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Salt Lake City — University of Utah researchers developed a new weapon to fight poachers who kill elephants, hippos, rhinos and other wildlife. By measuring radioactive carbon-14 deposited in tusks and teeth by open-air nuclear bomb tests, the method reveals the year an animal died, and thus whether the ivory was taken illegally.
“This could be used in specific cases of ivory seizures to determine when the ivory was obtained and thus whether it is legal,” said geochemist Thure Cerling, senior author of a study about the new method. It was published online the week of July 1 in the journal Proceedings of the National Academy of Sciences.
“The dating method is affordable and accessible to government and law enforcement agencies,” costing about $500 per sample, said the study’s first author, geochemist Kevin Uno, who did the research for his University of Utah Ph.D. thesis.
“It has immediate applications to fighting the illegal sale and trade of ivory that has led to the highest rate of poaching seen in decades,” said Uno, now a postdoctoral researcher at Columbia University’s Lamont-Doherty Earth Observatory.
Not only can the method help wildlife forensics to combat poaching, but “we’ve shown that you can use the signature in animal tissues left over from nuclear weapons testing in the atmosphere to study modern ecology and help us learn about fossil animals and how they lived,” said Cerling, a distinguished professor of geology and geophysics, and biology at the University of Utah.
The method uses the “bomb curve,” which is a graph – shaped roughly like an inverted “V” – showing changes in carbon-14 levels in the atmosphere – and thus absorbed by plants and animals in the food chain. The carbon-14 was formed in the atmosphere by U.S. and Soviet atmospheric nuclear weapons tests in Nevada and Siberia from 1952 through 1962. Those levels peaked in the 1960s and have declined ever since but still are absorbed by and measurable in plant and animal tissues.
The study was funded by the National Science Foundation, the National Geographic Society and the University of Utah. Cerling and Uno conducted it with geologist Jay Quade, a former Utah doctoral student now at the University of Arizona; Daniel C. Fisher, University of Michigan, Ann Arbor; George Wittemyer, Colorado State University; Iain Douglas-Hamilton, founder of Save the Elephants; and Samuel Andanje, Patrick Omondi and Moses Litoroh, all of the Kenya Wildlife Service.
Ivory Trade Drives Elephant Slaughter
International agreements banned most trade of raw ivory from Asian elephants after 1975 and African elephants after 1989. In the United States, raw and worked African ivory (jewelry, figurines, gun and knife handles) is legal if it was imported before 1989 or, if worked ivory is imported after, it must be at least 100 years old.
Yet tons of illegal ivory still are sold because dealers claim the ivory was taken before the ban and there has been no test to prove them wrong – until now.
“With an accurate age of the ivory, we can verify if the trade is legal or not” when the age is combined with existing DNA analysis to determine if an elephant is from Africa or Asia, said Uno, who earned his University of Utah Ph.D. last year. “Currently 30,000 elephants a year are slaughtered for their tusks, so there is a desperate need to enforce the international trade ban and reduce demand.”
Only 423,000 African elephants are left. Conservation groups say 70 percent of
smuggled ivory goes to China. The United States is the next biggest illegal market. Rising ivory prices have drawn organized crime and spurred militias in Darfur, Uganda, Sudan and Somalia to kill elephants and sell tusks so they can buy guns.
How the Study Was Performed
Neutrons from the nuclear tests bombarded nitrogen – the atmosphere’s most common gas – to turn some of it into carbon-14. Cosmic rays do that naturally at a low level, but open-air nuclear tests in the 1950s and 1960s sharply increased atmospheric, plant and animal carbon-14 levels, followed by a steady decline ever since.
The method in the study is a bit like telling a tree’s age by its rings, but instead of counting rings, Cerling, Uno and colleagues measured carbon-14 levels at various points along the lengths of elephants’ and hippos’ tusks and teeth.
The conventional way of measuring carbon-14 is to wait for and count when the isotope
decays radioactively. In the study, the researchers used accelerometer mass spectrometry, or AMS, which requires 1,000 times less material for analysis – a big advantage when sampling fossils or small pieces of worked ivory, Cerling said.