'Marijuana Map' Possible With Chemistry

July 12, 2007 — Marijuana seized in a drug bust is evidence against the possessor, but where it came from often remains a mystery. Now scientists have a way to pinpoint whether the drug came from Mexico or Canada, or even if it was grown inside or out.

The information could eventually lead to a drug database and "marijuana map" that could help drug enforcement officials track trafficking patterns and trace the contraband to its source.

"If you found out a lot of marijuana was coming in from a particular region, it could potentially shape the way you allocate the limited resources you have for law enforcement," said Matthew Wooller, an associate professor at the University of Alaska, Fairbanks.

The clue to the drug's origin lies at the atomic level in forms of elements known as stable isotopes that are associated with growing conditions.

All plants need water, but the isotopic signature of water — its hydrogen and oxygen — can differ depending on latitude. For example, water from Alaska has a larger proportion of oxygen and hydrogen than water from Brazil. A marijuana plant grown in Alaska can reflect the ratio when analyzed.

And just as looking at the stable isotope ratio of hydrogen and oxygen can say something about where a plant was grown, so too can nitrogen and carbon reveal something about how the plant was grown.

That's because some marijuana is grown outside, soaking up the carbon dioxide naturally present in the atmosphere, while other plants are grown inside and fed CO2 from a tank.

"Tank CO2 can have a different isotopic signature than the CO2 in the atmosphere around us now," said Wooller.

Nitrogen isotopes reveal what kind of fertilizer, if any, was used.

"The use of these four elements is especially interesting considering that oxygen and hydrogen will provide information related to water source, while the isotopic composition of carbon and nitrogen are related to others factors such as climate, temperature and nutrients availability on the soil," said Elisa Shibuya, a nuclear scientist at the University of Sao Paulo in Brazil.

Shibuya's team did similar analysis on cannabis using just two isotopes.

But while using a variety of isotopes can better pinpoint the drug, scientists need access to drug samples of known origin.

"The availability of these samples by a governmental body for these researchers only becomes possible — whether possible — after overcoming a huge bureaucracy," said Shibuya.

That bureaucracy could ultimately stand in the way of drug enforcement.

"You can't go out and collect your own samples," said Wooller. "There are strict chains of custody to allow the samples to come into our hands."

Wooller is already working closely with the university's police department to obtain the miniscule samples he needs to perform his analysis. And he is also looking for funding to devote a researcher to the project full time. If that happens, a marijuana map could take shape in the next few years, he said.