Retrospective analysis of acute inhalation toxicity studies: comparison of actual concentrations by filter and cascade impactor analyses.

Determination of acute inhalation toxicity is usually the initial step in the assessment and evaluation of the toxic characteristic of a substance that may be inhaled. Commonly, data from this bioassays may serve as a basis for classification and labeling and may also be used for the derivation of Emergency Response Guidance Levels. The focus of this analysis is on the comparative measurement of actual total mass concentrations in inhalation chambers obtained from independent filter (or alternative) analyses and cascade impactor analyses and whether the similarity/disparity of concentration measurements found by different equipment and sampling strategies could serve as robust criterion for the identification of inconclusive measurements. Potential artifacts leading to erroneous concentrations include anisokinetic sampling errors, obstructions of filters, errors related to the calculation/measurement of the sampled volume of atmospheres, wall losses or evaporation. The outcome of this analysis supports the conclusion that the mass concentrations obtained by the commonly performed cascade impactor analysis provide an important adjunct to the established procedures. In summary, the similarity of mass concentrations obtained independently by cascade impactor and filter analyses, i.e., sampling equipment with different aspiration efficiencies and collection media, improve the judgment whether the results from atmosphere characterization are 'conclusive' or 'inconclusive.'