS) in Queensland, Australia, respirable dust exposure sampling was undertaken using the method specified in AS 2985-2009. Analysis of the collected samples for alpha quartz was carried out using infrared spectroscopy. Lung function tests for the exposed workers at each quarry were conducted using an Easyone® spirometer. The aim of this study was to determine whether increased RCS exposure is associated with a reduction in lung function. Personal RCS exposures were pooled into similar exposure groups (SEGs), minimum variance unbiased estimates (MVUE), were plotted against the forced expiratory volumes in one second (FEV1) % of predicted for corresponding SEGs. Non-linear correlations were observed including natural log and polynomial function. Estimated (full shift) exposures pooled for each Similar Exposure Group (SEG) correlated with lung function measured as FEV1 % of predicted (p<0.05) as confirmed by the Kolmogorov goodness of fit test. Furthermore a trend test using SAS 9.4 resulted in p = 0.0013. A major finding for those workers exposed to RCS at 0.1 mg/m3 was loss of lung function greater than 20%. The increased loss of lung function was positively correlated with jobs associated with increased RCS exposure. When similar exposure groups were combined into three RCS exposure ranges categorised as high (≥ 0.09 - ≤ 0.20 mg/m3), medium (≥ 0.04 - ≤ 0.08 mg/m3) and low (< 0.04 mg/m3), analysis of variance (ANOVA) confirmed that the loss of lung function below the lower limit of normal (LLN) at 0.1mg/m3 TWA-8hrs, is significant (p < 0.05). A major finding from this study predicts that an abnormal loss of lung function may occur even when workers are exposed to RCS where the occupational exposure limit (TWA) is 0.1 mg/m3 or greater which is the case in many jurisdictions.