Methyl Bromide as a Building Disinfectant: Interaction with Indoor Materials and Resulting Byproduct Formation

Abstract

Several buildings were contaminated with Bacillus anthracis in the fall of 2001. These events required consideration of how to disinfect large indoor spaces for continued worker occupation. The interactions of gaseous disinfectants with indoor materials may inhibit the disinfection process, cause persistence of the disinfectant, and lead to possible byproduct formation and persistence. Methyl bromide (CH₃Br) is a candidate for disinfection/deactivation of biological agents in buildings. In this study, 24 indoor materials were exposed to CH₃Br for 16 hr at concentrations ranging from 100 to 2500 ppm in 48–L electropolished stainless steel chambers. CH₃Br concentrations were measured during and after disinfection. Its interactions with materials were observed to be small, with nearly complete and rapid desorption. Between 3% and 8% of CH₃Br adsorbed to four materials (office partition, ceiling tile, particle–board, and gypsum wallboard with satin paint), and the degree of adsorption decreased with increasing relative humidity. The percentage of adsorption to all other materials was <2%. This result suggests that when designing disinfection events with CH₃Br, loss to indoor materials can be neglected in terms of disinfectant dose calculations. Possible reaction products were identified and/or quantified before and after exposure to CH₃Br. Several monomethylated and dimethylated aliphatic compounds were observed in chamber air at low concentrations after the exposures of six materials to CH₃Br. Concentration increases also occurred for chemicals that were observed to naturally off–gas from materials before exposure to CH₃Br, suggesting that CH₃Br may play a role in enhancing the natural off–gassing of chemicals, for example, by competitive displacement of compounds that already existed in the materials. The results described in this paper should facilitate the design of building disinfection systems involving CH₃Br.