A fiscal reflection of the age.
From CNN:

Research presented this weekend reinforced previous findings that 90 percent of paper money circulating in U.S. cities contains traces of cocaine.
“When I was a young kid, my mom told me the dirtiest thing in the world is money,” said the researcher, Yuegang Zuo, professor of chemistry and biochemistry at the University of Massachusetts Dartmouth. “Mom is always right.”

Not only directly from drugs, doing drugs, buying and selling drugs – contamination comes from bank currency-counting machines.

Although the contaminated bills do not affect health, Negrusz said, they could cause 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.”

The US led the world for tainted money.
Canada followed with 85 percent and Brazil with 80 percent. China and Japan had the lowest, with 20 and 12 percent respectively.

Interesting about China:

Actually, we were surprised to find cocaine in Chinese bank note,” Zuo said after analyzing 112 samples from China.
After the Communist Party took over, the country was relatively free of drugs from 1949 until the 1980s because of harsh punishments against substance use, he said.
Two years ago, Zuo collaborated with Beijing scientists on testing bank notes and didn’t find any contamination with cocaine.
“In the last year, 2008, we found trace amounts of cocaine,” he said.

Drug pollution in the communist-cocaine netherworld.