Limitations in the Use of Particle Size-Selective Sampling Criteria in Occupational Epidemiology

Abstract

The American Conference of Governmental Industrial Hygienists (ACGIH) and the International Standards Organization (ISO) have both recently proposed similar sets of particulate sampling criteria. The criteria describe sample device collection efficiency, as a function of particle size, for inspirable, thoracic, and respirable particulate mass. The collection efficiency curves do not match the lung deposition curves at all particle sizes which leads to a bias between measured particulate (exposure) and deposited particulate (dose). This bias, as a function of particle size distribution, was examined for both the ACGIH and ISO proposed curves. Results indicate that the amount of bias varies with both geometric mean (mass median aerodynamic diameter) and geometric standard deviation. Thus, there will be a different exposure-dose relationship and exposure-response relationship for each particle size distribution. This can lead to additional variability in exposure-response analyses unless all members of the cohort are exposed to the same particle size distribution. In conclusion, “exposure” measurements, based upon either the ACGIH or ISO collection efficiency curves, may not be suitable for occupational epidemiology. If groups within a cohort are exposed to substantially different particle size distributions, total mass measurements and particle size distribution data should be collected. The mass distribution, coupled with lung deposition curves, can then be used to calculate an “exposure” that more accurately estimates “dose,” or deposited particulate. The resulting “exposure” data will have less variability and should improve the probability of observing a significant exposure-response relationship.