Loft information: dust is an archive of airborne particles. Credit: © GettyImages

Exercise bike? Dolls house? Nest of occasional tables? You can tell a lot about a person by what you find in their attic - including what air pollutants they have breathed, new research suggests.

Slowly accumulating between the piles of junk, attic dust provides a unique archive of potentially hazardous airborne particles going back to when the house was built. "It's a rough but good indicator of what air pollution was like," says environmental scientist Paul Lioy at Rutgers University in New Brunswick, New Jersey, who led the study1.

Lioy's team scooped dust from undisturbed attic corners in homes built between 1879 and 1995 in Dover Township, New Jersey. Dust from houses built during or after the 1970s had far lower concentrations of lead and the radioactive element caesium, the researchers found. Lead - which causes anaemia and mental retardation in children - was added to gasoline and was a major air pollutant before it was banned in the 1980s.

Caesium settled worldwide when testing of nuclear bombs peaked in the 1960s. Lioy's estimates of caesium levels in Dover Township's air tally well with other assessments.

The history of local air pollution is usually guessed at by looking back for records of emissions from sources such as nearby road traffic, factories or incinerators. But conditions at the time, such as wind and rain, could have influenced how pollutants moved around.

Attics are a way around the problem. In older houses they are well ventilated and sheltered from sunlight, which breaks down many pollutants. "People don't go up there very much," adds Lioy, meaning that dust is rarely removed.

The study found no significant amounts of radioactive strontium and iodine. These elements - and their likely source, Oyster Creek Nuclear Power Plant south of Dover Township - had been blamed for a cluster of childhood cancers in Dover Township. "That now seems unlikely," says Lioy.

But only very persistent pollutants stick around long enough to be detected in attic dust, warns environmental chemist James Cizdziel at the University of Nevada in Las Vegas - the first to identify caesium in attics near Nevada's nuclear-bomb test sites. And newer houses tend to have better insulation, which keeps outdoor air out. "It will become harder to find suitable attics," Cizdziel says.

Nonetheless, dangerous levels of toxic heavy metals such as chromium and cadmium, as well as long-lasting pesticides like DDT and chlordane, could still be detected in dust residues, Cizdziel concedes. He plans to rifle through lofts in search of the cause of a cluster of 16 cases of childhood leukaemia in the town of Fallon, Nevada.