New research finds that household dust hosts microbes that can break down cancer-causing environmental chemicals. However, the byproducts of this degradation may also harm health.

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The microbes in our household dust can fight off cancer-causing chemicals, but at what cost?

Our households are riddled with all kinds of microbes, some of which are good and some of which are dangerous. From our dishwashing sponges to our toothbrush holders, there are plenty of places in our homes where these tiny microorganisms can hide.

In particular, the dust that settles on our furniture and other surfaces contains a wide variety of fungi, as well as bacteria from the Staphylococcus and Streptococcus families.

Although such bacteria may harm our health — particularly if we have a weak immune system — new research finds that the microbes present in household dust also have an additional role: They help break down harmful environmental chemicals.

Specifically, a new study found that these dust bacteria can degrade phthalates, which belong to a class of chemicals that research has linked with cancer and other conditions.

Ashleigh Bope, a doctoral researcher in environmental science at The Ohio State University in Columbus, is the first author of the paper, which appears in the journal Environmental Science: Processes & Impacts.

Dust microbes fight off harmful chemicals

The primary purpose of phthalates is to soften plastic and vinyl to make it more flexible. There are phthalates in almost every household and consumer product, from blinds, wallpaper, and shower curtains to plastic toys, detergents, and food packaging.

Researchers do not yet fully understand the health impact of phthalates, but existing studies have suggested that these chemicals disrupt the endocrine system.

Experts believe that one particular phthalate, called Di (2-ethylhexyl) phthalate (DEHP), causes cancer.

Bope explains the motivation for the new study, saying, "[W]e know that [phthalates] can be degraded in other systems — like aquatic systems and soils — but we have high exposure to them indoors, so it was important for us to see if biodegradation was actually occurring in the indoor environment."

To find out, the researchers analyzed a piece of carpet from a randomly chosen household in Massachusetts, other pieces of carpet from three households in Ohio, and dust samples that they collected from the vacuum cleaners of the same homes.

Lab analyses revealed phthalates and microbes, as expected. Specifically, the researchers found the cancer-causing DEHP in higher concentrations than other phthalates.

Then, the researchers stored the pieces of carpet at different humidity levels to examine the interaction between the microbes and the phthalates.

They found that higher humidity levels helped the dust microbes multiply, noting that the higher the humidity and the number of microbes, the more phthalates these microbes degraded. However, breaking down the otherwise harmful phthalates may cause more health hazards, explain the researchers.

"We could see that the phthalates were degrading, but the byproducts of that degradation could be even more harmful," reports study co-author Sarah Haines.

"We really need to look at that more, especially at those elevated relative humidity conditions. It's not recommended to maintain a high relative humidity in your home due to increased potential for microbial growth."

The humidity levels that the team used in this research were almost double those of a typical home. When humidity is too high, microbes multiply exponentially, along with fungi and mold.

'The bigger picture'

Study co-author Karen Dannemiller, who is also the director of the Indoor Environmental Quality Laboratory at The Ohio State University, comments on the significance of the findings.

"Previously, people thought there really wasn't a lot of microbial activity happening in the indoor environment," she says. "We knew microbes were shed from human skin or tracked in from outdoors, and we thought they sat there and didn't do anything. This study shows that is not always the case."

"The big picture is that understanding these interactions can eventually lead to better building design to prevent exposure to some of these harmful compounds," adds Dannemiller.

"We know that both chemicals and microbes are there, so how can we create the healthiest buildings that we possibly can?"