Elements Employed to Trace Smuggled Tusks

By Weiss, Rick | Science News, August 25, 1990 | Go to article overview
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Elements Employed to Trace Smuggled Tusks

Weiss, Rick, Science News

Elements employed to trace smuggled tusks

Trace quantities of radioactive isotopes within ivory trinkets and African elephant tusks can divulge where in Africa those pieces originated, new research indicates. The finding suggests that telltale patterns of nuclear decay within black-market ivory may help conservationists track down hotspots of illegal elephant hunting and stem the decline of the endangered pachyderm.

The technique measures minute concentrations of naturally occurring radioactive elements in biological tissues. Archaeologists and ecologists frequently subject skeletal remains to such isotope analysis to learn about the diets that supported the growth of those bones. The new work applies this technique for the first time to elephants.

Working separately, two groups of researchers analyzed ivory and bone specimens from a total of more than 100 elephants that had died in 10 African countries. (Elephant bones are chemically almost identical to ivory but are easier to find, so the scientists often used them to validate their technique.) Using mass spectrometers, both teams measured the ratio of carbon-12 to its radioactive cousin, carbon-13. They also tallied the relative amounts of nitrogen-14 and radioactive nitrogen-15, and the ratio of strontium-87 to strontium-86. Each of the three isotope ratios describes a different aspect of the elephant's home turf: the climate in which it lived, the plants it ate and characteristics of the soil supporting those plants.

For example, carbon isotope ratios in bones and tusks can reflect metabolic differences in the plants the elephants have eaten. The grasses grazed by savannah-dwelling elephants use what's known as a [C.sub.4] pathway -- a highly efficient metabolic cascade that starts off with the production of a four-carbon sugar. In contrast, the trees browsed by elephants in wooded regions use the [C.sub.3] pathway. This relatively inefficient photosynthetic route starts with production of a three-carbon sugar. Since the [C.sub.3] pathway involves a greater number of carbon-adding steps -- each discriminating against the heavier, more cumbersome isotopes -- [C.sub.3] plants accumulate less carbon-13 than do [C.sub.4] plants. Ultimately, this inequity shows up in the tissues of tree-browsing elephants, providing a neat atomic signature of their diet.

Similarly, differences in climate -- particularly rainfall -- affect nitrogen isotope ratios in plants and plant feeders, although the mechanism remains poorly understood. And strontium isotope ratios in soil vary with the geologic age of the rock below. Strontium ratios become incorporated into the plants that grow there and can be measured in the skeletons of plant-eating animals.

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Elements Employed to Trace Smuggled Tusks


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