Diesel exhaust from sources such as buses, trucks, and farm equipment is a major component of air pollution around the world and has been linked with lung cancer and other illnesses. Both the Environmental Protection Agency and the National Toxicology Program, the interagency program charged with assessing the impact of different chemicals on human health, have classified diesel exhaust as a probable human carcinogen. Now, researchers have found a way to measure people’s exposures to this pollutant by tracking a specific chemical in their urine.
Found almost exclusively in diesel exhaust is a chemical called 1-nitropyrene, or 1-NP. The body breaks down inhaled 1-NP into several smaller molecules, called metabolites, that show up in urine.
Previous attempts to detect these metabolites in human urine have failed because the chemicals are in such low concentrations there. The metabolites themselves are also relatively water soluble. “Those kinds of chemicals, especially when they’re in low abundance, are quite a challenge to purify and detect,” says Christopher Simpson, an analytical chemist at the University of Washington in Seattle.
He and his colleagues at Kanazawa University in Japan have now developed a highly sensitive technique for capturing 1-NP metabolites in human urine. The team collected urine samples from 17 men and 5 women in Kanazawa City.
To isolate the metabolites, the researchers first incubated the urine samples with rayon containing a blue dye known to selectively bind to chemicals resembling the metabolites. The team then removed the chemicals bound to the rayon, further purified the sample, and extracted the specific 1-NP metabolites using high-performance liquid chromatography. A mass spectrometer identified the metabolites and measured their concentrations.
The technique was sensitive enough to detect five different metabolites that form in the body after exposure to diesel exhaust, the researchers report in the July Chemical Research in Toxicology.
“If these results are validated in further studies, the test may become very useful in documenting the amount of 1-NP that is absorbed in the body in various settings,” says Michael Thun, vice president of epidemiology and surveillance research at the American Cancer Society in Atlanta.
The next step, says Simpson, is to correlate the amount of metabolites in urine with the amount of diesel exhaust a person is exposed to. The researchers recently equipped truck and taxi drivers in urban areas of China and Peru with personal monitoring devices that collect air samples and measure the drivers’ exposure to 1-NP. The team also collects urine samples from these individuals on the same day as air samples are taken.
For comparison, the researchers are doing similar measurements on residents of Seattle, where the amount of diesel exhaust in the atmosphere is lower than that in the test areas of China and Peru.
Because the metabolites remain in urine only a short time, they can’t reveal how much diesel exhaust a person may have been exposed to years earlier, says Thun. Still, as new regulations force a shift toward cleaner diesel engines, biomarkers such as these could help evaluate the regulations’ effectiveness, says Simpson.