Dust blowing through city streets may seem harmless, but new research suggests it can contain hidden metals left behind by decades of human activity.
While the levels found in most places are not considered dangerous, scientists say the findings highlight an overlooked source of pollution that people may breathe in, especially during dry and windy weather.
Researchers from the University of Virginia collected and analyzed road dust from seven cities in the eastern United States to find out what it contained and whether it could pose a health risk to residents.
Their findings were published in the journal Environmental Science and Pollution Research.
The team gathered dust from dozens of public locations in each city, including parks, schools and downtown areas where people regularly walk, play and spend time outdoors.
They deliberately avoided collecting samples from the middle of busy highways, focusing instead on places where everyday exposure is more likely.
Back in the laboratory, the researchers tested the dust for a range of toxic metals, including lead, arsenic and cadmium. About one-third of the samples contained detectable amounts of these metals.
According to lead author Robin Truong, an environmental sciences doctoral student at the University of Virginia, the mix of metals found in road dust can tell the story of a city’s past. Older cities often carry traces of industries and activities that may no longer exist but have left lasting marks on the environment.
For example, Richmond, Virginia, showed traces of lead that researchers believe are linked to its history of coal-fired power plants and a waste incineration facility. Other cities also reflected their unique industrial and agricultural histories.
The researchers found that Trenton, New Jersey, and Wilmington, Delaware, had higher concentrations of metals than the other cities studied. These northeastern cities have long histories of industrial activity, which likely contributed to the higher levels.
Meanwhile, Charleston, South Carolina, and Augusta, Georgia, showed evidence of different historical influences. In these cities, past pesticide use and activities related to nearby ports appeared to have shaped the composition of the road dust.
Although the study found measurable amounts of potentially harmful metals, the overall results were reassuring. On average, the concentrations did not exceed current health recommendations.
Even so, the researchers note that road dust can become airborne during dry, windy conditions, increasing the chance that people will breathe it in. This means exposure may be greater during the summer months or during periods of drought, when dust is more easily stirred up by wind, traffic or construction.
People living in areas with a long industrial history may want to take simple precautions when air quality is poor, such as wearing a well-fitting mask outdoors or limiting time outside during particularly dusty days.
The study also highlights a gap in environmental monitoring. While the U.S. Environmental Protection Agency monitors several major air pollutants, including airborne lead and fine particles, it does not routinely monitor road dust itself or many of the other metals examined in this research.
The researchers hope their findings will encourage more studies of urban road dust and increase public awareness that pollution from the past can still linger in city environments today, even long after its original source has disappeared.
