Modeling Particle Resuspension for Estimating Exposure to Bacillus Spores

Abstract

A key challenge in assessing the risks of low level contamination following biological threat agent releases and subsequent decontamination is developing an understanding of the potential for airborne resuspension of agents that have deposited on surfaces within a building. Resuspension is a particularly difficult and important problem for the persistent and deadly biological threat agent that causes anthrax, Bacillus anthracis. The National Homeland Security Research Center of the U.S. Environmental Protection Agency, in collaboration with several other federal agencies, conducted the Biological Operation Testing and Evaluation (BOTE) study [1] to evaluate B. anthracis spore decontamination technologies and to better understand the potential inhalation exposures to spores before and after decontamination. The data collected in this study provide a unique resource to support the development of microbial exposure assessment methodologies, including the application of particulate modeling. Particulate transport modeling approaches that consider particulate characteristics and building features provide a means to quantify the distribution, transport and fate of agents in a building. Models exist to predict resuspension rates as a function of particle size, surface characteristics, human disturbance and other factors; however, these models have not been evaluated for their applicability and accuracy for determining potential inhalation exposure doses of Bacillus spores. Using the field sampling data collected in the BOTE study and resuspension rates determined using existing resuspension models, particulate transport models were used within building airflow and contaminant transport simulation tools to estimate potential inhalation exposure. Approaches to the use of such exposure modeling approaches for future risk assessment are also summarized.