Interday or intraday high-intensity exposures (i.e., exposure peaks) may be more relevant for initiating beryllium sensitisation (BeS); such exposures may exceed a threshold necessary to activate the immune response. This study evaluated the relationships of exposure metrics reflecting normal process variation and upset conditions with the prevalence of BeS.
In a study of workers employed from 1994–1999 at a primary beryllium manufacturing facility, exposure metrics were developed using personal full-shift measurement, 15 minutes to 24 hour process-specific area measurements, and process-upset information gleaned from historical reports. Quantitative intensity metrics included highest-ever job-specific average, maximum, 95th percentile, upper tolerance limit (UTL), exceedance fractions (>0.2 and >2 µg/m3), and the product of the geometric mean and geometric standard deviation (GMxGSD). Qualitative metrics included professional judgment of process-upsets (PJPU), and number of process-upset events (e.g., power outage). Relationships among these metrics were evaluated using Spearman correlation and their association with BeS was evaluated using logistic regression with splined and log-transformed exposures.
As anticipated, a high degree of correlation existed among metrics within full-shift measurements (rS: 0.57–0.99) and task/process measurements (rS: 0.56–0.96), and moderate correlation across the two measurement types (rS: 0.48–0.79). Most of these metrics were associated with BeS in logistic models of log-transformed exposures. In splined models, non-linear associations were observed with average, 95th percentile, UTL, and exceedance fraction > 2 µg/m3 from the personal samples. Strong associations with BeS were observed for GMxGSD (OR = 1.8 and 3.6) and PJPU (OR = 8.3 and 8.5) for medium and high categories compared to low category.
Professional judgments regarding process-upset potential and the combined GMxGSD were valuable in predicting BeS; each may reflect a different aspect of interday and intraday exposure peaks. Non-linear associations were possibly due to confounding by chemical form and/or skin exposure, use of respiratory protection, presence of a threshold and/or by genetic susceptibility.
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