Dust blowing through city streets may seem harmless, but new research suggests it can contain hidden metals left behind by decades of human activity. Back in the laboratory, the researchers tested the dust for a range of toxic metals, including lead, arsenic and cadmium. 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. In these cities, past pesticide use and activities related to nearby ports appeared to have shaped the composition of the road dust. Even so, the researchers note that road dust can become airborne during dry, windy conditions, increasing the chance that people will breathe it in.