Comparison of the Criteria for Sampling ‘Inhalable’ and ‘Respirable’ Aerosols

The United States Environmental Protection Agency has developed and is promoting the adoption of a new ‘inhalable’ particulate matter standard for sampling environmental aerosols based on a 15 μm cut size to evaluate the potential impact associated with inhalation deposition. On the other hand, the use of ‘respirable’ dust sampling is the time-honoured and tested means of collecting the particle fraction that is indicative of the potential risk to the lung of inhalation exposure to aerosols. In this report the relationship of these two concepts is critically reviewed in the perspective of the available human data on the deposition of inhaled particles. The BMRC and AEC criteria for ‘respirable’ dust samples and the recommendations of the ICRP Task Group on Lung Dynamics for nasal and tracheobronchial penetration are found to be somewhat like the EPA proposed intermediate standard even though that standard is based on physical-chemical data rather than biological considerations. The proposed ‘inhalable’ particle standard with its concomitant difficulties overemphasizes the large particle risk even for mouth breathing and appears to have limited utility. Continued use of the traditional respirable dust standards is recommended.