Monday, September 26, 2022

Human Body’s Exposure to Ozone Generates Highly Reactive Hydroxyl Radicals, Study Shows

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Hydroxyl radicals are highly reactive chemical species that attack most of the organic molecules.

High concentrations of OH radicals were found when people were exposed to ozone in a climate-controlled chamber, and were a product of a reaction with the skin-oil squalene. Image credit: Richard Duijnstee.

The vast majority of humans spend most of their time indoors and are exposed to a number of chemicals from various sources, including outdoor pollutants that find their way inside, gaseous emissions from building materials and furnishings, and products of activities such as cooking and cleaning.

Moreover, the human body is also a potent mobile source of emissions.

Chemical removal of gas-phase pollutants in outside air during daytime is mostly driven by the production of hydroxyl (OH) radicals, which are formed primarily by the photolysis of ozone by ultraviolet sunlight.

However, indoor air quality is much less impacted by this process, as glass windows largely filter out ultraviolet light.

While research has shown that some OH radicals can be generated by other means in indoor environments, few studies have evaluated the chemical influence human bodies in these environments.

“OH radicals are highly reactive species that are responsible for the oxidation of most pollutant gases,” said lead author Dr. Nora Zannoni from the Atmospheric Chemistry Department at the Max Planck Institute for Chemistry and her colleagues.

“Outdoors, OH radicals are formed primarily by the photolysis of ozone by short-wavelength sunlight, but that light is largely filtered out by glass windows, so what is the indoor OH radical environment like?”

In a series of experiments, Dr. Zannoni and co-authors found that high concentrations of OH radicals are generated when people were exposed to different concentrations of ozone within a climate-controlled, stainless-steel chamber.

They found that the skin-oil squalene reacted with ozone to produce 6-methyl-5-hepten-2-one (6-MHO), which was key to establishing this human-induced oxidation field.

What’s more, they found that isoprene from human breath and products of its interaction with OH also react with ozone to produce more OH radicals, suggesting that humans are a net source of reactive oxidants indoors.

“The findings have implications for the oxidation, lifetime, and perception of chemicals indoors and, ultimately, human health,” they said.

A paper on the findings was published this week in the journal Science.

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Nora Zannoni et al. 2022. The human oxidation field. Science 377 (6610): 1071-1077; doi: 10.1126/science.abn03

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