Natural or synthetic? Test reveals origin of chemicals in blubber.

Natural compounds akin to synthetic flame retardants wend their way up marine food chains and accumulate in whale blubber, researchers have found. It's the first time that scientists have used a new radiocarbondating method to determine whether potentially troublesome chemicals in the environment are of natural or synthetic origin.

The oceans contain thousands of naturally occurring organic compounds that incorporate the halogen atoms chlorine and bromine. Used by organisms for such purposes as self-defense, some of these halogenated chemicals have become valuable drugs, while others are harmful to people.

Human activities generate halogenated compounds that can be similar or identical to those made in nature. For example, polybrominated diphenyl ethers (PBDEs) are human-made flame retardants that some scientists suspect have negative health effects (SN: 10/25/03, p. 266). Certain sponges harbor similar but natural halogenated chemicals called methoxylated polybrominated diphenyl ethers (MeO-PBDEs).

MeO-PBDEs show up in other marine organisms, including whales, but it's been unclear whether they enter the environment as natural or synthetic chemicals. To determine that, Emma L. Teuten and her colleagues at Woods Hole (Mass.) Oceanographic Institute analyzed 10 kilograms of blubber from a True's beaked whale that died on a Virginia beach. The team extracted and purified samples of two MeO-PBDEs, MeO-BDE-47 and MeO-BDE-68, and measured the ratios of the isotopes carbon-14 and carbon-12 in each sample.

The ratio is telling because synthetic PBDEs contain almost no carbon-14, which is radioactive and gradually decays to carbon-12. That's because industrial chemicals are made from petroleum, whose original supply of carbon-14 already has mostly decayed. By contrast, carbon-14 is relatively abundant in organic compounds naturally produced by recent biological processes.

In the Feb. 11 Science, Teuten and her colleagues report finding plenty of carbon-14 in the blubber-derived MeO-PBDEs. This indicates that the chemicals are of natural origin, the researchers say.

The researchers found about 1 microgram of each of the sampled MeO-PBDEs per gram of lipids from the blubber. They measured similar amounts of several human-made halogenated compounds, including a by-product of the widely banned pesticide DDT. The researchers found only 0.04 microgram/gram of BDE-47, the most abundant synthetic cousin of the MeO-PBDEs.

Chemist Gordon Gribble, who studies natural halogenated compounds at Dartmouth College in Hanover, N.H., calls the study "wonderfully exciting." The same technique could be used to assign a natural or synthetic origin to other organic chemicals that accumulate in food chains, he says.

Physician David O. Carpenter of the University at Albany in Rensselaer, N.Y., says the new findings don't allay his concerns about the hazards of PBDEs. Last year, he and his colleagues detected the artificial chemicals in both wild and farm-raised salmon.