TELLTALE ISOTOPES IN MARIJUANA ARE NATURE'S TRACKING DEVICES

Every so often, a package of marijuana arrives in Jason B. West's
mail at the University of Utah in Salt Lake City. While Dr. West may
not be the only one on campus receiving deliveries of illegal drugs,
he is probably the only one getting them compliments of the federal government.

Dr. West's marijuana supply is decidedly not for consumption. It is
meticulously cataloged and managed, repeatedly weighed to make sure
none disappears, and returned to the sender (a laboratory at the
University of Mississippi) or destroyed when he is done with it.

With financing from the Office of National Drug Control Policy, Dr.
West, 34, is creating a model that can identify the geographic origin
of cannabis plants based on certain chemical calling cards. The
agency hopes to use the research to help decide where to concentrate
its resources.

The research, the Marijuana Signature Project, relies on stable
isotopes, which are forms of an element like nitrogen or oxygen, that
have distinct atomic masses. Long employed in ecological research,
stable isotopes are increasingly used for forensic purposes,
including investigations into blood doping, arson and trafficking in
contraband like drugs and endangered species.

"Stable isotopes are a signature on plant materials and things that
are derived from plants," said Dr. West, a research assistant
professor in the university's biology department. "Using them, you
can get information about where something grew and its growth environment."

Marijuana is the most pervasive illegal drug in the United States,
with 10,000 metric tons consumed yearly by Americans in their college
dormitories, suburban subdivisions, housing projects and Hollywood mansions.

Although suppliers in Mexico and Canada, especially British Columbia,
are gaining market share, most of the marijuana that is bought, sold
and smoked by Americans is grown domestically. Six states --
California, Hawaii, Kentucky, Oregon, Tennessee and Washington --
dominate domestic marijuana production. Beyond that, relatively
little is known about where the drug comes from and how it makes its
way around the country compared with what is known about harder drugs
like cocaine or heroin.

The drug control policy office is betting on stable isotopes to
identify unique markers in marijuana, distinguishing it not just by
geography but also by its cultivation method -- for example, indoor
versus outdoor.

"It's an epidemiological and forensic public health investigation,"
said David Murray, chief scientist at the agency and director of its
Counterdrug Technology Assessment Center.

Marijuana's status as an illegal substance is controversial, as is
the extent of its criminalization and the resources to control it.

Dr. West said his involvement in the project was not tied to any
particular policy judgment. "I strongly believe that part of the
picture in any policy development has to be the best possible
science, and in cases where my work can contribute to that, I think
that's great," he wrote in an e-mail message.

Carbon, hydrogen, nitrogen, oxygen and sulfur, the base elements of
nearly everything on the planet, exist in multiple forms, each with a
specific atomic mass. These are called stable isotopes, as opposed to
radioactive isotopes, which are unstable.

Many natural processes discriminate among these isotopes, a
phenomenon called fractionation. A phase change from gas to liquid,
for instance, weeds out the lighter isotopes, which tend to stay
behind in the gas form. When water rains from a cloud, the water
molecules in the rain contain heavier oxygen and hydrogen isotopes
than the water molecules that remain in the cloud.

The opposite occurs during evaporation, when lighter isotopes diffuse
into the atmosphere faster than their heavier counterparts.
Fractionation also occurs in enzymatic processes like photosynthesis.

In the marijuana project, Dr. West has found that cannabis plants
grown in different regions of the country contain distinct signatures
based on the isotopic composition of each region's water.

"Plants maintain the fingerprint of the climate and the environmental
conditions," said Gene Kelly, a professor of soil science at Colorado
State University and an expert on stable isotopes, who is not
affiliated with Dr. West's research. "Theoretically, high-elevation
pot plants should have one sort of signature, coastal California
plants another."

Already, the project has hinted at some potentially surprising
findings. The marijuana that makes its way to Dr. West's lab has come
primarily from drug busts. One specimen came from a medical marijuana
center in San Diego that the Drug Enforcement Administration raided.
While drug officials had assumed that the marijuana sold at the
dispensary would have been largely locally grown, the isotope
research suggested that just a small percentage was grown in the area.

"There's considerable movement from multiple sources," said Dr.
Murray, the chief scientist of the drug policy office. "And it ends
up that multiple streams of marijuana were present in a single
location being offered for sale."

While he cannot pinpoint a plant's exact home turf, Dr. West said he
could, with increasing accuracy, place it in within a region, called
an isoscape. On a map, the regions look like undulating bands of
color, with differences visible both north to south and west to east.
Dr. West has created computer models based on these isotopic
variations and other factors and is now trying to increase the
accuracy of the models.

Ratios of isotopes found in water vary from north to south largely
because of temperature differences. When condensation occurs at lower
temperatures, -- at higher latitudes and higher elevations -- lighter
isotopes remain in the water. The east-west variation is mainly
because of the movement of clouds that form over the oceans. As
clouds move over land, each time rain falls the heavier isotopes fall
to the ground while the lighter ones remain in the cloud.

"The rain gets lighter and lighter as the cloud moves across the land
surface," Dr. West said.

The more topographically unusual the growing area, the easier it is
to identify.

"If it were a sample that grew, say, in the mountains of Colorado, it
would be relatively easy to give a fairly restricted source
location," Dr. West said. "Something that may have grown out in
Kansas would have an isotope ratio that would be consistent with a
fairly large region."

To fine-tune the models, Dr. West is examining other isotopes found
in the marijuana plants. Nitrogen isotopes, for example, give clues
about whether fertilizer was used and what type. And carbon isotopes
can show whether the plant grew in a wet and shady or dry and sunny
climate, based on how a plant's physiology is affected by water availability.

Dr. West is not limiting his stable isotope investigations to illegal
substances. He is also using the isotopes to determine the origin of
wine grapes, a potentially important application for the field of
terroir. His research has shown that regions of the western United
States impart their own isotopic markers on the grapes grown there.

"There's not much out there that you can't run stable isotopes on,"
said Jim White, a geologist at the University of Colorado who runs
the stable isotope laboratory there and is not connected to the
marijuana project. "If I fed you with a food that had a unique
isotopic signature and then measured your breath, I could see how
quickly you were metabolizing."

Dr. White said that back in graduate school, he and his friends used
isotopes to find out how long it took for the water in their bodies
to completely cycle through. The experiment relied on several types
of beer with differing isotopic ratios.
Dr. West believes that his forensic investigations will have wider
applications, which may include answering questions about global
climate change.

"I think it has been a real two-way street between these targeted
forensics questions and more general ecological questions," Dr. West said.

Dr. Kelly agreed. "This shows us that there are things we do in very
basic research that have real-world applications," he said.

Meanwhile, Dr. Murray is optimistic that the Marijuana Signature
Project will help the agency better understand and control the flow
of the drugs.

"We can't go out and find this information because it's an illegal
activity where they shoot you in the back alley if you try to find
out," Dr. Murray said. "Today we're making guesses. This will guide
us toward a scientific basis."