Overview of testing methods used in inhalation toxicity: from facts to artifacts.

For smaller rodent species, homogenous in size and growth, small head or nose-only chambers are commonly used up to subchronic exposure durations, whereas larger whole-body exposure chambers are used for long-term exposures or exposure paradigms exceeding the normal working day. The advantages and disadvantages of each different technique have already been identified and published in detail. It is often believed best that whole-body inhalation chambers simulate potential human exposure to environmental chemicals or pesticides and this serves as a justification for preferring this mode of exposure. However, real-life exposure conditions of humans cannot be readily duplicated. A comparable mode of exposure may be employed rather than duplicating both the exposure regimens and atmospheres similar to those present in real-world settings. Especially in inhalation studies with complex mixtures, in which atmosphere generation is difficult to control, non-homogenous exposure atmospheres and artifacts are more likely to occur in larger whole-body chambers than in the smaller nose-only inhalation chambers. Inhalation studies with complex mixtures not only face all the challenges of traditional inhalation toxicity testing, but also they are frequently subject to artifacts not readily detected. Thus, a disproportionation of volatile and particulate constituents might occur in inhalation chambers depend on selected technical features, i.e., whether a dynamic or (quasi)static mode of exposure is chosen. Inappropriate timing of the sampling of biological specimens may lead to the underestimation of effects, especially in whole-body exposed animals.