Since the outbreak of COVID-19, surfaces in public places have been cleaned more frequently. While disinfectant solutions kill germs, they don’t really leave a bare surface behind. They deposit a thin film that does not wear off even after giving the surface a good polish. The researchers report. ACS ES&T Air show that residues left by commercial cleaning products contain a wider range of compounds that can affect indoor air quality than previously thought.

Residues on indoor surfaces — such as those accumulated during cooking or cleaning — may contain compounds that are potentially harmful if absorbed through the skin or if they become airborne. And breathe. To investigate the effects on indoor air quality, scientists study the gunk that builds up with laboratory models of surfaces. In the models, researchers start with the assumption that a thin film exists on any “clean” surface, but the origin and actual makeup of these films is unknown. Because the chemical compositions of commercial cleaning products differ from those used to prepare surfaces in the lab, Rachel O’Brien and colleagues hypothesized that commercial sanitizers may be a missing source for the films. Therefore, they decided to characterize the films left behind on recently cleaned surfaces.

Using an internal surface solvent extractor, researchers collected films directly from cleaned surfaces in a controlled lab setting and on regularly washed surfaces in university buildings. This method allowed them to capture and measure a wide array of compounds, including substances that barely vaporized. In contrast, only semivolatile organic compounds (SVOCs) are picked up by wiping the surface film with a solvent-damp cloth, the common method for analyzing films. The team’s analyzes of residue samples by mass spectrometry revealed that:

  • Films of commercial cleaning products on model lab surfaces and university building surfaces were different and more complex than previously thought.
  • While the composition of the films varied, they all contained SVOCs that can become airborne and affect indoor air quality.
  • This method confirmed the presence of low-volatile surfactants, the main constituents of soaps, thought to be from cleaning solutions. However, the effects of surfactants on surface films have not yet been elucidated.

As a result of these findings, the researchers say that more compounds may accumulate on cleaned surfaces than previously identified. He added that future indoor film studies should use surfaces treated with commercial cleaning products to more accurately identify how residues affect indoor air quality. And given the extent and regularity of cleaning in public places and people’s homes, more research is needed to determine the effects of low-volatile compounds on film development and behavior.

The authors acknowledge funding from the Alfred P. Sloan Foundation.