The term "dirty money" has never been more real, literally.
According to a report from CNN.com, recent research reinforced previous findings that 90 percent of paper money circulating in U.S. cities contains traces of cocaine.
The report says that in an average of 20 months in circulation, U.S. currency travels extensively, from ATMs, to coffee shops, convenience stores and newsstands, to hundreds, maybe thousands of hands.
Each touch to each bill bring specks of dirt, food, germs or even drug residue -- cocaine being detected on the majority of bills.
"When I was a young kid, my mom told me the dirtiest thing in the world is money," researcher Yuegang Zuo, professor of chemistry and biochemistry at the University of Massachusetts Dartmouth, told CNN. "Mom is always right."
While money that contains small traces of cocaine on it can be contaminated during drug deals or if a person uses it to snort the drug, it can also be contaminated at the bank.
If one counting machine has been contaminated, the rest of the bills become dirty as well. However, these bills have fewer remnants of cocaine. The report sad that in Zuo's experiment, the dollars had .006 micrograms, which is several thousands of times smaller than a single grain of sand.
Another interesting tidbit from the research was that $5, $10, $20 and $50 bills were more likely to be positive for cocaine than $1 bills. Why? Zuo said "$1 is a little too less to purchase cocaine."
In addition to cocaine, money contains a lot of different things, another being disease-causing organisms. For years, health agencies have advised people to wash their hands after touching cash for sanitary reasons. However, scientists such as Adam Negrusz, an associate professor of forensic sciences at the University of Illinois at Chicago, said he isn't worried about the cleanliness of money in terms of public health.
Although contaminated bills do not affect health, according to Negrusz, he said they could cause in a false positive drug test if a person, such as a law enforcement officer or banker, handles contaminated currency repeatedly.
"Imagine a bank teller who's working with cash-counting machine in the basement of the bank," Negrusz said. "Many of those bills, over 90 percent, are contaminated with cocaine. There is cocaine dust around the machines. These bank tellers breathe in cocaine. Cocaine gets into system, and you can test positive for cocaine. ... That's what's behind this whole thing that triggered testing money for drugs."
Zuo plans to compile data from his study to form a drug use map, saying it could provide insights about regional cocaine use. He said the rate of drug-contaminated money varied geographically from urban to less populated areas.
Bills from major cities like Miami, Detroit, and Boston tested positive for cocaine, but samples collected from smaller cities like Salt Lake City and Niagara Falls had 87 to 67 percent.
Also, bills were tested internationally, and it was found that bills from the U.S. had the highest percentage of cocaine.