Inhalation tests were developed, updated and refined during the past few decades to examine potential hazard of inhalable substances. In an inhalation study, atmospheres containing aerosols are generated in inhalation chambers, animals are exposed either nose-only or whole body to an atmosphere. The concentration of the test item in the atmospheres is to be determined appropriately. During the whole exposure period, the atmospheric concentrations have to be kept as constant as possible. For aerosols, particle size distributions have to be determined by cascade impactors or other equivalent devices.
This type of application provides the natural route of entry into the host and has gained significance in the regulatory context. OECD test guidelines (No. 403, 412 and 413) for inhalation exposure was adopted first time in 1982 and revised in 2009. A comprehensive guidance document (GD 39) was also released by OECD in 2009. Beside the OECD test guidelines there were guidelines released by European Commission Regulations (EC No 440/2008 in 30 May 2008) and US Environmental Protection Agency (OPPTS 870.1300 and 870.3465). The technical requirements described in these guidelines are comparable. Based on the determined no observed adverse effect concentration, considering certain inter- and intra-species differences, occupational limit concentrations can be derived.