The study, funded by the Robert Wood Johnson Foundation, looked at 52 non-smokers working in 39 different Oregon bars or restaurants that allow smoking.
"Even within a brief work shift, we can see increasing levels of this potent lung carcinogen," lead author Michael Stark, a Multnomah County Health Department employee, told The Oregonian newspaper.
The chemical NNK is known to cause a kind of lung tumor seen in smokers and in non-smokers who live or work with people who smoke, the newspaper said.
Employees of businesses that allowed smoking were almost six times more likely to have detectable levels of the carcinogen in their urine. The levels increased about 6 percent for every hour they were at work, Stark said.