By Olivia Wrigley

Mopping floors with bleach has been shown to release hazardous compounds into indoor spaces.

An international collaboration has found that mopping floors with bleach solution increases the presence of chlorine gas (Cl2), hypochlorous acid (HOCl) and other chlorine compounds in the surrounding air[i]. The researchers also identified a “suite” of other molecules present in the indoor air following bleach washing and modeled how these might go on to react both in the air and on other surfaces in the room.

Dr. Jon Abbatt

Commercially-available bleach is primarily made of sodium hypochlorite (NaOCl), and forms the highly-oxidizing antimicrobial HOCl upon mixing with water. Jon Abbatt’s team, based at the University of Toronto, Canada, washed a linoleum floor with standard, store-bought bleach diluted to the manufacturer’s specifications with water. They then measured the concentrations of chlorinated chemicals present in the air around it for 30–45 minutes, using both a chemical ionization mass spectrometer and a time-of-flight mass spectrometer.

The team found that the bleach chemicals volatilize from the linoleum surface and react with other chemicals in indoor air, as well as on indoor surfaces. One discovery Abbatt found “intriguing and dramatic” was that even in the laboratory, with an air turnover rate 1–2 orders of magnitude greater than in a typical household room, concentrations of Cl2 and HOCl remained elevated for a significant amount of time after mopping. The implication of this is that the chemicals will persist for a much longer time period inside typical homes.

Modeler Nicola Carslaw, from the University of York, UK, then investigated how the chlorinated chemicals released from mopping with bleach may further react once in the air. Photochemical and surface reactions under varying light intensities were studied. One significant finding was that with sufficient light intensity, the chlorine free radicals produced from bleach degradation can go on to form other oxidants such as the hydroxyl radical. Free radicals are very reactive with volatile organic compounds, and an increased number of them could significantly alter gas-phase and aerosol composition of the indoor air.

According to Abbatt, the take home message here is that “when we wash with bleach, the oxidation occurs not only on the surface we are washing but everywhere else too”. Carslaw agrees, adding that bleach washing produces a much “wider group of chemicals than previously thought”, and that “chemists need to work much more closely with toxicologists” in order to determine the health impacts of the resulting, chemically-altered air.

[i] Wong, J. P. S. Carslaw, N., Zhao, R., et al. Observations and impacts of bleach washing on indoor chlorine chemistry. Indoor Air. 2017;27:1082–1090.