Conceptual Model for Assessment of Inhalation Exposure: Defining Modifying Factors

The present paper proposes a source–receptor model to schematically describe inhalation ex-posure to help understand the complex processes leading to inhalation of hazardous substances. The model considers a stepwise transfer of a contaminant from the source to the receptor. The conceptual model is constructed using three components, i.e. (i) the source, (ii) various trans-mission compartments and (iii) the receptor, and describes the contaminant’s emission and its pattern of transport. Based on this conceptual model, a list of nine mutually independent prin-cipal modifying factors (MFs) is proposed: activity emission potential, substance emission potential, localized control, separation, segregation, dilution, worker behavior, surface contam-ination and respiratory protection. These MFs describe the exposure process at a high level of abstraction so that the model can be generically applicable. A list of exposure determinants un-derlying each of these principal MFs is proposed to describe the exposure process at a more detailed level. The presented conceptual model is developed in conjunction with an activity tax-onomy as described in a separate paper. The proposed conceptual model and MFs should b