The dust in our homes and the air we breathe harbor a complex stew of chemicals. Some, like oxygen, sustain life. Others are pollution stemming from things like car exhaust or from tiny scraps of household products. A pair of new studies adds a level of much-needed detail about exactly how widespread such toxic exposures can be.

A new analysis, published Wednesday in Environmental Science & Technology, reaffirmed that consumer product chemicals including phthalates, phenols and flame retardants are ubiquitous components of household dust. These substances are present at such high levels that researchers say it is likely we are inhaling and accidentally eating small amounts of these chemicals every day, although we don't yet know whether this level of exposure is enough to do harm.

Such exposures occur after the chemicals flake off of products including building materials, electrical cords or perfume, says senior author Ami Zota, a professor of environmental and occupational health at The George Washington University. To better understand the scale of such exposures she and her colleagues collected the findings of 26 peer-reviewed studies and one unpublished data set on indoor dust samples from 14 states. The samples came from urban, suburban and rural settings, and included houses as well as other locations like schools and workplaces. The 10 most common chemicals in the study were found in over 90 percent of samples, which suggests they come from items present in most people's households and communities.

The most abundant chemical in the analysis was di(2-ethylhexyl) phthalate (DEHP), a phthalate that is used in flexible plastics as well as in cosmetics and personal care products. In mice and rats, ingesting high doses of DEHP interferes with the development of the male reproductive system and is linked to liver cancer. When the investigators ranked the chemicals according to how much preschool-aged children were likely to ingest, the flame retardant tris(2-chloroethyl) phosphate (TCEP) came out on top. TCEP has been linked to cancer and brain damage in mice, but like many of these household chemicals we don't know whether it might be dangerous to humans.

An important limitation of the study is that it only looked at the types and amounts of chemicals present in dust—not the health of people who spent time in places where the dust was collected. For many of the chemicals, we don't yet know what amount should be considered hazardous for long-term exposure, Zota says. And we don't know whether some of the chemicals might be more harmful in combination than they are individually.

Tracey Woodruff, who was not involved with the new analysis, calls the work a “great contribution” to the study of chemicals in household dust. She's the director of the Program on Reproductive Health and the Environment at the University of California, San Francisco, and she was previously a senior scientist and policy analyst at the U.S. Environmental Protection Agency. “The dust is out there. We know the chemicals are in the dust,” she says. “Now we have a better picture of what that looks like and also what we’re going to be ingesting, which is really important for thinking about risks.”

In the Air

A second study raises new questions about air exposures we might encounter outside the home. Work published in Proceedings of the National Academy of Sciences on September 6 suggests magnetite nanoparticles, typically found in the air, may travel farther than previously believed throughout the human body and ultimately lodge in human brain tissue. Such particles from air pollution have long been linked to respiratory disease, Woodruff says, but the link to brain health is “newly being appreciated.”

The researchers examined 37 samples of brain tissue from people who had lived in Manchester, England, and in Mexico City. They used a sensitive magnet to confirm that magnetic particles were present in the brains and then looked for the particles under a transmission electron microscope. Although our bodies produce a small amount of magnetite—a mineral made of iron and oxygen—specific characteristics of the magnetite particles researchers found in the brain samples suggest these substances did not come from the body. Typically, such particles appear crystal-shaped under an electron microscopic. Yet Barbara Maher, who studies magnetic minerals that occur in the environment at Lancaster University, and her team found that most of the samples from the brain were actually smooth and round.

That shape, along with other clues like particle size and the presence of other metals, suggests they were produced at high temperatures—likely in the engines of vehicles. “In essence they are molten droplets,” Maher says. ”If they cool quickly enough, they keep that spherical shape.”

The particles are small enough that they can enter the brain through the olfactory nerve via the nose. Nobody has yet proved that magnetite contributes to Alzheimer's or any other disease—magnetite has been detected previously in the brains of some Alzheimer’s patients—but the mineral is known to create free radicals that can damage cells. As a result, Maher believes it is “highly improbable” that the particles' presence in the brain is harmless.

“The levels of magnetite they found in the brain are much higher than have been found in other studies,” says Jon Dobson, who studies magnetic nanoparticles in biomedicine at the University of Florida and was not involved in the study. There is a chance the high levels were from accidental contamination in the lab, in spite of the researchers' careful steps to avoid it, he says. But if the high levels are simply due to the patients being exposed to high levels of pollution, future studies involving a control group from less polluted areas could confirm the findings.

Removing nanoparticles and consumer product chemicals from our environment is a big job that would require major policy changes, for example banning the most toxic chemical from products. In the meantime, though, both Zota and Woodruff note that washing your hands before you eat can significantly reduce your accidental intake of the chemicals found in dust. They also recommend vacuuming with a high-efficiency particulate air (HEPA) filter, which is designed to remove very fine particles.

Maher points out that walking farther away from busy roads may also help to reduce how much exhaust you breathe in. Even walking on the downhill side of the road, she says, rather than the uphill side where drivers burn more fuel as they accelerate, may make a difference. “Any distance that you can put between you and the source of the particles is a good thing.”