The Dirty Truth of Indoor Cleaning Products

Many of us spend most our time indoors—in homes, workplaces, vehicles, and other leisure spaces. In fact, the Environmental Protection Agency estimates that the average American spends 93% of their life indoors: 87% inside buildings, and 6% in automobiles.¹

Various dynamics in indoor spaces contribute to air quality and exposures, but despite its importance, our understanding of indoor chemicals is more limited than that for the outdoor environment.² In particular, surfaces play a key role—much more than they do outdoors.³ They can easily become coated with thin organic films, which act as a both a source and a sink for semi-volatile organic compounds—and as a reactive site for chemical transformations. These semi-volatiles can dynamically partition between the gas phase and various condensed-phase sites, moving between airborne particles, settled dust, or surface films.⁴

Surfaces are also key touch points, allowing us to absorb chemicals across the skin. It's fairly obvious to most that over time, substances settle and accumulate on various indoor surfaces—ones we can see such as dust and condensation, as well as invisible residues from cooking, smoking, personal care, and other indoor products and activities. But it might be less counterintuitive to many of us that cleaning products specifically designed for surfaces can also contribute to these organic films. Much like the hand sanitizers that became ubiquitous during the COVID-19 pandemic, disinfectant solutions eliminate germs but do not remove dirt or produce a bare surface. Instead, according to the authors of this 2017 Environmental Science & Technology study, "Most indoor surfaces are covered with a thin film of accumulated grime. These films are mixtures of sorbed water, sorbed organics, inorganic molecules and ions, and deposited airborne particles."⁵

Now, recent work reported in ACS ES&T Air shows that the residues left behind by commercial cleaning products contain a much larger range of compounds that could impact indoor air quality than previously thought.⁶ To measure this, researchers collected indoor surface films and characterized the organic chemicals present. Surfaces sampled in different buildings across an academic site contained residues from cleaning products, including both ionic and non-ionic surfactants. This suggests these chemicals are retained on impermeable surfaces such as glass even after wiping or polishing—but also on nearby surfaces, since many cleaning products have a spray applicator that generates aerosols.

In addition to having a potential impact on human health, these organic indoor films could also affect lab protocols, and the authors argue that the idea of a “cleaned surface” should be reevaluated for those running relevant laboratory studies, field studies, and models. Specifically, laboratory cleaning procedures based on pure water or organic solvents may not represent what is found on indoor surfaces. In the future, laboratory studies of indoor film growth should consider using surfaces cleaned with commercial cleaning solutions to better represent real indoor surfaces.

Previous research by members of the same team has looked at films as part of HOMEChem—the House Observations of Microbial and Environmental Chemistry study.^7,8 This is a collaborative field investigation designed to examine how everyday activities influence the emissions, chemical transformations, and removal of trace gases and particles in indoor air. They showed that the films that typically build up in a kitchen environment are chemically similar to cooking organic aerosol, but contain larger molecules.

Call for Papers: Indoor Air Pollution, Health Effects and Mitigation

In an effort to further the field and increase our understanding around indoor air pollution, and health risks and mitigation, Environment & Health is seeking contributions for an upcoming Virtual Special Issue. This collection will provide insights on indoor air pollution exposure, health risks and mitigation, including those of both chemicals and biologicals.

Do you have innovative research to share with the community? Check out the invited topics and submission guidelines.

References

1. Klepeis, N. et al. The National Human Activity Pattern Survey (NHAPS): a resource for assessing exposure to environmental pollutants. J. Exposure Science & Environmental Epidemiology 2001, 11, 231–252.
2. Habre, R. et al. Why Indoor Chemistry Matters: A National Academies Consensus Report. Environ. Sci. Technol. 2022, 56, 15, 10560–10563.
3. Manuja, A. et al. Surface Area in Indoor Environments. Environ. Sci. Process. Impacts 2019, 21 (8), 1384–1392.
4. Lunderberg, D. M. et al. Surface Emissions Modulate Indoor SVOC Concentrations through Volatility-Dependent Partitioning. Environ. Sci. Technol. 2020, 54, 11, 6751–6760.
5. Wu, Y. et al. Adsorption of Phthalates on Impervious Indoor Surfaces. Environ. Sci. Technol. 2017, 51, 5, 2907–2913.
6. O’Brien, R. et al. Contributions of Cleaning Solution Residues to Indoor Organic Surface Films. ACS EST Air 2024, 1, 2, 129–138.
7. O’Brien, R. et al. Emerging investigator series: chemical and physical properties of organic mixtures on indoor surfaces during HOMEChem. Environmental Science: Processes & Impacts 2021, 4.
8. Farmer, D. K. et al. Overview of HOMEChem: House Observations of Microbial and Environmental Chemistry. Environmental Science: Processes & Impacts 2019, 8.