By Jimmy Mattila, a graduate student in the Farmer Group at Colorado State University (Twitter: @JimmyMattila)


Chemical processes involved in bleach cleaning leading to human exposure
Chemical processes involved in bleach cleaning leading to human exposure. © American Chemical Society https://pubs.acs.org/doi/10.1021/acs.est.9b05767

 

Bleach, an aqueous solution consisting of sodium hypochlorite (NaOCl) and other oxidizers/surfactants, is a commonly used cleaning product in household and workplace environments. The efficacy of bleach stems from its potent antimicrobial and oxidizing properties. Bleach cleaning emits volatile chlorinated and nitrogenated chemical compounds, which can detrimentally impact indoor air quality and human health. Toxic and likely carcinogenic organochlorides, such as chloroform (CHCl3) and carbon tetrachloride (CCl4) have been measured at elevated levels in indoor air during bleach use. Bleach cleaning also produces chloramines, which are known respiratory irritants. Mixing bleach with ammonia (NH3) or acids (such as HCl or vinegar) indoors produces dangerous amounts of chloramines and chlorine gas (Cl2), respectively. The accidental mixture of bleach and acid recently lead to the tragic death of an employee at a Buffalo Wild Wings restaurant. Knowledge of the emissions and indoor chemistry from bleach use, and the subsequent impacts toward health and indoor air quality, are therefore imperative to the well-being of consumers and employees who frequently clean with bleach indoors.

We recently investigated the volatile emissions, and subsequent indoor chemistry of bleach use during a series of highly-controlled, reproducible experiments during the HOMEChem campaign. Here, we performed high time-resolution measurements of several reactive chlorine- and nitrogen-containing compounds in indoor air during bleach cleaning. Bleach cleaning introduces part-per-billion (ppb) levels of hypochlorous acid (HOCl), Cl2, nitryl chloride (ClNO2), and nitrogen trichloride (NCl3) to indoor air—several orders of magnitude higher than what is typically observed in the outdoor air. Kinetic chemical modeling (a collaboration with the MOCCIE team) revealed that multiphase chemistry occurring within the applied bleach solution, and on indoor surfaces (i.e. floors, walls, etc.) were central in controlling production of these bleach-related compounds. Ventilation and uptake to indoor surfaces were important in removing these compounds from indoor air.

Photochemical reactions between HOCl/Cl2 and light from outdoors was expected to produce hydroxyl (OH) and chlorine (Cl) free radicals in indoor air, in accordance with a previous study of indoor bleach emissions. These free radicals are key players in outdoor atmospheric oxidation chemistry, and likely increase oxidation of indoor volatile organic compounds (VOCs). Another recent study found that non-photochemical reactions of HOCl/Cl2 with limonene—a common indoor VOC; followed by photochemically-driven OH/Cl radical oxidation leads to the formation of indoor particulate matter—a pollutant associated with respiratory, cardiovascular, and other health concerns.

Gaseous NCl3 reached ppb levels for periods of an hour or more during bleach cleaning experiments at HOMEChem, which is likely harmful to individuals with asthma or sensitive breathing passages. Levels of HOCl during these periods were high enough to undergo rapid chlorination reactions with squalene, a major component of human skin oil. Authors of a recent study investigating this chemistry speculate these reactions also occur on human lung tissue upon inhalation of HOCl fumes, and likely contribute to skin and respiratory irritation commonly associated with bleach use. Levels of Cl2 reported herein were likely not acutely harmful to health, though chronic exposure may be of concern.

Given the serious health and IAQ concerns associated with bleach use, we implore readers to consider alternative cleaning methods whenever possible. If bleach use is absolutely crucial, we recommend users prepare bleach solutions per manufacturer instructions (i.e. dilute solution sufficiently with water, and never mix with other cleaning solutions), and clean in a well-ventilated environment.

Read our recent study on volatile emissions and chemistry during bleach cleaning at HOMEChem here: https://pubs.acs.org/doi/10.1021/acs.est.9b05767