Radiocarbon Clues Help Track Down Poached Elephant Ivory
The value of elephant ivory has skyrocketed in the past few years. That's led to a huge increase in elephant poaching in Africa and, in turn, created new urgency to stop the trade. And as poachers have become savvier, scientists have devised more sophisticated methods of catching the thieves.
A pound of ivory is now worth more than $1,000, with wildlife experts attributing the rise in price largely to consumers, especially in Asia, who have new money to spend on ivory carvings.
Trying to stop the trade is messy because different countries banned ivory trade at different times. So some ivory taken before those bans went into effect may be legal to trade. There also have been a few legal sales of stockpiled ivory over the past decade. So it can be hard to tell whether a piece of ivory in a shipping container or on someone's bookcase is legal or not.
That's something geochemist Kevin Uno is trying to fix. At the University of Utah, Uno worked out a way to "date" a piece of ivory by measuring how much radioactive carbon it contains.
"We use the adage 'you are what you eat' in the type of work we do," Uno says.
Here's how it works. Nuclear bomb tests in the 1950s and '60s pumped a lot of radiocarbon into the atmosphere. This radioactive carbon went everywhere — including into plants that elephants eat.
Since bomb testing ended in the '60s, that radiocarbon has been slowly dwindling. Scientists can chart its decline year by year.
So, for example, a leaf in Africa in 1990 has a different radiocarbon "flavor" than one in 2010.
"And an elephant comes along and eats that [newer] leaf," Uno says. "Well, that leaf has essentially locked in the concentration of radiocarbon from the atmosphere [in 2010]."
Then, some of that radiocarbon goes into the elephant's tusk.
"Once it's fixed in the tissue — in the tusk or the hair — it's locked in," Uno says.
At the bottom end of a tusk, the wide, fat part is the crucial date — the year the tusk stopped growing, when the elephant died.
George Wittemyer, a conservation biologist at Colorado State University, collaborated in the research.
"The dating can be very effective in terms of identifying if the tusks are all from a relatively recent time," Wittemyer says. "For example, if all those elephants were killed in the last year, that would be indicative that this ivory is indeed from very contemporary poaching."
Such evidence refutes the common claims of illegal traffickers that the ivory they are selling is from older tusks, harvested before trade bans were put into effect. In fact, poachers sometimes artificially weather or "age" ivory to make it look old. Radiocarbon dating, theoretically, could see through that deception.
Recently, scientists have successfully used another high-tech tool to determine the origin of an ivory sample. DNA from a tusk, as well as some chemical isotopes, can indicate which elephant population it's from — like northern Tanzania or South Africa. Knowing where an elephant lived and when it died could help determine whether it was taken before or after a ban in that country.
Richard Ruggiero has monitored wildlife trade in Africa for decades, most recently with the U.S. Fish and Wildlife Service. He says traffickers are increasingly part of well-organized, well-funded crime syndicates, using ivory much the way groups once used blood diamonds.
"They do a risk-benefit analysis, [with] risk being the probability of being detected," Ruggiero says. "A tool like the one we're talking about would make prosecutions easier and therefore raise the risk."
The research appears in the latest issue of the Proceedings of the National Academy of Sciences.
Copyright 2020 NPR. To see more, visit https://www.npr.org.