Rome is known as a heady and stimulating city, but is that because it's a vibrant cultural center where modern life buzzes against a backdrop of thousands of years of history, or because small quantities of cocaine waft through the streets?
Researchers at Italy's Institute of Atmospheric Pollution Research have published the results of a year-long study that monitored psychotropic substances in the air of eight Italian cities: Bologna, Florence, Milan, Naples, Palermo, Rome, Turin and Verona.
The scientists found trace quantities of marijuana and cocaine in the air of all eight cities, with the highest total drug concentrations in Turin and the lowest in Palermo. Other substances monitored included nicotine and caffeine, which were also detected in all of the cities.
But the miniscule concentrations detected — about 0.26 nanograms of cocaine per meter cubed in Turin, where levels of that drug were highest — are not nearly enough to alter the mind states of Italy's city dwellers. A typical grain of salt weighs about 80,000 nanograms.
The authors of the study say their research gives insight into geographical drug-use trends (while Turin seems to have the most active cocaine trade, the college towns of Florence and Bologna have the most free-floating marijuana particles) and hope the results will be used to inform policy.
Cocaine use in Italy has also left an imprint on other parts of the environment. In 2005, scientists at Milan's Mario Negri Institute for Pharmacological Research checked the Po River in northern Italy for benzoylecgonine, a unique byproduct of cocaine that's expelled in a user's urine. Their study found levels that corresponded to the daily consumption of about 8.8 pounds (4 kilograms) of cocaine in the region.
In America, no analogous survey of psychotropic drugs in urban air has been published. But trace quantities of a range of pharmaceuticals, from epilepsy medication to sex hormones, have been found in American drinking-water sources.
And a 2009 study led by a scientist at the University of Massachusetts Dartmouth found that between 85 and 90 percent of paper money in America is dusted with small quantities of cocaine. Bills can become contaminated during drug deals; while being used directly to imbibe cocaine, as when they're rolled up to snort the drug; or in banks' currency-counting machines, where the bills mingle with already-contaminated money.
Follow Life's Little Mysteries on Twitter @llmysteries. We're also on Facebook & Google+.