Biocidal effectiveness of combustion products of iodine-bearing reactive materials against aerosolized bacterial spores

Mechanochemically prepared metal-based iodine bearing reactive materials (RMs), generate I₂ gas among other combustion products, and are therefore of interest as biocidal additives in agent defeat applications. In order to facilitate future use of these RMs, a phenomenological model is proposed that describes biocidal effectiveness of ternary Al·B·I₂ composites against aerosolized spores of Bacillus thuringiensis (Btk), a Bacillus anthracis surrogate. The model is based on experiments, in which aerosolized spores passed through an enclosed flow system, where on a sub-second time scale they were exposed to elevated temperatures and combustion products of different RM powders injected in an air-acetylene flame. Temperature distribution, and flow conditions in the exposure chamber were varied to achieve different temperature, iodine concentration profiles, and exposure times. The exposure effect was quantified experimentally via an inactivation factor IF, defined as the inverse fraction of microorganisms surviving the exposure. The process observed in the experiments was described using computational fluid dynamics (CFD) modeling, treating the bacterial spores as 1-µm unit-density particles injected in the airflow, and assuming continuous iodine release during RM particle combustion. To quantify the biocidal effect for each spore, an integral exposure function was introduced consisting of two Arrhenius terms corresponding to pure thermal and iodine-related inactivation. The corresponding activation energies were found as E₁ = 5 kJ/mol, and E₂ = 10 kJ/mol, respectively. The rate constant for the iodine-concentration dependent term was found as 32.3 m³/mol multiplied by the iodine concentration in mol/m³. A critical total exposure threshold was identified. Since the model proposed here depends only on thermal exposure and on iodine, it may be valid for a wider range of iodine bearing RMs.