Chemistry Catches Cocaine at Source

Scientists can pin a sample’s origin to one of these five Andes cocaine-growing regions. Ehleringer

Law-enforcement officials have a new weapon in the hunt for South American growers who cultivate coca plants for cocaine production. Scientists in the United States have devised a method for identifying the hidden chemical stamp of the narcotic’s geographical origin.

The research team analyzed 200 sets of coca leaves of known origin provided by the Drug Enforcement Administration (DEA) to determine the signatures for five distinct coca-growing regions in the Andes. With this database, the team pinpointed the origin of their cocaine samples with 96 percent accuracy, as reported in the Nov. 16 Nature. More recently, the researchers used the database to identify additional samples.

The method works because cocaine retains the chemical signature of the environment in which it grew, says James Ehleringer of the University of Utah in Salt Lake City. Various isotopes—atoms of the same element that have slightly different masses—of carbon and nitrogen find their way into coca plants in different proportions based on climatic conditions such as humidity, length of the dry season, and soil nutrients.

These isotopic ratios correctly identified the birthplace of 90 percent of the samples tested, says Ehleringer, who did the study with colleagues from both the University of Utah and a DEA laboratory in McLean, Va. Trace molecules, called alkaloids, provided the researchers with further distinctions among genetically different coca plants grown in various valleys, raising the accuracy further, Ehleringer says.

“This is the right approach,” says Yves-Loic Martin of the Nantes, France-based biotechnology company Eurofins Scientific. The company analyzes the purity and origin of foods and recently has studied heroin and a few cocaine samples.

Martin says he would like to see more data. The team’s conclusion of 96 percent accuracy could be “a little bit optimistic,” he notes.

Recent unpublished results of analyses by the U.S. group support the high accuracy claim, says Ehleringer. His team is also working out whether year-to-year climate variations, such as those from El Niño, affect identification of the five growing regions. Preliminary results indicate they don’t, he says.

The new method can trace the drugs one step farther back than can techniques now in wide use, most of which search for chemicals introduced by processing practices common to particular regions, says Ehleringer. The DEA is about to start using the new system, he adds.

“Such technology would assist in tracking the original exporters…and determining drug-trafficking routes,” comments Paul Marsh, a spokesman for the Drug Analysis Section of the Royal Canadian Mounted Police.

“Through the United Nations Drug Control Program, this technology could assist field crews in reporting areas of cultivation and potential drug yields. It could also aid in determining where crop-eradication efforts should be focused,” he says.

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