Temporal Trends in Variability of Respirable Dust and Respirable Quartz Concentrations in the European Industrial Minerals Sector.

While between- and within-worker variability have been studied quite extensively, hardly any research is available that examines long-term trends in the variability of occupational exposure. In this first study on trends in occupational exposure variability temporal changes in the variability of respirable dust and respirable quartz concentrations within the European industrial minerals sector were demonstrated. Since 2000 the European Industrial Minerals Association's Dust Monitoring Program (IMA-DMP) has systematically collected respirable dust and respirable quartz measurements. The resulting IMA-DMP occupational exposure database contains at present approximately 40 000 personal full-shift measurements, collected at 177 sites owned by 39 companies, located in 23 European countries. Repeated measurements of workers performing their duties within a specific site-job-campaign combination allowed estimation of within- and between-worker variability in exposure concentrations. Overall day-to-day variability predominated the between-worker variability for both respirable dust concentrations and quartz concentrations. The within-worker variability in concentrations by job was two to three times higher for respirable quartz than for respirable dust. The median between-worker variability in respirable dust concentrations was low and further reduced over time. For quartz concentrations the same phenomenon albeit somewhat less strong was observed. In contrast, for the within-worker variability in concentrations downward and upward temporal trends were apparent for both respirable dust and respirable quartz. The study shows that the (relative) size of temporal variability is large and unpredictable and therefore regular measurement campaigns are needed to ascertain compliance to occupational exposure limit values.